Brain Advance Access published online on September 7, 2007
Brain, doi:10.1093/brain/awm170
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Do vegetative patients retain aspects of language comprehension? Evidence from fMRI
1Impaired Consciousness Study Group, Wolfson Brain Imaging Centre, University of Cambridge, 2Department of Psychology, University College London, London, 3MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, UK,4Department of Psychology, Queen's University, Kingston, Ontario, Canada,5Division of Anaesthesia and 6Academic Neurosurgery Unit, University of Cambridge, UK
Correspondence to:
Martin Coleman, Impaired Consciousness Study Group, Wolfson Brain Imaging Centre, Box 65, Addenbrookes Hospital, Cambridge, CB2 2QQ, UK E-mail: mrc30{at}cam.ac.uk
A diagnosis of vegetative state is made if a patient demonstrates no evidence of awareness of self or environment, no evidence of sustained, reproducible, purposeful or voluntary behavioural response to sensory stimuli and critically no evidence of language comprehension. For those patients who retain peripheral motor function, rigorous behavioural assessment is usually able to determine retained function. However, some patients do not retain the ability to respond overtly to command and it is becoming increasingly accepted that assessment of these patients should include techniques, which do not rely on any ‘motor action’ on the part of the patient. Here, we apply a hierarchical functional magnetic resonance imaging (fMRI) auditory processing paradigm to determine the extent of retained language processing in a group of 14 aetiologically heterogeneous patients who met the diagnostic criteria for either the vegetative state (n = 7), the minimally conscious state (n = 5), or who were in a severely disabled condition having emerged from a minimally conscious state (n = 2). Three different levels of speech processing were assessed: (i) Low-level auditory responses were measured using a contrast between a set of auditory stimuli and a silence baseline; (ii) mid-level speech perception processing abilities were assessed by comparing intelligible speech to unintelligible noise stimuli and (iii) high-level semantic aspects of speech processing were assessed by comparing sentences that were made difficult to understand by the presence of words that were semantically ambiguous compared to matched low-ambiguity sentences. As expected the two severely disabled, but conscious patients showed preserved speech processing at all three levels. However, contrary to the diagnostic criteria defining the vegetative state, three patients (1 traumatic, 2 non-traumatic aetiology) demonstrated some evidence of preserved speech processing. The remaining four patients (1 traumatic, 3 non-traumatic aetiology) with a diagnosis of vegetative state showed no significant activation in response to sound compared with silence. These results provide further evidence that a subset of patients fulfilling the behavioural criteria for the vegetative state retain islands of preserved cognitive function.
Key Words: vegetative state; minimally conscious state; speech processing; functional magnetic resonance imaging
Abbreviations: CRS, coma recovery scale; FDS, false discovery rate; fMRI, functional magnetic resonance imaging; GCS, Glasgow coma score; MCS, minimally conscious state; PET, positron emission tomography; ROI, region of interest; SCN, signal-correlated noise; VS, vegetative state
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Received March 6, 2007. Revised June 27, 2007. Accepted June 29, 2007.
*These authors contributed equally to this work.
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