Prefrontal unit activity and delayed response: relation to cue location versus direction of response.

Two monkeys were trained to perform 3 kinds of spatial tasks (right-left DR, up-down DR, and conditional position discrimination with delay). In the conditional position task, the animal was required to respond to the right (left) choice key when the cue had been presented on the upper (lower) position. Single unit activity was recorded from the principalis area of the dorsolateral prefrontal cortex while the animal was performing the tasks. Once a differential delay unit (i.e., unit showing specificity during the delay period for two kinds of trials) was found in right-left DR (or up-down DR), the same unit was tested in the other tasks. A total of 32 differential delay units were investigated sufficiently to allow comparison of all 3 conditions. The results indicate that there are two types of differential delay units. The first type showed a clear dependence on the cue location, while the second type was related to the direction of the impending response. Activity of the second type of differential delay unit during the delay period served to predict the occurrence of errors, whereas this relation between unit discharge and correct or incorrect responses was not seen for the first type of differential delay unit.