Name: stimulus-specific cortical visual evoked potential morphological patterns
Uploaded: 2019-05-12T14:00:00
Description: Watch this Scientific Journal Video about Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns at JoVE.com

This research was supported by the University of Texas at Austin Moody College of Communication Grant Preparation Award and the University of Texas at Austin Office of the Vice President of Research Special Research Grant.

All methods described here have been approved by the Institutional Review Board (IRB) for Human Research at the University of Texas at Austin.
1. Stimuli Characteristics
<ol>
	<li>Create object stimuli using open source images available through the Bank of Standardized Stimuli (BOSS). This database consists of standardized images used throughout visual cognitive experiments.&#160; Download four images (e.g., ball02, book01a, brick, button03) with a high rate of identification (above 75%)<sup...

<ol>
	<li>Lascano, A. M., Lalive, P. H., Hardmeier, M., Fuhr, P., Seeck, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+evoked+potentials+in+neurology:+A+review+of+techniques+and+indications.">Clinical evoked potentials in neurology: A review of techniques and indications.</a> Journal of Neurology, Neurosurgery, and Psychiatry. 88 (8), 688-696 (2017).</li><li>Mehta, R. K., Parasuraman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuroergonomics:+A+review+of+applications+to+physical+and+cognitive+work.">Neuroergonomics: A review of applications to physical and cognitive work.</a> Frontiers in Human Neuroscience. 7, 889 (2013).</li><li>Kuba, M., Kubova, Z., Kremlacek, J., Langrova, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motion-onset+VEPs:+Characteristics,+methods,+and+diagnostic+use.">Motion-onset VEPs: Characteristics, methods, and diagnostic use.</a> Vision Research. 47 (2), 189-202 (2007).</li><li>Tobimatsu, S., Celesia, G. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+of+human+visual+pathophysiology+with+visual+evoked+potentials.">Studies of human visual pathophysiology with visual evoked potentials.</a> Clinical Neurophysiology. 117 (7), 1414-1433 (2006).</li><li>Tremblay, E., 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=Delayed+early+primary+visual+pathway+development+in+premature+infants:+High+density+electrophysiological+evidence.">Delayed early primary visual pathway development in premature infants: High density electrophysiological evidence.</a> PLoS One. 9 (9), e107992 (2014).</li><li>Allison, T., Puce, A., Spencer, D. D., McCarthy, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophysiological+studies+of+human+face+perception.+I:+Potentials+generated+in+occipitotemporal+cortex+by+face+and+non-face+stimuli.">Electrophysiological studies of human face perception. I: Potentials generated in occipitotemporal cortex by face and non-face stimuli.</a> Cerebral Cortex. 9, 415-430 (1999).</li><li>Grill-Spector, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+neural+basis+of+object+perception.">The neural basis of object perception.</a> Current Opinions in Neurobiology. 13, 159-166 (2003).</li><li>Mitchell, T. V., Neville, 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=Asynchronies+in+the+development+of+electrophysiological+responses+to+motion+and+color.">Asynchronies in the development of electrophysiological responses to motion and color.</a> Journal of Cognitive Neuroscience. 16, 1363-1374 (2004).</li><li>Armstrong, B. A., Neville, H. J., Hillyard, S. A., Mitchell, T. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Auditory+deprivation+affects+processing+of+motion,+but+not+color.">Auditory deprivation affects processing of motion, but not color.</a> Cognitive Brain Research. 14, 422-434 (2002).</li><li>Donner, T. H., Siegel, M., Oostenveld, R., Fries, P., Bauer, M., Engel, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Population+activity+in+the+human+dorsal+pathway+predicts+the+accuracy+of+visual+motion+detection.">Population activity in the human dorsal pathway predicts the accuracy of visual motion detection.</a> Journal of Neurophysiology. 98, 345-359 (2007).</li><li>Bonfiglio, L., 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=Defective+chromatic+and+achromatic+visual+pathways+in+developmental+dyslexia:+Cues+for+an+integrated+intervention+programme.">Defective chromatic and achromatic visual pathways in developmental dyslexia: Cues for an integrated intervention programme.</a> Restorative Neurology and Neuroscience. 35 (1), 11-24 (2017).</li><li>Campbell, J., Sharma, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+cross-modal+re-organization+in+children+with+cochlear+implants.">Visual cross-modal re-organization in children with cochlear implants.</a> PLoS ONE. 11 (1), e0147793-e0147718 (2016).</li><li>Campbell, J., Sharma, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+visual+evoked+potential+morphological+patterns+for+apparent+motion+processing+in+school-aged+children.">Distinct visual evoked potential morphological patterns for apparent motion processing in school-aged children.</a> Frontiers in Human Neuroscience. 10 (71), 277 (2016).