Functional Imaging Reveals Movement Preparatory Activity in the Vegetative State

Abstract

The vegetative state (VS) is characterized by the absence of awareness of self or the environment and preserved autonomic functions. The diagnosis relies critically on the lack of consistent signs of purposeful behavior in response to external stimulation. Yet, given that patients with disorders of consciousness often exhibit fragmented movement patterns, voluntary actions may go unnoticed. Here we designed a simple motor paradigm that could potentially detect signs of purposeful behavior in VS patients with mild to severe brain damage by examining the neural correlates of motor preparation in response to verbal commands. Twenty-four patients who met the diagnostic criteria for VS were recruited for this study. Eleven of these patients showing preserved auditory evoked potentials underwent functional magnetic resonance imaging (fMRI) to test for basic speech processing. Five of these patients, who showed word related activity, were included in a second fMRI study aimed at detecting functional changes in premotor cortex elicited by specific verbal instructions to move either their left or their right hand. Despite the lack of overt muscle activity, two patients out of five activated the dorsal premotor cortex contralateral to the instructed hand, consistent with movement preparation. Our results may reflect residual voluntary processing in these two patients. We believe that the identification of positive results with fMRI using this simple task, may complement the clinical assessment by helping attain a more precise diagnosis in patients with disorders of consciousness.

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“…a Denotes a minimally conscious state b Denotes a minimally conscious state except for anoxic aetiology [70] c Denotes emergence from the minimally conscious state activation) [61] and imagine swimming (resulting in supplementary motor area activation) [62]. Concurrently, cheaper and portable techniques using event related potential or electromyography active paradigms have been developed to detect possible signs of command following not assessable by clinical behavioural examination.…”

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“…84 Patients with DOC are asked to perform cognitive tasks in motor (for example, "imagine playing tennis"), visuospatial (for example, "imagine walking around in your house") or visual (for example, "look at the face") domains. 21,[85][86][87][88][89] This approach provided an opportunity to ask yes-no questions to a patient with an initial clinical diagnosis of VS (but later shown to be in MCS). 85 It should be stressed, however, that many of the tested patients in MCS who showed behavioural signs of command-following failed to show a response to these active fMRI tests, leading to false-negative findings.…”

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“…These specific activation patterns were not different from those previously observed in a cohort of healthy volunteers [38]. Since this report, similar command-following paradigms in patients with DOC have asked patients to 'look at a screen and silently name the objects as they appear' (resulting in language network activation) [39], 'move your hand' (resulting in premotor cortex activation) [40], 'imagine swimming' (resulting in supplementary motor area activation) [41] and recently also to 'focus on either the face or house of an overlaid image' [42].…”