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Brain mechanisms of normal and impaired consciousness - Hal Blumenfeld
Stanford Neurosciences Institute Seminar Series Presents
Brain mechanisms of normal and impaired consciousness
Hal Blumenfeld, PhD
Professor of Neurology and Professor of Neuroscience and of Neurosurgery at Yale University
Host: Jin-Hyung Lee
Combining data from normal perceptual tasks and impaired states such as epilepsy may provide important new insights into mechanisms of consciousness.
Consciousness depends on widespread brain networks, so it has long been mysterious why focal seizures impair consciousness. In focal temporal lobe seizures, intracranial EEG and blood flow imaging show depressed frontoparietal function resembling slow wave sleep. Experimental models demonstrate activation of subcortical inhibitory neurons which switch off subcortical arousal, leading to depressed cortical function and impaired consciousness. Deep brain stimulation of thalamus and brainstem arousal circuits can restore consciousness and purposeful behavior during and after seizures.
During normal conscious perception of visual stimuli at 50% detection threshold intracranial EEG demonstrates a wave of broadband gamma activity through successive regions of association cortex. Meanwhile, specific visual, association cortex and default mode networks undergo polyphasic on/off switching that may control information flow. fMRI measurements with the same task show transient activation of cortical-subcortical arousal and attention networks with conscious perception.
Normal conscious perception and pathological states like epilepsy share common anatomical and physiological mechanisms for activity changes in large-scale networks.