Monkey prefrontal neuronal activity coding the forthcoming saccade in an
oculomotor delayed matching-to-sample task.
RYOHEI HASEGAWA, TOSHIYUKI SAWAGUCHI, AND KISOU KUBOTA.
Department of Behavioral and Brain Sciences, Primate Research Institute,
Kyoto University, Kanrin, Inuyama, Aichi 484, Japan.
APStracts 4:0249N, 1997.
ABSTRACT
To determine the role of the dorsolateral prefrontal cortex (PFC) in the
selection of memory-guided saccadic eye movements, we recorded the activities
of PFC neurons while macaque monkeys performed an oculomotor delayed matching-
to-sample task. The task was designed to dissociate motor factors from visual
factors in the selection and retention of the direction of the forthcoming
saccade during delay periods after the visual cue but before the GO signal was
presented. While the monkey fixated on a central fixation spot (FX period, 1
s), a sample cue (one of four geometric figures) and a matching cue composed
of two geometric figures were presented in succession (SC and MC periods,
respectively, 0.5 s) with a brief delay (D1 period, 1 or 1.5 s). After another
delay (D2 period, 1.5 s), the monkey made a saccade (GO period, < 0.5 s)
toward one of four locations (the goal) which had been indicated by the
combination of the sample and matching cues in the MC period. We recorded the
activities of 224 neurons in the periprincipal sulcal area of three
hemispheres of two monkeys. Sixty five neurons (29%) showed a significant
increase in activity during the D2 period. Some of these also responded during
other phases of the task (SC period, n = 32; D1, 22; MC, 53; GO, 47). Some of
the activity during the D2 (52/65, 80%) and GO (40/47, 85%) periods was
associated with the direction of the forthcoming saccade ('direction-
selective'). Although most MC-period activities of D2 neurons were direction-
selective (38/53, 73%), a fraction of them (14/38) were also affected by both
saccade direction and matching cue pattern. To compare quantitatively the
contribution of motor (saccade direction) and visual (matching-cue pattern)
factors to the activity of D2 neurons, we calculated directional and visual
dependency indices (DDI and VDI) for each of the three periods (MC, D2 and
GO). In both the D2 and GO periods, D2 neurons with high DDI values and low
VDI values predominated. In the MC period, however, there was no significant
difference between the distributions of DDI and VDI values. These findings
suggest that PFC neurons store the direction of memory-guided saccades during
a delay period prior to eye movement and that the same neurons may be involved
in the decision-making process that underlies the selection of the saccade
direction during the MC period.
Received 3 June 1996; accepted in final form 10 September 1997.
APS Manuscript Number J442-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997