Name: characterizing the relationship between eye movement parameters and cognitive functions in non-demented parkinson's disease patients with eye tracking
Uploaded: 2019-09-26T14:30:00
Description: Watch this Scientific Journal Video about Characterizing the Relationship Between Eye Movement Parameters and Cognitive Functions in Non-demented Parkinson's Disease Patients with Eye Tracking at JoVE

The authors would like to thank Dr. Harvey Hung for his advice&#160;on the manuscript.

This research project was approved by the Joint Chinese University of Hong Kong-New Territories East Cluster Clinical Research Ethics Committee (CREC Ref. No.: 2015.263).
1. Participants Recruitment and Baseline Assessment
<ol>
	<li>Recruit Parkinson&#39;s disease patients aged less than or equal to 70 from a neurology specialist clinic with the diagnosis made based on the United Kingdom Parkinson&#39;s Disease Society (UKPDS) Brain Bank Diagnostic Criteria12....

<ol>
	<li>Hely, M. A., Reid, W. G. J., Adena, M. A., Halliday, G. M., Morris, J. G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Sydney+Multicenter+Study+of+Parkinson&#8217;s+disease:+The+inevitability+of+dementia+at+20+years.">The Sydney Multicenter Study of Parkinson&#8217;s disease: The inevitability of dementia at 20 years.</a> Movement Disorders. 23 (6), 837-844 (2008).</li><li>Braak, H., Del Tredici, K., Bratzke, H., Hamm-Clement, J., Sandmann-Keil, D., R&#252;b, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Staging+of+the+intracerebral+inclusion+body+pathology+associated+with+idiopathic+Parkinson's+disease+(preclinical+and+clinical+stages).">Staging of the intracerebral inclusion body pathology associated with idiopathic Parkinson's disease (preclinical and clinical stages).</a> Journal of Neurology. 249, 1-5 (2002).</li><li>Williams-Gray, C. 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=The+distinct+cognitive+syndromes+of+Parkinson&#8217;s+disease:+5+year+follow-up+of+the+CamPaIGN+cohort.">The distinct cognitive syndromes of Parkinson&#8217;s disease: 5 year follow-up of the CamPaIGN cohort.</a> Brain. 132 (11), 2958-2969 (2009).</li><li>Buter, T. C., van den Hout, A., Matthews, F. E., Larsen, J. P., Brayne, C., Aarsland, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dementia+and+survival+in+parkinson+disease:+A+12-year+population+study.">Dementia and survival in parkinson disease: A 12-year population study.</a> Neurology. 70 (13), 1017-1022 (2008).</li><li>Aarsland, D., Larsen, J. P., Tandberg, E., Laake, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predictors+of+nursing+home+placement+in+Parkinson's+disease:+A+population-based,+prospective+study.">Predictors of nursing home placement in Parkinson's disease: A population-based, prospective study.</a> Journal of the American Geriatrics Society. 48 (8), 938-942 (2000).</li><li>Rascol, 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=Abnormal+ocular+movements+in+parkinson's+disease:+Evidence+for+involvement+of+dopaminergic+systems.">Abnormal ocular movements in parkinson's disease: Evidence for involvement of dopaminergic systems.</a> Brain. 112 (5), 1193-1214 (1989).</li><li>Orban De Xivry, J. J., Lef&#232;vre, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Saccades+and+pursuit:+Two+outcomes+of+a+single+sensorimotor+process.">Saccades and pursuit: Two outcomes of a single sensorimotor process.</a> Journal of Physiology. 584 (1), 11-23 (2007).</li><li>Crawford, T. J., 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=Inhibitory+control+of+saccadic+eye+movements+and+cognitive+impairment+in+Alzheimer's+disease.">Inhibitory control of saccadic eye movements and cognitive impairment in Alzheimer's disease.</a> Biological Psychiatry. 57 (9), 1052-1060 (2005).</li><li>Archibald, N. K., Hutton, S. B., Clarke, M. P., Mosimann, U. P., Burn, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+exploration+in+Parkinson's+disease+and+Parkinson's+disease+dementia.">Visual exploration in Parkinson's disease and Parkinson's disease dementia.</a> Brain. 136 (3), 739-750 (2013).</li><li>Litvan, I., 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=Diagnostic+criteria+for+mild+cognitive+impairment+in+Parkinson's+disease:+Movement+Disorder+Society+Task+Force+guidelines.">Diagnostic criteria for mild cognitive impairment in Parkinson's disease: Movement Disorder Society Task Force guidelines.</a> Movement Disorders. 27 (3), 349-356 (2012).</li><li>R&#246;sler, 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=Alterations+of+visual+search+strategy+in+Alzheimer's+disease+and+aging.">Alterations of visual search strategy in Alzheimer's disease and aging.</a> Neuropsychology. 14 (3), 398-408 (2000).</li><li>Hughes, A. J., Daniel, S. E., Kilford, L., Lees, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Accuracy+of+clinical+diagnosis+of+idiopathic+Parkinson's+disease:+A+clinico-pathological+study+of+100+cases.">Accuracy of clinical diagnosis of idiopathic Parkinson's disease: A clinico-pathological study of 100 cases.</a> Journal of Neurology Neurosurgery and Psychiatry. 55 (3), 181-184 (1992).</li><li>Chiu, H. F. K., Lee, H. C., Chung, W. S., Kwong, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reliability+and+Validity+of+the+Cantonese+Version+of+Mini-Mental+State+Examination-A+Preliminary+Study.">Reliability and Validity of the Cantonese Version of Mini-Mental State Examination-A Preliminary Study.</a> Hong Kong Journal of Psychiatry. 4 (2), 25 (1994).</li><li>Wong, 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+validity,+reliability+and+clinical+utility+of+the+Hong+Kong+Montreal+Cognitive+Assessment+(HK-MoCA)+in+patients+with+cerebral+small+vessel+disease.">The validity, reliability and clinical utility of the Hong Kong Montreal Cognitive Assessment (HK-MoCA) in patients with cerebral small vessel disease.