Abstract
Prefrontal neurons exhibit saccade-related activity and pre-saccadic memory-related activity often encodes the directions of forthcoming eye movements, in line with demonstrated prefrontal contribution to flexible control of voluntary eye movements. However, many prefrontal neurons exhibit post-saccadic activity that is initiated well after the initiation of eye movement. Although post-saccadic activity has been observed in the frontal eye field, this activity is thought to be a corollary discharge from oculomotor centers, because this activity shows no directional tuning and is observed whenever the monkeys perform eye movements regardless of goal-directed or not. However, prefrontal post-saccadic activities exhibit directional tunings similar as pre-saccadic activities and show context dependency, such that post-saccadic activity is observed only when monkeys perform goal-directed saccades. Context-dependency of prefrontal post-saccadic activity suggests that this activity is not a result of corollary signals from oculomotor centers, but contributes to other functions of the prefrontal cortex. One function might be the termination of memory-related activity after a behavioral response is done. This is supported by the observation that the termination of memory-related activity coincides with the initiation of post-saccadic activity in population analyses of prefrontal activities. The termination of memory-related activity at the end of the trial ensures that the subjects can prepare to receive new and updated information. Another function might be the monitoring of behavioral performance, since the termination of memory-related activity by post-saccadic activity could be associated with informing the correctness of the response and the termination of the trial. However, further studies are needed to examine the characteristics of saccade-related activities in the prefrontal cortex and their functions in eye movement control and a variety of cognitive functions.
Highlights
It is well known that both the frontal and supplementary eye fields participate in eye movement control, since (1) electrical stimulation of these areas evokes saccadic eye movements (e.g., Bruce et al, 1985); (2) lesion of these areas causes deficits in voluntary eye movements (e.g., Latto and Cowey, 1971a,b); and (3) eye movement-related activity is observed in many neurons in these areas (e.g., Bizzi, 1967, 1968; Bizzi and Schiller, 1970; Bruce and Goldberg, 1985)
The characteristics of directional selectivity and context dependency are similar between pre- and post-saccadic activities in the prefrontal cortex. These results indicate that the prefrontal cortex participates in the control of purposive saccadic eye movements, similar to the frontal eye field
In contrast to the traditional idea that post-saccadic activity is a corollary discharge from oculomotor centers, post-saccadic activity observed in the prefrontal cortex is not a corollary discharge because of its context-dependent nature
Summary
Reviewed by: Nandakumar Narayanan, University of Iowa Carver College of Medicine, USA Vincent Prevosto, Duke University, USA. Post-saccadic activity has been observed in the frontal eye field, this activity is thought to be a corollary discharge from oculomotor centers, because this activity shows no directional tuning and is observed whenever the monkeys perform eye movements regardless of goal-directed or not. The termination of memory-related activity at the end of the trial ensures that the subjects can prepare to receive new and updated information. Another function might be the monitoring of behavioral performance, since the termination of memory-related activity by post-saccadic activity could be associated with informing the correctness of the response and the termination of the trial.
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