Unresponsive patient plays mental tennis

An unconscious, outwardly unresponsive patient apparently was capable of understanding and responding to certain commands as measured by functional MRI.

The 23-year-old woman, in a persistent vegetative state for five months since emerging from a coma after a traffic accident, activated predicted cortical areas in a manner indistinguishable from that of controls when researchers asked her to imagine playing tennis or moving around her home (Science 2006:313:1402).

"The observed brain activation patterns are the classic neural correlates of these two mental imagery tasks," said lead author Dr. Adrian Owen, assistant director of neuroimaging at Cambridge University.

While Owen and colleagues said the results indicated the woman was aware, they cautioned not to generalize from a single patient who suffered relatively few cerebral lesions to most other vegetative state patients. These patients typically have massive structural brain lesions.

The study, however, has renewed the debate on what it means to be conscious. Two key properties of conscious processing in humans are the ability to report mental states and to spontaneously engage in intentional actions or interactions with the environment.

"If this patient is actually conscious, why wouldn't she be able to engage in intentional motor acts, given that she had not suffered functional or structural lesions of the motor pathways?" asked Dr. Lionel Naccache of France's INSERM research institute in a commentary published with the report.

Nevertheless, the fact that the patient heard instructions only once and maintained an activated neural network for 30 seconds is impressive, Naccache said.

In the study, researchers compared responses in four brain regions of the patient with those of 12 healthy volunteers. The activity observed in the patient was within the normal range of responses in all four regions. Investigators acknowledged the possibility of the brain automatically reacting to their instruction but said it's highly unlikely, given the complexity of the commands and the richness of the imagery.

The patient's brain activated speech-specific areas when the researchers spoke sentences. No responses were recorded when the patient listened to acoustically matched noise sequences. Sentences of an ambiguous nature, such as those containing the words "creek" or "creak," elicited a functional response that reflected the operation of semantic processes critical for speech comprehension. These responses, however, are not equivocal evidence that a person is consciously aware, Owen said.

To address the question of conscious awareness, researchers then asked the woman to imagine she was playing tennis and to imagine she was visiting all of the rooms of her house, starting from the front door. The tennis request elicited activity in the supplementary motor area, while the house tour activated the parahippocampal gyrus, posterior parietal cortex, and lateral premotor cortex.

The authors concluded that these results represented a clear act of intention, "which confirmed beyond any doubt that she was consciously aware of herself and her surroundings."

A negative response in such patients, however, cannot be seen as lack of awareness because false-negative findings are common in functional neuroimaging, the authors said.

For more information from the Diagnostic Imaging archives:

In politics, brain shows true colors

fMRI links autism with white matter anomaly

fMRI hints at the source of bipolar disorder

fMRI unveils the neurobiology of anxiety