</li><li>Doucet, M. E., Gosselin, F., Lassonde, M., Guillemot, J. P., Lepore, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+visual-evoked+potentials+to+radially+modulated+concentric+patterns.">Development of visual-evoked potentials to radially modulated concentric patterns.</a> Neuroreport. 16 (6), 1753-1756 (2005).</li><li>Doucet, M. E., Bergeron, F., Lassonde, M., Ferron, P., Lepore, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cross-modal+reorganization+and+speech+perception+in+cochlear+implant+users.">Cross-modal reorganization and speech perception in cochlear implant users.</a> Brain. 129 (12), 3376-3383 (2006).</li><li>Kubova, Z., 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=Difficulties+of+motion-onset+VEP+interpretation+in+school-age+children.">Difficulties of motion-onset VEP interpretation in school-age children.</a> Documenta Ophthalmologica. 128, 121-129 (2014).</li><li>Gould, I. C., Rushworth, M. F., Nobre, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indexing+the+graded+allocation+of+visuospatial+attention+using+anticipatory+alpha+oscillations.">Indexing the graded allocation of visuospatial attention using anticipatory alpha oscillations.</a> Journal of Neurophysiology. 105, 1318-1326 (2011).</li><li>Hanslmayr, S., Aslan, A., Staudigl, T., Klimesch, W., Hermann, C. S., Bauml, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prestimulus+oscillations+predict+visual+perception+performance+between+and+within+subjects.">Prestimulus oscillations predict visual perception performance between and within subjects.</a> Neuroimage. 37, 1465-1543 (2007).</li><li>Toosi, T., Tousi, E. K., Esteky, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Learning+temporal+context+shapes+prestimulus+alpha+oscillations+and+improves+visual+discrimination+performance.">Learning temporal context shapes prestimulus alpha oscillations and improves visual discrimination performance.</a> Journal of Neurophysiology. 118 (2), 771-777 (2017).</li><li>Brodeur, M. B., Dionne-Dostie, E., Montreuil, T., Lepage, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Bank+of+Standardized+Stimuli+(BOSS),+a+new+set+of+480+normative+photos+of+objects+to+be+used+as+visual+stimuli+in+cognitive+research.">The Bank of Standardized Stimuli (BOSS), a new set of 480 normative photos of objects to be used as visual stimuli in cognitive research.</a> PLoS One. 5 (5), e10773 (2010).</li><li>Brodeur, M. B., 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+Bank+of+Standardized+Stimuli+(BOSS):+Comparison+between+French+and+English+norms.">The Bank of Standardized Stimuli (BOSS): Comparison between French and English norms.</a> Behavior Research Methods. 44, 961-970 (2012).</li><li>Suttle, C., Harding, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+of+transient+VEPs+to+luminance+and+chromatic+pattern+onset+and+offset.">Morphology of transient VEPs to luminance and chromatic pattern onset and offset.</a> Vision Research. 39 (8), 1577-1584 (1999).</li><li>Campbell, J., Sharma, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cross-modal+re-organization+in+adults+with+early+stage+hearing+loss.">Cross-modal re-organization in adults with early stage hearing loss.</a> PLoS One. 9 (2), e90594 (2014).</li><li>Campbell, J., Sharma, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compensatory+changes+in+cortical+resource+allocation+in+adults+with+hearing+loss.">Compensatory changes in cortical resource allocation in adults with hearing loss.</a> Frontiers in Systems Neuroscience. 7, 71 (2013).</li><li>Debener, S., Hine, J., Bleeck, S., Eyles, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Source+localization+of+auditory+evoked+potentials+after+cochlear+implantation.">Source localization of auditory evoked potentials after cochlear implantation.</a> Psychophysiology. 45 (1), 20-24 (2008).</li><li>Gilley, P. M., Sharma, A., Dorman, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cortical+reorganization+in+children+with+cochlear+implants.">Cortical reorganization in children with cochlear implants.</a> Brain Research. 1239, 56-65 (2008).</li><li>Neuner, I., Arruba, J., Felder, J., Shah, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+EEG-fMRI+acquisition+at+low,+high+and+ultra-high+magnetic+fields+up+to+9.4+T:+Perspectives+and+challenges.">Simultaneous EEG-fMRI acquisition at low, high and ultra-high magnetic fields up to 9.4 T: Perspectives and challenges.</a> Neuroimage. 15 (102), 71-79 (2014).</li><li>Schulte-Korne, G., Bartling, J., Deimel, W., Remschmidt, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+evoked+potential+elicited+by+coherently+moving+dots+in+dyslexic+children.">Visual evoked potential elicited by coherently moving dots in dyslexic children.</a> Neuroscience Letters. 357 (3), 207-210 (2004).</li><li>Zhang, R., Hu, Z., Roberson, D., Zhang, L., Li, H., Liu, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+processes+underlying+the+&#8220;same&#8221;-+&#8220;different&#8221;+judgment+of+two+simultaneously+presented+objects&#8212;an+EEG+study.">Neural processes underlying the &#8220;same&#8221;- &#8220;different&#8221; judgment of two simultaneously presented objects&#8212;an EEG study.</a> PLoS One. 8 (12), e81737 (2013).</li></ol>

