Resting brain activity in disorders of consciousness

Abstract

Objective: To quantitatively synthesize results from neuroimaging studies that evaluated patterns of resting functional activity in patients with disorders of consciousness (DOC).Methods: We performed a systematic review and coordinate-based meta-analysis of studies published up to May 2014. Studies were included if they compared resting-state functional neuroimaging data acquired in patients with DOC (coma, minimally conscious state, emergence from minimally conscious state, or vegetative state) with a group of healthy controls. Coordinate-based meta-analysis was performed in studies that included voxel-based comparisons at the whole-brain level and if analysis was accomplished with data-driven approaches.Results: A total of 36 studies (687 patients, 637 healthy controls) were included in the systematic review. Reported DOC were vegetative state (43.2%), coma (23.4%), minimally conscious state (22.8%), and emergence from minimally conscious state (1.6%); the most common etiologies of DOC were traumatic brain injury (37.7%) and anoxic brain injury (36.9%). Functional neuroimaging was accomplished using fMRI (16 studies), PET (15 studies), SPECT (4 studies), and both PET and SPECT in one study. Meta-analysis in 13 studies (272 patients, 259 healthy controls) revealed consistently reduced activity in patients with DOC in bilateral medial dorsal nucleus of the thalamus, left cingulate, posterior cingulate, precuneus, and middle frontal and medial temporal gyri. Conclusions:In patients with DOC evaluated in the resting state, functional neuroimaging indicates markedly reduced activity within midline cortical and subcortical sites, anatomical structures that have been linked to the default-mode network. Studies are needed to determine the relation between activation (and coherence) within these structures and the emergence of conscious awareness. Neurology ® 2015;84:1272-1280 GLOSSARY ALE 5 activation likelihood estimate; ALFF 5 amplitude of low-frequency fluctuations; BOLD 5 blood oxygen level-dependent; CRS-R 5 Coma Recovery Scale-Revised; DMN 5 default mode network; DOC 5 disorders of consciousness; EMCS 5 emergence from minimally conscious state; FDG 5 fluorodeoxyglucose; HC 5 healthy control; ICA 5 independent component analysis; MCS 5 minimally conscious state; MNI 5 Montreal Neurological Institute; PCC 5 posterior cingulate cortex; ReHo 5 regional homogeneity; ROI 5 region of interest; TBI 5 traumatic brain injury; VS 5 vegetative state.Coma is a cardinal sign of brain injury resulting from trauma, stroke, cardiac arrest, infection, or metabolic causes. While coma is a transient state from which the majority of subjects awaken, a subset of patients develop a more prolonged impairment in consciousness, such as the vegetative state (VS) or minimally conscious state (MCS). Despite considerable research, states such as coma, VS, and MCS-collectively termed disorders of consciousness (DOC)-remain poorly understood regarding their neural basis, clinical recognition, and long-term outcome.1,2 Neurophysiologic...

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“…This was particularly the case for regions which form part of the default mode network, including the precuneus, which is implicated in episodic memory, visuospatial processing, self-reflection and aspects of consciousness (Fox, Spreng, Ellamil, Andrews-Hanna, & Christoff, 2015;Hannawi, Lindquist, Caffo, Sair, & Stevens, 2015;Kwok & Macaluso, 2015). Target appearance also attenuated activity within motor, auditory, and somatosensory areas, putatively reflecting the rich multisensory nature of internal thoughts (e.g., Fox, Nijeboer, Solomonova, Domhoff, & Christoff, 2013;Hasenkamp et al, 2012).…”

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“…1,5 This observation is supported by electrophysiologic findings, 6 suggesting a possible pathophysiologic continuum from coma to recovered consciousness, of which coma and evolution into the arousal/awareness dissociation characterizing VS and MCS would be only transitional phases. The functional core impairment was shared by all DOC conditions in the meta-analyses by Hannawi et al 1 and Lutkenhoff et al, 5 but more complex patterns were common, including associations of clinical measures characterizing VS and MCS with tissue atrophy in subcortical structures. 1,5 Heterogeneities in etiology or in the extension and severity of brain damage (possibly crucial in this regard) would result in preserved neural structures and residual resources 7 and could question the boundaries between the conventional DOC conditions.…”

“…Dongchao Shen, Linyi; Zhaobo Shen, Liying Cui, Beijing, China: I read the article by Hannawi et al 1 on resting brain activity in disorders of consciousness. Activation likelihood estimate (ALE) meta-analysis allows the investigation of shared brain activation across individual experiments by quantitatively identifying brain locations consistently associated with different tasks or at resting state.…”