Activity Linked to Externally Cued Saccades in Single Units Recorded from
Hippocampal, Parahippocampal and Inferotemporal Areas of Macaques
Stanislaw Sobotka, Anna Nowicka, and James L. Ringo
Department of Neurobiology and Anatomy, University of Rochester Medical
Center Rochester, NY, 14642, USA, Department of Neurophysiology, Nencki
Institute of Experimental Biology, 02-093 Warsaw, Poland
APStracts 4:113N, 1997.
ABSTRACT
We studied whether target-directed, externally-commanded saccadic eye
movements (saccades) induced activity in single units in inferotemporal
cortex, the hippocampal formation and parahippocampal gyrus. The monkeys were
first required to fix their gaze on a small cross presented to the left or
right of center on the monitor screen. The cross was extinguished and a
random 600-1000ms thereafter, a small dot was presented for 200 ms. The dot
was located either 10 deg above, below, right or left of the position on which
the fixation cross had been. The monkey made a saccadic eye movement to this
dot (in darkness). The neuronal activity around this goal-directed saccade was
analyzed. In addition, control conditions were systematically imposed in which
similar dots were presented, but the monkey's task was to withhold the
saccade. We recorded 290 units from two monkeys. From this group, 134 met two
criteria, i, they did not show visual response in control trials and, ii, they
had spike rates above 2 Hz. These were analyzed further; 53% (71/134) showed
modulation related to the target directed saccade, 29% (39/134) showed
saccadic modulation during spontaneous eye movements. These two groups were
only weakly correlated. Of the units with significant saccadic modulation, 17%
(12/71) showed significant directional selectivity, and 13% (9/71) showed
significant position selectivity (p<0.01). At a lower criterion (p<0.05)
almost half (33/71) showed one or the other spatial selectivity. Primates use
saccades to acquire visual information. The appearance of strong saccadic
modulation in brain structures previously characterized as mnemonic suggests
the possibility that the mnemonic circuitry uses an extra-retinal signal
linked to saccades to control visual memory processes, e.g., synchronizing
mnemonic processes to the pulsatile visual data inflow.
Received 13 December 1996; accepted in final form 18 June 1997.
APS Manuscript Number J968-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997