Editors' ChoiceTraumatic Brain Injury

Imaging covert consciousness

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Science Translational Medicine  09 Aug 2017:
Vol. 9, Issue 402, eaao2260
DOI: 10.1126/scitranslmed.aao2260

Abstract

Imaging and electroencephalography help to detect covert consciousness after acute brain injury.

A decade ago, the discovery that functional magnetic resonance imaging (fMRI) signals could detect cognitive functions in comatose or vegetative patients spurred new research into consciousness. In patients with severe traumatic brain injury (TBI), early regaining of consciousness is associated with better recovery; however, the lack of unequivocal methods to determine consciousness limits the ability to prognosticate functional outcomes and creates major clinical and ethical issues for families facing decisions about continuations of life-sustaining treatments. Edlow et al. used fMRI and electroencephalographic (EEG) data to measure covert consciousness in acute severe TBI patients and correlated these findings with long-term clinical outcomes. Included in the study were 16 TBI patients and 16 age-matched controls. At the time of enrollment (average time 9.2 days after TBI), patients’ cognitive statuses ranged from coma to minimally conscious to post-traumatic confusional states (PTCS).

Consciousness was defined by the presence of command-following (CMD) or passive auditory stimulation-induced (HMD) responses on EEG and fMRI signals. The main finding was that 4 of the 8 patients without behavioral evidence of language function had CMD and 2 out of 8 had evidence of HMD, making a total of 6 out of 8 patients who showed evidence of consciousness not detected by the standard clinical assessment. Although the study is an important step to improving our understanding of how to assess consciousness to predict outcomes after severe brain injury, several limitations limit the strength of these findings. The sample size was small, with a wide range of severity of the impairment of consciousness. Although 16 patients were enrolled, only 8 lacked evidence of language function. Importantly, the fMRI and EEG signals used as correlates of consciousness were seen in only 69 to 75% of normal controls. In addition, all survivors improved their clinical statuses to at least PTCS by 6 months. The lack of patients who survived but never regained consciousness limits the findings. Larger studies with more uniform and rigid inclusion criteria and outcome diversity are needed to assess the ability of fMRI and EEG to reliably predict long-term clinical outcomes.

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