The authors have no acknowledgements.

<ol>
	<li>Kroenke, K., Mangelsdorff, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Common+symptoms+in+ambulatory+care:+incidence,+evaluation,+therapy,+and+outcome.">Common symptoms in ambulatory care: incidence, evaluation, therapy, and outcome.</a> The American Journal of Medicine. 86 (3), 262-266 (1989).</li><li>Neuhauser, H. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epidemiology+of+vestibular+vertigo:+A+neurotologic+survey+of+the+general+population.">Epidemiology of vestibular vertigo: A neurotologic survey of the general population.</a> Neurology. 65 (6), 898-904 (2005).</li><li>Kroenke, K., Hoffman, R. M., Einstadter, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+common+are+various+causes+of+dizziness?+A+critical+review.">How common are various causes of dizziness? A critical review.</a> Southern Medical Journal. 93 (2), 160-167 (2000).</li><li>Halmagyi, G. M., Curthoys, I. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+clinical+sign+of+canal+paresis.">A clinical sign of canal paresis.</a> Archives of Neurology. 45 (7), 737-739 (1988).</li><li>Halmagyi, G. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Video+Head+Impulse+Test.">The Video Head Impulse Test.</a> Frontiers in Neurology. (8), (2017).</li><li>Van Esch, B. F., Nobel-Hoff, G. E., van Benthem, P. P., vander Zaag-Loonen, H. J., Bruintjes, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+vestibular+hypofunction:+start+with+the+video-head+impulse+test.">Determining vestibular hypofunction: start with the video-head impulse test.</a> European Archives of Oto-Rhino-Laryngology. 273 (11), 3733-3739 (2016).</li><li>Cleworth, T. W., Carpenter, M. G., Honegger, F., Allum, J. H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differences+in+head+impulse+results+due+to+analysis+techniques.">Differences in head impulse results due to analysis techniques.</a> Journal of Vestibular Research. 27 (2-3), 163-172 (2017).</li><li>Curthoys, I. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Video+Head+Impulse+Test+(vHIT).">The Video Head Impulse Test (vHIT).</a> Balance Function Assessment and Management 2nd ed. , 391-430 (2014).</li><li>MacDougall, H. G., Weber, K. P., McCarvie, L. A., Halmagyi, G. M., Curthoys, I. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+video+head+impulse+test:+diagnostic+accuracy+in+peripheral+vestibulopathy.">The video head impulse test: diagnostic accuracy in peripheral vestibulopathy.</a> Neurology. 73 (14), 1134-1141 (2009).</li><li>Agrawal, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+quantitative+head+impulse+testing+using+search+coils+versus+video-oculography+in+older+individuals.">Evaluation of quantitative head impulse testing using search coils versus video-oculography in older individuals.</a> Otology and Neurotology. 35 (2), 283-288 (2014).</li><li>MacDougall, H. G., McGarvie, L. A., Halmagyi, G. M., Curthoys, I. S., Weber, K. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+video+Head+Impulse+Test+(vHIT)+detects+vertical+semicircular+canal+dysfunction.">The video Head Impulse Test (vHIT) detects vertical semicircular canal dysfunction.</a> PLoS One. 8 (4), 61488 (2013).</li><li>Suh, M. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Goggle+Slippage+on+the+Video+Head+Impulse+Test+Outcome+and+Its+Mechanisms.">Effect of Goggle Slippage on the Video Head Impulse Test Outcome and Its Mechanisms.</a> Otology and Neurotology. 38 (1), 102-109 (2017).</li><li>Migliaccio, A. A., Cremer, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+2D+modified+head+impulse+test:+a+2D+technique+for+measuring+function+in+all+six+semi-circular+canals.">The 2D modified head impulse test: a 2D technique for measuring function in all six semi-circular canals.</a> Journal of Vestibular Research. 21 (4), 227-234 (2011).</li><li>Abrahamsen, E. R., Christensen, A. E., Hougaard, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intra-+and+Interexaminer+Variability+of+Two+Separate+Video+Head+Impulse+Test+Systems+Assessing+All+Six+Semicircular+Canals.">Intra- and Interexaminer Variability of Two Separate Video Head Impulse Test Systems Assessing All Six Semicircular Canals.</a> Otology and Neurotology. 39 (2), 113-122 (2018).</li><li>. ICS Impulse USB, user guide, Doc. No. 7-50-2060-EN/03 Part No. 7-50-20600-EN Available from: <a target="_blank" href="https://partners.natus.com/asset/resource/file/otometrics/asset/7-50-2060-EN_03.PDF">https://partners.natus.com/asset/resource/file/otometrics/asset/7-50-2060-EN_03.PDF</a> (2017)</li><li>Mantokoudis, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+the+vestibulo-ocular+reflex+with+video-oculography:+nature+and+frequency+of+artifacts.">Quantifying the vestibulo-ocular reflex with video-oculography: nature and frequency of artifacts.</a> Audiology and Neurotology. 20 (1), 39-50 (2015).</li><li>Pattersson, J. N., Bassett, A. M., Mollak, C. M., Honaker, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+Hand+Placement+Tecnique+on+the+Video+Head+Impulse+Test+(vHIT)+in+Younger+and+Older+Adults.">Effects of Hand Placement Tecnique on the Video Head Impulse Test (vHIT) in Younger and Older Adults.</a> Otology and Neurotology. 36 (6), 1061-1068 (2015).</li><li>Kim, T. H., Kim, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+aging+and+direction+of+impulse+in+video+head+impulse+test.">Effect of aging and direction of impulse in video head impulse test.</a> Laryngoscope. 128 (6), 228-233 (2018).</li><li>Lee, S. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+the+Video+Head+Impulse+Test+(vHIT)+Gains+Between+Two+Commercially+Available+Devices+and+by+Different+Analytical+Methods.">Comparison of the Video Head Impulse Test (vHIT) Gains Between Two Commercially Available Devices and by Different Analytical Methods.</a> Otology and Neurotology. 39 (5), 297-300 (2018).</li><li>McGarvie, L. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Video+Head+Impulse+Test+(vHIT)+of+Semicircular+Canal+Function+-+Age-Dependent+Normative+Values+of+VOR+Gain+in+Healthy+Subjects.">The Video Head Impulse Test (vHIT) of Semicircular Canal Function - Age-Dependent Normative Values of VOR Gain in Healthy Subjects.</a> Frontiers in Neurology. (6), (2015).</li><li>Bansal, S., Sinha, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+VOR+gain+function+and+its+test-retest+reliability+in+normal+hearing+individuals.">Assessment of VOR gain function and its test-retest reliability in normal hearing individuals.</a> European Archives of Oto-Rhino-Laryngology. 273 (10), 3167-3173 (2016).</li><li>Matino-Soler, E., Esteller-More, E., Martin-Sanchez, J. C., Martinez-Sanchez, J. M., Perez-Fernandez, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normative+data+on+angular+vestibulo-ocular+responses+in+the+yaw+axis+measured+using+the+video+head+impulse+test.">Normative data on angular vestibulo-ocular responses in the yaw axis measured using the video head impulse test.</a> Otology and Neurotology. 36 (3), 466-471 (2015).</li><li>Mossman, B., Mossman, S., Purdie, G., Schneider, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age+dependent+normal+horizontal+VOR+gain+of+head+impulse+test+as+measured+with+video-oculography.">Age dependent normal horizontal VOR gain of head impulse test as measured with video-oculography.</a> Journal of Otolaryngology Head and Neck. , (2015).</li><li>Yilmaz, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Time+and+Direction+Information+on+Video+Head+Impulse+Gains.">Influence of Time and Direction Information on Video Head Impulse Gains.</a> Journal of International Advanced Otology. 13 (3), 363-367 (2017).</li></ol>

