Visual exploration in Parkinson's disease and Parkinson's disease dementia

Vestibular dysfunction in Parkinson's disease: a neglected topic

Dizziness and postural instability are frequently observed symptoms in patient with Parkinson's disease (PD), potentially linked to vestibular dysfunction. Despite their significant impact on quality of life, these symptoms are often overlooked and undertreated in clinical practice. This review aims to summarize symptoms associated with vestibular dysfunction in patients with PD and discusses vestibular-targeted therapies for managing non-specific dizziness and related symptoms. We conducted searches in PubMed and Web of Science using keywords related to vestibular dysfunction, Parkinson's disease, dizziness, and postural instability, alongside the reference lists of relevant articles. The available evidence suggests the prevalence of vestibular dysfunction-related symptoms in patients with PD and supports the idea that vestibular-targeted therapies may be effective in improving PD symptoms.

Abnormal eye movements increase as motor disabilities and cognitive impairments become more evident in Multiple Sclerosis: A novel eye-tracking study

Background

Eye movements can reflect brain alterations and inform on the presence of motor disabilities and cognitive impairments in people with multiple sclerosis (pwMS).

Objective

The aim of the study was to determine the correlation between motor and cognitive measurements and eye movement parameters when performing the n-back task (NBKT).

Methods

This was a cross-sectional study carried out at Ramos Mejía Hospital, a center specialized in demyelinating diseases in Buenos Aires, Argentina. The study population consisted of 66 patients with relapsing-remitting multiple sclerosis (RRMS) and 5 patients with secondary progressive multiple sclerosis (SPMS). pwMS performed the n-back test while using a device head mounted display (HMD) with eyetracking capabilities in order to capture eye movement. Clinical motor and cognitive measures were assessed with Expanded Disability Status Scale (EDSS), Nine Hole Peg Test (NHPT), Timed 25-Foot Walk (T25FW), and Symbol Digit Modalities Test (SDMT).

Results

pwMS showed strong and statistically significant correlations between gaze duration; number of fixations, saccade amplitude and motor disabilities and cognitive impairments as measured by EDSS, NHPT, T25FW, and SDMT.

Conclusion

This study found significant correlations between eye movement behavior and motor and cognitive disability in pwMS. These findings suggest that eye movements have the potential to be used as a surrogate biomarker in MS progression.

Gaze-speech coordination during social interaction in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) can affect social interaction and communication as well as motor and cognitive processes. Speech is affected in PD, as is the control of voluntary eye movements which are thought to play an important role in 'turn taking' in conversation.

AIMS

This study aimed to measure eye movements during spoken conversation in PD to assess whether differences in patterns of eye gaze are linked to disrupted turn taking and impaired communication efficiency.

METHODS & PROCEDURE

Eleven participants with mild PD and 14 controls completed a two-player guessing game. During each 3 min game turn, one of the players had to guess the names of as many objects as possible based only on the other player's description. Eye movements were recorded simultaneously in both participants using mobile eye trackers along with speech onset and offset times.

OUTCOMES & RESULTS

When people with PD played the role of describer, the other player guessed fewer objects compared to when controls described objects. When guessing objects, people with PD performed just as well as controls. Analysis of eye fixations showed that people with PD made longer periods of fixation on the other player's face relative to controls and a lower number of such 'gaze on face' periods.

CONCLUSIONS & IMPLICATIONS

A combination of oculomotor, cognitive and speech abnormalities may disrupt communication in PD. Better public awareness of oculomotor, speech and other deficits in the condition could improve social connectedness in people with Parkinson's.

WHAT THIS PAPER ADDS

What is already known on this subject? Parkinson's disease is known to affect the control of voluntary eye movements. Direction of eye gaze is important in spoken conversation as a cue to turn-taking, but no studies have examined whether eye movements are different during communication in people with Parkinson's. What this paper adds to existing knowledge? People with Parkinson's showed longer periods of eye fixation during conversations compared to controls. Delays and overlaps between speech turns were also affected in patients. What are the clinical implications of this work? Better knowledge of the effect of the disease on eye gaze control amongst clinicians may help improve communication and social connectedness for patients in the future.

Eye tracking assessment of Parkinson's disease: a clinical retrospective analysis

Parkinson's disease (PD) presents a significant clinical challenge due to its profound motor and cognitive impacts. Early diagnosis is crucial for implementing effective, stage-based treatment strategies. Recently, eye-tracking technology has emerged as a promising tool for the non-invasive diagnosis and monitoring of various neurological disorders, including PD. This retrospective study analyzed eye-tracking parameters, specifically visually-guided saccades (VGS), in PD patients within a clinical setting. We reviewed eye-tracking data from 62 PD patients, focusing on eye movement performance in horizontal and vertical VGS tasks. Our findings revealed significant correlations between demographic profiles, Mini-Mental State Examination (MMSE) scores, pattern recognition, and spatial working memory tests with saccadic performance in PD patients. Despite the retrospective nature of the study, our results support the potential of eye-tracking technology as a valuable diagnostic tool in PD assessment and monitoring. Future research should prioritize longitudinal studies and more comprehensive assessments to further understand and enhance the clinical application of eye-tracking in PD.

Visual Dysfunction in Parkinson's Disease

Non-motor symptoms in Parkinson's disease (PD) include ocular, visuoperceptive, and visuospatial impairments, which can occur as a result of the underlying neurodegenerative process. Ocular impairments can affect various aspects of vision and eye movement. Thus, patients can show dry eyes, blepharospasm, reduced blink rate, saccadic eye movement abnormalities, smooth pursuit deficits, and impaired voluntary and reflexive eye movements. Furthermore, visuoperceptive impairments affect the ability to perceive and recognize visual stimuli accurately, including impaired contrast sensitivity and reduced visual acuity, color discrimination, and object recognition. Visuospatial impairments are also remarkable, including difficulties perceiving and interpreting spatial relationships between objects and difficulties judging distances or navigating through the environment. Moreover, PD patients can present visuospatial attention problems, with difficulties attending to visual stimuli in a spatially organized manner. Moreover, PD patients also show perceptual disturbances affecting their ability to interpret and determine meaning from visual stimuli. And, for instance, visual hallucinations are common in PD patients. Nevertheless, the neurobiological bases of visual-related disorders in PD are complex and not fully understood. This review intends to provide a comprehensive description of visual disturbances in PD, from sensory to perceptual alterations, addressing their neuroanatomical, functional, and neurochemical correlates. Structural changes, particularly in posterior cortical regions, are described, as well as functional alterations, both in cortical and subcortical regions, which are shown in relation to specific neuropsychological results. Similarly, although the involvement of different neurotransmitter systems is controversial, data about neurochemical alterations related to visual impairments are presented, especially dopaminergic, cholinergic, and serotoninergic systems.

