title: Volatile anesthetics disrupt frontal-posterior recurrent information transfer at gamma frequencies in rat.
abstract: We seek to understand neural correlates of anesthetic-induced unconsciousness. We hypothesize that cortical integration of sensory information may underlie conscious perception and may be disrupted by anesthetics. A critical role in frontal-posterior interactions has been proposed, and gamma (20-60 Hz) oscillations have also been assigned an essential role in consciousness. Here we investigated whether general anesthetics may interfere with the exchange of information encoded in gamma oscillations between frontal and posterior cortices. Bipolar electrodes for recording of event-related potentials (ERP) were chronically implanted in the primary visual cortex, parietal association and frontal association cortices of six rats. Sixty light flashes were presented every 5s, and ERPs were recorded at increasing concentrations of halothane or isoflurane (0-2%). Information exchange was estimated by transfer entropy, a novel measure of directional information transfer. Transfer entropy was calculated from 1-s wavelet-transformed ERPs. We found that (1) feedforward transfer entropy (FF-TE) and feedback transfer entropy (FB-TE) were balanced in conscious-sedated state; (2) anesthetics at concentrations producing unconsciousness augmented both FF-TE and FB-TE at 30 Hz but reduced them at 50 Hz; (3) reduction at 50 Hz was more pronounced for FB-TE, especially between frontal and posterior regions; (4) at high concentrations, both FF-TE and FB-TE at all frequencies were at or below conscious-sedated baseline. Our findings suggest that inhalational anesthetics preferentially impair frontal-posterior FB information transfer at high gamma frequencies consistent with the postulated role of frontal-posterior interactions in consciousness.
authors: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA.
authors: Olga A
authors: OA
authors: Imas
authors: Kristina M
authors: KM
authors: Ropella
authors: B Douglas
authors: BD
authors: Ward
authors: James D
authors: JD
authors: Wood
authors: Anthony G
authors: AG
authors: Hudetz
mesh_terms: D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology; D003243:Consciousness / Q000187:drug effects* / Q000502:physiology; D003344:Cortical Synchronization / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D005625:Frontal Lobe / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009434:Neural Pathways / Q000187:drug effects* / Q000502:physiology; D010296:Parietal Lobe / Q000187:drug effects / Q000502:physiology; D010465:Perception / Q000187:drug effects / Q000502:physiology; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012677:Sensation / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology
chemical_list: D018685:Anesthetics, Inhalation