Orbital-thalamic Network for the Regulation of Cortical Synchronization

Abstract:
Cortical synchronization is observed in many tasks. We investigated the contribution of orbital frontal cortex to cortical synchronization in the alpha band. Orbito-frontal cortex differentially affects the synchronicity of alpha EEG activity in response to visual stimuli over frontal areas. Control subjects and patients with orbital frontal damage detected infrequent target-triangles which were preceded by novel stimuli. Increases in evoked (phase-locked) alpha and decreases in induced (non phase-locked) alpha power were observed in normals in response to detected targets. Evoked alpha activity over lateral frontal cortex was significantly higher in patients than in age-matched controls. The decrease of induced alpha in response to stimuli was suppressed for patients. These findings indicate a higher degree of cortical synchronicity subsequent to orbital frontal cortex damage. These findings support the previously formulated hypothesis that frontal cortex regulates the thalamic driving of cortical alpha activity in the human EEG. A neuroanatomical model for orbital-thalamic EEG synchronization is proposed. Supported by NINDS Grant 21135.