Machine Learning and Eye Movements Give Insights into Neurodegenerative Disease Mechanisms

Humans are a vision-dominated species; what we perceive depends on where we look. Therefore, eye movements (EMs) are essential to our interactions with the environment, and experimental findings show EMs are affected in neurodegenerative disorders (ND). This could be a reason for some cognitive and movement disorders in ND. Therefore, we aim to establish whether changes in EM-evoked responses can tell us about the progression of ND, such as Alzheimer's (AD) and Parkinson's diseases (PD), in different stages. In the present review, we have analyzed the results of psychological, neurological, and EM (saccades, antisaccades, pursuit) tests to predict disease progression with machine learning (ML) methods. Thanks to ML algorithms, from the high-dimensional parameter space, we were able to find significant EM changes related to ND symptoms that gave us insights into ND mechanisms. The predictive algorithms described use various approaches, including granular computing, Naive Bayes, Decision Trees/Tables, logistic regression, C-/Linear SVC, KNC, and Random Forest. We demonstrated that EM is a robust biomarker for assessing symptom progression in PD and AD. There are navigation problems in 3D space in both diseases. Consequently, we investigated EM experiments in the virtual space and how they may help find neurodegeneration-related brain changes, e.g., related to place or/and orientation problems. In conclusion, EM parameters with clinical symptoms are powerful precision instruments that, in addition to their potential for predictions of ND progression with the help of ML, could be used to indicate the different preclinical stages of both diseases.

Which Test Is the Best to Assess Visuo-Cognitive Impairment in Patients with Parkinson's Disease with Mild Cognitive Impairment and Dementia? A Systematic Review and Meta-Analysis

BACKGROUND

Visuo-cognitive impairment is common in patients with Parkinson's disease with mild cognitive impairment (PD-MCI) and constitutes a prognostic factor for the conversion to Parkinson's disease dementia (PDD). However, systematic analyses on which neuropsychological tests are most suitable to assess visuo-cognition in PD-MCI and PDD and to differentiate these cognitive stages are lacking.

OBJECTIVE

To review neuropsychological tests used to assess visuo-cognition including visuo-perceptual and visuo-spatial processing, visuo-constructive copying and drawing on command abilities; and to identify the visuo-cognitive subdomain as well as tests most suitable to discriminate between PD-MCI and PDD.

METHODS

MEDLINE, PsycINFO, Web of Science Core Collection, and CENTRAL were systematically searched for relevant studies assessing visuo-cognitive outcomes in patients with PD-MCI and PDD. Risk of bias was assessed using a customized form based on well-established tools. Random-effect meta-analyses were conducted.

RESULTS

33 studies were included in the systematic review. Data of 19 studies were entered in meta-analyses. Considerable heterogeneity regarding applied tests, test versions, and scoring systems exists. Data indicate that visuo-constructive command tasks are the subdomain best suited to discriminate between PD-MCI and PDD. Furthermore, they indicate that the Rey-Osterrieth-Complex-Figure Test (ROCF), Corsi Block-Tapping Test, Judgment of Line Orientation (JLO), and Clock Drawing Test (CDT) are tests able to differentiate between the two stages.

CONCLUSION

We provide suggestions for suitable visuo-cognitive tests (Corsi Block-Tapping Test, or JLO, ROCF, CDT) to improve diagnostic accuracy. Methodological challenges (e.g., heterogeneity of definitions, tests) are discussed and suggestions for future research are provided.

REGISTRATION

https://www.crd.york.ac.uk/prospero/, ID: CRD42018088244.

Impact of Visual Impairment on Vision-Related Quality of Life in Parkinson's Disease

BACKGROUND

Visual impairment is frequent and highly disabling in Parkinson's disease (PD); however, few studies have comprehensively evaluated its impact on vision-related quality of life.

OBJECTIVE

To evaluate the relationship between visual function tests and the visual impairment perceived by PD patients in daily living activities.

METHODS

We cross-sectionally evaluated 62 PD patients and 33 healthy controls (HC). Visual disability was measured with a comprehensive battery of primary visual function and visual cognition tests (visual outcomes), and vision-related quality of life was evaluated with the National Eye Institute 25-Item Visual Function Questionnaire (NEI VFQ-25). The relationship between visual outcomes and NEI VFQ-25 sub-scores was analyzed with Pearson's correlations and stepwise linear regression.

RESULTS

In PD patients, and not in HC, most NEI VFQ-25 sub-scores were significantly correlated with Cube Analysis and Dot Counting from Visual Object and Space Perception (VOSP) battery (visual perception), Clock Drawing Test (visuoconstructive capacity) and Trail Making Test part-A (visual attention and processing speed) and to a lesser extent with high- and low-contrast visual acuity. Dot Counting (VOSP) was the test primarily associated with most NEI VFQ-25 sub-scores (5 out of 12). Roth-28 color test was the one that best explained the variance of Peripheral Vision (R2: 0.21) and Role Difficulties (R2: 0.36) sub-scores of NEI VFQ-25, while photopic contrast sensitivity explained 41% of Driving sub-score variance.

CONCLUSION

Vision-related quality of life in PD is mainly influenced by alterations in visual perception, visuoconstructive capacity and visual attention and processing speed. Future studies are warranted to confirm and further extend our findings.

Application of Eye Tracking Technology in Medicine: A Bibliometric Analysis

Eye tracking provides a quantitative measure of eye movements during different activities. We report the results from a bibliometric analysis to investigate trends in eye tracking research applied to the study of different medical conditions. We conducted a search on the Web of Science Core Collection (WoS) database and analyzed the dataset of 2456 retrieved articles using VOSviewer and the Bibliometrix R package. The most represented area was psychiatry (503, 20.5%) followed by neuroscience (465, 18.9%) and psychology developmental (337, 13.7%). The annual scientific production growth was 11.14% and showed exponential growth with three main peaks in 2011, 2015 and 2017. Extensive collaboration networks were identified between the three countries with the highest scientific production, the USA (35.3%), the UK (9.5%) and Germany (7.3%). Based on term co-occurrence maps and analyses of sources of articles, we identified autism spectrum disorders as the most investigated condition and conducted specific analyses on 638 articles related to this topic which showed an annual scientific production growth of 16.52%. The majority of studies focused on autism used eye tracking to investigate gaze patterns with regards to stimuli related to social interaction. Our analysis highlights the widespread and increasing use of eye tracking in the study of different neurological and psychiatric conditions.

The effectiveness of eye tracking in the diagnosis of cognitive disorders: A systematic review and meta-analysis

Background

Eye tracking (ET) is a viable marker for the recognition of cognitive disorders. We assessed the accuracy and clinical value of ET for the diagnosis of cognitive disorders in patients.

Methods

We searched the Medline, Embase, Web of Science, Cochrane Library, and Pubmed databases from inception to March 2, 2021, as well as the reference lists of identified primary studies. We included articles written in English that investigated ET for cognitive disorder patients—Mild cognitive impairment (MCI), Alzheimer’s disease (AD), Amyotrophic lateral sclerosis (ALS), and dementia. Two independent researchers extracted the data and the characteristics of each study; We calculated pooled sensitivities and specificities. A hierarchical summary of receiver performance characteristics (HSROC) model was used to test the diagnostic accuracy of ET for cognitive impairment (CI).

Findings

11 studies met the inclusion criteria and were included in qualitative comprehensive analysis. Meta-analysis was performed on 9 trials using Neuropsychological Cognitive Testing (NCT) as the reference standard. The comprehensive sensitivity and specificity of ET for detecting cognitive disorders were 0.75 (95% CI 0.72–0.79) and 0.73 (95% CI 0.70 to 0.76), respectively. The combined positive likelihood ratio (LR+) was 2.74 (95%CI 2.32–3.24) and the negative likelihood ratio (LR−) was 0.27 (95%CI 0.18–0.42).