Dan Dupont Hougaard has received funding for theoretical courses on vHIT from Otometrics.

The experimental design provided should enable examiners to complete vHIT testing of all six SCCs of the best possible quality. There are several critical steps within the protocol that need to be followed meticulously in order to obtain reliable test results. The pretest evaluation is important because several conditions/diseases may either compromise or alter results. For instance, eye muscle palsies, strabismus, or pupillary malformations may seriously affect the test results even if vestibular function is normal. Calibration of the equipment preceding each test is also very critical, because an imprecise or wrong calibration may greatly influence the results. Special attention should also be given when performing the actual test. The participant needs to be cooperative during the test and, when applying the head impulse, special emphasis should given to directing the impulse towards the correct and desired plane.
Both methods described for vHIT testing possess strengths and weaknesses. Especially when performing vertical vHIT tests, the examiner must consider the positions of the head, eyes, and visual target. The position of the head during head impulses can be with the patient facing the wall or with the head rotated 45&#176; to either side. Practitioners can either turn the head or entire body to obtain this position. It should also be taken into consideration which positions are optimal to individual patients, as cooperation during testing is crucial.&#160; Eye movement during testing of the vertical SCCs in the 3D vHIT is both vertical and torsional. In the 2D modified vHIT test method, the torsional component is eliminated by lateralization of the eyeball during testing. The torsional component may add noise to the test, and lateralization of the eyeball may induce artifacts especially from the eyelids or eyelashes. The examiner must also consider the fact that numerous head impulses applied in the vertical planes with continuous lateralization of the eye is fatiguing to a patient. The visual target also needs to be adjusted to each patient&#8217;s eye level. If this is not the case, artifacts and noise may alter the test, and it may be difficult for the patient to keep their eyes on the target if the target is not placed optimally during testing. After completion of the test, the examiner most conclude if test results are of sufficient quality and, if necessary, whether or not to perform all steps of the test again. A final evaluation of the test is mandatory and should include manual removal of any noise and/or artifacts before a final conclusion is drawn15,16.
It is of utmost importance that the examiner is aware of potential artifact triggers during the entire vHIT test procedure. There are many different steps during the test that may individually influence final test results5,12,17,18,19. It is important to be aware that the two important parameters provided by the vHIT test, saccades and mean gain values, may not be correct due to artifacts and/or noise and not because of a compromised VOR function. No standard mean gain calculation method exists, and individual manufacturers use different calculation methods. The examiner must thus use caution when comparing mean gain values obtained by different gain calculation methods.
One particular study found no significant mean gain value differences between several vHIT systems if the same gain calculation method was applied19. However, another recent study found differences in mean gain values depending on both the device and gain calculation method used20. Obtaining normative data for each individual vHIT device is therefore advisable21,22,23,24. Several other factors may alter the mean gain values, among these being goggle slippage (either due to a loose strap or examiner touching the googles), too short of a distance to the wall, and any covert saccades (in case the AUC gain calculation method is used)8,12,17,19,25. Furthermore, no clear definition of pathological saccades exists. Therefore, interpretation of the head and eye velocity graphs following the examination is needed to determine whether or not saccades are present. The conclusions drawn after final analysis upon test completion are subject to inter-rater variation and require previous experience with vHIT testing. It is recommended to use precise and uniform criteria defining pathological saccades. Until a consensus is reached on this matter, application of the four standard criteria, defined in a recent study14, is recommended.
During the last decade, vestibular testing has undergone a revolution. Many clinical bedside tests have been replaced by equipment that enables objective testing of all five paired vestibular end organs. vHIT is superior to the subjective bedside head impulse test and is now offered at many clinics and hospitals worldwide as the initial test of vestibular function in vertiginous patients. The test is fast and can be performed with only minor discomfort to the participant. The test is susceptible to several sources of error, which are more likely to occur if the test is not performed following certain predefined standards. Definition of clinical skills, previous experience, and specific requirements/qualifications need to be clearly defined for both clinical use and research purposes before optimal use of the vHIT test is possible. A recent study indicated that some level of prior experience is beneficial when performing the vHIT; therefore, it is recommended that future examiners undergo systematic training before performing vHIT in a clinical setting14. The vHIT test is not just a &#8220;plug and play&#8221; test; however, if performed correctly, it offers excellent objective diagnostics of vestibular system functioning. This test has a high positive predictive value and offers a specificity very close to one hundred percent14.

An erratum was issued for: <a href="https://www.jove.com/video/59012/functional-testing-all-six-semicircular-canals-with-video-head">Testing of all Six Semicircular Canals with Video Head Impulse Test Systems</a>. The article title was updated.
The article title was updated from:
Functional Testing of all Six Semicircular Canals with Video Head Impulse Test Systems
to:
Testing of all Six Semicircular Canals with Video Head Impulse Test Systems

An erratum was issued for: <a href="https://www.jove.com/video/59012/functional-testing-all-six-semicircular-canals-with-video-head">Testing of all Six Semicircular Canals with Video Head Impulse Test Systems</a>. The article title was updated.

