|
 Brain activity during tennis imagery in the patient and a group of 12 healthy volunteers. Picture: sciencemag.org
The vegetative state is one of the least understood and most ethically troublesomeconditions in modern medicine. The term escribes a unique disorder in which patientswho emerge from coma appear to be awake but how no signs of awareness. Although the diagnosis depends crucially on there being no reproducible evidence of purposeful behavior inresponse to external stimulation.
Adrian Owen and his colleagues at the Medical Research Council
Cognition and Brain Sciences Unit and the Wolfson Brain Imaging Centre,
Addenbrooke's Hospital, in Cambridge, UK, together with researchers at
the Cyclotron Research Centre and Neurology Department, at the
University of Liège, Belgium, used functional magnetic resonance
imaging (fMRI) to measure the neural responses of the 23-year old
patient. The patient had existed in a persistent vegetative state (PVS)
for five months since emerging from a coma following a car accident in
July 2005.
The team recorded the brain response of twelve
healthy volunteers asked to imagine themselves playing tennis and then
to picture themselves walking around their homes. Specific regions of
the brain involved in controlling movement were activated. The team
then asked the patient the same questions and obtained almost identical
fMRI patterns to those seen in the healthy volunteers. Similar results
had been obtained in initial tests with responses to simple words.
This, the researchers say, represents the first evidence of awareness
in a patient in a persistent vegetative state. Patients have been shown
to respond transiently to the spoken word, but Owen says that the
observed activity lasted for the duration of the test until they asked
the patient to stop "playing tennis".
 Active centers in btains of healthy volonteers and vegetative patients. Picture: www.mrc-cbu.cam.ac.uk/~adrian.
The conventional
definition of PVS states that patients cannot experience pain and
suffering as these are attributes of consciousness. Owen's work could
represent a challenge to that tenet especially if these preliminary
investigations prove reproducible in other PVS patients. "We need to
try this technique in other patients," Owen told SpectroscopyNOW, "in
particular those for whom existing clinical investigations have left
some ambiguity about the diagnosis." The next step will be to establish
whether or not fMRI could be developed to allow some form of
communication with such patients, he added.
Lionel
Naccache of the Clinical Neurophysiology Department, at Hôpital de la
Pitié-Salpêtrière, in Paris, France, however, questions whether the
patient is conscious in the strictest sense. "If this patient is
actually conscious, why wouldn't she be able to engage in intentional
motor acts," he asks, "given that she had not suffered functional or
structural lesion of the motor pathways?" Fundamentally, the test of
consciousness is the patient's own exclamations. "The ability to report
one's own mental state is the fundamental property of consciousness,"
says Naccache. Clearly the patient investigated by Owen could not do
this. Their indirect probing of brain function may ultimately have
interpretations other than the PVS patient having consciousness.
Naccache adds that the work nevertheless, "paves the way for future
functional brain-imaging studies on comatose and vegetative state
patients." He suggests that careful experimental design and fMRI
studies of other patients may take us closer to a more direct indicator
of consciousness without our having to rely on the patient declaring,
"I think, therefore I am!"
RelatedLinks:
Owen et al., "Detecting Awareness in the Vegetative State", Science 2006:Vol. 313. no. 5792, p. 1402
DOI: 10.1126/science.1130197
Adrian Owen Homepage
Written using materials from MRI Spectroscopy.
|