Conclusions

This review showed that ET technology could be used to detect the decline in CI, clinical use of ET techniques in combination with other tools to assess CI can be encouraged.

Differential effects of aging and cognitive decline on visual exploration behavior in the elderly

Visual exploration disturbance has been examined in the elderly, mainly from the perspective of associations with cognitive function. However, it remains unknown whether this is a consequence of cognitive decline, age-related changes independent of cognitive decline, or both. In this study, 15 healthy elderly individuals were evaluated using two figure-matching tasks representing visual information processing (clock-matching and inverted clock-matching tasks). Cognitive functions were evaluated for each subject using the Mini-Mental State Examination (MMSE). Infrared eye-movement assessments were used to analyze eye movements during task performance. Behavioral analyses showed that age was associated with longer reaction time, while MMSE score was associated with higher accuracy on the inverted clock-matching task. Analyses of eye-movement parameters showed that MMSE score was negatively associated with a parameter indicating difficulty in the efficiency of visual exploration planning, while age was tended to be positively associated with the sum of saccade times in each trial, both predominantly on the inverted clock-matching task. Our approaches highlighted that age and cognitive decline are separately associated with eye-movement characteristics: cognitive decline is associated with difficulty in visual exploration planning, particularly in situations that require substantial visual working memory resources, whereas aging may be associated with oculomotor dysfunction.

Europium coordination polymer particles based electrospun nanofibrous film for point-of-care testing of copper (II) ions

Excess free copper in serum has been identified to induce neurodegenerative diseases such as Alzheimer's disease, thus it is very important to determine copper (II) ions (Cu²⁺) content for human health test. Herein we developed a point-of-care testing (POCT) platform through a luminescence "on-off" recognition mechanism of serum copper. Microsized europium coordination polymer particles (Eu-CPs), which was prepared with citric acid (CA) and europium nitrate hexahydrate through a hydrothermal route, were then successfully loaded with the mixture of 2,6-pyridinedicarboxylic acid (DPA) and poly(vinyl alcohol) (PVA) to form electrospun nanofibrous films (ENFFs). The as-prepared Eu-CPs/DPA/PVA ENFFs exhibited red emission at 618 nm when exciting at 280 nm, with the quantum yields of 22.2% owing to the antenna effect from DPA to Eu³⁺. Furthermore, the strong luminescence could be selectively quenched by Cu²⁺ through coordination with DPA to interrupt the antenna effect. With that, Cu²⁺ was successfully detected in the range of 2-45 μM with a detection of limit of 1.3 μM, well matching with the requirement of clinic test of excess free copper induced neurodegenerative diseases. As a proof of concept at last, this POCT platform was used to detect free copper in spiked serum samples with a recovery of 101.1%-105.2%, demonstrating that this platform provides significant potential for use in clinical test.

Spatial attention and spatial short term memory in PSP and Parkinson's disease

Progressive Supranuclear Palsy (PSP) is a neurodegenerative disorder characterised by deterioration in motor, oculomotor and cognitive function. A key clinical feature of PSP is the progressive paralysis of eye movements, most notably for vertical saccades. These oculomotor signs can be subtle, however, and PSP is often misdiagnosed as Parkinson's disease (PD), in its early stages. Although some of the clinical features of PD and PSP overlap, they are distinct disorders with differing underlying pathological processes, responses to treatment and prognoses. One key difference lies in the effects the diseases have on cognition. The oculomotor system is tightly linked to cognitive processes such as spatial attention and spatial short-term memory (sSTM), and previous studies have suggested that PSP and PD experience different deficits in these domains. We therefore hypothesised that people with PSP (N = 15) would experience problems with attention (assessed with feature and conjunction visual search tasks) and sSTM (assessed with the Corsi blocks task) compared to people with PD (N = 16) and Age Matched Controls (N = 15). As predicted, feature and conjunction search were sgnificantly slower in the PSP group compared to the other groups, and this deficit was significantly worse for feature compared to conjunction search. The PD group did not differ from AMC on feature search but were significantly impaired on the conjunction search. The PSP group also had a pronounced vertical sSTM impairment that was not present in PD or AMC groups. It is argued that PSP is associated with specific impairment of visuospatial cognition which is caused by degeneration of the oculomotor structures that support exogenous spatial attention, consistent with oculomotor theories of spatial attention and memory.

Vision, attention, and driving

Safe driving demands the coordination of multiple sensory and cognitive functions, such as vision and attention. Patients with neurologic or ophthalmic disease are exposed to selective pathophysiologic insults to driving-critical systems, placing them at a higher risk for unsafe driving and restricted driving privileges. Here, we evaluate how vision and attention contribute to unsafe driving across different patient populations. In ophthalmic disease, we focus on macular degeneration, glaucoma, diabetic retinopathy, and cataract; in neurologic disease, we focus on Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Unsafe driving is generally associated with impaired vision and attention in ophthalmic and neurologic patients, respectively. Furthermore, patients with ophthalmic disease experience some degree of impairment in attention. Similarly, patients with neurologic disease experience some degree of impairment in vision. While numerous studies have demonstrated a relationship between impaired vision and unsafe driving in neurologic disease, there remains a dearth of knowledge regarding the relationship between impaired attention and unsafe driving in ophthalmic disease. In summary, this chapter confirms-and offers opportunities for future research into-the contribution of vision and attention to safe driving.

Prolonged visual fixation as a surrogate marker of cholinergic deficit in Parkinson's disease: A 2-year follow-up study

INTRODUCTION

The search for biomarkers of cognitive impairment in Parkinson's disease is driven by the potential clinical applications in disease prognostication. Various eye tracking studies on cognitive functions in Parkinson's disease suggest a promising role of eye movement parameters as a biomarker for cognitive decline but the clinical utility has not been validated in longitudinal studies. The present study aims to investigate the longitudinal progression of eye fixation duration in a visual search task and its correlation with domain-specific cognitive impairment.

METHOD

This is a 2-year follow-up study on a group of non-demented Parkinson's disease patients, with baseline eye movement metrics and multi-domain cognitive functions measured, to assess the association between domain-specific cognitive impairment and progression of visual fixation duration.

RESULTS

A total of 49 from the original 62 non-demented Parkinson's disease patients were re-examined at a 2-year follow-up. 15 cases (31%) were classified as having mild cognitive impairment. Visual fixation duration was significantly prolonged after 2 years. Using repeated measures ANOVA, impairment in semantic verbal fluency, visual and verbal recognition memory and orienting function of attention had a significant effect on prolonging visual fixation over time.

CONCLUSION

Correlation between prolonged visual fixation and multiple domains of cognitive impairment related to cholinergic dysfunction in repeated measures over two years provides preliminary evidence for the eye tracking paradigm as a surrogate marker for cholinergic deficit in Parkinson's disease. The clinical utility in terms of disease prognostication is yet to be confirmed in prospective longitudinal studies with longer follow-up periods.