The goal of this methodological report was to evaluate the feasibility in recording differential CVEP morphology by using visual object and motion stimuli specifically designed to separately stimulate ventral and dorsal streams in passive viewing tasks6,7,8, both with and without variation of ISIs (jitter)19. Conditions were not designed to be directly compared, rather, observations were made as to whethe...

Electroencephalography (EEG) is a tool that offers an inexpensive and non-invasive approach to the study of cortical processing, especially when compared to cortical assessment methods such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and diffusion tensor imaging (DTI)1. EEG also provides high temporal resolution, which is not possible to attain when using measures such as fMRI, PET, or DTI2. High temporal resolution is critical when examining central temporal function in order to obtain millisecond-precision of neurophysiologic mechanisms related to the processing of specific input or events.&#160; In the central visual system, cortical visual evoked potentials (CVEPs) are a popular approach in studying time-locked neural processes in the cerebral cortex.&#160; CVEP responses are recorded and averaged over a number of event trials, resulting in peak components (e.g., P1, N1, P2) arising at specific millisecond intervals. The timing and amplitude of these peak neural responses can provide information concerning cortical processing speed and maturation, as well as deficits in cortical function3,4,5.&#160;&#160;
CVEPs are specific to the type of visual input presented to the viewer. Using certain stimuli in a CVEP paradigm, it is possible to observe the function of distinct visual networks such as the ventral stream, involved in processing form and color, or parvocellular and magnocellular input6,7,8, and the dorsal stream, which largely processes motion or magnocellular input9,10. CVEPs generated by these networks have been useful not only in better understanding typical neurophysiologic mechanisms underlying behavior but also in the targeted treatment of atypical behaviors in clinical populations. For example, delayed CVEP components in both dorsal and ventral networks have been reported in children with dyslexia, which suggests that visual function in both these networks should be targeted when designing an intervention plan11.&#160; Thus, CVEPs recorded via EEG offer a powerful clinical tool through which to assess both typical and atypical visual processes.&#160;
In a recent study, high-density EEG was used to measure the apparent motion-onset CVEPs in typically developing children, with the goal of examining variable CVEP responses and related visual cortical generators across development. Participants passively viewed apparent motion stimuli12,13,14,15, which consisted of both shape&#160;change and motion,&#160;designed to simultaneously stimulate dorsal and ventral streams. It was found that approximately half of the children responded with a CVEP waveform shape, or morphology, consisting of three peaks (P1-N1-P2, pattern A).&#160; This morphology is a classic CVEP response observed throughout the literature. In contrast, the other half of the children presented with a morphological pattern comprised of five peaks (P1-N1a-P2a-N1b-P2b, pattern B). To our knowledge, the robust occurrence and comparison of these morphological patterns have not previously been discussed in CVEP literature in either child or adult populations, although variable morphology has been noted in both apparent-motion and motion-onset CVEPs14,16. Furthermore, these morphological differences would not have been apparent in research using other cortical functional assessment methods, such as fMRI or PET, due to the low temporal resolution of these measures.
To determine the cortical generators of each peak in CVEP patterns A and B, source localization analyses were performed, which is a statistical approach used to estimate the most likely cortical regions involved in the CVEP response12,13. For each peak, regardless of the morphological pattern, primary and higher-order visual cortices were identified as sources of the CVEP signal.&#160; Thus, it appears that the main difference underlying CVEP morphology elicited by apparent motion is that those with pattern B activate visual cortical regions additional times during processing. Because these types of patterns have not been previously identified in the literature, the purpose of the additional visual processing in those with CVEP pattern B remains unclear.&#160; Therefore, the next aim in this line of research is to gain a better understanding of the cause of the differential CVEP morphology and whether such patterns may relate to visual behavior in both typical and clinical populations.&#160;
The first step in understanding why some individuals might demonstrate one CVEP morphology versus another is to determine whether these responses are intrinsic or extrinsic in nature.&#160; In other words, if an individual demonstrates one pattern in response to a visual stimulus, will they respond with a similar pattern to all stimuli?&#160; Or is this response stimulus-dependent, specific to the visual network or networks activated?
To answer this question, two passive visual paradigms were designed, intended to separately activate specific visual networks. The stimulus presented in the initial study was designed to stimulate both dorsal and ventral streams simultaneously; thus, it was unknown if one or both networks were involved in generating specific waveform morphology. In the current methodological approach, the paradigm designed to stimulate the ventral stream is composed of highly identifiable objects in basic shapes of squares and circles, eliciting object-onset CVEPs. The paradigm designed to stimulate the dorsal stream consists of visual motion via a radial field of coherent central dot motion dots at a fixed speed toward a fixation point, eliciting motion-onset CVEPs.&#160;
A second question that arose as a result of the initial study was whether differential VEP morphology could be due to participant anticipation of upcoming stimuli13. For instance, research has shown that top-down cortical oscillatory activity occurring prior to a target stimulus may predict subsequent CVEP and behavioral responses to some degree17,18,19. The apparent motion paradigm in the first study employed non-randomized frames of a radial star and circle with consistent inter-stimulus intervals (ISIs) of 600 ms. This design may have encouraged the expectation and prediction of the upcoming stimulus, with resulting oscillatory activity affecting subsequent CVEP morphology12,13,19.&#160;&#160;
To address this issue, the visual object and motion paradigms in the current protocol are designed with both consistent ISIs of the same temporal value and randomized ISIs with different temporal values (i.e., jitter).&#160; Using this approach, it may be possible to determine how temporal variation can affect VEP morphology within distinct visual networks. Altogether, the aim of the described protocol is to determine if the visual object and motion stimuli would be sensitive to variations in CVEP morphology and whether the temporal variation of stimuli presentation would affect characteristics of the CVEP response, including peak latency, amplitude, and morphology. For the purpose of the current paper, the goal is to determine the feasibility of the methodological approach. It is hypothesized that both visual objects and motion may elicit variable morphology (i.e., patterns A and B will be observed across subjects in response to both stimuli) and that temporal variation would affect object-onset and motion-onset CVEP components.&#160;