Erratum: Testing of all Six Semicircular Canals with Video Head Impulse Test Systems

Vertigo is the third most common complaint among patients seeking general medical advice and has a lifetime prevalence of 7.8 percent1,2. It is often difficult to determine whether the cause of vertigo is due to disease within the vestibular organs or disease in other parts of the body, because vertigo may be the presenting symptom of numerous diseases3. Traditionally, vestibular testing has been difficult and time-consuming for the clinician and often not very pleasant for the participant. Many of these tests have been done as bedside examinations that rely upon a very skilled examiner and cooperative, dizzy patient. A well-recognized method for bedside testing of vestibular function was introduced in 1988 and termed the &#34;head impulse test&#34;4. Throughout the last decade, there has been rapid development of existing test procedures and methods as well as a rise in new methods of testing. Various laboratory tests, which evaluate the function of the vestibular system, are now commercially available. In 2009, a new test method, video head impulse testing (vHIT), became commercially available. With this test, clinicians around the world are now able to test functioning of the six semicircular canals (SCCs) of the vestibular system objectively and quickly (5-10 min), with only minor discomfort to the patient5. The vHIT test has revolutionized vestibular testing, and in many clinics and hospitals around the world, it is now considered the most important initial test for both acute and chronic vertiginous patients6.
There are several manufacturers of vHIT systems around the world. Some of the most widespread vHIT systems include the EyeSeeCam (Denmark), ICS Impulse (Denmark), and VHIT Ulmer (France) (see Table of Materials). The first two mentioned vHIT systems are quite similar in design and further described in this article (and referred to as vHIT systems A and B, respectively). Both these vHIT systems provide a lightweight goggle that contains a high-speed camera for the recording of eye movements and a sensor that measures head velocity7. Accompanying software needs to be installed on a laptop computer, and the goggle is connected via a USB cable connection to the same computer. During vHIT testing, the goggles are mounted on the patient&#8217;s head and attached firmly. Participants keep their eyes fixed on a target on the wall while the examiner applies fast, abrupt, and unpredictable head impulses in the plane of the semicircular canal being tested. The vHIT provides the examiner with a report that includes 1) a graph depicting head and eye velocity as a function of time and 2) a calculated numeric value termed the &#34;mean gain value&#34;.
After completion of the vHIT test, the software calculates the mean gain value, which is defined as the eye velocity in &#176;/s divided by the head velocity in &#176;/s for each of the SCCs being tested. Individual vHIT systems assess the function of the SCCs by means of testing the vestibular-ocular reflex (VOR), but they often calculate the mean gain value by various methods. The vHIT system A uses the regression gain method, which allows for graphical data analysis over the entire velocity range of head impulses. Following vHIT test completion, it provides the average regression plot slope (a best-fit line through data points at different head velocities with accompanying gain values). The vHIT system B uses the area-under-the-curve (AUC) method for calculation of gain values. The area under the eye velocity record is divided by the area under the head velocity record. This area VOR gain is less affected by minor deviations in eye velocity, which may affect VOR gain calculated from only eye velocity records7. When using the AUC method, the gain value is calculated as the ratio of cumulative slow-phase eye velocity over cumulative head velocity from the onset of the head impulse to the moment at which head velocity returns to zero.
Additionally, unlike the bedside head impulse test, vHIT enables the examiner to detect compensatory eye movements and saccades [both occurring after head movement has stopped (overt saccades) and saccades occurring during the head movement (covert saccades)] by analyzing the graphs provided in the accompanying report8,9. Conclusions on whether or not pathological saccades are present require subjective assessment of the test report, as no consensus exists on the definition of pathological saccades. However, if the software with ICS impulse identifies saccades as pathological, these curves are marked as red. Eye recordings are analyzed differently by the two vHIT systems. In system B, the center of mass of the pupil is determined and used, along with the timestamps from the images, to determine the eye velocities.&#160;These are used along with the head velocities for the gain calculations. In system A, lateral and vertical eye movement velocities are analyzed. If only the pupil is analyzed, only the horizontal and vertical components of eye-in-head position enter a vector analysis algorithm that calculates the VOR gain.
The vHIT test is considered an objective test. This test, however, is technically demanding for the examiner to perform. Head impulses, applied to the participant, need to be unpredictable in both timing and direction, and they need to be delivered at peak head velocities between 150&#176; and 250&#176; per second with an amplitude of 5&#176; to 20&#176;, ideally8,9,10,11. Another prerequisite for successful testing is that the participant is able to understand and comply with the given instructions8. The test is also susceptible to several sources of error, with the most common being goggle slippage8,11,12 and noise/artifacts due to poor pupil detecting and tracking8. The company software discards impulses with too much noise/artifacts during testing. Upon completion of the test, it is often necessary to manually remove additional noise and/or artifacts that the software did not detect and remove automatically.
Both vHIT systems use the same test method for horizontal vHIT testing. Vertical SCC testing is, however, more difficult to perform than horizontal SCC testing. With testing of the vertical SCCs, head impulses are more technical demanding to deliver, the eye movements include a torsional component, the test is more susceptible to goggle slippage, and the test is more uncomfortable for the participant11. The traditional method used for vHIT testing is termed &#34;3D vHIT testing&#34;&#160;and is used when performing vertical SCC testing with the vHIT system A. In response to these challenges, a 2D modified vHIT test method has been developed13. This method, which provides near total removal of the rotational part of the eye movements during testing, is used when performing vertical SCC testing with the vHIT system B. Illustrations and a more detailed description of these two vHIT test methods are provided in the results section. A recent study included both of the abovementioned vHIT systems14. Because these vHIT systems use separate test methods for vertical SCC testing, both the 2D and 3D vHIT test methods were used in the evaluation of vestibular function. The name of the 3D test method may be misleading, as most commercially available vHIT test systems currently measure eye movements in only two dimensions. However, the original test is referred to as the 3D test method throughout this article. The abovementioned two vHIT test methods are described in detail. It should also be noted that 2D vHIT testing is possible with the vHIT system A, but to the best of our knowledge, this test method has not yet been validated for this vHIT system.

