Consciousness: its neurobiology and the major classes of impairment

Abstract

Human consciousness requires brainstem, basal forebrain, and diencephalic areas to support generalized arousal, and functioning thalamocortical networks to respond to environmental and internal stimuli. Disconnection of these interconnected systems, typically from cardiac arrest and traumatic brain injury, can result in disorders of consciousness. Brain injuries can also result in loss of motor output out of proportion to consciousness, resulting in misdiagnoses. The authors review pathology and imaging studies and derive mechanistic models for each of these conditions. Such models may guide the development of target-based treatment algorithms to enhance recovery of consciousness in many of these patients.

Figure 1

A simplified model of a network that drives goal-directed behavior together with targets for specific interventions. Abbreviations: ACC- anterior cingulate cortex; GPi – globus pallidus pars interna; ILN – intralaminar nuclei of the thalamus; MSN – medium spiny neurons; PFC – prefrontal cortex. Blue arrows represent glutamatergic synapses and red represent GABAergic synapses unless otherwise noted.

Figure 2

Non-invasive imaging evidence of command-following in a patient with severe brain injury who was behaviorally locked-in. A. FMRI demonstrating increased activity (orange) in supplementary motor and other cortical areas when the patient was asked to imagine swimming versus a resting baseline (Adapted from ). B. Spectral analysis of EEG in the same subject performing the imagination of the swimming task at a different time. Example power spectra for 2 channels are on the right; the image on the left summarizes significant spectral changes across all channels and frequencies tested. Headmaps below summarize amplitude of power change across all channels at the frequencies listed directly above (Adapted from ).