Attention systems and the organization of the human parietal cortex

Event-related functional magnetic resonance imaging was used to compare act ivity in the human parietal cortex in two attention-switching paradigms. On each trial of the visual switching (VS) paradigm, subjects attended to one of two visual stimuli on the basis of either their color or shape. Trials were presented in blocks interleaved with cues instructing subjects to eith er continue attending to the currently relevant dimension or to switch to t he other stimulus dimension. In the response switching (RS) paradigm, subje cts made one of two manual responses to the single stimulus presented on ea ch trial. The rules for stimulus-response mapping were reversed on differen t trials. Trials were presented in blocks interleaved with cues that instru cted subjects to either switch stimulus-response mapping rules or to contin ue with the current rule. Brain activity at "switch" and "stay" events was compared. The results revealed distinct parietal areas concerned with visua l attentional set shifts (VS) and visuomotor intentional set shifts (RS). I n VS, activity was recorded in the lateral part of the intraparietal region . In RS, activity was recorded in the posterior medial intraparietal region and adjacent posterior superior and dorsomedial parietal cortex. The resul ts also suggest that the basic functional organization of the intraparietal sulcus and surrounding regions is similar in both macaque and human specie s.