<table><tbody><tr><td>EyeSeeCam</td><td>Interacoustics, Denmark</td><td></td><td>Video Head Impulse Test Equipment</td></tr><tr><td>ICS Impulse</td><td>Otometrics, Denmark</td><td></td><td>Video Head Impulse Test Equipment</td></tr><tr><td>VHIT Ulmer</td><td>Synapsys, France</td><td></td><td>Video Head Impulse Test Equipment</td></tr><tr><td>OtoAccess</td><td>Interacoustics, Denmark</td><td></td><td>Software for Video Head Impulse Test</td></tr><tr><td>OTOsuite</td><td>Otometrics, Denmark</td><td></td><td>Software for Video Head Impulse Test</td></tr><tr><td>aVOR App</td><td>Iphone App</td><td></td><td>Mid section images in figure 4 have been modified from this app</td></tr></tbody></table>

testing of all six semicircular canals with video head impulse test systems

Throughout the last decade, there has been a rapid development of existing test procedures and methods evaluating the human vestibular system. In 2009 and 2013, commercially available video Head Impulse Testing (vHIT) has enabled clinicians to examine the function of all three paired semicircular canals within the vestibular system. The vHIT test has revolutionized vestibular testing and, at many clinics and hospitals around the world, this test is now considered the most important initial test of vertiginous patients. There are several manufacturers of vHIT systems around the world. A test protocol for two of the most widespread vHIT systems, EyeSeeCam and ICS Impulse, will be presented. Included in this protocol is a description of the two different test methods termed 2D vHIT testing and 3D vHIT testing. The vHIT system includes a lightweight goggle with accompanying software. The test is fast (5-10 min) and can be done with minimal discomfort to the person being examined. However, there are many steps of the test, and each of these steps may alter the final test results, if the individual steps of the test are not performed correctly. It is therefore of paramount importance that the examiner is familiar with the potential noise and/or artifact triggers. Systematic training of future examiners before performing vHIT in a clinical setting and compliance with this protocol may minimize these challenges of the test. The vHIT test is not just a &#8220;plug and play&#8221; test. However, if carried out correctly, this test offers excellent objective assessment of the function of the high frequency domain of the vestibular system. It has a very high positive predictive value and offers a specificity very close to one hundred percent.