Disease Classification Based on Eye Movement Features With Decision Tree and Random Forest

Medical research shows that eye movement disorders are related to many kinds of neurological diseases. Eye movement characteristics can be used as biomarkers of Parkinson's disease, Alzheimer's disease (AD), schizophrenia, and other diseases. However, due to the unknown medical mechanism of some diseases, it is difficult to establish an intuitive correspondence between eye movement characteristics and diseases. In this paper, we propose a disease classification method based on decision tree and random forest (RF). First, a variety of experimental schemes are designed to obtain eye movement images, and information such as pupil position and area is extracted as original features. Second, with the original features as training samples, the long short-term memory (LSTM) network is used to build classifiers, and the classification results of the samples are regarded as the evolutionary features. After that, multiple decision trees are built according to the C4.5 rules based on the evolutionary features. Finally, a RF is constructed with these decision trees, and the results of disease classification are determined by voting. Experiments show that the RF method has good robustness and its classification accuracy is significantly better than the performance of previous classifiers. This study shows that the application of advanced artificial intelligence (AI) technology in the pathological analysis of eye movement has obvious advantages and good prospects.

Ocular fixations and presaccadic potentials to explain pareidolias in Parkinson's disease

In Parkinson's disease, a precursor phenomenon to visual hallucinations presents as 'pareidolias' which make ambiguous forms appear meaningful. To evoke and detect pareidolias in patients, a noise pareidolia test was recently developed, although its task-dependent mechanisms are yet to be revealed. When subjected to this test, we hypothesized that patients exhibiting pareidolias would show altered top-down influence of visual processing allowing us to demonstrate the influence of pareidolic illusionary behaviour in Parkinson's disease patients. To that end, we evaluated eye-movement strategies and fixation-related presaccadic activity on scalp EEG when participants performed the test. Twelve healthy controls and 21 Parkinson's disease patients, evaluated for cognitive, visuo-spatial and executive functions, took a modified computer-based version of the noise pareidolia test in a free-viewing EEG eye-tracking experiment. Eye-tracking metrics (fixation-related durations and counts) documented the eye movement behaviour employed in correct responses (face/noise) and misperceptions (pareidolia/missed) during early and late visual search conditions. Simultaneously, EEG recorded the presaccadic activity in frontal and parietal areas of the brain. Based on the noise pareidolia test scores, we found certain Parkinson's disease patients exhibited pareidolias whereas others did not. ANOVA on eye-tracking data showed that patients dwelled significantly longer to detect faces and pareidolias which affected both global and local search dynamics depending on their visuo-perceptual status. Presaccadic activity in parietal electrodes for the groups was positive for faces and pareidolias, and negative for noise, though these results depended mainly on saccade size. However, patients sensitive to pareidolias showed a significantly higher presaccadic potential on frontal electrodes independent of saccade sizes, suggesting a stronger frontal activation for pareidolic stimuli. We concluded with the following interpretations (i) the noise pareidolia test specifically characterizes visuo-perceptual inadequacies in patients despite their wide range of cognitive scores, (ii) Parkinson's disease patients dwell longer to converge attention to pareidolic stimuli due to abnormal saccade generation proportional to their visuo-perceptual deficit during early search, and during late search, due to time-independent alteration of visual attentional network and (iii) patients with pareidolias show increased frontal activation reflecting the allocation of attention to irrelevant targets that express the pareidolic phenomenon. While the disease per se alters the visuo-perceptual and oculomotor dynamics, pareidolias occur in Parkinson's disease due to an abnormal top-down modulation of visual processing that affects visual attention and guidance to ambiguous stimuli.

Connectivity Between Brain Networks Dynamically Reflects Cognitive Status of Parkinson's Disease: A Longitudinal Study

BACKGROUND

Cognitive impairment in Parkinson's disease (PD) is associated with altered connectivity of the resting state networks (RSNs). Longitudinal studies in well cognitively characterized PD subgroups are missing.

OBJECTIVES

To assess changes of the whole-brain connectivity and between-network connectivity (BNC) of large-scale functional networks related to cognition in well characterized PD patients using a longitudinal study design and various analytical methods.

METHODS

We explored the whole-brain connectivity and BNC of the frontoparietal control network (FPCN) and the default mode, dorsal attention, and visual networks in PD with normal cognition (PD-NC, n = 17) and mild cognitive impairment (PD-MCI, n = 22) as compared to 51 healthy controls (HC). We applied regions of interest-based, partial least squares, and graph theory based network analyses. The differences among groups were analyzed at baseline and at the one-year follow-up visit (37 HC, 23 PD all).

RESULTS

The BNC of the FPCN and other RSNs was reduced, and the whole-brain analysis revealed increased characteristic path length and decreased average node strength, clustering coefficient, and global efficiency in PD-NC compared to HC. Values of all measures in PD-MCI were between that of HC and PD-NC. After one year, the BNC was further increased in the PD-all group; no changes were detected in HC. No cognitive domain z-scores deteriorated in either group.

CONCLUSION

As compared to HC, PD-NC patients display a less efficient transfer of information globally and reduced BNC of the visual and frontoparietal control network. The BNC increases with time and MCI status, reflecting compensatory efforts.

The intersection between the oculomotor and hippocampal memory systems: empirical developments and clinical implications

Decades of cognitive neuroscience research has shown that where we look is intimately connected to what we remember. In this article, we review findings from human and nonhuman animals, using behavioral, neuropsychological, neuroimaging, and computational modeling methods, to show that the oculomotor and hippocampal memory systems interact in a reciprocal manner, on a moment-to-moment basis, mediated by a vast structural and functional network. Visual exploration serves to efficiently gather information from the environment for the purpose of creating new memories, updating existing memories, and reconstructing the rich, vivid details from memory. Conversely, memory increases the efficiency of visual exploration. We call for models of oculomotor control to consider the influence of the hippocampal memory system on the cognitive control of eye movements, and for models of hippocampal and broader medial temporal lobe function to consider the influence of the oculomotor system on the development and expression of memory. We describe eye movement-based applications for the detection of neurodegeneration and delivery of therapeutic interventions for mental health disorders for which the hippocampus is implicated and memory dysfunctions are at the forefront.

Visual search and target detection during simulated driving in Parkinson's disease

Patients with Parkinson's Disease (PD) often exhibit difficulties with visual search that may impede their ability to recognize landmarks and cars while driving. The main objective of this study was to investigate visual search performances of both billboards and cars in patients with PD using a driving simulator. A second objective was to examine the role of cognitive functions in performing the visual search task while driving. Nineteen patients with PD (age: 68 ± 8yo, sex (Men/Women): 15/4) and 14 controls (age: 60 ± 11yo, sex: 7/7) first performed a battery of cognitive tests. They then drove in a simulator and were instructed to follow a lead vehicle while searching for billboards with the letter A (stationary target) or red cars (moving target) among other distractors. Accuracy and response times of visual search were the main outcome variables. Standard deviation of lateral position (SDLP) was the secondary outcome. During driving, patients were less accurate in identifying the targets, particularly for the stationary billboards located in the outer periphery. Within the group of patients, significant correlations were found between several measures of cognitive tests and simulator-based visual search accuracy. By contrast, only the score on the MOCA test correlated significantly with visual search accuracy in controls. Findings suggest that patients with PD have impaired visual search for more eccentric stationary targets while driving a simulator, which is likely due to cognitive deficits. Difficulties identifying objects in the outer periphery may have implications for driving safety. Decreased functional field of view under increased cognitive load may have attributed to the difficulties identifying these landmarks. This may impact the ability to identify, anticipate, and respond to important information (e.g., pedestrians, navigation signs, landmarks), especially in complex driving situations (e.g. urban driving or intersections).Future studies should be conducted in a larger sample size to determine whether a visual search task on a driving simulator may predict on-road driving performances.

