| The current experiment used rapid acquisition event-related FMRI to examine neural substrates of inhibition of return (IOR) and endogenous versus exogenous attentional processes. In addition, we also examined differences between valid versus invalid trials for both exogenous and endogenous orienting. We operationally defined these modes of orienting according to the strict behavior parameters established in the cognitive literature. In contrast to most theories of IOR, results provide evidence that cortical rather than retinotectal pathways mediate IOR. This cortical pathway is similar to the large-scale cortical network that produces volitional shifts of spatial attention. In direct comparisons to exogenous facilitation, both IOR and endogenous orienting yielded similar foci of activation in left posterior parietal lobes, superior temporal gyrus, and hMT+. IOR also resulted in foci of activation in motor exploratory areas and the cortical and subcortical epicenters of visual-spatial attention. Endogenous processes resulted in bilateral activation of the TPJ and visual centers, right inferior parietal lobule, and right FEF. A comparison of invalid versus valid endogenous orienting resulted in activation of a the right superior parietal lobe, right inferior parietal lobe, right intraparietal sulcus, and right middle frontal gyrus consistent with the large-scale neural network that has been previously proposed. In contrast to the endogenous condition, a comparison of invalid versus valid exogenous trials resulted in activation of the left post-central gyrus, left motor areas, and right caudate nucleus. These results are incorporated into a functional model of the development of neural substrates involved in orienting visual attention{09}based on evolutionary theory. |
