Consciousness: Its Neurobiology and the Major Classes of Impairment

Abstract

Summary Normal human consciousness requires brainstem, basal forebrain, and diencephalic areas to support generalized arousal, as well as functioning thalamocortical networks to become aware of, and respond to environmental and internal stimuli. Injury to or disconnection of these interconnected systems, typically from cardiac arrest and traumatic brain injury, can result in disorders of consciousness, including coma, vegetative state, minimally conscious state, and akinetic mutism. Similar brain injuries can also result in loss of motor output out of proportion to consciousness, resulting in misdiagnoses of disorders of consciousness. We review pathology and imaging studies and derive mechanistic models for each of these conditions, to aid in the assessment and prognosis of individual patients. We further suggest how such models may guide the development of target-based treatment algorithms to enhance recovery of consciousness in many of these patient.

Decreased functional connectivity between the mediodorsal thalamus and default mode network in patients with disorders of consciousness

“…Damage to these connections can cause severe movement deficit, even in the absence of motor system injury. Accordingly, the circuits forming these connections are assumed to play a significant role in the pathology of DOC (18). The present study supports this idea by showing impaired functional connectivity between the mediodorsal thalamus (including the mediodorsal nucleus) and medial prefrontal/anterior cingulate cortex in DOC patients.…”

Motor System Interactions in the Beta Band Decrease during Loss of Consciousness

“…For cortical and subcortical interactions, in particular, this hypothesis is supported by functional imaging studies of the recovery of awareness following traumatic unconsciousness (Goldfine and Schiff, 2011, Laureys and Schiff, 2012), and by the finding that cortical-subcortical structural connectivity correlates with levels of awareness in patients with severe head trauma (Fernandez-Espejo et al, 2011, Zheng et al, 2014). Our results support this hypothesis since two measures which reflect interactions between brain regions, coherence and cross-structure PAC, both decrease during loss of consciousness.…”

Structural brain injury in patients with disorders of consciousness: A voxel-based morphometry study

“…Detectability of consciousness with behavioural examinations, such as the CRS-R [46][47][48], is dependent on at least three different factors: brain arousal, internal and external awareness (perception), and the possibility to mount an appropriate response [71]. Each one of these factors can be influenced by the widespread injury that was found to be associated with DOC.…”