New insights into facial emotion recognition in Parkinson's disease with and without mild cognitive impairment from visual scanning patterns

Background

Recognizing emotional facial expressions is crucial for social interactions. Cognitive impairment and oculomotor abnormalities are common features of Parkinson's disease (PD) which may contribute to the performance in facial emotion recognition (FER) in PD.

Objective

The aim of this study was to analyze eye movement behavior during a facial emotion recognition (FER) task with respect to cognitive state in PD patients and healthy controls.

Methods

Eye movements of 24 non-demented, non-depressed PD patients (12 with intact cognitive functions and 12 with Mild Cognitive Impairment (MCI) according to MDS task force criteria level 2), and 12 age-, sex and education-matched healthy controls were recorded during visual exploration of 28 emotional (happiness, surprise, disgust, anger, fear and sadness) and neutral faces. Participants were asked to identify the displayed emotion out of a sevenfold multiple choice question.

Results

PD-MCI patients showed reduced FER with specific impairment of anger recognition. Although the scanned area of PD patients with intact cognition was significantly restricted, they did not differ in FER from healthy subjects. While healthy subjects and cognitively intact PD patients scanned faces with preference for mouth and eyes, patients with PD-MCI tended to look at the center of the face and spent significantly less time fixating the mouth.

Conclusions

Ineffective visual exploration may contribute to impaired emotion recognition in PD. Visual scanning of emotional faces is altered in PD even in the absence of cognitive impairment. The progression to PD-MCI may result in further deterioration of scanning behavior and FER impairment.

Measuring emotion recognition by people with Parkinson's disease using eye-tracking with dynamic facial expressions

BACKGROUND

Motion is an important cue to emotion recognition, and it has been suggested that we recognize emotions via internal simulation of others' expressions. There is a reduction of facial expression in Parkinson's disease (PD), which may influence the ability to use motion to recognise emotions in others. However, the majority of previous work in PD has used only static expressions. Moreover, few studies have used eye-tracking to explore emotion processing in PD.

NEW METHOD

We measured accuracy and eye movements in people with PD and healthy controls when identifying emotions from both static and dynamic facial expressions.

RESULTS

The groups did not differ overall in emotion recognition accuracy, but motion significantly increased recognition only in the control group. Participants made fewer and longer fixations when viewing dynamic expressions, and interest area analysis revealed increased gaze to the mouth region and decreased gaze to the eyes for dynamic stimuli, although the latter was specific to the control group.

COMPARISON WITH EXISTING METHODS

Ours is the first study to directly compare recognition of static and dynamic emotional expressions in PD using eye-tracking, revealing subtle differences between groups that may otherwise be undetected.

CONCLUSIONS

It is feasible and informative to use eye-tracking with dynamic expressions to investigate emotion recognition in PD. Our findings suggest that people with PD may differ from healthy older adults in how they utilise motion during facial emotion recognition. Nonetheless, gaze patterns indicate some effects of motion on emotional processing, highlighting the need for further investigation in this area.

Multimodal visual exploration disturbances in Parkinson's disease detected with an infrared eye-movement assessment system

Parkinson's disease (PD) reportedly show disturbed visual exploration. However, whether this disturbance is due to dysfunctional visual information processing remains unclear. To clarify the effects of PD on visual information processing when exploring for targets and to compare disease effects with aging effects, we used an infrared eye-movement assessment system. Cognitively normal PD patients (n = 13), healthy age-matched (n = 17) and young controls (n = 36) participated in this study, and were evaluated using two figure-matching tasks representing visual information processing (clock-matching and inverted clock-matching tasks) and saccade tasks representing oculomotor function. With figure-matching tasks, PD patients showed significantly larger numbers of images watched in a single trial compared to healthy age-matched controls on the inverted clock-matching task. No aging effects was found in these variables. In contrast, no disease effect was apparent for reaction time, which was significantly longer in healthy age-matched controls than in healthy young controls. For saccade tasks, PD patients showed significantly smaller saccade size than healthy age-matched controls on the antisaccade task, but no aging effects were evident. Our approaches highlighted that visual exploration disturbance in PD may be due to dysfunctional visual information processing in addition to dysfunctional oculomotor processing. These disease effects may differ from aging effects.

Evidence From Parkinson's Disease That the Superior Colliculus Couples Action and Perception

BACKGROUND

Action and perception should be coordinated for good visual-motor performance. The mechanism coupling action and perception may be a prominence map in the intermediate layer of the superior colliculus that modulates motor and attentional/perceptual processes. This coordination comes with a cost: the misperception that briefly overlapping stimuli are separated in time. Our model predicts that abnormal intermediate layer of the superior colliculus inhibition, such as that arising from increased basal ganglia output, would affect the action and perception coupling, and it would worsen the misperception.

OBJECTIVE

To test the prominence map model by measuring reaction times and perceptions in human intermediate layer of the superior colliculus dysfunction.

METHODS

We measured the saccadic and perceptual reaction time changes and the percept for different temporal asynchronies between fixation point offset and peripheral target onset in Parkinson's disease (PD).

RESULTS

We found that increased basal ganglia inhibitory output to the intermediate layer of the superior colliculus prominence map disrupted the normal coupling of action and perception. With increasing temporal asynchronies, the PD perceptual reaction times increased approximately 3 times more than the increase of the saccadic reaction times. Also, PD subjects misperceive small overlaps as gaps for temporal asynchronies up to 3 times longer than controls. The results can be reproduced by an intermediate layer of the superior colliculus rostral-caudal gradient of inhibition.

CONCLUSION

These findings support the hypothesis that a prominence map in the intermediate layer of the superior colliculus couples action and perception through modulation of attention. A dysfunction of this network quantifies abnormal basal ganglia output and could underlie visual deficits, including common, yet poorly understood, misperceptions and visual-motor deficits of PD. © 2019 International Parkinson and Movement Disorder Society.

Parkinson's disease and changes in the appreciation of art: A comparison of aesthetic and formal evaluations of paintings between PD patients and healthy controls

Parkinson's disease (PD) is a progressing neurodegenerative disease predominantly involving the loss of dopamine producing neurons with hallmark symptoms of motor disorders and cognitive, motivational, emotional, and perceptual impairments. Intriguingly, PD can also be connected-often anecdotally-with a sudden burst of artistic creativity, motivation, or changed quality/style of produced art. This has led to growing empirical interest, promising a window into brain function and the unique neurological signature of artists. This topic also fits a growing interest from researchers in other areas, including Alzheimer's or other dementia, which have suggested that specific changes in art production/appraisal may provide a unique basis for therapy, diagnosis, or understanding of these diseases. However, whether PD also shows similar impacts on how we perceive and evaluate art has never been systematically addressed. We compared a cohort of PD patients against age-matched healthy controls, asking participants to rate paintings using scales of liking and beauty and terms pertaining to artworks' formal and conceptual qualities previously designed to provide a rubric for symptom identification. We found no evidence for PD-related differences in liking or beauty. However, PD patients showed higher ratings on assessed "emotionality," potentially relating to the tie between PD, dopamine pathways, and emotion/reward.

