BRAIN ATTENTION NETWORKS DYNAMICS – EVIDENCE FROM HUMAN INTRACEREBRAL AND MEG RECORDINGS IN HEALTH AND DISEASE – BRANDY

Attention allows us to explore the environment and to effectively respond to external events. Attention sets priorities on the basis of our goals and of the salience of external stimuli. Human visual attention relies on distinct dorsal and ventral fronto-parietal networks, but little is known about their dynamics, because hitherto our knowledge mostly depends on fMRI, which has limited temporal resolution. BRANDY aims at building an anatomo-functional model of human visual attention. Specifically, BRANDY has three main objectives: Work Package (WP) 1 will determine the precise dynamics of normal visual attention on a fine-scale; WP2 will provide important evidence on neurotypical and impaired attention in neglect patients using a network-perspective. WP3 will build comprehensive anatomical and functional models of neurotypical and pathological human visual attention.

WP1 will employ intracerebral recordings, a method with unrivalled spatial and temporal resolution for the human brain, during the performance of attention tasks. We shall recruit patients with drug-refractory epilepsy, who are implanted with depth electrodes in preparation for surgical treatment. Time windows showing epileptic activity will be excluded from analysis, in order to obtain the best possible approximation to normal attention. The attention networks will be identified in each patient by using resting state MRI and advanced white matter tractography. The results will pinpoint the neural populations supporting different aspects of attention within each network, discern their temporal behavior and reveal the neurotypical dynamics of the interaction between the two networks. They will also guide the analyses of WP2.

WP2 will focus on the function and dynamics within each cortical attention network and between the networks as a whole, in healthy controls and in patients with right hemisphere damage and visual neglect, a common and disabling condition that deeply affects attention functions. We shall use non-invasive magneto-encephalography (MEG), which measure neuronal activity with excellent temporal resolution and wide spatial coverage but with lower spatial precision compared with intracerebral recordings. The results will reveal the pathological alterations in attention networks' dynamics, consequent on right hemisphere lesions.

Concomitantly with intracerebral and MEG recordings, we shall record two behavioral measures – manual response times and eye movements. Manual response times will be collected while participants perform cued detection tasks and maintain central fixation. We shall also obtain high-resolution tracking of eye movements to monitor fixation and explore microsaccades. Microsaccades are small, automatic eye movements occurring during fixation, which have been closely connected to attention for perceptual events, and in particular to stimulus-dependent orienting of attention. The data will provide complementary measures of attentional modulation of behavior, yet unexplored in neglect patients.

A unified interpretation of the multi-modal data collected will be provided by building comprehensive models of human visual attention (WP3), using two state-of-the-art modeling approaches: Graph theoretical analysis and behavioral dynamic causal modeling (bDCM). The relation of ocular responses with manual response times and with structural and functional brain measures will thus provide a novel and rich picture of the anatomical and functional neural bases of attention and its behavioral correlates. Hence, the insights gained through these innovative approaches will extend our knowledge on attention processes in health and disease. Our results will have the potential to lead to the development of better rehabilitation strategies, which will address dramatic societal issues such as the social reinsertion of stroke patients.