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			<td height="21" style="height:21px;width:216px;">E-Prime 2.0</td>
			<td style="width:240px;">Psychology Software Tools, Inc</td>
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			<td style="width:279px;">Used in data acquisition</td>
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			<td height="21" style="height:21px;width:216px;">Net Amps 400</td>
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			<td height="21" style="height:21px;width:216px;">iMac (27-inch)</td>
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			<td>Used in data acquisition</td>
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			<td height="21" style="height:21px;width:216px;">Optiplex 7020 Computer</td>
			<td style="width:240px;">Dell</td>
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			<td>Stimulus computer</td>
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			<td height="21" style="height:21px;width:216px;">HydroCel GSN EEG net</td>
			<td style="width:240px;">Electrical Geodesics, Inc</td>
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			<td>Used in data acqusition</td>
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			<td height="21" style="height:21px;width:216px;">1 ml pipette</td>
			<td style="width:240px;">Electrical Geodesics, Inc</td>
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			<td>Used to lower impedances</td>
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			<td height="21" style="height:21px;width:216px;">Johnson&#39;s Baby Shampoo</td>
			<td style="width:240px;">Johnson &#38; Johnson</td>
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			<td style="width:240px;">Electrical Geodesics, Inc</td>
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			<td>Used in impedance solution</td>
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			<td height="42" style="height:42px;width:216px;">Control III Disinfectant Germicide</td>
			<td style="width:240px;">Control III</td>
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			<td>Used in disinfectant solution</td>
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			<td height="21" style="height:21px;">32-inch LCD monitor&#160;</td>
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			<td>Used to present stimuli</td>
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			<td height="21" style="height:21px;width:216px;">Matlab (R2016b)</td>
			<td style="width:240px;">MathWorks</td>
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			<td>Used in data analysis</td>
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			<td height="63" style="height:63px;width:216px;">EEGlab v14.1.2</td>
			<td style="width:240px;">Swartz Center for Computational Neuroscience, University of California, San Diego</td>
			<td style="width:269px;">https://sccn.ucsd.edu/eeglab/index.php</td>
			<td>Used in data analysis</td>
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			<td height="42" style="height:42px;width:216px;">BOSS Database</td>
			<td style="width:240px;">Bank of Standardized Stimuli</td>
			<td style="width:269px;">https://sites.google.com/site/bosstimuli/</td>
			<td>Used in generation of visual object stimuli&#160;</td>
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			<td height="21" style="height:21px;width:216px;">Psychtoolbox-3</td>
			<td>Psychophysics Toolbox Version 3 (PTB-3)</td>
			<td style="width:269px;">http://psychtoolbox.org/</td>
			<td>Used in generation of visual motion stimuli</td>
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stimulus-specific cortical visual evoked potential morphological patterns

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using 128-channel high-density electroencephalography (EEG). The specific aim of the described stimuli and analyses is to examine whether it is feasible to replicate previously reported CVEP morphological patterns elicited by an apparent motion stimulus, designed to simultaneously stimulate both ventral and dorsal central visual networks, using object and motion stimuli designed to separately stimulate ventral and dorsal visual cortical networks.&#160; Four visual paradigms are presented: 1. Randomized visual objects with consistent temporal presentation. 2. Randomized visual objects with inconsistent temporal presentation (or jitter).&#160; 3. Visual motion via a radial field of coherent central dot motion without jitter.&#160; 4. Visual motion via a radial field of coherent central dot motion with jitter.&#160; These four paradigms are presented in a pseudo-randomized order for each participant.&#160; Jitter is introduced in order to view how possible anticipatory-related effects may affect the morphology of the object-onset and motion-onset CVEP response.&#160; EEG data analyses are described in detail, including steps of data exportation from and importation to signal processing platforms, bad channel identification&#160;and removal, artifact rejection, averaging, and categorization of average CVEP morphological pattern type based upon latency ranges of component peaks. Representative data show that the methodological approach is indeed sensitive in eliciting differential object-onset and motion-onset CVEP morphological patterns and may, therefore, be useful in addressing the larger research aim. Given the high temporal resolution of EEG and the possible application of high-density EEG in source localization analyses, this protocol is ideal for the investigation of distinct CVEP morphological patterns and the underlying neural mechanisms which generate these differential responses.&#160; &#160; &#160;&#160;

Figure 3 and Figure 4 show the representative object-onset and motion-onset CVEP results of five participants, aged 19-24 years, who passively viewed each visual paradigm. This design allowed observation of CVEP responses elicited by visual objects (with and without jitter) and visual motion (with and without jitter) both within and across subjects according to each condition.&#160; Participant CVEPs were grouped according to the morphological pattern elicited b...

Watch this Scientific Journal Video about Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns at JoVE.com

Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns

In this paper, we present a protocol to investigate differential cortical visual evoked potential morphological patterns through stimulation of ventral and dorsal networks using high-density EEG. Visual object and motion stimulus paradigms, with and without temporal jitter, are described. Visual evoked potential morphological analyses are also outlined.&#160;&#160;

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using ...

