Cerebral representation and the role of monoamines for selective attention

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To examine functional organization of the prefrontal cortex (PFC) for selective attention, we made local inactivation with muscimol at several sites of the dorsolateral PFC, while monkeys were performing an oculomotor visual search (OVS) task and its control task, an oculomotor detection (OD) task. In the OVS task, the subject fixated a central fixation spot, and a peripheral stimulus array appeared, which consisted of a target and 7 distracters. When the array appeared, the subject was required to make a saccade to the target. The OD task was exactly the same as the OVS task, except that only a target appeared without distracters. Thus, OVS task, but not the OD task, required selective attention. We found that the muscimol injection at each site induced deficits in the OVS, but not OD, task for a few particular target locations. There was a gross topographical relationship between the target location affected and the injection site. Further, to examine the involvement of monoamines in the selective attention process of the PFC, we injected noradrenergic antagonists into the dorsolateral PFC, while the monkeys were performing the OVS and OD tasks. It was found that yohimbine, an arpha-2 receptor antagonist, induced a specific deficit in the OVS task. Alpha-1 or beta-antagonist did not have any effect on either OVS or OD task. These findings suggest that 1) the dorsolateral PFC contains "attention map" for representing the selective attention process and 2) arpha-2 receptors of this area play an important role for the selective attention process.