Effects of visual blur on microsaccades during visual exploration

Microsaccades shift the image on the fovea and counteract visual fading. They also serve as an optimal sampling strategy while viewing complex visual scenes. Microsaccade production relies on the amount of retinal error or acuity demand of a visual task. The goal of this study was to assess the effects of blur induced by uncorrected refractive error on visual search. Eye movements were recorded in fourteen healthy subjects with uncorrected and corrected refractive error while they performed a) visual fixation b) blankscene viewing c) visual search (spot the difference) tasks. Microsaccades, saccades, correctly identified differences and reaction times were analyzed. The frequency of microsaccades and correctly identified differences were lower in the uncorrected refractive error during visual search. No similar change in microsaccades was seen during blank-scene viewing and gaze holding tasks. These findings suggest that visual blur, hence the precision of an image on the fovea, has an important role in calibrating the amplitude of microsaccades during visual scanning.

Co-occurrence of Convergence Insufficiency and Cognitive Impairment in Parkinsonian Disorders: A Pilot Study

Background: Convergence insufficiency (CI) in parkinsonian conditions causes disabling visual symptoms during near tasks and usually manifests as double vision. Since double vision is more common in patients who report cognitive symptoms, we sought to determine if symptomatic CI, as opposed to asymptomatic CI, could serve as a marker of cognitive impairment in parkinsonian disorders. Methods: Twenty-four participants with parkinsonian disorders (18 Parkinson's disease, 5 progressive supranuclear palsy, 1 multiple system atrophy) and objective findings of convergence insufficiency on neuro-ophthalmologic examination were included. Subjective visual symptoms and cognitive complaints were recorded, and the Self-Administered Gerocognitive Examination was used as a global cognitive screening measure. Results: 54.1% of parkinsonian participants had cognitive impairment, but there were no significant differences in the degree of convergence insufficiency, measured by near point of convergence (NPC), or cognitive outcomes between those with symptomatic CI, and asymptomatic CI. However, NPC was greater for those with cognitive impairment (x = 18.4 cm), compared to those who were cognitively intact (x = 12.5 cm, p = 0.003). Conclusions: Cognitive impairment commonly co-occurs in parkinsonian disorders with convergence insufficiency and is associated with significantly greater NPC distances. Clinicians should have a high index of suspicion for cognitive impairment in patients with objective findings of convergence insufficiency, whether symptomatic or not. Further investigation of convergence insufficiency in relationship to cognitive impairment in parkinsonian disorders is warranted, as there may be a shared mechanism of dysfunction.

The Role of Neuronal Oscillations in Visual Active Sensing

Visual perception is most often studied as a "passive" process in which an observer fixates steadily at point in space so that stimuli can be delivered to the system with spatial precision. Analysis of neuronal signals related to vision is generally keyed to stimulus onset, stimulus movement, etc.; i.e., events external to the observer. In natural "active" vision, however, information is systematically acquired by using eye movements including rapid (saccadic) eye movements, as well as smooth ocular pursuit of moving objects and slower drifts. Here we consider the use of alternating saccades and fixations to gather information from a visual scene. The underlying motor sampling plan contains highly reliable information regarding "where" and "when" the eyes will land, this information can be used predictively to modify firing properties of neurons precisely at the time when this "contextual" information is most useful - when a volley of retinal input enters the system at the onset of each fixation. Analyses focusing on neural events leading to and resulting from shifts in fixation, as well as visual events external to the observer, can provide a more complete and mechanistic understanding of visual information processing. Studies thus far suggest that active vision may be a fundamentally different from that process we usually study with more traditional passive viewing paradigms. In this Perspective we note that active saccadic sampling behavior imposes robust temporal patterning on the activity of neuron ensembles and large-scale neural dynamics throughout the brain's visual pathways whose mechanistic effects on information processing are not yet fully understood. The spatio-temporal sequence of eye movements elicits a succession of temporally predictable quasi-rhythmic sensory inputs, whose encoding is enhanced by entrainment of low frequency oscillations to the rate of eye movements. Review of the pertinent findings underscores the fact that temporal coordination between motor and visual cortices is critical for understanding neural dynamics of active vision and posits that phase entrainment of neuronal oscillations plays a mechanistic role in this process.

Why would Parkinson's disease lead to sudden changes in creativity, motivation, or style with visual art?: A review of case evidence and new neurobiological, contextual, and genetic hypotheses

Parkinson's disease (PD) is a devastating diagnosis with, however, potential for an extremely intriguing aesthetic component. Despite motor and cognitive deficits, an emerging collection of studies report a burst of visual artistic output and alterations in produced art in a subgroup of patients. This provides a unique window into the neurophysiological bases for why and how we might create and enjoy visual art, as well as into general brain function and the nature of PD or other neurodegenerative diseases. However, there has not been a comprehensive organization of literature on this topic. Nor has there been an attempt to connect case evidence and knowledge on PD with present understanding of visual art making in psychology and neuroaesthetics in order to propose hypotheses for documented artistic changes. Here, we collect the current research on this topic, tie this to PD symptoms and neurobiology, and provide new theories focusing on dopaminergic neuron damage, over-stimulation from dopamine agonist therapy, and context or genetic factors revealing the neurobiological basis of the visual artistic brain.

Eye Movements in Neuropsychological Tasks

This chapter reviews how recording and analysis of eye movements have been applied to understanding cognitive functioning in patients with neurological disease. Measures derived from the performance of instructed eye movement tests such as the anti-saccade and memory-guided saccade tasks have been shown to be associated with cognitive test performance and the early stages of neurodegenerative disorders including Alzheimer's and Parkinson's disease. Other researchers have taken an ecological approach and recorded the uninstructed pattern of saccades made by patients during performance of established neuropsychological tasks. Studies that have analysed the eye movement strategies used in a number of widely used tests are reviewed, including the Corsi blocks, Tower of London, 'CANTAB' Spatial Working Memory and Brixton Spatial Anticipation test. The findings illustrate that eye movements are not purely in the service of vision, but support visuospatial working memory and forward action planning. Eye movement tests and measures also have potential for application in the assessment and diagnosis of neurological disease and cognitive impairment. Establishing large-scale normative data sets in healthy older adults and use of machine learning multivariate classifier algorithms may be key to further developing eye tracking applications in neuropsychological assessment.