Prerequisites for a valid and precise test result include correct, meticulous, and thorough pretest calibrations. For reports following a correct calibration with the vHIT system A, refer to Figure 1 and Figure 2. Calibration with the system B is done in one step for all six SCCs by asking participants to switch their gazes between the two dots that appear when the lasers are on (see Figure 3). Be careful to check that the eye and head velocities match after this calibration is done. A correct calibration includes a &#8710; value below 21. For a detailed description of the calibration procedures, please refer to the manual provided by the manufacturer15,16.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59012/59012fig1.jpg" /> 
Figure 1: Standard calibration prior to testing of horizontal SCCs with vHIT system A. It should be ensured that &#34;Eye in Image&#34;&#160;(image on the left) contains markings equivalent to the four outer limits as well as one in the center and that &#34;Eye in Space&#34;&#160;is depicted as a cross with vertical and horizontal lines in zero degrees. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59012/59012fig2.jpg" /> 
Figure 2: Head calibration for testing prior to testing of vertical SCCs with vHIT system A. Shown is a 3D representation of head movements with respect to the earth. Horizontal and vertical directions are shown together with head movements with respect to the possibly oblique axes of the inertial sensor. The three polar diagrams show the head movements from three different perspectives. Grey dots: raw head movement, black dots: calibrated head movement, solid grey line: camera orientation, solid black line: head orientation. Far left: grey and black dots must follow a line in the right-left direction (horizontal), middle: black and grey dots must follow a line in the superior-inferior direction (vertical), far right: black and grey dots must follow two perpendicular lines looking like a cross. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59012/59012fig3.jpg" /> 
Figure 3: Calibration procedure setup with vHIT system B. Ask the patient to position the left and right dots equidistant on each side of the fixation dot. As the procedure continues, only one dot at a time will be illuminated and the participant is asked to keep their gaze on the visible dot. As the participant&#8217;s gaze switches, the system tracks the movement of the pupil. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Testing of the horizontal SCCs are done in a similar fashion with both types of equipment. For testing of the vertical SCCs, either the 2D or 3D test method may be used. Please refer to Figure 4 for a detailed description of the two test methods when testing all six SCCs.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59012/59012fig4.jpg" /> 
Figure 4: Visualization of the vHIT test procedures. The left side illustrates the 3D vHIT procedure with vHIT system A. The right side illustrates the 2D modified vHIT procedure with vHIT system B. The middle section illustrates orientation of the semicircular canals (SCCs) being tested. The middle section illustrations are modifications of images taken from a smartphone application (see Table of Materials) and are used with permission from the copyright owner. For horizontal SCC testing, the examiner placed his hands on the patient&#8217;s jaw, delivering head impulses to each side. For vertical SCC testing, the examiner placed his dominant hand (in this study, both examiners were right-handed) on the top of the head and other hand beneath the chin. (a-c) Illustrations of the performance of the 3D vHIT using vHIT system A. In all three setups, the patient is facing the camera and the head is rotated in the direction of the SCCs being tested. (a) Right anterior left posterior (RALP) SCC testing. (b) Horizontal SCC testing. (c) Left anterior right posterior (LARP) SCC testing. (g&#8211;i) Starting position of the head; arrows illustrate the direction in which the head is rotated; the set of SCCs being tested is marked with red. (d&#8211;f) Illustrations of the performance of the 2D modified vHIT using vHIT system B. (d) RALP SCC testing with the subject turned 45&#176; to the left and the impulses being delivered by either rotating the head forward or backward. (e) Horizontal SCC testing. (f) LARP SCC testing with the subject turned 45&#176; to the right and the impulses being delivered by either rotating the head forward or backward. By rotating the patient&#8217;s head 45&#176; prior to RALP and LARP testing, the eyes align with the axis of the vertical SCCs being tested; therefore, primarily vertical eye movements are produced when applying head impulses. (h), (j), and (k) show the starting positions of the head; the arrows illustrate the direction in which the head is rotated; the set of SCCs being tested is marked with gray. LARP indicates left-anterior-right-posterior plane; RALP indicates right-anterior-left-posterior plane. Reproduction of this figure has been granted with permission. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Every time the vHIT test is performed, all individual steps of the test are important, as they may affect or alter test results. Following completion of every vHIT test, the examiner must go through the report meticulously to determine if results are valid. Special attention must be made to make sure that no noise or artifacts are included in the report. Eight different types of artifacts that may alter results have been described (see Figure 5). Even though the accompanying software removes a lot of noise and/or artifacts from the report, manual deletion of noise and/or artifacts may be needed as an additional step of the evaluation. If the test was carried out properly and participant cooperated fully during the testing, a conclusion of either a normal vestibular function or true compromised function may be drawn following evaluation and interpretation of the report. Please refer to Figure 6, Figure 7, and Figure 8 for test reports following examinations of participants with normal SCC function. Prerequisites for a normal complete vHIT test include mean gain values within the normal range as well as absence of pathological saccades. When mean gain values lie within the normal range, head and eye velocities are almost similar, and the corresponding curves are almost identical in the mirrored view.&#160; When no pathological saccades are present, the depiction of both head and eye velocities closely match both during and after application of the head impulses.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59012/59012fig5.jpg" /> 
Figure 5: Visualization of eight different artifacts. Each type of artifact is illustrated by a graph as well as accompanying images depicting the test situation triggering the individual artifact (x-axis: time (seconds), y-axis: head and eye velocity (&#176;/s)). Black and red lines indicate eye velocities and head velocities, respectively. The image on the left within a panel shows a subject being tested with vHIT system A, whereas the image on the right shows a subject being tested with vHIT system B. The appurtenant graph shows traces for eye and head movements related to the artifact. (a) Wrong calibration (high gain), (b) touching goggles (two peaks), (c) patient inattention (eye trace goes wrong direction), (d) bounce (head overshoot), (e) loose strap (delay/phase shift), (f) pupil tracking loss (trace oscillations), (g) mini-blink (pseudo-saccade), (h) blink (pseudo-saccade)17. This figure has been modified with permission17. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/59012/59012fig6.jpg" /> 
Figure 6: Report with normal findings for lateral SCCs. It should be noted that the curves for both head and eye velocities match, all mean gain values are within the normal range (0.80-1.20), and there are no pathological saccades present. (A) vHIT system B report. Left: gain values are depicted as individual dots representing coherent pars of peak head velocities and gain values; red = right side, blue = left side. Mean gain values are also shown as a numerical value (0.91 and 1). &#160;Right: x-axis = time (milliseconds), y-axis = head and eye velocities. Head and eye velocities are shown in the same direction (mirrored view) to ease the interpretation. (B) vHIT system A report. Left: x-axis = time (milliseconds), y-axis = head and eye velocities (&#176;/s). Head and eye velocities are shown in opposite directions. Right: gain values are depicted as a best fitted line through individual dots representing coherent pars of peak head velocities and peek eye velocities (first y-axis) as well as gain values (second y-axis); red = right side, blue = left side. Mean gain values are also shown as a numerical value (1.07 and 1.07). <a href="https://www.jove.com/files/ftp_upload/59012/59012fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/59012/59012fig7.jpg" /> 
Figure 7: Report with normal findings for all six SCCs following vHIT system A testing. It should be noted that the curves for both head and eye velocities match, all mean gain values are within the normal range (0.80-1.20) or higher, and there are no pathological saccades present. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/59012/59012fig8.jpg" /> 
Figure 8: Report with normal findings for all six SCCs following vHIT system B testing. It should be noted that the curves for both head and eye velocities match, all mean gain values are within the normal range (0.80-1.20), and there are no pathological saccades present. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In order to conclude that the vestibular function is reduced a low mean gain value AND pathological saccades must be present. When low mean gain values are present, the amplitude of eye velocity is significantly lower than the corresponding amplitude of head velocity. Pathological saccades must also be present if the examination is truly pathological. These saccades might occur during or after the head movement. In order to conclude if saccades are truly pathological, the examiner must evaluate the saccades in terms of frequency, latency, direction, and amplitude. Please refer to Figure 9 and Figure 10 for examples.
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/59012/59012fig9.jpg" /> 
Figure 9: Pathological test results after testing with the vHIT system A. Overt saccades are seen after head movement has stopped (A), covert saccades are seen during the head movement (B), and sometimes a mixture of both are seen (C). It should also be noted that mean gain values are below the normal range on the ipsilateral side of the pathological saccades. In (B) and (C), number 1 in red indicates covert saccades, number 2 in red indicates overt saccades, and number 3 in red indicate small correctional saccades that are classified as non-pathological saccades. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/59012/59012fig10.jpg" /> 
Figure 10: Pathological test results after testing with the vHIT system B. Overt saccades are seen after head movement has stopped (A), covert saccades are seen during the head movement (B), and sometimes a mixture of both are seen (C). It should also be noted that mean gain values are below the normal range on the ipsilateral side of the pathological saccades. In (C), number 1 in blue indicates covert saccades and number 2 in blue indicates overt saccades. <a href="https://www.jove.com/files/ftp_upload/59012/59012fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Testing of all Six Semicircular Canals with Video Head Impulse Test Systems at JoVE.com

Testing of all Six Semicircular Canals with Video Head Impulse Test Systems

This protocol describes how to correctly perform the video head impulse test with two separate test systems commonly used worldwide. Both the 2D and 3D video head impulse test methods are described.

Throughout the last decade, there has been a rapid development of existing test procedures and methods evaluating the human vestibular system. In 2009 and ...

testing-all-six-semicircular-canals-with-video-head-impulse-test

Research

Education

JoVE Core

JoVE Journal

Electrical Engineering

Medicine

Unit 1

First and Second-Order Circuits

SCIENTISTS IN ACTION

30.3K Views.  Aalborg University Hospital. This protocol describes how to correctly perform the video head impulse test with two separate test systems commonly used worldwide. Both the 2D and 3D video head impulse test methods are described.