</a> Dementia and Geriatric Cognitive Disorders. 28 (1), 81-87 (2009).</li><li>Fahn, S., Elton, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Members+of+the+UPDRS+Development+Committee.+Unified+Parkinson's+disease+rating+scale.">Members of the UPDRS Development Committee. Unified Parkinson's disease rating scale.</a> Recent Development in Parkinson's Disease. 2, 293-304 (1987).</li><li>Hoehn, M. M., Yahr, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parkinsonism:+onset,+progression,+and+mortality.">Parkinsonism: onset, progression, and mortality.</a> Neurology. 17 (5), 427-427 (1967).</li><li>Wu, P. C., Chang, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Psychometric+properties+of+the+Chinese+version+of+the+Beck+Depression+Inventory-II+using+the+Rasch+model.">Psychometric properties of the Chinese version of the Beck Depression Inventory-II using the Rasch model.</a> Measurement and Evaluation in Counseling and Development. 41 (1), 13-31 (2008).</li><li>Chiu, H. F., 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+modified+Fuld+Verbal+Fluency+Test:+a+validation+study+in+Hong+Kong.">The modified Fuld Verbal Fluency Test: a validation study in Hong Kong.</a> The journals of gerontology. Series B, Psychological sciences and social sciences. 52 (5), 247-250 (1997).</li><li>Chan, A. S., Kwok, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hong+Kong+list+learning+test:+manual+and+preliminary+norm.">Hong Kong list learning test: manual and preliminary norm.</a> Hong Kong: Department of Psychological and Clinical Psychology Center. , (1999).</li><li>Robbins, T. W., James, M., Owen, A. M., Sahakian, B. J., McInnes, L., Rabbitt, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cambridge+Neuropsychological+Test+Automated+Battery+(CANTAB):+A+Factor+Analytic+Study+of+a+Large+Sample+of+Normal+Elderly+Volunteers.">Cambridge Neuropsychological Test Automated Battery (CANTAB): A Factor Analytic Study of a Large Sample of Normal Elderly Volunteers.</a> Dementia and Geriatric Cognitive Disorders. 5 (5), 266-281 (1994).</li><li>Lee, T. M. C., Wang, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Neuropsychological Measures: Normative Data for Chinese. , (2010).</li><li>Birant, D., Kut, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ST-DBSCAN:+An+algorithm+for+clustering+spatial-temporal+data.">ST-DBSCAN: An algorithm for clustering spatial-temporal data.</a> Data and Knowledge Engineering. 60 (1), 208-221 (2007).</li><li>Wong, O. 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=Eye+movement+parameters+and+cognitive+functions+in+Parkinson's+disease+patients+without+dementia.">Eye movement parameters and cognitive functions in Parkinson's disease patients without dementia.</a> Parkinsonism and Related Disorders. 52, 43-48 (2018).</li><li>Muslimovic, D., Post, B., Speelman, J. D., Schmand, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cognitive+profile+of+patients+with+newly+diagnosed+Parkinson+disease.">Cognitive profile of patients with newly diagnosed Parkinson disease.</a> Neurology. 65 (8), 1239-1245 (2005).</li><li>Winograd-Gurvich, C., Georgiou-Karistianis, N., Fitzgerald, P. B., Millist, L., White, O. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-paced+saccades+and+saccades+to+oddball+targets+in+Parkinson's+disease.">Self-paced saccades and saccades to oddball targets in Parkinson's disease.</a> Brain Research. 1106 (1), 134-141 (2006).</li><li>Briand, K. A., Strallow, D., Hening, W., Poizner, H., Sereno, A. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+voluntary+and+reflexive+saccades+in+Parkinson's+disease.">Control of voluntary and reflexive saccades in Parkinson's disease.</a> Experimental Brain Research. 129 (1), 38-48 (1999).</li><li>Rivaud-P&#233;choux, S., Vidailhet, M., Brandel, J. P., Gaymard, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mixing+pro-+and+antisaccades+in+patients+with+parkinsonian+syndromes.">Mixing pro- and antisaccades in patients with parkinsonian syndromes.</a> Brain. 130 (1), 256-264 (2007).</li><li>Perneczky, R., Ghosh, B. C. P., Hughes, L., Carpenter, R. H. S., Barker, R. A., Rowe, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Saccadic+latency+in+Parkinson's+disease+correlates+with+executive+function+and+brain+atrophy,+but+not+motor+severity.">Saccadic latency in Parkinson's disease correlates with executive function and brain atrophy, but not motor severity.</a> Neurobiology of Disease. 43 (1), 79-85 (2011).</li><li>Matsumoto, 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=Small+saccades+restrict+visual+scanning+area+in+Parkinson's+disease.">Small saccades restrict visual scanning area in Parkinson's disease.</a> Movement Disorders. 26 (9), 1619-1626 (2011).</li><li>MacAskill, M. R., Anderson, T. J., Jones, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptive+modification+of+saccade+amplitude+in+Parkinson's+disease.">Adaptive modification of saccade amplitude in Parkinson's disease.</a> Brain. 125 (7), 1570-1582 (2002).</li><li>Salvucci, D. D., Goldberg, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identifying+fixations+and+saccades+in+eye-tracking+protocols.">Identifying fixations and saccades in eye-tracking protocols.</a> Proceedings of the 2000 symposium on Eye tracking research &amp; applications. , 71-78 (2000).</li><li>Rana, A. Q., Kabir, A., Dogu, O., Patel, A., Khondker, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevalence+of+blepharospasm+and+apraxia+of+eyelid+opening+in+patients+with+parkinsonism,+cervical+dystonia+and+essential+tremor.">Prevalence of blepharospasm and apraxia of eyelid opening in patients with parkinsonism, cervical dystonia and essential tremor.</a> European Neurology. 68 (5), 318-321 (2012).</li></ol>