Using this protocol and future studies with larger sample sizes may determine whether variable cortical visual evoked potential morphology is dependent upon stimulus type, extrinsic, or the viewer, intrinsic. Variable visual evoked potential morphology can only be viewed using the high temporal resolution of EEG, which is also cost-effective, non-invasive, and requires minimal recording time versus other methodologies. Demonstrating the procedure will be Mashhood Nielsen, the lab manager and an undergraduate research assistant from my laboratory.After escorting the participant into the EEG recording room, measure the head circumference of the participant in centimeters, and select the appropriate EEG net size. Measure and mark the midpoint of the scalp for the placement of the reference electrode. Prepare one liter of warm water mixed with five milliliters of baby shampoo and 1, 100 grams of potassium chloride.Place the EEG net in the solution and allow the net to soak in the solution for five minutes. Turn on the stimulus presentation computer and the EEG acquisition computer. Place a towel or other absorbent material around the participant's neck to prevent the solution from dripping onto his or her clothes and instruct the participant to close his or her eyes.Then firmly grip the EEG net with both hands and place it onto the participant's head. Ensure that the net is placed symmetrically on the scalp head, with the reference electrode at the scalp midline point that was measured. Tighten the chin and ocular net lines to ensure a secure connection between the scalp and electrodes.Ask the participant if he or she is comfortable, and if anything needs to be adjusted. Connect the EEG net to the amplifier. Check for the proper electrode impedance values with an average target of 10 kiloohms.To reduce impedance values, use a one milliliter pipette to apply the potassium chloride solution onto the scalp and electrodes that have a high impedance. Continue this process until adequate impedance values across the electrodes are achieved. Instruct the participant to focus on the visual stimuli that will appear on the monitor.The viewing distance is approximately 65 inches. Use a pseudo random number generator to determine the order of presentation for the four visual paradigms, and begin the visual tasks and EEG recording. If ongoing EEG shows high myogenic or exactly 60 hertz activity, pause the experiment to recheck electrode scalp connectivity.Repeat the visual tasks and EEG recording for the visual object paradigm, the visual object with the temporal jitter paradigm, the visual motion paradigm, and the visual motion with temporal jitter paradigm. At the conclusion of the experiment, instruct the participants to close his or her eyes in order to prevent the solution from entering his or her eyes when removing the net. Begin by loosening the chin and ocular net lines.Then slowly remove the net by gently pulling the chin strap up and over the participant's head. Disconnect the EEG net from the amplifier. Begin the disinfection process by placing the EEG cap in and out of a bucket filled with water and rinsing under a faucet.Then, prepare the disinfectant solution by adding approximately two liters of water to the disinfectant bucket and mixing 15 milliliters of disinfectant with the water. Immerse the sensor end of the net in the disinfectant. Set a timer for two minutes.Continuously plunge the net up and down. Leave the net soaking for another eight minutes. After that, remove the EEG cap from the disinfectant solution.Place the EEG net in and out of the electrode bucket filled with water and under running water to rinse. Repeat the washing four times and allow the net to air dry. To start EEG analyses, using a one hertz high-pass filter, transfer EEG files into MatLab for analysis via the EEGLAB toolbox.Choose the file option from the drop down menu, and click on import data. Select using EEGLAB functions and plugins from the menu. Next, click on the appropriate export file format.Choose edit'from the drop down menu, and select channel locations'to reassign channel locations based on the type of electrode montage. Click on look up locations'and select the ellipse to locate the path of the electrode montage file of interest. To assign pre-and post-stimulus times, enter a value of 0.1 seconds in the start time box.To baseline correct data according to the prestimulus interval, select prestimulus baseline correct'Remove bad channels using probability at a Z-score threshold of 2.5. Verify identification or removal of bad channels by plotting all electrodes. If needed, manually remove channels with mean voltage amplitudes outside of the range of 30 to 30 microvolts.Then, perform artifact rejection by entering values of 100 microvolts and 100 microvolts, and note the channels with voltages outside the range for the entire segments. If they constitute 60%or more of the rejected trials, manually remove these bad channels. Repeat this step as many times as necessary.Following the artifact removal steps, ensure that a minimum of 100 sweeps are accepted. Then, plot the channels of interest to categorize morphological patterns. If cVEP morphology is characterized by a large positive peak at approximately 100 to 115 milliseconds p1, followed by a negative peak at approximately 140 to 180 milliseconds n1, and a positive peak at approximately 165 to 240 milliseconds p2, choose Pattern A.If cVEP morphology is characterized by positive and negative peaks at approximately 100 to 115 milliseconds p1, 140 to 180 milliseconds n1a, 180 to 240 milliseconds p2a, 230 to 280 milliseconds n1b, and 260 to 350 milliseconds p2b, choose Pattern B.To create a group average, append individual data sets together according to the morphological pattern visually observed.Name and save the newly merged data set file. The object onset cVEP results of five participants aged 19 to 24 years, who passively viewed each visual paradigm, are obtained. In the objects with no temporal jitter condition, two participants were found to present with Pattern A, while three presented with pattern B.Similarly, in the objects with temporal jitter condition, two subjects presented with Pattern A, and three with Pattern B.It may also be observed that jitter effects amplitude and latency in each object onset cVEP pattern.However, in contrast to the object onset cVEPs, motion onset cVEP morphological patterns for each participant were consistent across jitter condition. Furthermore, the Pattern B group average shows no clear evidence of the multiple peak components, typically present for both with and without temporal jitter. Similar to the objects paradigm, jitter in the motion paradigm appears to affect motion onset cVEP characteristics in both morphological patterns.Categorization of cVEP morphology is not currently performed. But morphological patterns can reflect specific visual cortical processes. Consideration of these patterns may clarify underlying neurophysiological function related to behavior.Magnetoencephalography, or MEG, may provide complimentary temporal information regarding visual evoke potentials. While simultaneous FMRI assessment could provide high spatial resolution concerning differential cortical network activation related to morphology. If electrodes are positioned inappropriately and/or impedances are high, interpretation of data will be difficult and possibly meaningless.When disinfecting the net, remember to be careful with the disinfectant, and do not get it close to the eyes. Dispose of it properly.

