Saccades in Huntington's disease: predictive tracking and interaction between release of fixation and initiation of saccades
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J R Tian1, D S Zee, A G Lasker
1Department of Neurology, Johns Hopkins University, School of Medicine, Baltimore, MD.
Insights
Huntington's disease (HD) patients exhibit impaired predictive eye movements. However, their ability to initiate externally triggered saccades remains comparable to normal subjects, suggesting specific neural pathway involvement.
Area of Science:
- Neuroscience
- Ophthalmology
- Genetics
Background:
- Huntington's disease (HD) is a neurodegenerative disorder affecting motor control.
- Saccadic eye movements are crucial for visual attention and information gathering.
Purpose of the Study:
- To investigate saccadic eye movement abnormalities in Huntington's disease patients.
- To differentiate between internally generated and externally triggered saccade deficits in HD.
Main Methods:
- Comparison of saccadic eye movements between 21 HD patients and 21 normal subjects.
- Utilized predictive tracking and gap/overlap tasks to assess saccade initiation.
- Measured saccade latency and accuracy under different task conditions.
Main Results:
- HD patients showed significant deficits in anticipating predictable visual target location and timing.
- Both HD patients and normal subjects demonstrated reduced saccade latency in the gap task compared to the overlap task.
- HD patients exhibited prolonged saccade latency in predictive tracking (+170 msec) versus normal subjects (-78 msec).
Conclusions:
- HD patients display greater impairments in initiating internally generated saccades than externally triggered ones.
- This deficit pattern suggests involvement of frontal lobe-basal ganglia circuits in HD.
- Parietal-superior collicular pathways may be relatively spared in Huntington's disease.
Abstract:
We compared saccadic eye movements in 21 patients with Huntington's disease (HD) and 21 normal subjects. In a predictive tracking task, HD patients were unable to anticipate normally the timing and location of a visual target that alternated its position predictably (+/- 10 degrees, 0.5 Hz; mean latency of +170 msec in HD and -78 msec in normal subjects). HD patients and normal subjects, however, showed comparable decreases in saccade latency (110 msec in HD, 124 msec in normal subjects) when the fixation target was turned off 200 msec before (gap task) versus 200 msec after (overlap task) the appearance of an unexpected peripheral stimulus. Taken together, these findings support the idea that HD patients show greater defects in initiating internally generated than in initiating externally triggered saccades. This dichotomy is likely due to involvement of frontal lobe--basal ganglia structures in HD, with relative sparing of parietal--superior collicular pathways.