The protocol presented above was designed as the first part of a longitudinal study in exploring the potential clinical utility of eye movement parameters as surrogate markers for cognitive functions in Parkinson&#39;s disease. While there are studies that examine more classical eye tracking paradigms such as self-paced saccade, reflexive saccade, and anti-saccade25,26,27, a visual search task was used in this study to measure e...

Parkinson&#8217;s disease is classically a motor disorder; yet, the disease is also associated with cognitive deficits, and progression into dementia is common1. The pathophysiology of cognitive impairment in Parkinson&#39;s disease is not well understood. It is thought to be related to alpha-synuclein deposition in the cortical area based on Braak&#39;s staging2. It was also proposed that a dual syndrome of degeneration of the dopaminergic and the cholinergic system leads to different cognitive deficits with prognostic implication3. More research is needed to further elucidate the exact mechanisms involved in cognitive impairment in Parkinson&#39;s disease. On the clinical aspect, the presence of cognitive impairment has a significant impact on prognosis4,5. Assessment of cognitive function in clinical practice is, therefore, essential. However, a lengthy cognitive assessment is limited by patients&#8217; mental and motor conditions. Therefore, a noninvasive and simple measurement that can reflect the disease&#39;s burden on cognitive function is needed.
The eye movement abnormalities are widely described detectable signs of Parkinson&#39;s disease from its early stages6, yet the pathophysiology is even less well-characterized than that of cognitive impairment. The generation of eye movement is through a transformation of the visual sensory input, subserved by an intertwined cortical and subcortical network, into signals to the oculomotor nuclei in the brainstem for effect7. Involvement of Parkinson&#39;s disease pathologies in these networks may lead to observable eye movement abnormalities. There is, perhaps overlapping of neuroanatomical structures that govern the control of eye movement and cognitive function. Furthermore, there have been studies examining the relationship between saccadic eye movement and cognitive function in other neurodegenerative disorders8. On such grounds, it is worthwhile to explore the use of eye movement parameters as a proxy marker of cognitive functions in Parkinson&#39;s disease. One cross-sectional study9 showed that reduced saccadic amplitude and longer fixation duration was associated with the severity of global cognitive impairment in Parkinson&#39;s disease. However, there is a lack of data on the correlation between eye movement parameters and specific cognitive domains. The significance and need of measurement of specific cognitive domains, rather than a general cognitive state, is that individual cognitive domain informs differential prognostic information in Parkinson&#39;s disease3 and they are subserved by different neural networks. The aim of this study is to explore the specific relationship between eye movement metrics and different cognitive functions. This is the first step to establish a foundation on which the development of biomarkers of cognitive decline in Parkinson&#39;s disease using eye tracking technology could be built.
The experimental paradigm presented is composed of 2 major parts: the cognitive assessment and the eye tracking task. The cognitive assessment battery encompassed a range of cognitive functions, including attention and working memory, executive function, language, verbal memory and visuospatial function. The choice of these 5 cognitive domains is based on the Movement Disorder Society Task Force Guidelines for the mild cognitive impairment in Parkinson&#39;s disease10, and a set of locally available cognitive tests were selected to build the assessment battery. In a previous similar eye tracking study on Parkinson&#39;s disease cognition mentioned9, the author extracted the eye movement parameters while the subjects were engaged in visual cognitive tasks, where the parameters may potentially be influenced by the subject&#39;s cognitive ability. As this study aimed to assess the correlation between the eye movement parameters and different cognitive domains, the potential confounding effect of cognitive abilities on the eye parameters must be addressed. In this regards, a visual search task, adapted from another eye tracking study on Alzheimer&#8217;s disease11, was employed to capture the eye movement parameters of the subjects. During the task, subjects had to search for a single number on a computer screen among multiple alphabet distracters. This task would elicit the alternate use of saccadic eye movement and visual fixation, the abnormalities of which are described widely in Parkinson&#39;s disease. The identification and differentiation of number and alphabet is an overlearned task where the demand for cognitive functions is only minimal and would, therefore, be suitable to answer the research question of this study. A computer program was developed based on the specifications and design as stated by R&#246;sler et al.11. in their original study to be run within the in-built software of our eye tracker. An in-house algorithm for classification and analysis of the eye tracking data was also developed for this study.