stimulus-specific-cortical-visual-evoked-potential-morphological

Research

JoVE Journal

Neuroscience

Physiological, Morphological and Neurochemical Characterization of Neurons Modulated by Movement

The role of individual neurons and their function in neuronal circuits is fundamental to understanding the neuronal mechanisms of sensory and motor functions. Most investigations of sensorimotor mechanisms rely on either examination of neurons while an animal is static1,2 or record extracellular neuronal activity during a movement.3,4 While these studies have provided the fundamental background for sensorimotor function, they either do not evaluate functional information which occurs during a movement or are limited in their ability to fully characterize the anatomy, physiology and neurochemical phenotype of the neuron. A technique is shown here which allows extensive characterization of individual neurons during an in vivo movement. This technique can be used not only to study primary afferent neurons but also to characterize motoneurons and sensorimotor interneurons. Initially the response of a single neuron is recorded using electrophysiological methods during various movements of the mandible followed by determination of the receptive field for the neuron. A neuronal tracer is then intracellularly injected into the neuron and the brain is processed so that the neuron can be visualized with light, electron or confocal microscopy (Fig. 1). The detailed morphology of the characterized neuron is then reconstructed so that neuronal morphology can be correlated with the physiological response of the neuron (Figs. 2,3). In this communication important key details and tips for successful implementation of this technique are provided. Valuable additional information can be determined for the neuron under study by combining this method with other techniques. Retrograde neuronal labeling can be used to determine neurons with which the labeled neuron synapses; thus allowing detailed determination of neuronal circuitry. Immunocytochemistry can be combined with this method to examine neurotransmitters within the labeled neuron and to determine the chemical phenotypes of neurons with which the labeled neuron synapses. The labeled neuron can also be processed for electron microscopy to determine the ultrastructural features and microcircuitry of the labeled neuron. Overall this technique is a powerful method to thoroughly characterize neurons during in vivo movement thus allowing substantial insight into the role of the neuron in sensorimotor function.

A technique is described to quantify the in vivo physiological response of mammalian neurons during movement and correlate the physiology of the neuron with neuronal morphology, neurochemical phenotype and synaptic microcircuitry.

The role of individual neurons and their function in neuronal circuits is fundamental to understanding the neuronal mechanisms of sensory and motor ...

Determination of Mitochondrial Membrane Potential and Reactive Oxygen Species in Live Rat Cortical Neurons

Mitochondrial membrane potential (&Delta;&Psi;m) is critical for maintaining the physiological function of the respiratory chain to generate ATP. A significant loss of &Delta;&Psi;m renders cells depleted of energy with subsequent death. Reactive oxygen species (ROS) are important signaling molecules, but their accumulation in pathological conditions leads to oxidative stress. The two major sources of ROS in cells are environmental toxins and the process of oxidative phosphorylation. Mitochondrial dysfunction and oxidative stress have been implicated in the pathophysiology of many diseases; therefore, the ability to determine &Delta;&Psi;m and ROS can provide important clues about the physiological status of the cell and the function of the mitochondria. 
Several fluorescent probes (Rhodamine 123, TMRM, TMRE, JC-1) can be used to determine &Delta;&psi;m in a variety of cell types, and many fluorescence indicators (Dihydroethidium, Dihydrorhodamine 123, H2DCF-DA) can be used to determine ROS. Nearly all of the available fluorescence probes used to assess &Delta;&Psi;m or ROS are single-wavelength indicators, which increase or decrease their fluorescence intensity proportional to a stimulus that increases or decreases the levels of &Delta;&Psi;m or ROS. Thus, it is imperative to measure the fluorescence intensity of these probes at the baseline level and after the application of a specific stimulus. This allows one to determine the percentage of change in fluorescence intensity between the baseline level and a stimulus. This change in fluorescence intensity reflects the change in relative levels of &Delta;&Psi;m or ROS. In this video, we demonstrate how to apply the fluorescence indicator, TMRM, in rat cortical neurons to determine the percentage change in TMRM fluorescence intensity between the baseline level and after applying FCCP, a mitochondrial uncoupler. The lower levels of TMRM fluorescence resulting from FCCP treatment reflect the depolarization of mitochondrial membrane potential. We also show how to apply the fluorescence probe H2DCF-DA to assess the level of ROS in cortical neurons, first at baseline and then after application of H2O2. This protocol (with minor modifications) can be also used to determine changes in &#x2206;&#x03A8;m and ROS in different cell types and in neurons isolated from other brain regions.

We demonstrate application of the fluorescence indicator, TMRM, in cortical neurons to determine the relative changes in TMRM fluorescence intensity before and after application of a specific stimulus. We also show application of the fluorescence probe H2DCF-DA to assess the relative level of reactive oxygen species in cortical neurons.

Mitochondrial membrane potential (&Delta;&Psi;m) is critical for maintaining the physiological function of the respiratory chain to generate ATP.  A ...

