POSITRON-EMISSION TOMOGRAPHY STUDIES OF CROSS-MODALITY INHIBITION IN SELECTIVE ATTENTIONAL TASKS - CLOSING THE MINDS EYE

It is a familiar experience that we tend to close our eyes or divert o ur gaze when concentrating attention on cognitively demanding tasks. W e report on the brain activity correlates of directing attention away from potentially competing visual processing and toward processing in another sensory modality. Results are reported from a series of positr on emission tomography studies of the human brain engaged in somatosen sory tasks, in both ''eyes open'' and ''eyes closed'' conditions. Duri ng these tasks, there was a significant decrease in the regional cereb ral blood flow in the visual cortex, which occurred irrespective of wh ether subjects had to close their eyes or were instructed to keep thei r eyes open. These task-related deactivations of the association areas belonging to the nonrelevant sensory modality were interpreted as bei ng due to decreased metabolic activity. Previous research has clearly demonstrated selective activation of cortical regions involved in atte ntion demanding modality-specific tasks; however, the other side of th is story appears to be one of selective deactivation of unattended are as.