Vergence and Strabismus in Neurodegenerative Disorders

Maintaining proper eye alignment is necessary to generate a cohesive visual image. This involves the coordination of complex neural networks, which can become impaired by various neurodegenerative diseases. When the vergence system is affected, this can result in strabismus and disorienting diplopia. While previous studies have detailed the effect of these disorders on other eye movements, such as saccades, relatively little is known about strabismus. Here, we focus on the prevalence, clinical characteristics, and treatment of strabismus and disorders of vergence in Parkinson’s disease, spinocerebellar ataxia, Huntington disease, and multiple system atrophy. We find that vergence abnormalities may be more common in these disorders than previously thought. In Parkinson’s disease, the evidence suggests that strabismus is related to convergence insufficiency; however, it is responsive to dopamine replacement therapy and can, therefore, fluctuate with medication “on” and “off” periods throughout the day. Diplopia is also established as a side effect of deep brain stimulation and is thought to be related to stimulation of the subthalamic nucleus and extraocular motor nucleus among other structures. In regards to the spinocerebellar ataxias, oculomotor symptoms are common in many subtypes, but diplopia is most common in SCA3 also known as Machado–Joseph disease. Ophthalmoplegia and vergence insufficiency have both been implicated in strabismus in these patients, but cannot fully explain the properties of the strabismus, suggesting the involvement of other structures as well. Strabismus has not been reported as a common finding in Huntington disease or atypical parkinsonian syndromes and more studies are needed to determine how these disorders affect binocular alignment.

Eye movement parameters and cognitive functions in Parkinson's disease patients without dementia

BACKGROUND

Cognitive deficits and eye movement abnormalities have been demonstrated to be detectable early clinical manifestations of Parkinson's disease. Understanding the relationship between these phenotypes may yield insight into the underlying anatomical pathways, assisting in the search for simple non-invasive markers of early neurodegeneration.

OBJECTIVE

To explore the correlations between eye movement parameters with multi-domain cognitive functions in patients suffering from Parkinson's disease without dementia.

METHOD

This is a cross-sectional case-control study of Parkinson's disease patients without dementia. Participants underwent global and domain-specific cognitive tests and an eye-tracking visual search task to characterize eye movement parameters.

RESULTS

62 Chinese Parkinson's disease patients without dementia and 62 sex-, age- and education-matched controls were recruited. The disease group performed worse in multiple cognitive tasks and exhibited a smaller saccadic amplitude. Negative correlations between the eye fixation duration and performance in semantic verbal fluency, verbal and visual recognition memory tasks were observed, though there was no moderation effect on the correlations due to the presence of Parkinson's disease. A common cholinergic deficit in the temporal and parietal regions may account for the observed correlations. The lack of association with predominantly frontal-executive tasks may suggest specificity of these correlations.

CONCLUSION

Prolonged visual fixation duration is correlated with poorer performance in semantic verbal fluency, verbal and visual recognition memory tasks in Parkinson's disease patients without dementia, although these correlations are not specific. The clinical utility of eye movement parameters as an early marker for cognitive decline in Parkinson's disease warrants further exploration in longitudinal studies.

Establishing a New Screening System for Mild Cognitive Impairment and Alzheimer's Disease with Mental Rotation Tasks that Evaluate Visuospatial Function

BACKGROUND

The mental rotation task is well-known for the assessment of visuospatial function; however, it has not been used for screening of dementia patients.

OBJECTIVE

The aim of this study was to create a simple screening test for patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD) by focusing on non-amnestic symptoms.

METHODS

Age-matched healthy controls (age 75.3±6.8), patients with MCI (76.5±5.5), and AD (78.2±5.0) participated in this study. They carried out mental rotation tasks targeting geometric graphics or alphabetical characters with three rotating angles (0°, 90°, and 180°) and indicated the correct answer. Response accuracy and reaction time were recorded along with their eye movements using an eye tracker. To quantify their visual processing strategy, the run count ratio (RC ratio) was calculated by dividing the mean number of fixations in incorrect answers by that in correct answers.

RESULTS

AD patients showed lower accuracy and longer reaction time than controls. They also showed a significantly greater number of fixation and smaller saccade amplitude than controls, while fixation duration did not differ significantly. The RC ratio was higher for AD, followed by MCI and control groups. By setting the cut-off value to 0.47 in the 180° rotating angle task, we could differentiate MCI patients from controls with a probability of 80.0%.

CONCLUSIONS

We established a new screening system for dementia patients by evaluating visuospatial function. The RC ratio during a mental rotation task is useful for discriminating MCI patients from controls.

Do you see what I see? Mobile eye-tracker contextual analysis and inter-rater reliability

Mobile eye-trackers are currently used during real-world tasks (e.g. gait) to monitor visual and cognitive processes, particularly in ageing and Parkinson’s disease (PD). However, contextual analysis involving fixation locations during such tasks is rarely performed due to its complexity. This study adapted a validated algorithm and developed a classification method to semi-automate contextual analysis of mobile eye-tracking data. We further assessed inter-rater reliability of the proposed classification method. A mobile eye-tracker recorded eye-movements during walking in five healthy older adult controls (HC) and five people with PD. Fixations were identified using a previously validated algorithm, which was adapted to provide still images of fixation locations (n = 116). The fixation location was manually identified by two raters (DH, JN), who classified the locations. Cohen’s kappa correlation coefficients determined the inter-rater reliability. The algorithm successfully provided still images for each fixation, allowing manual contextual analysis to be performed. The inter-rater reliability for classifying the fixation location was high for both PD (kappa = 0.80, 95% agreement) and HC groups (kappa = 0.80, 91% agreement), which indicated a reliable classification method. This study developed a reliable semi-automated contextual analysis method for gait studies in HC and PD. Future studies could adapt this methodology for various gait-related eye-tracking studies.

Retinal degeneration in progressive supranuclear palsy measured by optical coherence tomography and scanning laser polarimetry

This cross-sectional study compared the retinal morphology between patients with progressive supranuclear palsy (PSP) and healthy controls. (The retinal nerve fiber layer (RNFL) around the optic disc and the retina in the macular area of 22 PSP patients and 151 controls were investigated by spectral domain optical coherence tomography (SD-OCT). Additionally, the RNFL and the nerve fiber index (NFI) were measured by scanning laser polarimetry (SLP). Results of RNFL measurements with SD-OCT and SLP were compared to assess diagnostic discriminatory power. Applying OCT, PSP patients showed a smaller RNFL thickness in the inferior nasal and inferior temporal areas. The macular volume and the thickness of the majority of macular sectors were reduced compared to controls. SLP data showed a thinner RNFL thickness and an increase in the NFI in PSP patients. Sensitivity and specificity to discriminate PSP patients from controls were higher applying SLP than SD-OCT. Retinal changes did not correlate with disease duration or severity in any OCT or SLP measurement. PSP seems to be associated with reduced thickness and volume of the macula and reduction of the RNFL, independent of disease duration or severity. Retinal imaging with SD-OCT and SLP might become an additional tool in PSP diagnosis.

Non-motor features of Parkinson disease

Many of the motor symptoms of Parkinson disease (PD) can be preceded, sometimes for several years, by non-motor symptoms that include hyposmia, sleep disorders, depression and constipation. These non-motor features appear across the spectrum of patients with PD, including individuals with genetic causes of PD. The neuroanatomical and neuropharmacological bases of non-motor abnormalities in PD remain largely undefined. Here, we discuss recent advances that have helped to establish the presence, severity and effect on the quality of life of non-motor symptoms in PD, and the neuroanatomical and neuropharmacological mechanisms involved. We also discuss the potential for the non-motor features to define a prodrome that may enable the early diagnosis of PD.

