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A twitch of consciousness: defining the boundaries of vegetative and minimally conscious states
  1. Quentin Noirhomme,
  2. Caroline Schnakers,
  3. Steven Laureys
  1. Coma Science Group, Cyclotron Research Centre and Neurology Department, University of Liège, Liège, Belgium
  1. Professor Steven Laureys, Coma Science Group, Cyclotron Research Centre and Neurology Department, University of Liège, Sart Tilman B30, 4000 Liège, Belgium; steven.laureys{at}

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Some patients awaken from their coma but only show reflex motor activity. This condition of wakeful (eyes open) unawareness is called the vegetative state. In 2002, a new clinical entity coined “minimally conscious state” defined patients who show more than reflex responsiveness but remain unable to communicate their thoughts and feelings. Emergence from the minimally conscious state is defined by functional recovery of verbal or non-verbal communication.1 Our empirical medical definitions aim to propose clearcut borders separating disorders of consciousness such as coma, vegetative state and minimally conscious state but clinical reality shows that these boundaries can often be fuzzy (fig 1). Recent clinical, electrophysiological and neuroimaging studies are shedding light on these challenging limits of consciousness encountered following severe acute brain damage.

Figure 1 Drawing sharp borders behaviourally, defining the progressive transitions from coma, to vegetative state, to minimally conscious state, to emergence from the minimally conscious state, remains very challenging. Recent studies are shedding new light on the boundaries of these disorders of consciousness.

At the patient’s bedside, it is very challenging to differentiate reflex or automatic motor behaviour from movements indicating signs of consciousness, and hence some minimally conscious patients might be misdiagnosed as being vegetative. For some motor responses (eg, blinking to visual threat, brief fixation, normal flexion response to …

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  • Funding: Supported by funds from the Belgian “Fonds de la Recherche Scientifique” (FNRS), “Action de Recherche Concertée (ARC) de la Communauté Française”, the Queen Elisabeth Foundation, European Commission and the Mind Science Foundation.

  • Competing interests: None.

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