Video: Testing of all Six Semicircular Canals with Video Head Impulse Test Systems

Three Dimensional Vestibular Ocular Reflex Testing Using a Six Degrees of Freedom Motion Platform

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the vestibular organ results in mild to severe equilibrium problems, such as vertigo, dizziness, oscillopsia, gait unsteadiness nausea and/or vomiting. A good and frequently used measure to quantify gaze stabilization is the gain, which is defined as the magnitude of compensatory eye movements with respect to imposed head movements. To test vestibular function more fully one has to realize that 3D VOR ideally generates compensatory ocular rotations not only with a magnitude (gain) equal and opposite to the head rotation but also about an axis that is co-linear with the head rotation axis (alignment). Abnormal vestibular function thus results in changes in gain and changes in alignment of the 3D VOR response.
Here we describe a method to measure 3D VOR using whole body rotation on a 6DF motion platform. Although the method also allows testing translation VOR responses 1, we limit ourselves to a discussion of the method to measure 3D angular VOR. In addition, we restrict ourselves here to description of data collected in healthy subjects in response to angular sinusoidal and impulse stimulation.
Subjects are sitting upright and receive whole-body small amplitude sinusoidal and constant acceleration impulses. Sinusoidal stimuli (f = 1 Hz, A = 4&deg;) were delivered about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5&deg; in azimuth. Impulses were delivered in yaw, roll and pitch and in the vertical canal planes. Eye movements were measured using the scleral search coil technique 2. Search coil signals were sampled at a frequency of 1 kHz.
The input-output ratio (gain) and misalignment (co-linearity) of the 3D VOR were calculated from the eye coil signals 3.
Gain and co-linearity of 3D VOR depended on the orientation of the stimulus axis. Systematic deviations were found in particular during horizontal axis stimulation. In the light the eye rotation axis was properly aligned with the stimulus axis at orientations 0&deg; and 90&deg; azimuth, but gradually deviated more and more towards 45&deg; azimuth.
The systematic deviations in misalignment for intermediate axes can be explained by a low gain for torsion (X-axis or roll-axis rotation) and a high gain for vertical eye movements (Y-axis or pitch-axis rotation (see Figure 2). Because intermediate axis stimulation leads a compensatory response based on vector summation of the individual eye rotation components, the net response axis will deviate because the gain for X- and Y-axis are different.
In darkness the gain of all eye rotation components had lower values. The result was that the misalignment in darkness and for impulses had different peaks and troughs than in the light: its minimum value was reached for pitch axis stimulation and its maximum for roll axis stimulation.
Case Presentation
Nine subjects participated in the experiment. All subjects gave their informed consent. The experimental procedure was approved by the Medical Ethics Committee of Erasmus University Medical Center and adhered to the Declaration of Helsinki for research involving human subjects.
Six subjects served as controls. Three subjects had a unilateral vestibular impairment due to a vestibular schwannoma. The age of control subjects (six males and three females) ranged from 22 to 55 years. None of the controls had visual or vestibular complaints due to neurological, cardio vascular and ophthalmic disorders.
The age of the patients with schwannoma varied between 44 and 64 years (two males and one female). All schwannoma subjects were under medical surveillance and/or had received treatment by a multidisciplinary team consisting of an othorhinolaryngologist and a neurosurgeon of the Erasmus University Medical Center. Tested patients all had a right side vestibular schwannoma and underwent a wait and watch policy (Table 1; subjects N1-N3) after being diagnosed with vestibular schwannoma. Their tumors had been stabile for over 8-10 years on magnetic resonance imaging.

A method is described to measure three-dimensional vestibulo ocular reflexes (3D VOR) in humans using a six degrees of freedom (6DF) motion simulator. The gain and misalignment of the 3D angular VOR provide a direct measure of the quality of vestibular function. Representative data on healthy subjects are provided

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the ...

Neuroscience

Assessing the Autonomic and Behavioral Effects of Passive Motion in Rats using Elevator Vertical Motion and Ferris-Wheel Rotation

The overall goal of this study is to assess the autonomic and behavioral effects of passive motion in rodents using the elevator vertical motion and Ferris-wheel rotation devices. These assays can help confirm the integrity and normal functioning of the autonomic nervous system. They are coupled to quantitative measures based on defecation counting, open-field examination, and balance beam crossing. The advantages of these assays are their simplicity, reproducibility, and quantitative behavioral measures. The limitations of these assays are that the autonomic reactions could be epiphenomena of non-vestibular disorders and that a functioning vestibular system is required. Examination of disorders such as motion sickness will be greatly aided by the detailed procedures of these assays.

Protocols are presented to assess the autonomic and behavioral effects of passive motion in rodents using elevator vertical motion and Ferris-wheel rotation.

The overall goal of this study is to assess the autonomic and behavioral effects of passive motion in rodents using the elevator vertical motion and ...

Behavior

Using Unidirectional Rotations to Improve Vestibular System Asymmetry in Patients with Vestibular Dysfunction

The vestibular system provides information about head movement and mediates reflexes that contribute to balance control and gaze stabilization during daily activities. Vestibular sensors are located in the inner ear on both sides of the head and project to the vestibular nuclei in the brainstem. Vestibular dysfunction is often due to an asymmetry between input from the two sides. This results in asymmetrical neural inputs from the two ears, which can produce an illusion of rotation, manifested as vertigo. The vestibular system has an impressive capacity for compensation, which serves to rebalance how asymmetrical information from the sensory end organs on both sides is processed at the central level. To promote compensation, various rehabilitation programs are used in the clinic; however, they primarily use exercises that improve multisensory integration. Recently, visual-vestibular training has also been used to improve the vestibulo-ocular reflex (VOR) in animals with compensated unilateral lesions. Here, a new method is introduced for rebalancing the vestibular activity on both sides in human subjects. This method consists of five unidirectional rotations in the dark (peak velocity of 320&#176;/s) toward the weaker side. The efficacy of this method was shown in a sequential, double-blinded clinical trial in 16 patients with VOR asymmetry (measured by the directional preponderance in response to sinusoidal rotations). In most cases, VOR asymmetry decreased after a single session, reached normal values within the first two sessions in one week, and the effects lasted up to 6 weeks. The rebalancing effect is due to both an increase in VOR response from the weaker side and a decrease in response from the stronger side. The findings suggest that unidirectional rotation can be used as a supervised rehabilitation method to reduce VOR asymmetry in patients with longstanding vestibular dysfunction.

