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Voluntary brain processing in disorders of consciousness

From Coma Science Group, Cyclotron Research Centre (C.S., M.B., A.V., M.-A.B., S.L.), and Department of Cognitive Sciences (S.M.), University of Liège, Belgium; UMR 5020 (F.P.), CNRS–Université Claude Bernard Lyon 1, Lyon, France; Division of Physiological Psychology (M.S.), University of Salzburg, Austria; and Departments of Intensive Care (D.L., P.D.) and Neurology (M.B., G.M., S.L.), CHU Sart Tilman, Liège, Belgium.

Address correspondence and reprint requests to Dr. Caroline Schnakers, Coma Science Group, Centre de Recherches du Cyclotron, Sart Tilman, B30, University of Liège, 4000 Liège, Belgium C.Schnakers{at}student.ulg.ac.be

Background: Disentangling the vegetative state from the minimally conscious state is often difficult when relying only on behavioral observation. In this study, we explored a new active evoked-related potentials paradigm as an alternative method for the detection of voluntary brain activity.

Methods: The participants were 22 right-handed patients (10 traumatic) diagnosed as being in a vegetative state (VS) (n = 8) or in a minimally conscious state (MCS) (n = 14). They were presented sequences of names containing the patient’s own name or other names, in both passive and active conditions. In the active condition, the patients were instructed to count her or his own name or to count another target name.

Results: Like controls, MCS patients presented a larger P3 to the patient’s own name, in the passive and in the active conditions. Moreover, the P3 to target stimuli was higher in the active than in the passive condition, suggesting voluntary compliance to task instructions like controls. These responses were even observed in patients with low behavioral responses (e.g., visual fixation and pursuit). In contrast, no P3 differences between passive and active conditions were observed for VS patients.

Conclusions: The present results suggest that active evoked-related potentials paradigms may permit detection of voluntary brain function in patients with severe brain damage who present with a disorder of consciousness, even when the patient may present with very limited to questionably any signs of awareness.

Abbreviations: CRS-R = Coma Recovery Scale-Revised; EOG = electro-oculogram; ERP = evoked-related potentials; MCS = minimally conscious state; SON = subject’s own name; UN = unfamiliar first names; VS = vegetative state.

Supplemental data at www.neurology.org

Funded by the Belgium Federal Public Service for Public Health, Belgian "Fonds National de la Recherche Scientifique" (FNRS), "Centre Hospitalier" of the University of Liège, French Speaking Community of Belgium Concerted Research Action, J.S. McDonnell Foundation, European Commission, and Mind Science Foundation (Texas).

Disclosure: The authors report no disclosures.

Received April 14, 2008. Accepted in final form August 7, 2008.

Correspondence: