Electrophysiological Dynamics of Default Network Suppression

Distributed brain networks compete with one another in the service of information processing. One dramatic example is antagonism between networks that support internally directed cognition, often collectively referred to as the default network, and networks that orient to external events and drive action. Here we combined within-individual precision functional neuroimaging and intracranial electrophysiology to investigate network competition at high spatiotemporal resolution. In six patients, robust antagonism between networks was established during a target detection task. Network-assigned electrophysiological recordings displayed concordant responses, including in single-neuron firing rates, and further revealed the temporal dynamics of network competition. Networks involved in salience detection and action planning showed early, transient responses that peaked near the participant response. Default network suppression occurred later, reflected in decreases in high-frequency broadband activity and in single-neuron firing rates in response to targets. Examining subcortical regions revealed rapid activity increases in the thalamus and posterior hippocampus aligned to the participant response. Critically, a late evolving, sustained suppression was observed throughout the hippocampus. These findings suggest that, across cortical and subcortical regions, network competition is temporally layered. Furthermore, the hippocampus can be dissociated along its long axis during competition. Such push-pull antagonism may be fundamental to advanced human cognition, and its disruption may underlie mental illness.