Cortical control of voluntary saccades in Parkinson's disease and pre-emptive perception

Monitoring Eye Movement in Patients with Parkinson's Disease: What Can It Tell Us?

Parkinson's disease (PD) affects approximately 10 million individuals worldwide. Visual impairments are a common feature of PD. Patients report difficulties with visual scanning, impaired depth perception and spatial navigation, and blurry and double vision. Examination of PD patients reveals abnormal fixational saccades, strabismus, impaired convergence, and abnormal visually-guided saccades. This review aims to describe objective features of abnormal eye movements in PD and to discuss the structures and pathways through which these abnormalities may manifest.

A Systematic Survey of Research Trends in Technology Usage for Parkinson's Disease

Parkinson's disease (PD) is a neurological disorder with complicated and disabling motor and non-motor symptoms. The complexity of PD pathology is amplified due to its dependency on patient diaries and the neurologist's subjective assessment of clinical scales. A significant amount of recent research has explored new cost-effective and subjective assessment methods pertaining to PD symptoms to address this challenge. This article analyzes the application areas and use of mobile and wearable technology in PD research using the PRISMA methodology. Based on the published papers, we identify four significant fields of research: diagnosis, prognosis and monitoring, predicting response to treatment, and rehabilitation. Between January 2008 and December 2021, 31,718 articles were published in four databases: PubMed Central, Science Direct, IEEE Xplore, and MDPI. After removing unrelated articles, duplicate entries, non-English publications, and other articles that did not fulfill the selection criteria, we manually investigated 1559 articles in this review. Most of the articles (45%) were published during a recent four-year stretch (2018-2021), and 19% of the articles were published in 2021 alone. This trend reflects the research community's growing interest in assessing PD with wearable devices, particularly in the last four years of the period under study. We conclude that there is a substantial and steady growth in the use of mobile technology in the PD contexts. We share our automated script and the detailed results with the public, making the review reproducible for future publications.

Direct and indirect effects of attention and visual function on gait impairment in Parkinson's disease: influence of task and turning

Gait impairment is a core feature of Parkinson's disease (PD) which has been linked to cognitive and visual deficits, but interactions between these features are poorly understood. Monitoring saccades allows investigation of real-time cognitive and visual processes and their impact on gait when walking. This study explored: (i) saccade frequency when walking under different attentional manipulations of turning and dual-task; and (ii) direct and indirect relationships between saccades, gait impairment, vision and attention. Saccade frequency (number of fast eye movements per-second) was measured during gait in 60 PD and 40 age-matched control participants using a mobile eye-tracker. Saccade frequency was significantly reduced in PD compared to controls during all conditions. However, saccade frequency increased with a turn and decreased under dual-task for both groups. Poorer attention directly related to saccade frequency, visual function and gait impairment in PD, but not controls. Saccade frequency did not directly relate to gait in PD, but did in controls. Instead, saccade frequency and visual function deficit indirectly impacted gait impairment in PD, which was underpinned by their relationship with attention. In conclusion, our results suggest a vital role for attention with direct and indirect influences on gait impairment in PD. Attention directly impacted saccade frequency, visual function and gait impairment in PD, with connotations for falls. It also underpinned indirect impact of visual and saccadic impairment on gait. Attention therefore represents a key therapeutic target that should be considered in future research.

Gait in Parkinson's disease: A visuo-cognitive challenge

Vision and cognition have both been related to gait impairment in Parkinson's disease (PD) through separate strands of research. The cumulative and interactive effect of both (which we term visuo-cognition) has not been previously investigated and little is known about the influence of cognition on vision with respect to gait. Understanding the role of vision, cognition and visuo-cognition in gait in PD is critical for data interpretation and to infer and test underlying mechanisms. The purpose of this comprehensive narrative review was to examine the interdependent and interactive role of cognition and vision in gait in PD and older adults. Evidence from a broad range of research disciplines was reviewed and summarised. A key finding was that attention appears to play a pivotal role in mediating gait, cognition and vision, and should be considered emphatically in future research in this field.

Are patients with Parkinson's disease blind to blindsight?

In Parkinson's disease, visual dysfunction is prominent. Visual hallucinations can be a major hallmark of late stage disease, but numerous visual deficits also occur in early stage Parkinson's disease. Specific retinopathy, deficits in the primary visual pathway and the secondary ventral and dorsal pathways, as well as dysfunction of the attention pathways have all been posited as causes of hallucinations in Parkinson's disease. We present data from patients with Parkinson's disease that contrast with a known neuro-ophthalmological syndrome, termed 'blindsight'. In this syndrome, there is an absence of conscious object identification, but preserved 'guess' of the location of a stimulus, preserved reflexive saccades and motion perception and preserved autonomical and expressive reactions to negative emotional facial expressions. We propose that patients with Parkinson's disease have the converse of blindsight, being 'blind to blindsight'. As such they preserve conscious vision, but show erroneous 'guess' localization of visual stimuli, poor saccades and motion perception, and poor emotional face perception with blunted autonomic reaction. Although a large data set on these deficits in Parkinson's disease has been accumulated, consolidation into one specific syndrome has not been proposed. Focusing on neuropathological and physiological data from two phylogenetically old and subconscious pathways, the retino-colliculo-thalamo-amygdala and the retino-geniculo-extrastriate pathways, we propose that aberrant function of these systems, including pathologically inhibited superior colliculus activity, deficient corollary discharges to the frontal eye fields, dysfunctional pulvinar, claustrum and amygdaloid subnuclei of the amygdala, the latter progressively burdened with Lewy bodies, underlie this syndrome. These network impairments are further corroborated by the concept of the 'silent amygdala'. Functionally being 'blind to blindsight' may facilitate the highly distinctive 'presence' or 'passage' hallucinations of Parkinson's disease and can help to explain handicaps in driving capacities and dysfunctional 'theory of mind'. We propose this synthesis to prompt refined neuropathological and neuroimaging studies on the pivotal nuclei in these pathways in order to better understand the networks underpinning this newly conceptualized syndrome in Parkinson's disease.

Cortical control of saccades in Parkinson disease and essential tremor

A number of studies suggest that some features of essential tremor (ET) and Parkinson disease (PD) overlap. Besides tremor, also some cognitive features have been implicated in ET and PD. There is recent evidence that a common genetic mutation occurs in ET and PD. Saccadic eye movements could provide an easily quantifiable procedure to help in the differential diagnosis in early PD and ET. Being able to distinguish early on the two diseases may help in tailoring therapy. Cortical control of saccades and antisaccades as they pertain to the potential discrimination of PD and ET is reviewed. Imaging and electrophysiological studies are highlighted; however, there are still few studies. Hopefully this review will stimulate further research, in particular in the direction of differences and similarities in the neural circuits involved in PD and ET.