<table border="0" cellpadding="0" cellspacing="0" style="width:1008px;" width="1007">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Computer&#160;</td>
			<td style="width:121px;">Intel</td>
			<td style="width:505px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Computerized cognitive assessment tool</td>
			<td style="width:121px;">CANTAB</td>
			<td style="width:505px;">CANTAB Research Suite</td>
			<td>Contains Pattern Recognition Memory, Spatial Span, and Stockings of Cambridge</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Eye Movement Analyzer</td>
			<td style="width:121px;">Lab Viso Limited</td>
			<td style="width:505px;"></td>
			<td>https://github.com/lab-viso-limited/visual-search-analyzer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Eye tracker</td>
			<td style="width:121px;">Tobii</td>
			<td style="width:505px;">Tx300</td>
			<td>23 inch computer screen with resolution of 1920x1080, Sampling rate at 300Hz</td>
		</tr>
		<tr height="105">
			<td height="105" style="height:105px;width:215px;">Hong Kong List Leanrning Test</td>
			<td style="width:121px;">Department of Psychology, The Chinese University of Hong Kong</td>
			<td style="width:505px;">The Hong Kong List Learning Test (HKLLT) 2nd Edition</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:215px;">Stroop test</td>
			<td style="width:121px;">Laboratory of Neuropsychology, The University of Hong Kong</td>
			<td style="width:505px;">Neuropsychological Measures: Normative Data for Chinese, Second Edition (Revised)</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Tobii Studio</td>
			<td style="width:121px;">Tobii</td>
			<td style="width:505px;">Tobii Studio version 3.2.2</td>
			<td>Computer programme for running the visual search task</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Visual Search Task</td>
			<td style="width:121px;">Lab Viso Limited</td>
			<td style="width:505px;"></td>
			<td>https://www.labviso.com/#products</td>
		</tr>
	</tbody>
</table>

characterizing the relationship between eye movement parameters and cognitive functions in non-demented parkinson's disease patients with eye tracking

Cognitive impairment is a common phenomenon in Parkinson&#8217;s disease that has implications on the prognosis. A simple, noninvasive and objective proxy measurement of cognitive function in Parkinson&#8217;s disease will be helpful in detecting early cognitive decline. As a physiological metric, eye movement parameter is not confounded by the subject&#39;s attributes and intelligence and can function as a proxy marker if it correlates with cognitive functions. To this end, this study explored the relationship between the eye movement parameters and performance in cognitive tests in multiple domains. In the experiment, a visual search task with eye tracking was set up, where subjects were asked to look for a number embedded in an array of alphabets scattered randomly on a computer screen. The differentiation between the number and the alphabet is an overlearned task such that the confounding effect of cognitive ability on the eye movement parameters is minimized. The average saccadic amplitude and fixation duration were captured and calculated during the visual search task. The cognitive assessment battery covered domains of frontal-executive functions, attention, verbal and visual memory. It was found that prolonged fixation duration was associated with poorer performance in verbal fluency, visual and verbal memory, allowing further exploration on the use of eye movement parameters as proxy markers for cognitive function in Parkinson&#8217;s disease patients. The experimental paradigm has been found to be highly tolerable in our group of Parkinson&#39;s disease patients and could be applied transdiagnostically to other disease entities for similar research questions.

The full result of this study is available in the original paper published23. Parkinson&#8217;s disease subjects (n = 67) were recruited and completed the assessment. However, 5 cases failed to complete the visual search task as they wore progressive lens incompatible with the eye tracker and their data was discarded. The mean age of the subjects was 58.9 years (SD = 7.5 years) with a male to female ratio of 1.7:1. 62 healthy age-, sex-, and education-matched controls were recruited for comparison...

Watch this Scientific Journal Video about Characterizing the Relationship Between Eye Movement Parameters and Cognitive Functions in Non-demented Parkinson's Disease Patients with Eye Tracking at JoVE

Characterizing the Relationship Between Eye Movement Parameters and Cognitive Functions in Non-demented Parkinson&#039;s Disease Patients with Eye Tracking

Here, we present a protocol to study the relationship between the eye movement parameters and cognitive functions in non-demented Parkinson&#39;s disease patients. The experiment used an eye tracker to measure the saccadic amplitude and fixation duration in a visual search task. The correlation with performance in multi-domain cognitive tasks was subsequently measured.

