Recent studies show that cells in the somatosensory cortex are involved in
the short-term retention of tactile information. In addition, some somatose
nsory cells appear to retain visual information that has been associated wi
th the touch of an object. The presence of such cells suggests that nontact
ile stimuli associated with touch have access to cortical neuron networks e
ngaged in the haptic sense. Thus, we inferred that somatosensory cells woul
d respond to behaviorally associated visual and tactile stimuli. To test th
is assumption, single units were recorded from the anterior parietal cortex
(Brodmann's areas 3a, 3b, 1, and 2) of monkeys performing a visuo-haptic d
elay task, which required the memorization of a visual cue for a tactile ch
oice. Most cells responding to that cue responded also to the corresponding
object presented for tactile choice. Significant correlations were observe
d in some cells between their differential reactions to tactile objects and
their differential reactions to the associated visual cues. Some cells wer
e recorded in both the cross-modal task and a haptic unimodal task, where t
he animal had to retain a tactile cue for a tactile choice. In most of thes
e cells, correlations were observed between stimulus-related firing in corr
esponding cue periods of the two tasks. These findings suggest that cells i
n somatosensory cortex are the components of neuronal networks representing
tactile information. Associated visual stimuli may activate such networks
through visuo-haptic associations established by behavioral training.