Transretinal ERG Recordings from Mouse Retina: Rod and Cone Photoresponses

There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light whereas cones operate continuously under rapidly changing bright light conditions. Absorption of light by rod- and cone-specific visual pigments in the outer segments of photoreceptors triggers a phototransduction cascade that eventually leads to closure of cyclic nucleotide-gated channels on the plasma membrane and cell hyperpolarization. This light-induced change in membrane current and potential can be registered as a photoresponse, by either classical suction electrode recording technique1,2 or by transretinal electroretinogram recordings (ERG) from isolated retinas with pharmacologically blocked postsynaptic response components3-5. The latter method allows drug-accessible long-lasting recordings from mouse photoreceptors and is particularly useful for obtaining stable photoresponses from the scarce and fragile mouse cones. In the case of cones, such experiments can be performed both in dark-adapted conditions and following intense illumination that bleaches essentially all visual pigment, to monitor the process of cone photosensitivity recovery during dark adaptation6,7. In this video, we will show how to perform rod- and M/L-cone-driven transretinal recordings from dark-adapted mouse retina. Rod recordings will be carried out using retina of wild type (C57Bl/6) mice. For simplicity, cone recordings will be obtained from genetically modified rod transducin &alpha;-subunit knockout (T&alpha;-/-) mice which lack rod signaling8.

We describe a relatively simple method of transretinal electroretinogram (ERG) recordings for obtaining rod and cone photoresponses from intact mouse retina. This approach takes advantage of the block of synaptic transmission from photoreceptors to isolate their light responses and record them using field electrodes placed across the isolated flat-mounted retina.

There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light ...

Functional Calcium Imaging in Developing Cortical Networks

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in intact spinal cord, brainstem, retina, cortex and dissociated neuronal culture preparations. During periods of spontaneous activity, neurons depolarize to fire single or bursts of action potentials, activating many ion channels. Depolarization activates voltage-gated calcium channels on dendrites and spines that mediate calcium influx. Highly synchronized electrical activity has been measured from local neuronal networks using field electrodes. This technique enables high temporal sampling rates but lower spatial resolution due to integrated read-out of multiple neurons at one electrode. Single cell resolution of neuronal activity is possible using patch-clamp electrophysiology on single neurons to measure firing activity. However, the ability to measure from a network is limited to the number of neurons patched simultaneously, and typically is only one or two neurons. The use of calcium-dependent fluorescent indicator dyes has enabled the measurement of synchronized activity across a network of cells. This technique gives both high spatial resolution and sufficient temporal sampling to record spontaneous activity of the developing network.
A key feature of newly-forming cortical and hippocampal networks during pre- and early postnatal development is spontaneous, synchronized neuronal activity (Katz &amp; Shatz, 1996; Khaziphov &amp; Luhmann, 2006). This correlated network activity is believed to be essential for the generation of functional circuits in the developing nervous system (Spitzer, 2006). In both primate and rodent brain, early electrical and calcium network waves are observed pre- and postnatally in vivo and in vitro (Adelsberger et al., 2005; Garaschuk et al., 2000; Lamblin et al., 1999). These early activity patterns, which are known to control several developmental processes including neuronal differentiation, synaptogenesis and plasticity (Rakic &amp; Komuro, 1995; Spitzer et al., 2004) are of critical importance for the correct development and maturation of the cortical circuitry.
In this JoVE video, we demonstrate the methods used to image spontaneous activity in developing cortical networks. Calcium-sensitive indicators, such as Fura 2-AM ester diffuse across the cell membrane where intracellular esterase activity cleaves the AM esters to leave the cell-impermeant form of indicator dye. The impermeant form of indicator has carboxylic acid groups which are able to then detect and bind calcium ions intracellularly.. The fluorescence of the calcium-sensitive dye is transiently altered upon binding to calcium. Single or multi-photon imaging techniques are used to measure the change in photons being emitted from the dye, and thus indicate an alteration in intracellular calcium. Furthermore, these calcium-dependent indicators can be combined with other fluorescent markers to investigate cell types within the active network.

Spontaneous activity of developing neuronal networks can be measured using AM-ester forms of calcium-sensitive indicator dyes. Changes in intracellular calcium, indicating neuronal activation, are detected as transient changes in indicator fluorescence with one- or two-photon imaging. This protocol can be adapted for a range of developmentally-dependent neuronal networks in vitro.

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in ...

Extracting Visual Evoked Potentials from EEG Data Recorded During fMRI-guided Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological effects. Specifically, by creating a transient interference with the normal activity of a target region and measuring changes in an electrophysiological signal, we can establish a causal link between the stimulated brain area or network and the electrophysiological signal that we record. If target brain areas are functionally defined with prior fMRI scan, TMS could be used to link the fMRI activations with evoked potentials recorded. However, conducting such experiments presents significant technical challenges given the high amplitude artifacts introduced into the EEG signal by the magnetic pulse, and the difficulty to successfully target areas that were functionally defined by fMRI. Here we describe a methodology for combining these three common tools: TMS, EEG, and fMRI. We explain how to guide the stimulator&#39;s coil to the desired target area using anatomical or functional MRI data, how to record EEG during concurrent TMS, how to design an ERP study suitable for EEG-TMS combination and how to extract reliable ERP from the recorded data. We will provide representative results from a previously published study, in which fMRI-guided TMS was used concurrently with EEG to show that the face-selective N1 and the body-selective N1 component of the ERP are associated with distinct neural networks in extrastriate cortex. This method allows us to combine the high spatial resolution of fMRI with the high temporal resolution of TMS and EEG and therefore obtain a comprehensive understanding of the neural basis of various cognitive processes.

This paper describes a method for collecting and analyzing electroencephalography (EEG) data during concurrent transcranial magnetic stimulation (TMS) guided by activations revealed with functional magnetic resonance imaging (fMRI). A method for TMS artifact removal and extraction of event related potentials is described as well as considerations in paradigm design and experimental setup.

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological ...