Characterizing the Relationship Between Eye Movement Parameters and Cognitive Functions in Non-demented Parkinson's Disease Patients with Eye Tracking

Cognitive impairment is a common phenomenon in Parkinson&#8217;s disease that has implications on the prognosis. A simple, noninvasive and objective proxy ...

Our protocol aims to study the relationship between eye-movement metrics and cognitive functions in a group of non-demented Parkinson's Disease patients that suffer from both occular-motor and cognitive dysfunction. To design the trial images for the visual search task, use the numbers four, six, seven, and nine exclusively. Ensure that the location of the target number is randomized from trial to trial with the rule that each number can not be in the same visual quadrant for more than three successive trials.Do not use ambiguous letters such as I and O, and set the size of the fixation cross, letters, and numbers at a 0.85 degree visual angle. Set the program to allow a time lapse of 1.5 seconds after Enter is pressed, before the display of the central fixation cross is switched to a trial image to begin a trial. Ensure that the screen will go blank with the fixation cross reappearing as the mouse is clicked or after 10 seconds have elapsed from the beginning of a trial, whichever is earlier.Then set the program to generate a csv file that contains the time stamps of the beginning and end of each trial. After conducting a clinical diagnostic interview with the subject and if available, their relatives to exclude dementia and to screen for cognitive impairment using the Mini-Mental State Examination and Montreal Cognitive Assessment, evaluate the subject's visual acuity with a Snellen chart. Then, in a quiet room with an adequate light source, set up a screen based eye-tracker with a sampling rate of at least 300 Hertz, a computer, a mouse, and a standard keyboard.A chin rest placed 60 centimeters in front of the eye checker screen and the appropriate cognitive assessment tools. To set up for a visual search task, position the subject on a chair with their chin on the chin rest and their forehead against a bar to minimize any head movement. Align the subject's eyes to approximately the center of the computer screen and click the start button in the eye tracking program.Click start to calibrate the eye tracker with the built-in calibration program. And ask the subject to gaze at the red dot moving across the screen with nine fixation points while keeping their head still. View the calibration plot to check the quality of the calibration, making sure that the length of the green lines, which represent the error vectors fall within the gray circles.Then click Accept to proceed to the visual search task. To initiate a practice trial, instruct the subject to fix their gaze on the central fixation cross and press Enter on the keyboard to begin the trial. The computer screen will display a single number and 79 randomly scattered distractor letters.Instruct the subject to look as quickly as possible for the number and to simultaneously click on the mouse while stating the number aloud as soon as the number is located. Then cross check whether the stated number is correct and repeat the practice trial four more times. For eye tracking data processing and analysis in the replay section of the computer program, check the sample's percentage of the eyes during the visual search task.Click play for the recording, to check the quality of the data by eyeballing the visualized scan path video generated. Discard all of the subject's data if it is grossly erroneous. And discard any trials in which the subject clicked the mouse accidentally or prematurely.In the data export section of the program, select GazePointX and GazePointY Click export data to export the subject's data and save the data as a csv file. In the interface of the visual search analyzer, select the exported data as the input of the eye data and the generated csv file as the input of the action data. Select ST DB Scan as the classification algorithm and click run.Then click summary to generate a spreadsheet file containing the main saccade amplitude and the mean fixation duration of the subject. To design the visual search analyzer, program the analyzer such that it extracts and analyzes only the data from the beginning to the end of the trial using the generated csv file. To program the analyzer such that it fills in the data lost due to eye blinking, average the x and y coordinates of the gaze point immediately before and after the blinking.Then use the algorithm based on the ST DB scan to program the analyzer such that it classifies the raw data into either saccade or fixation. Consistent with previous studies, in this analysis, the Parkinson's disease group showed a poorer performance in multiple cognitive tasks, compared to the control group. Using the in-house algorithm for classification of the visual search task data, fixations and saccades can be identified and extracted for calculation and analysis.Indeed, the disease group had a smaller mean saccadic amplitude compared to the control group, and the mean fixation duration was not significantly different between the groups. In this evaluation, after adjusting for covariates, negative correlations were found between the mean fixation duration, the performance in the verbal recognition memory and discrimination score, in the pattern recognition memory, and in the categorical verbal fluency test within the fruit and vegetable categories. However, there was no significant interactions found in these correlations between the disease and control groups, suggesting that the correlations are not specific to the disease group.The design of the visual search task is important as the aim is to minimize the interference of the cognitive ability of the distractor eye movement parameters. If this research task is highly tolerable it can be applied to trans-diagnostically to other new degenerative disorder to answer similar research questions.