A novel computational model to probe visual search deficits during motor performance

Successful execution of many motor skills relies on well-organized visual search (voluntary eye movements that actively scan the environment for task-relevant information). Although impairments of visual search that result from brain injuries are linked to diminished motor performance, the neural processes that guide visual search within this context remain largely unknown. The first objective of this study was to examine how visual search in healthy adults and stroke survivors is used to guide hand movements during the Trail Making Test (TMT), a neuropsychological task that is a strong predictor of visuomotor and cognitive deficits. Our second objective was to develop a novel computational model to investigate combinatorial interactions between three underlying processes of visual search (spatial planning, working memory, and peripheral visual processing). We predicted that stroke survivors would exhibit deficits in integrating the three underlying processes, resulting in deteriorated overall task performance. We found that normal TMT performance is associated with patterns of visual search that primarily rely on spatial planning and/or working memory (but not peripheral visual processing). Our computational model suggested that abnormal TMT performance following stroke is associated with impairments of visual search that are characterized by deficits integrating spatial planning and working memory. This innovative methodology provides a novel framework for studying how the neural processes underlying visual search interact combinatorially to guide motor performance.

NEW & NOTEWORTHY

Visual search has traditionally been studied in cognitive and perceptual paradigms, but little is known about how it contributes to visuomotor performance. We have developed a novel computational model to examine how three underlying processes of visual search (spatial planning, working memory, and peripheral visual processing) contribute to visual search during a visuomotor task. We show that deficits integrating spatial planning and working memory underlie abnormal performance in stroke survivors with frontoparietal damage.

A spiking Basal Ganglia model of synchrony, exploration and decision making

To make an optimal decision we need to weigh all the available options, compare them with the current goal, and choose the most rewarding one. Depending on the situation an optimal decision could be to either “explore” or “exploit” or “not to take any action” for which the Basal Ganglia (BG) is considered to be a key neural substrate. In an attempt to expand this classical picture of BG function, we had earlier hypothesized that the Indirect Pathway (IP) of the BG could be the subcortical substrate for exploration. In this study we build a spiking network model to relate exploration to synchrony levels in the BG (which are a neural marker for tremor in Parkinson's disease). Key BG nuclei such as the Sub Thalamic Nucleus (STN), Globus Pallidus externus (GPe) and Globus Pallidus internus (GPi) were modeled as Izhikevich spiking neurons whereas the Striatal output was modeled as Poisson spikes. The model is cast in reinforcement learning framework with the dopamine signal representing reward prediction error. We apply the model to two decision making tasks: a binary action selection task (similar to one used by Humphries et al., 2006) and an n-armed bandit task (Bourdaud et al., 2008). The model shows that exploration levels could be controlled by STN's lateral connection strength which also influenced the synchrony levels in the STN-GPe circuit. An increase in STN's lateral strength led to a decrease in exploration which can be thought as the possible explanation for reduced exploratory levels in Parkinson's patients. Our simulations also show that on complete removal of IP, the model exhibits only Go and No-Go behaviors, thereby demonstrating the crucial role of IP in exploration. Our model provides a unified account for synchronization, action section, and explorative behavior.

Parallel basal ganglia circuits for voluntary and automatic behaviour to reach rewards

The basal ganglia control body movements, value processing and decision-making. Many studies have shown that the inputs and outputs of each basal ganglia structure are topographically organized, which suggests that the basal ganglia consist of separate circuits that serve distinct functions. A notable example is the circuits that originate from the rostral (head) and caudal (tail) regions of the caudate nucleus, both of which target the superior colliculus. These two caudate regions encode the reward values of visual objects differently: flexible (short-term) values by the caudate head and stable (long-term) values by the caudate tail. These value signals in the caudate guide the orienting of gaze differently: voluntary saccades by the caudate head circuit and automatic saccades by the caudate tail circuit. Moreover, separate groups of dopamine neurons innervate the caudate head and tail and may selectively guide the flexible and stable learning/memory in the caudate regions. Studies focusing on manual handling of objects also suggest that rostrocaudally separated circuits in the basal ganglia control the action differently. These results suggest that the basal ganglia contain parallel circuits for two steps of goal-directed behaviour: finding valuable objects and manipulating the valuable objects. These parallel circuits may underlie voluntary behaviour and automatic skills, enabling animals (including humans) to adapt to both volatile and stable environments. This understanding of the functions and mechanisms of the basal ganglia parallel circuits may inform the differential diagnosis and treatment of basal ganglia disorders.

Detection of third and sixth cranial nerve palsies with a novel method for eye tracking while watching a short film clip

OBJECT

Automated eye movement tracking may provide clues to nervous system function at many levels. Spatial calibration of the eye tracking device requires the subject to have relatively intact ocular motility that implies function of cranial nerves (CNs) III (oculomotor), IV (trochlear), and VI (abducent) and their associated nuclei, along with the multiple regions of the brain imparting cognition and volition. The authors have developed a technique for eye tracking that uses temporal rather than spatial calibration, enabling detection of impaired ability to move the pupil relative to normal (neurologically healthy) control volunteers. This work was performed to demonstrate that this technique may detect CN palsies related to brain compression and to provide insight into how the technique may be of value for evaluating neuropathological conditions associated with CN palsy, such as hydrocephalus or acute mass effect.

METHODS

The authors recorded subjects' eye movements by using an Eyelink 1000 eye tracker sampling at 500 Hz over 200 seconds while the subject viewed a music video playing inside an aperture on a computer monitor. The aperture moved in a rectangular pattern over a fixed time period. This technique was used to assess ocular motility in 157 neurologically healthy control subjects and 12 patients with either clinical CN III or VI palsy confirmed by neuro-ophthalmological examination, or surgically treatable pathological conditions potentially impacting these nerves. The authors compared the ratio of vertical to horizontal eye movement (height/width defined as aspect ratio) in normal and test subjects.

RESULTS

In 157 normal controls, the aspect ratio (height/width) for the left eye had a mean value ± SD of 1.0117 ± 0.0706. For the right eye, the aspect ratio had a mean of 1.0077 ± 0.0679 in these 157 subjects. There was no difference between sexes or ages. A patient with known CN VI palsy had a significantly increased aspect ratio (1.39), whereas 2 patients with known CN III palsy had significantly decreased ratios of 0.19 and 0.06, respectively. Three patients with surgically treatable pathological conditions impacting CN VI, such as infratentorial mass effect or hydrocephalus, had significantly increased ratios (1.84, 1.44, and 1.34, respectively) relative to normal controls, and 6 patients with supratentorial mass effect had significantly decreased ratios (0.27, 0.53, 0.62, 0.45, 0.49, and 0.41, respectively). These alterations in eye tracking all reverted to normal ranges after surgical treatment of underlying pathological conditions in these 9 neurosurgical cases.

CONCLUSIONS

This proof of concept series of cases suggests that the use of eye tracking to detect CN palsy while the patient watches television or its equivalent represents a new capacity for this technology. It may provide a new tool for the assessment of multiple CNS functions that can potentially be useful in the assessment of awake patients with elevated intracranial pressure from hydrocephalus or trauma.