Local Neuronal Connectivity Contributes to Loss and Return of Consciousness During Anesthesia Anthony G. Hudetz (Anesthesiology, University of Michigan, Ann Arbor, MI ) C20
A currently popular approach to investigate the neural correlates of consciousness is by anesthetizing subjects and then allowing them to regain consciousness. What neural functions recover when consciousness is regained? One hypothesis has been that information exchange between frontal and parietal association regions of the cerebral cortex are critical for one to be in a conscious state. In fact, general anesthetics appear to suppress the functional connectivity between frontal and parietal cortex. What are the neurophysiological events that lead to such a change in long-range communication in the cortex? Moreover, do distant neurons disconnect from each more than those nearby? In other words, is the effect local or global? We investigated whether local neuronal interactions in visual cortex were influenced by anesthetics. To this end, single-unit neuronal activity was measured in freely moving adult rats using chronically implanted microelectrode arrays while the inhaled concentration of the anesthetic desflurane was stepwise increased and decreased. Rats were completely immobilized and presumably unconscious at the highest anesthetic concentration. We found that desflurane anesthesia reversibly decreased neuronal interactions between primary and secondary visual cortex, especially in the deep cortical layers (L5-L6). Neurons in these layers participate in top-down recurrent feedback from higher to lower cortical regions. These findings suggest that neuronal disconnection also occurs locally, among hierarchically arranged sensory regions and may contribute to global functional disconnection underlying anesthetic-induced unconsciousness.