characterizing-relationship-between-eye-movement-parameters-cognitive

Research

JoVE Journal

Neuroscience

Eye Movement Monitoring of Memory

Explicit (often verbal) reports are typically used to investigate memory (e.g. "Tell me what you remember about the person you saw at the bank yesterday."), however such reports can often be unreliable or sensitive to response bias 1, and may be unobtainable in some participant populations. Furthermore, explicit reports only reveal when information has reached consciousness and cannot comment on when memories were accessed during processing, regardless of whether the information is subsequently accessed in a conscious manner. Eye movement monitoring (eye tracking) provides a tool by which memory can be probed without asking participants to comment on the contents of their memories, and access of such memories can be revealed on-line 2,3. Video-based eye trackers (either head-mounted or remote) use a system of cameras and infrared markers to examine the pupil and corneal reflection in each eye as the participant views a display monitor. For head-mounted eye trackers, infrared markers are also used to determine head position to allow for head movement and more precise localization of eye position. Here, we demonstrate the use of a head-mounted eye tracking system to investigate memory performance in neurologically-intact and neurologically-impaired adults. Eye movement monitoring procedures begin with the placement of the eye tracker on the participant, and setup of the head and eye cameras. Calibration and validation procedures are conducted to ensure accuracy of eye position recording. Real-time recordings of X,Y-coordinate positions on the display monitor are then converted and used to describe periods of time in which the eye is static (i.e. fixations) versus in motion (i.e., saccades). Fixations and saccades are time-locked with respect to the onset/offset of a visual display or another external event (e.g. button press). Experimental manipulations are constructed to examine how and when patterns of fixations and saccades are altered through different types of prior experience. The influence of memory is revealed in the extent to which scanning patterns to new images differ from scanning patterns to images that have been previously studied 2, 4-5. Memory can also be interrogated for its specificity; for instance, eye movement patterns that differ between an identical and an altered version of a previously studied image reveal the storage of the altered detail in memory 2-3, 6-8. These indices of memory can be compared across participant populations, thereby providing a powerful tool by which to examine the organization of memory in healthy individuals, and the specific changes that occur to memory with neurological insult or decline 2-3, 8-10.

Eye movement monitoring (or eye tracking) reveals where in space the eyes linger, when and for how long. Here, we demonstrate how eye tracking can be used to investigate the integrity of memory in multiple participant populations, without requiring verbal, or otherwise explicit, reports.

Explicit (often verbal) reports are typically used to investigate memory (e.g. "Tell me what you remember about the person you saw at the bank ...

Semi-Quantitative Determination of Dopaminergic Neuron Density in the Substantia Nigra of Rodent Models using Automated Image Analysis

Estimation of the number of dopaminergic neurons in the substantia nigra is a key method in pre-clinical Parkinson's disease research. Currently, unbiased stereological counting is the standard for quantification of these cells, but it remains a laborious and time-consuming process, which may not be feasible for all projects. Here, we describe the use of an image analysis platform, which can accurately estimate the quantity of labeled cells in a pre-defined region of interest. We describe a step-by-step protocol for this method of analysis in rat brain and demonstrate it can identify a significant reduction in tyrosine hydroxylase positive neurons due to expression of mutant &#945;-synuclein in the substantia nigra. We validated this methodology by comparing with results obtained by unbiased stereology. Taken together, this method provides a time-efficient and accurate process for detecting changes in dopaminergic neuron number, and thus is suitable for efficient determination of the effect of interventions on cell survival.

Here we present an automated method for semi-quantitative determination of dopaminergic neuron number in the rat substantia nigra pars compacta.

Estimation of the number of dopaminergic neurons in the substantia nigra is a key method in pre-clinical Parkinson's disease research. Currently, unbiased ...

Immunostaining of Whole-Mount Retinas with the CLARITY Tissue Clearing Method

The tissue hydrogel delipidation method (CLARITY), originally developed by the Deisseroth laboratory, has been modified and widely used for immunostaining and imaging of thick brain samples. However, this advanced technology has not yet been used for whole-mount retinas. Although the retina is partially transparent, its thickness of approximately 200 &#181;m (in mice) still limits the penetration of antibodies into the deep tissue as well as reducing light penetration for high-resolution imaging. Here, we adapted the CLARITY method for whole-mount mouse retinas by polymerizing them with an acrylamide monomer to form a nanoporous hydrogel and then clearing them in sodium dodecyl sulfate to minimize protein loss and avoid tissue damage. CLARITY-processed retinas were immunostained with antibodies for retinal neurons, glial cells, and synaptic proteins, mounted in a refractive index matching solution, and imaged. Our data demonstrate that CLARITY&#160;can improve the quality of standard immunohistochemical staining and imaging for retinal neurons and glial cells in whole-mount preparation. For instance, 3D resolution of fine axon-like and dendritic structures of dopaminergic amacrine cells were much improved by CLARITY. Compared to non-processed whole-mount retinas, CLARITY can reveal immunostaining for synaptic proteins such as postsynaptic density protein 95. Our results show that CLARITY renders the retina more optically transparent after the removal of lipids and preserves fine structures of retinal neurons and their proteins, which can be routinely used for obtaining high-resolution imaging of retinal neurons and their subcellular structures in whole-mount preparation.

Here we present a protocol to adapt the CLARITY method of the brain tissues for whole-mount retinas to improve the quality of standard immunohistochemical staining and high-resolution imaging of retinal neurons and their subcellular structures.

The tissue hydrogel delipidation method (CLARITY), originally developed by the Deisseroth laboratory, has been modified and widely used for immunostaining ...

