Electrofunctional Imaging of Brain Activations During Endogenous and Exogenous Orienting of Visuospatial Attention

Several studies proposed that endogenous orienting of visual attention to space locations elicits activity in different regions of the dorsal frontal and parietal cortices, while, in contrast, exogenously induced attention triggers increased activity in regions near the right temporo-parietal junction and ventral frontal cortex, which may in turn trigger the involvement of portions of this same dorsal frontoparietal network. More recent evidence also suggested that the dorsal fronto-parietal network sends “biasing” signals to the sensory cortices to increase the basic activity, thus facilitating stimulus processing. To tap at the timing and differences in the “biasing” of the visual cortices in exogenous and endogenous cuing conditions as related to differences in the neurodynamic activation of the various regions of the fronto-parietal networks elicited by the spatial cue, a research program was carried out administering visual targets under different pre-cueing conditions: Spatially valid Cue (SC), Central neutral Cue (CC), and No Cue (NC). Event-related potentials (ERPs) of the brain were recorded from 128 channels and source-reconstructions were carried out by means of 3D MRI-images based LORETA. The sources computed for the SC-CC Difference Wave (DW) showed the activation of the right SPL (BA7), FEF (BA8) and Precentral-Frontal (BA6) areas, besides several more posterior areas, in between the cue and the target. A neat positive biasing of ERP responses recorded at the parietal and parietal-occipital scalp sites corresponded to these intracranial activations. Target administration resulted in a strengthening of the magnitude of the aforementioned sources already at early C1 & P1 levels, as well as an activation of IACC (BA32). Unlike the endogenous condition, source reconstructions for the exogenous orienting (i.e., CC-NC DW) revealed instead a mostly left-sided pool of dipole activations induced by the spatially neutral cues, among which the MFG BA6, SFG BA8, MFG BA47, and Angular gyrus (BA39). Target presentation added the right MFG (BAA8) of a rather small magnitude to this representative pool of intracranial sources. All in all, the present findings provide a more detailed spatio-temporal neurodynamic functional picture of endogenous and exogenous orienting of visual attention than previous research.