DIFFERENTIAL ACTIVATION OF RIGHT SUPERIOR PARIETAL CORTEX AND INTRAPARIETAL SULCUS BY SPATIAL AND NONSPATIAL ATTENTION

Neuropsychological and functional neuroimaging studies have implicated the right posterior parietal cortex (PPC) in human spatial attention. We tested the hypothesis that this area is also involved in nonspatia l aspects of attention and working memory using positron emission tomo graphy in healthy volunteers. In an initial experiment, digits were pr esented in pseudo-random spatial locations, and subjects attended eith er to locations or digits in order to detect single targets(attention condition) or to sequences of stimuli (working memory (WM) condition). Right superior parietal cortex (BA7) and intraparietal sulcus (IPS) w ere active during both spatial (locations) and nonspatial (digits) tas ks compared to rest, although more so for the former. Additionally, ri ght PPC was activated to an even greater extent during tests of WM tha n of attention, especially for tests of spatial WM. There were no diff erences in activation of dorsolateral prefrontal cortex in the spatial versus nonspatial versions of the task, contrary to many previous stu dies. A follow-up experiment which presented abstract objects in a fix ed, central location confirmed that right IFS was active during tests of nonspatial attention and also that this activation is not due to in cidental spatial representation of digit stimuli, However BA7 was not activated by this nonspatial, non-digit attentional task. Overall, the se data suggest first that right IFS is recruited for both nonspatial and spatial attention and WM. Second, right BA7 is recruited specifica lly for spatial (both direct and indirect) forms of attentional proces sing. Finally, PPC activations in spatial WM tasks are likely to be du e to a combination of spatial perception, attention, and WM, rather th an to any of these individually. (C) 1998 Academic Press.