A new rehabilitation method is presented for rebalancing the vestibular system in patients with asymmetric responses, which consists of unidirectional rotations toward the weaker side. By directly modifying the vestibular pathway rather than enhancing the multisensory aspects of compensation, asymmetry can be normalized within 1-2 sessions and show lasting effects.

The vestibular system provides information about head movement and mediates reflexes that contribute to balance control and gaze stabilization during ...

Estimating Vestibular Perceptual Thresholds Using a Six-Degree-Of-Freedom Motion Platform

Vestibular perceptual thresholds refer to the motion intensity required to enable a participant to detect or discriminate a motion based on vestibular input. Using passive motion profiles provided by six degree-of-motion platforms, vestibular perceptual thresholds can be estimated for any kind of motion and thereby target each of the sub-components of the vestibular end-organ. Assessments of vestibular thresholds are clinically relevant as they complement diagnostic tools such as caloric irrigation, the head impulse test (HIT), or vestibular evoked myogenic potentials (VEMPs), which only provide information on sub-components of the vestibular system, but none of them allow for assessing all components. There are several methods with different advantages and disadvantages for estimating vestibular perceptual thresholds. In this article, we present a protocol using an adaptive staircase algorithm and sinusoidal motion profiles for an efficient estimation procedure. Adaptive staircase algorithms consider the response history to determine the peak velocity of the next stimuli and are the most commonly used algorithms in the vestibular domain. We further discuss the impact of motion frequency on vestibular perceptual thresholds.

In this article, we describe the methods, procedures, and technologies required to estimate vestibular perceptual thresholds using a six-degree-of-freedom motion platform.

Vestibular perceptual thresholds refer to the motion intensity required to enable a participant to detect or discriminate a motion based on vestibular ...

Implementing Vestibular Disorder Screening Tests

Screening People on Standing Balance with Romberg Testing and Walking Balance with Tandem Walking

The goal of this protocol is to inform readers about the exact procedures to use to perform two screening tests for vestibular disorders: tandem walking (TW) with eyes closed, also known as heel-toe walking, and the Clinical Test of Sensory Integration and Balance (CTSIB), which is also known as the modified Romberg. The study describes the steps for performing each test and each of the three CTSIB subtests so that the reader will be able to replicate the test conditions for use in the clinic, in the clinical laboratory, or in any other situation needing valid and reliable screening for balance skill which might be affected by changes in vestibular system function. The procedures detailed here can be easily administered and take less than 1 min per trial. References to published papers with normative data are provided. The representative results section includes examples of data collected with these screening tests.

Author Spotlight: Developing Low-Tech Balance Assessment Methods for Broad-Spectrum Healthcare Applications 

This article describes procedures for screening people for standing and walking balance impairments using two normed, rapid, low-tech balance tests.

The goal of this protocol is to inform readers about the exact procedures to use to perform two screening tests for vestibular disorders: tandem walking ...

An Endoscopic Transcanal Transpromontorial Approach for Vestibular Schwannomas using a Computer-Based Three-Dimensional Imaging System

A 2D monocular endoscope has been used in transcanal transpromontory vestibular schwannoma surgery instead of craniotomy. However, the absence of depth perception is the limitation of this approach. With the loss of depth perception, the surgeon will be not able to perform delicate and particularly complicated surgery. A binocular endoscope has been developed to provide stereoscopic vision with better depth perception for complicated anatomic structures and has been applied in some endoscopic surgeries. However, the diameter of the endoscope is a limitation in the performance of transcanal otologic surgeries. A small diameter endoscope facilitates easier surgery in a restricted space. A computer-based 3D imaging system can obtain 3D images in real-time using a small monocular endoscope. In this study, to evaluate the feasibility of a computer-based 3D imaging system for endoscopic lateral skull base surgery, we applied this 3D imaging system in a transcanal transpromontorial approach in two patients with vestibular schwannomas. The surgical procedure was completed without complication in these two cases. There was no mortality, perioperative complications, nor notable postoperative complications. Using this computer-based 3D imaging system, a better depth perception and stereoscopic vision was observed compared to a conventional 2D endoscope. The improvement in depth perception offers superior management of the complicated surgical anatomy.

Here, we present a transcanal transpromontorial approach for vestibular schwannomas using a computer-based three-dimensional (3D) imaging system combined with a two-dimensional (2D) endoscope. This system provided stereoscopic vision, better depth perception and reduced visual fatigue. This 3D imaging system enabled the application of 3D vision technology in endoscopic lateral skull base surgery.

A 2D monocular endoscope has been used in transcanal transpromontory vestibular schwannoma surgery instead of craniotomy. However, the absence of depth ...

Assessment of Static Graviceptive Perception in the Roll-Plane using the Subjective Visual Vertical Paradigm

Vestibular disorders are among the most common syndromes in medicine. In recent years, new vestibular diagnostic systems have been introduced that allow the examination of all semicircular canals in the clinical setting. Assessment methods of the otolithic system, which is responsible for the perception of linear acceleration and perception of gravity, are far less in clinical use. There are several experimental approaches for measuring the perception of gravity. The most frequently used method is the determination of the subjective visual vertical. This is usually measured with the head in an upright position. We present here an assessment method for testing otolith function in the roll plane. The subjective visual vertical is measured in the head upright position as well as with head inclination of &#177; 15&#176; and &#177; 30&#176; in the roll plane. This extended functional paradigm is an easy-to-perform clinical test of otolith function and ensures increased information content for the detection of impaired graviceptive perception.

The perception of gravity is commonly determined by the subjective visual vertical in the head upright position. The additional assessment at head tilts of &#177; 15&#176; and &#177; 30&#176; in the roll plane ensures increased information content for the detection of impaired graviceptive perception.

Vestibular disorders are among the most common syndromes in medicine. In recent years, new vestibular diagnostic systems have been introduced that allow ...

