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 nonspatial aspects of attention and working memory using positron emission tomography in healthy volunteers. In an initial experiment, digits were presented in pseudo-random spatial locations, and subjects attended either 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) were active during both spatial (locations) and nonspatial (digits) tasks compared to rest, although more so for the former. Additionally, right PPC was activated to an even greater extent during tests of WM than of attention, especially for tests of spatial WM. There were no differences in activation of dorsolateral prefrontal cortex in the spatial versus nonspatial versions of the task, contrary to many previous studies. A follow-up experiment which presented abstract objects in a fixed, central location confirmed that right IPS was active during tests of nonspatial attention and also that this activation is not due to incidental spatial representation of digit stimuli. However, BA7 was not activated by this nonspatial, nondigit attentional task. Overall, these data suggest first that right IPS is recruited for both nonspatial and spatial attention and WM. Second, right BA7 is recruited specifically for spatial (both direct and indirect) forms of attentional processing. Finally, PPC activations in spatial WM tasks are likely to be due to a combination of spatial perception, attention, and WM, rather than to any of these individually.