Different mechanisms in redirecting visual spatial attention

We used event-related fMRI to investigate the functional neuroanatomy of different processes in directing visual spatial attention. For this purpose, we used noninformative peripheral cues (brightening of one of two boxes 7.5° left and right of fixation) followed by the target at an stimulus onset asynchrony (SOA) of 100ms, respectively 500ms (Posner & Cohen, 1984). In accord with the literature, valid cues exerted a facilitatory effect on reaction time at SOA=100ms and an inhibitory effect (inhibition of return, IOR) at SOA=500ms. Whereas directing at SOA=100ms is considered to be a purely attentional phenomenon, IOR is discussed to be a compound of at least partly independend attentional and occulomotor processes. Analysis of functional data revealed a significant interaction of cue validity (valid, invalid) x SOA (100ms, 500ms) in left frontopolar cortex (FPC, BA 10), right anterior middle frontal gyrus (MFG, BA 10), left posterior MFG (BA 9), right angular gyrus (AG, BA 19), right anterior superior temporal sulcus (STS, BA 21), and left middle insula (BA 13). Anterior MFG and STS showed signal increases with IOR, whereas less insular activation with IOR was observed. Activity in FPC, posterior MFG and AG increased with invalid cues at SOA=100ms. We conclude that the redirection of attention to invalidly cued targets and the process related to IOR are relying on different neural systems