Measuring the Influence of Magnetic Vestibular Stimulation on Nystagmus, Self-Motion Perception, and Cognitive Performance in a 7T MRT

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called magnetic vestibular stimulation (MVS). In this article, we present an experimental setup in a 7T MRT scanner (MRI scanner) that allows the investigation of the influence of strong magnetic fields on nystagmus as well as perceptual and cognitive responses. The strength of MVS is manipulated by altering the head positions of the participants. The orientation of the participants&#39; semicircular canals with respect to the static magnetic field is assessed by combining a 3D magnetometer and 3D constructive interference in steady-state (3D-CISS) images. This approach allows to account for intra- and inter-individual differences in participants&#8217; responses to MVS. In the future, MVS can be useful for clinical research, for example, in the investigation of compensatory processes in vestibular disorders. Furthermore, it could foster insights into the interplay between vestibular information and cognitive processes in terms of spatial cognition and the emergence of self-motion percepts under conflicting sensory information. In fMRI studies, MVS can elicit a possible confounding effect, especially in tasks influenced by vestibular information or in studies comparing vestibular patients with healthy controls.

In this article, we describe the experimental setup, material, and procedures to assess reflexive eye movements, self-motion perception, and cognitive tasks under magnetic vestibular stimulation, as well as the anatomical orientation of the vestibular organs, in a 7 Tesla Magnetic resonance tomography (7T-MRT) scanner.

Strong magnetic fields induce dizziness, vertigo, and nystagmus due to Lorentz forces acting on the cupula in the semi-circular canals, an effect called ...

Surgical Treatment of an Endolymphatic Sac Tumor

Endolymphatic sac tumors (ELST) are low-grade papillary adenocarcinoma originating from the endolymphatic sac. Usually slow-growing, with local aggressiveness and a low risk of distant metastases, ELST can be sporadic but also frequently associated with von Hippel Lindau disease. The current treatment of ELST is primarily surgical resection. A 55-year-old woman accessed our otologic tertiary level referral center for a sudden worsening of hearing loss in her left ear and vertigo. A magnetic resonance (MRI) and computer tomography scan study subsequently showed a mass in the petrous bone; hence, the presence of an ELST was hypothesized. After embolization of the mass, the patient underwent surgical removal of the lesion. The resection of the mass was done through a translabirinthine approach, with an uneventful procedure. No residual disease remained after surgery. After 24 months of radiologic follow up with MRI, there are no signs of recurrence disease. This paper reports the management of this sporadic ELST, as well as the follow up results, providing clinicians this protocol for the handling of such a challenging otologic skull base surgery and rare disease.

Here, we discuss clinical and radiological features of endolymphatic sac tumors and report the methodology and results of a surgical removal in a case in care at our otologic referral center.

Endolymphatic sac tumors (ELST) are low-grade papillary adenocarcinoma originating from the endolymphatic sac. Usually slow-growing, with local ...

Equilibrium and Balance

The inner ear assumes dual functionalities of auditory perception and equilibrium maintenance. The vestibule is the organ responsible for balance. This organ contains mechanoreceptors, specifically hair cells, endowed with stereocilia, which aid in deciphering information regarding the position and motion of our heads. Two intrinsic components, the utricle and saccule, help perceive head position, while the semicircular canals track head movement. Neurological messages initiated in the vestibular ganglion are sent to the brainstem and cerebellum via the vestibulocochlear nerve.
The macula, a tissue found in the utricle and saccule, consists of surrounding support cells encircling the hair cells. The stereocilia, extensions of the hair cells, are embedded in a gelatinous substance called the otolithic membrane. This membrane is topped with a layer of calcium carbonate crystals or otoliths. The otoliths render the otolithic membrane heavy, causing it to move independently from the macula during head movements. In the event of a head tilt, the otolithic membrane, which slides over the macula, is influenced by gravity. This movement subsequently results in the bending of the stereocilia, causing specific hair cells to depolarize while others hyperpolarize. The brain decodes the precise head position through the depolarization pattern of hair cells.
The vestibule extends to form three ring-like structures, the semicircular canals. These are arranged in different planes: one horizontally and the other two vertically at approximately 45 degrees relative to the sagittal plane. Each canal base is connected to a dilated region called the ampulla, which houses hair cells that respond to rotational head movements. The stereocilia of these hair cells extend into a structure called the cupula, located on top of the ampulla. When the head rotates in a plane corresponding to a semicircular canal, the fluid inside the canal lags, causing the cupula to deflect oppositely to the head movement. The semicircular canals encompass several ampullae arranged both horizontally and vertically. This arrangement allows the vestibular system to decipher the direction of diverse head movements within three-dimensional (3-D) space.
Common disorders of the vestibular system:
Motion sickness:
The fundamental cause of motion sickness resides in the complex interactions between our sensory systems. The vestibular system in the inner ear plays a crucial role in maintaining balance and spatial orientation. During travel, the visual input may not align with the signals from the vestibular system, causing a sensory conflict that leads to the symptoms of motion sickness. This disparity between visual and vestibular inputs triggers neurochemical changes within the brain. Specifically, the neurotransmitter histamine is released in higher amounts, contributing to the onset of motion sickness symptoms.
Several factors can influence the onset of motion sickness. Vehicle type is one such factor; some people may be more susceptible to car motion sickness, while others may experience it more frequently on boats or airplanes. The route of travel can also contribute to the severity of motion sickness. For example, winding roads or turbulent flights may trigger more intense symptoms. Individual susceptibility is another key factor. Some people are naturally more prone to motion sickness than others, and various genetic and environmental factors can influence this.
Symptoms of motion sickness can include nausea, vomiting, dizziness, and headaches. These symptoms can significantly impact an individual&#39;s daily life, particularly if they need to travel frequently for work or personal reasons.
Benign paroxysmal positional vertigo (BPPV):
Benign paroxysmal positional vertigo (BPPV) is the most common vestibular disorder. It occurs when tiny calcium particles clump up in the inner ear, causing brief episodes of mild to intense dizziness. Diagnosis is typically through the Dix-Hallpike test, which involves observing involuntary eye movements as the patient&#39;s head is moved into specific positions. Treatment often involves maneuvers to move the calcium deposits out of the canal they&#39;re affecting.
Vestibular neuritis:
Vestibular neuritis, an inner ear inflammation usually caused by viral infections, leads to sudden, severe vertigo, nausea, and imbalance. Diagnosis typically involves ruling out other causes of these symptoms. Treatments usually focus on alleviating the symptoms and may include medications, vestibular rehabilitation therapy, and lifestyle changes.