Macaque Lateral Intraparietal Area and Oculomotor Behaviors

Computation and Neural Systems

Li, Chiang-Shan Ray ; Andersen, Richard A.

University:California Institute of Technology

Department:Biology

关键词: Computation and Neural Systems;   

Others  :  https://thesis.library.caltech.edu/7602/1/Li%20%201996.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Neurons in the primate lateral intraparietal area (area LIP) carry visual,saccade-related and eye position activities. The visual and saccade activitiesare anchored in a retinotopic framework and the overall response magnitudeis modulated by eye position. It was proposed that the modulation by eyeposition might be the basis of a distributed coding of target locations in ahead-centered space. Other recording studies demonstrated that area LIP isinvolved in oculomotor planning. These results overall suggest that area LIPtransforms sensory information for motor functions. In this thesis I furtherexplore the role of area LIP in processing saccadic eye movements byobserving the effects of reversible inactivation of this area. Macaque monkeyswere trained to do visually guided and memory saccades and a doublesaccade task to examine the use of eye position signal. Finally, by intermixingvisual saccades with trials in which two targets were presented at oppositesides of the fixation point, I examined the behavior of visual extinction.

In chapter 2, I will show that lesion of area LIP results in increased latencyof contralesional visual and memory saccades. Contralesional memorysaccades are also hypometric and slower in velocity. Moreover, theimpairment of memory saccades does not vary with the duration of the delayperiod. This suggests that the oculomotor deficits observed after inactivationof area LIP is not due to the disruption of spatial memory.

In chapter 3, I will show that lesion of area LIP does not severely affect theprocessing of spontaneous eye movement. However, the monkeys madefewer contralesional saccades and tended to confine their gaze to theipsilesional field after inactivation of area LIP. On the other hand, lesion ofarea LIP results in extinction of the contralesional stimulus. When the initialfixation position was varied so that the retinal and spatial locations of thetargets could be dissociated, it was found that the extinction behavior couldbest be described in a head-centered coordinate.

In chapter 4, I will show that inactivation of area LIP disrupts the use of eyeposition signal to compute the second movement correctly in the doublesaccade task. If the first saccade steps into the contralesional field, the errorrate and latency of the second saccade are both increased. Furthermore, thedirection of the first eye movement largely does not have any effect on theimpairment of the second saccade. I will argue that this study providesimportant evidence that the extraretinal signal used for saccadic localizationis eye position rather than a displacement vector.

In chapter 5, I will demonstrate that in parietal monkeys the eye driftstoward the lesion side at the end of the memory saccade in darkness. Thisresult suggests that the eye position activity in the posterior parietal cortex isactive in nature and subserves gaze holding.

Overall, these results further support the view that area LIP neurons encodespatial locations in a craniotopic framework and is involved in processingvoluntary eye movements.