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in retinal diseases, and testing therapeutic interventions. The ex vivo electroretinogram (ERG) allows the quantification of contributions from individual cell types in the isolated retina by addition of specific pharmacological agents and evaluation of tissue-intrinsic changes independently of systemic influences. Retinal light responses can be measured using a specialized ex vivo ERG specimen holder and recording setup, modified from existing patch clamp or microelectrode array equipment. Particularly, the study of ON-bipolar cells, but also of photoreceptors, has been hampered by the slow but progressive decline of light responses in the ex vivo ERG over time. Increased perfusion speed and adjustment of the perfusate temperature improve ex vivo retinal function and maximize response amplitude and stability. The ex vivo ERG uniquely allows the study of individual retinal neuronal cell types. In addition, improvements to maximize response amplitudes and stability allow the investigation of light responses in retina samples from large animals, as well as human donor eyes, making the ex vivo ERG a valuable addition to the repertoire of techniques used to investigate retinal function.

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Modification of existing multielectrode array or patch clamp equipment makes the ex vivo electroretinogram more widely accessible. Improved methods to record and maintain ex vivo light responses facilitate the study of photoreceptor and ON-bipolar cell function in the healthy retina, animal models of eye diseases, and human donor retinas.

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in ...

In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

The optic nerve collects axons signals from the retinal ganglion cells and transmits visual signal to the brain. Large animal models of optic nerve injury are essential for translating novel therapeutic strategies from rodent models to clinical application due to their closer similarities to humans in size and anatomy. Here we describe some in vivo methods to evaluate the function and structure of the retinal ganglion cells (RGCs) and optic nerve (ON) in large animals, including visual evoked potential (VEP), pattern electroretinogram (PERG) and optical coherence tomography (OCT). Both goat and non-human primate were employed in this study. By presenting these in vivo methods step by step, we hope to increase experimental reproducibility among different labs and facilitate the usage of large animal models of optic neuropathies.

In Vivo Methods to Assess Retinal Ganglion Cell and Optic Nerve Function and Structure in Large Animals

Here we demostrate several in vivo tests (flash visual evoked potential, pattern electroretinogram and optic coherence tomography) in goat and rhesus macaque to understand the structure and function of the optic nerve and its neurons.

The optic nerve collects axons signals from the retinal ganglion cells and transmits visual signal to the brain. Large animal models of optic nerve injury ...

The 6-hydroxydopamine Rat Model of Parkinson's Disease

Motor symptoms of Parkinson's disease (PD)-bradykinesia, akinesia, and tremor at rest-are consequences of the neurodegeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) and dopaminergic striatal deficit. Animal models have been widely used to simulate human pathology in the laboratory. Rodents are the most used animal models for PD due to their ease of handling and maintenance. Moreover, the anatomy and molecular, cellular, and pharmacological mechanisms of PD are similar in rodents and humans. The infusion of the neurotoxin, 6-hydroxydopamine (6-OHDA), into a medial forebrain bundle (MFB) of rats reproduces the severe destruction of dopaminergic neurons and simulates PD symptoms. This protocol demonstrates how to perform the unilateral microinjection of 6-OHDA in the MFB in a rat model of PD and shows the motor deficits induced by 6-OHDA and predicted dopaminergic lesions through the stepping test. The 6-OHDA causes significant impairment in the number of steps performed with the contralateral forelimb.

The 6-hydroxydopamine Rat Model of Parkinson&#039;s Disease

The 6-hydroxydopamine (6-OHDA) model has been used for decades to advance the understanding of Parkinson's Disease. In this protocol, we demonstrate how to perform unilateral nigrostriatal lesions in the rat by injecting 6-OHDA in the medial forebrain bundle, assess motor deficits, and predict lesions using the stepping test.

Motor symptoms of Parkinson's disease (PD)-bradykinesia, akinesia, and tremor at rest-are consequences of the neurodegeneration of dopaminergic neurons in ...

Organotypic Retinal Explant Cultures from Macaque Monkey

Hereditary retinal degeneration (RD) is characterized by progressive photoreceptor cell death. Overactivation of the cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) pathway in photoreceptor cells causes photoreceptor cell death, especially in models harboring phosphodiesterase 6b (PDE6b) mutations. Previous studies on RD have used mainly murine models such as rd1 or rd10 mice. Given the genetic and physiological differences between mice and humans, it is important to understand to which extent the retinas of primates and rodents are comparable. Macaques share a high level of genetic similarity with humans. Therefore, wild-type macaques (aged 1-3 years) were selected for the in vitro culture of retinal explants that included the retina-retinal pigment epithelium (RPE)-choroid complex. These explants were treated with different concentrations of the PDE6 inhibitor zaprinast to induce the cGMP-PKG signaling pathway and simulate RD pathogenesis. cGMP accumulation and cell death in primate retinal explants were subsequently verified using immunofluorescence and the TUNEL assay. The primate retinal model established in this study may serve for relevant and effective studies into the mechanisms of cGMP-PKG-dependent RD, as well as for the development of future treatment approaches.

Retinal explants obtained from wild-type macaques were cultured in vitro. Retinal degeneration and the cGMP-PKG signaling pathway was induced using the PDE6 inhibitor zaprinast. cGMP accumulation in the explants at different zaprinast concentrations was verified using immunofluorescence.

