Abstract
It is generally believed that the prefrontal cortex has a critical role for intelligence, which could be closely related to the ability of response selection. However, prefrontal patients and monkeys do not show severe deficit in a simple task situation. To uncover the prefrontal dysfunction, more demanding task is required. We trained Japanese monkeys to perform a go/no-go task where they had to use selective attention to one aspect of a compound visual stimulus (a moving random pattern of colored dots) to make the correct response. In this task, the monkeys should make a go or no-go response depending on either the color or the motion direction of the compound stimulus. In previous studies we have showed that the neuronal network system in the prefrontal cortex is hierarchically organized to generate appropriate behavioral codes and top-down attention can modulate the activity level of these long-term stimulus-response codes depending on task requirements with suppressing irrelevant codes. Based on the results, here we propose a model that can explain how irrelevant stimulus-response codes compete with relevant stimulus-response codes in prefrontal cortex. To test the plausibility of the model, reversible inactivation studies were done in various sub-regions in prefrontal cortex of the monkeys. Inactivation was not effective in less competitive situations, but severely effective in a competitive situation, which had been expected by our model. [Jpn J Physiol 54 Suppl:S15 (2004)]
