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Abstract:
During the waking state, the brain is sensitive to a vast array of input signals of both internal and external origin. An efficient strategy to reduce this complexity is to dedicate resources to select stimulus features and spatial locations. Due to the ever-changing environment and needs of the organism, the locus of attention must be frequently re-oriented. Much evidence indicates the importance of large-scale networks spanning the frontal, parietal and occipital lobes in the control of visuospatial attention yet little is known about the time-varying intra- and inter-areal dynamics during the re-orienting process. We recorded from a 252 channel ECoG grid implanted onto the left hemispheres of two monkeys performing a cued covert spatial attention task. Our results confirm the presence of a large-scale network spanning frontal, parietal and occipital cortex. The most ubiquitous aspect of this network is time-varying beta-frequency power dynamics exhibited by frontal cortex, the intraparietal sulcus (IPS) and V4. Attentional re-orienting appears to be initiated by a desynchronization of high-beta frequency power in superior frontal cortex. Desynchronization of beta and high-beta oscillations in the frontal-parietal attention network appear to be critical for the switching of attentional locus, yet these frequency bands play differential roles once the attentional locus is established. Finally, we characterize the temporal profiles of the inter-areal dynamics between these local networks via the analysis of Granger-causal directed interactions.
It is an attractive hypothesis that beta frequency local dynamics and global interactions function to stabilize cortical state, and thus must necessarily desynchronize when a reorganization of cortical state is required, followed by a rebound once the new state is established. In such a fashion, this network may gate stimulus driven gamma band activity and reinforce specific interactions between cortical areas that correspond to the selection of a particular location of the visual environment.
