Primate frontal lesions and the temporal structure of behavior

Removal of the frontal cortex of primates results in a psychological deficit usually classified in terms of short‐term memory. This classification is based on impairment in per formance of delayed response or alternation type tasks. The present experiments were un dertaken in order to utilize this frontal preparation to learn more about the short‐term memory process as well as to delineate more precisely the frontal lobe deficit. Rhesus mon keys with lesions of the dorsolateral frontal cortex were tested in a situation where the classical alternation task with 5 second delay (Right‐Left‐Right‐Left) was modified by in terposing a 15 second interval between each R‐L couplet ( R‐L ⃛ R‐L ⃛). This modification made it possible for monkeys with frontal lesions who had failed the classical task to perform with very few errors. Two additional alternation experiments, one interposing light and one interposing sound between trials, failed to produce such effective performance. These experiments suggest that proper temporal structuring, or parsing, of the stream of stimuli to which the organism is subject, is a more important variable in the mechanism of short‐term memory than is the maintenance of a neural trace per se. They also suggest that the frontal cortex of primates is critically involved in the temporal structuring of behavior.