Subtype-selective Electroporation of Cortical Interneurons

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression of genes of interest to specific neuronal subtypes has proven remarkably challenging due to the relative scarcity of specific promoter elements. GABAergic interneurons constitute a neuronal population with extensive genetic and morphological diversity. Indeed, more than 11 different subtypes of GABAergic interneurons have been characterized in the mouse cortex1. Here we present an adapted protocol for selective targeting of GABAergic populations. We achieved subtype selective targeting of GABAergic interneurons by using the enhancer element of the homeobox transcription factors Dlx5 and Dlx6, homologues of the Drosophila distal-less (Dll) gene2,3, to drive the expression of specific genes through in utero electroporation.

This procedure shows how to target interneurons in the developing mouse forebrain by means of in utero electroporation. This technique was particularly efficient to achieve selective gene expression in interneuron subtypes destined to the superficial layers of the cortex.

The study of central nervous system (CNS) maturation relies on genetic targeting of neuronal populations. However, the task of restricting the expression ...

Functional and Morphological Assessment of Diaphragm Innervation by Phrenic Motor Neurons

This protocol specifically focuses on tools for assessing phrenic motor neuron (PhMN) innervation of the diaphragm at both the electrophysiological and morphological levels. Compound muscle action potential (CMAP) recording following phrenic nerve stimulation can be used to quantitatively assess functional diaphragm innervation by PhMNs of the cervical spinal cord in vivo in anesthetized rats and mice. Because CMAPs represent simultaneous recording of all myofibers of the whole hemi-diaphragm, it is useful to also examine the phenotypes of individual motor axons and myofibers at the diaphragm NMJ in order to track disease- and therapy-relevant morphological changes such as partial and complete denervation, regenerative sprouting and reinnervation. This can be accomplished via whole-mount immunohistochemistry (IHC) of the diaphragm, followed by detailed morphological assessment of individual NMJs throughout the muscle. Combining CMAPs and NMJ analysis provides a powerful approach for quantitatively studying diaphragmatic innervation in rodent models of CNS and PNS disease.

Compound muscle action potential recording quantitatively assesses functional diaphragm innervation by phrenic motor neurons. Whole-mount diaphragm immunohistochemistry assesses morphological innervation at individual neuromuscular junctions. The goal of this protocol is to demonstrate how these two powerful methodologies can be used in various rodent models of spinal cord disease.

This protocol specifically focuses on tools for assessing phrenic motor neuron (PhMN) innervation of the diaphragm at both the electrophysiological and ...

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise from extra-retinal sources. Ex vivo ERG provides an efficient method to dissect the function of retinal cells directly from an intact isolated retina of animals or donor eyes. In addition, ex vivo ERG can be used to test the efficacy and safety of potential therapeutic agents on retina tissue from animals or humans. We show here how commercially available in vivo ERG systems can be used to conduct ex vivo ERG recordings from isolated mouse retinas. We combine the light stimulation, electronic and heating units of a standard in vivo system with custom-designed specimen holder, gravity-controlled perfusion system and electromagnetic noise shielding to record low-noise ex vivo ERG signals simultaneously from two retinas with the acquisition software included in commercial in vivo systems. Further, we demonstrate how to use this method in combination with pharmacological treatments that remove specific ERG components in order to dissect the function of certain retinal cell types.

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

Ex vivo ERG can be used to record electrical activity of retinal cells directly from isolated intact retinas of animals or humans. We demonstrate here how common in vivo ERG systems can be adapted for ex vivo ERG recordings in order to dissect the electrical activity of retinal cells.

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise ...

Visual Evoked Potential Recording in a Rat Model of Experimental Optic Nerve Demyelination

The visual evoked potential (VEP) recording is widely used in clinical practice to assess the severity of optic neuritis in its acute phase, and to monitor the disease course in the follow-up period. Changes in the VEP parameters closely correlate with pathological damage in the optic nerve. This protocol provides a detailed description about the rodent model of optic nerve microinjection, in which a partial demyelination lesion is produced in the optic nerve. VEP recording techniques are also discussed. Using skull implanted electrodes, we are able to acquire reproducible intra-session and between-session VEP traces. VEPs can be recorded on individual animals over a period of time to assess the functional changes in the optic nerve longitudinally. The optic nerve demyelination model, in conjunction with the VEP recording protocol, provides a tool to investigate the disease processes associated with demyelination and remyelination, and can potentially be employed to evaluate the effects of new remyelinating drugs or neuroprotective therapies.

Focal demyelination is induced in the optic nerve using lysolecithin microinjection. Visual evoked potentials are recorded via skull electrodes implanted over the visual cortex to examine the signal conduction along the visual pathway in vivo. This protocol details the surgical procedures underlying electrode implantation and optic nerve microinjection.

The visual evoked potential (VEP) recording is widely used in clinical practice to assess the severity of optic neuritis in its acute phase, and to ...

Simultaneous Recording of Electroretinography and Visual Evoked Potentials in Anesthetized Rats

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. The ERG waveform can be broken down into components that reflect responses from different retinal neuronal and glial cell classes. The early components of the VEP waveform represent the integrity of the optic nerve and higher cortical centers. These recordings can be conducted in isolation or together, depending on the application. The methodology described in this paper allows simultaneous assessment of retinal and cortical visual evoked electrophysiology from both eyes and both hemispheres. This is a useful way to more comprehensively assess retinal function and the upstream effects that changes in retinal function can have on visual evoked cortical function.

This protocol describes simultaneous measurement of electroretinogram and visual evoked potentials in anesthetized rats.

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the ...