Neuronal responses to a delayed-response delayed-reward go/nogo task in the monkey posterior insular cortex.
Anatomical connections of the insular cortex suggest its involvement in cognition, emotion, memory, and behavioral manifestation. However, there have been few neurophysiological studies on the insular cortex in primates, in relation to such higher cognitive functions. In the present study, neural activity was recorded from the monkey insular cortex during performance of a delayed-response delayed-reward go/nogo task. In this task, visual stimuli indicating go or nogo responses associated with reward (reward trials) and with no reward (no-reward trials) were presented after eye fixation. In the reward trials, the monkey was required to release a button during presentation of the 2nd visual stimuli after a delay period (delay 1). Then, a juice reward was delivered after another delay (delay 2). The results indicated that the neurons responding in each epoch of the task were topographically localized within the insular cortex, consistent with the previous anatomical studies indicating topographical distributions of afferent inputs from other subcortical and cortical sensory areas. Furthermore, some insular neurons 1) nonspecifically responded to the visual cues and during fixation; 2) responded to the visual cues predicting reward and during the delay period before reward delivery; 3) responded differentially in go/nogo trials during the delay 2; and 4) responded around button manipulation. The observed patterns of insular-neuron responses and the correspondence of their topographical localization to those in previous anatomical studies suggest that the insular cortex is involved in attention- and reward-related functions and might monitor and integrate activities of other brain regions during cognition and behavioral manifestation.