Functional MRI in disorders of consciousness: advantages and limitations

We discuss recent developments in the use of neuroimaging and, in particular, functional MRI, in the assessment of patients diagnosed as vegetative state or minimally conscious state.

In the last year, there has been a substantial increase in the number of research studies published which have used state-of-the-art neuroimaging methods to assess residual cognitive functioning in patients diagnosed with disorders of consciousness. Work using functional MRI has demonstrated aspects of retained speech processing, emotional processing, comprehension and even conscious awareness in a small number of patients behaviourally meeting the criteria defining the vegetative and minimally conscious states.

The assessment of patients with disorders of consciousness relies heavily upon the subjective and consequently fallible interpretation of observed behaviour. Recent studies have demonstrated an important role for functional MRI in the identification of residual cognitive function in these patients. Such studies may be particularly useful when there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. In our opinion, the future use of functional MRI will substantially increase our understanding of disorders of consciousness following severe brain injury.