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Using Saccadometry with Deep Brain Stimulation to Study Normal and Pathological Brain Function
Published on: July 14, 2016
Frontal eye field signals that may trigger the brainstem saccade generator
Edward L Keller1, Byeong-Taek Lee, Kyoung-Min Lee
1Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA. elk@ski.org
Progress in Brain Research
|August 23, 2008
Summary
Normal saccades are single, smooth eye movements. This study found that frontal eye field (FEF) neurons, but not superior colliculus (SC) neurons, activate before the first saccade in two-step eye movements, potentially explaining fragmented saccades in neurological disorders.
Area of Science:
- Neuroscience
- Ophthalmology
- Neurology
Background:
- Saccades are rapid eye movements crucial for visual perception.
- Fragmented saccades, occurring in multi-step sequences, are characteristic of certain neurological disorders like Parkinson's disease and late-onset Tay-Sachs disease (LOTS).
- Normal individuals can also exhibit two-step saccades during cognitively demanding tasks.
Purpose of the Study:
- To investigate the neural mechanisms underlying single-step versus two-step saccades.
- To compare neuronal activity in the superior colliculus (SC) and frontal eye field (FEF) during visually guided choice saccade tasks in monkeys.
- To elucidate the role of FEF and SC in initiating and sustaining saccadic eye movements.
Main Methods:
- Neuronal activity was recorded in the SC and FEF of monkeys performing a visually guided choice saccade task.
- Activity was analyzed during trials with single-step saccades versus trials with two-step saccades.
- Discharge patterns of neurons were compared relative to the onset of the first saccade.
Main Results:
- A class of frontal eye field (FEF) neurons exhibited a burst of activity preceding the first saccade in two-step movements.
- Neurons in the rostral and caudal superior colliculus (SC) were not modulated at the time of the first saccade.
- These findings suggest FEF neurons may trigger saccade initiation before downstream systems are fully engaged.
Conclusions:
- A precise balance between triggering and sustaining neural inputs is essential for normal single-step saccades.
- Differences in FEF and SC activity during two-step saccades may offer insights into the pathology of fragmented saccades in disease states.
- FEF's role in saccade initiation is highlighted, potentially explaining saccadic abnormalities in neurological conditions.
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