Jr. Gibson et Jhr. Maunsell, SENSORY MODALITY SPECIFICITY OF NEURAL ACTIVITY RELATED TO MEMORY IN VISUAL-CORTEX, Journal of neurophysiology, 78(3), 1997, pp. 1263-1275
Previous studies have shown that when monkeys perform a delayed match-
to-sample (DMS) task, some neurons in inferotemporal visual cortex are
activated selectively during the delay period when the animal must re
member particular visual stimuli. This selective delay activity may be
involved in short-term memory. It does not depend on visual stimulati
on: both auditory and tactile stimuli can trigger selective delay acti
vity in inferotemporal cortex when animals expect to respond to visual
stimuli in a DMS task. We have examined the overall modality specific
ity of delay period activity using a variety of auditory/visual cross-
modal and unimodal DMS tasks. The crossmodal DMS tasks involved making
specific long-term memory associations between visual and auditory st
imuli, whereas the unimodal DMS tasks were standard identity matching
tasks. Delay activity existed in auditory/visual cross-modal DMS tasks
whether the animal anticipated responding to visual or auditory stimu
li. No evidence of selective delay period activation was seen in a pur
ely auditory DMS task. Delay-selective cells were relatively common in
one animal where they constituted up to 53% neurons tested with a giv
en task. This was only the case for up to 9% of cells in a second anim
al. In the first animal, a specific long-term memory representation fo
r learned cross-modal associations was observed in delay activity, ind
icating that this type of representation need not be purely visual. Fu
rthermore, in this same animal, delay activity in one cross-modal task
, an auditory-to-visual task, predicted correct and incorrect response
s. These results suggest that neurons in inferotemporal cortex contrib
ute to abstract memory representations that can be activated by input
from other sensory modalities, but these representations are specific
to visual behaviors.