Hereditary retinal degeneration (RD) is characterized by progressive photoreceptor cell death. Overactivation of the cyclic guanosine monophosphate ...

An In Situ Immunostaining Protocol for Parkinson&#039;s Disease Study

Histological Examination of Mitochondrial Morphology in a Parkinson's Disease Model

Mitochondria play a central role in the energy metabolism of cells, and their function is especially important for neurons due to their high energy demand. Therefore, mitochondrial dysfunction is a pathological hallmark of various neurological disorders, including Parkinson's disease. The shape and organization of the mitochondrial network is highly plastic, which allows the cell to respond to environmental cues and needs, and the structure of mitochondria is also tightly linked to their health. Here, we present a protocol to study mitochondrial morphology in situ based on immunostaining of the mitochondrial protein VDAC1 and subsequent image analysis. This tool could be particularly useful for the study of neurodegenerative disorders because it can detect subtle differences in mitochondrial counts and shape induced by aggregates of &#945;-synuclein, an aggregation-prone protein heavily involved in the pathology of Parkinson's disease. This method allows one to report that substantia nigra pars compacta dopaminergic neurons harboring pS129 lesions show mitochondrial fragmentation (as suggested by their reduced Aspect Ratio, AR) compared to their healthy neighboring neurons in a pre-formed fibril intracranial injection Parkinson model.

Author Spotlight: Establishing a New Fluorescence-Based Protocol for In Vivo Mitochondrial Morphology Analysis in Parkinson&#039;s Disease

This study presents a method to analyze the morphology of mitochondria based on immunostaining and image analysis in mouse brain tissue in situ. It also describes how this allows one to detect changes in mitochondrial morphology induced by protein aggregation in Parkinson's disease models.

Mitochondria play a central role in the energy metabolism of cells, and their function is especially important for neurons due to their high energy ...

Python-Based Tool for Quantitative Optokinetic Reflex Assessment in Animals

PyOKR: A Semi-Automated Method for Quantifying Optokinetic Reflex Tracking Ability

The study of behavioral responses to visual stimuli is a key component of understanding visual system function. One notable response is the optokinetic reflex (OKR), a highly conserved innate behavior necessary for image stabilization on the retina. The OKR provides a robust readout of image tracking ability and has been extensively studied to understand visual system circuitry and function in animals from different genetic backgrounds. The OKR consists of two phases: a slow tracking phase as the eye follows a stimulus to the edge of the visual plane and a compensatory fast phase saccade that resets the position of the eye in the orbit. Previous methods of tracking gain quantification, although reliable, are labor intensive and can be subjective or arbitrarily derived. To obtain more rapid and reproducible quantification of eye tracking ability, we have developed a novel&#160;semi-automated analysis program, PyOKR, that allows for quantification of two-dimensional eye tracking motion in response to any directional stimulus, in addition to being adaptable to any type of video-oculography equipment. This method provides automated filtering, selection of slow tracking phases, modeling of vertical and horizontal eye vectors, quantification of eye movement gains relative to stimulus speed, and organization of resultant data into a usable spreadsheet for statistical and graphical comparisons. This quantitative and streamlined analysis pipeline, readily accessible via PyPI import, provides a fast and direct measurement of OKR responses, thereby facilitating the study of visual behavioral responses.

Author Spotlight: A Streamlined and Accessible Analysis Method to Quantify Optokinetic Reflex Tracking Responses

We describe here PyOKR, a semi-automated quantitative analysis method that directly measures eye movements resulting from visual responses to two-dimensional image motion. A Python-based user interface and analysis algorithm allows for higher throughput and more accurate quantitative measurements of eye-tracking parameters than previous methods.

The study of behavioral responses to visual stimuli is a key component of understanding visual system function. One notable response is the optokinetic ...

Visualizing Retinal Synaptic Structures in 3D with Volume Electron Microscopy

Preparation of Retinal Samples for Volume Electron Microscopy

Volume electron microscopy (Volume EM) has emerged as a powerful tool for visualizing the 3D structure of cells and tissues with nanometer-level precision. Within the retina, various types of neurons establish synaptic connections in the inner and outer plexiform layers. While conventional EM techniques have yielded valuable insights into retinal subcellular organelles, their limitation lies in providing 2D image data, which can hinder accurate measurements. For instance, quantifying the size of three distinct synaptic vesicle pools, crucial for synaptic transmission, is challenging in 2D. Volume EM offers a solution by providing large-scale, high-resolution 3D data. It is worth noting that sample preparation is a critical step in Volume EM, significantly impacting image clarity and contrast. In this context, we outline a sample preparation protocol for the 3D reconstruction of photoreceptor axon terminals in the retina. This protocol includes three key steps: retina dissection and fixation, sample embedding processes, and selection of the area of interest.

Author Spotlight: Retinal Neuroscience Studies with Volume Electron Microscopy

This protocol describes the detailed steps for preparing retinal samples for volume electron microscopy, focusing on the structural features of retinal photoreceptor terminals.