fMRI Study Clouds Definition of Vegetative State
Raising a host of questions, from practical to philosophical, English and Belgian investigators showed that some patients with profound disorders of consciousness may be able to communicate—albeit in rudimentary fashion and with the aid of a million-dollar machine. Their functional MRI study of patients in persistent vegetative or “minimally conscious” state is available online today at the NEJM web site.
Among 54 severely disabled patients, investigators found that 5 could “willfully modulate their brain activity,” as seen on fMRI pictures, in response to suggested motor imagery. Specifically when these patients were asked to imagine playing tennis, parts of the supplementary motor area reliably lit up. Four of the 5 patients could also respond to suggested spatial imagery, like navigating through a familiar city, by activating the parahippocampal gyrus. Follow-up bedside testing showed “some sign of awareness” in 3 of the 5 patients—suggesting that voluntary behavioral cues were missed before the fMRI assessment or that fMRI training primed these patients to respond behaviorally at the bedside (the former seems more likely).
The investigators then selected 1 patient with reliable fMRI responses to undergo training that correlated the motor imagery with “yes” and the spatial imagery with “no.” The patient was then able to use the technique during fMRI to accurately answer yes-no questions, like Is your father’s name Alexander? However, back at the bedside, no form of communication could be established with this patient.
All 5 responsive patients had traumatic brain injury without anoxic damage (among 32 in the study population). It is important to note that none of the 16 patients with anoxic brain injury responded (a fact that editorialist Allan Ropper also stresses).* Before fMRI testing, 4 of the responsive patients were diagnosed with vegetative state, including the patient who underwent communication training.
The American Academy of Neurology, the flagship organization for practicing US neurologists, provides the following criteria for the diagnosis of vegetative state:
- No evidence of awareness of self or environment and an inability to interact with others
- No evidence of sustained, reproducible, purposeful, or voluntary behavioral responses to visual, auditory, tactile, or noxious stimuli
- No evidence of language comprehension or expression
- Intermittent wakefulness manifested by the presence of sleep-wake cycles
- Sufficiently preserved hypothalamic and brainstem autonomic functions to permit survival with medical and nursing care
- Bowel and bladder incontinence
- Variably preserved cranial nerve and spinal reflexes
Minimally conscious state, which acknowledges the intermediate stage between no and some awareness in the severely brain damaged, is defined as follows:
A condition of severely altered consciousness in which minimal but definite behavioral evidence of self or environmental awareness is demonstrated.
Diagnosis: limited but clearly discernible self or environmental awareness on a reproducible or sustained basis by demonstrating one or more behaviors, including, following simple commands, gesturing yes/no answers to questions, intelligible verbalizations, purposeful behavior, appropriate smiling or crying, reaching for and touching objects, and pursuit eye movements.
Course: may be a transient stage in the recovery after severe head injury or other brain insult or a permanent condition.
Results of this fMRI study suggest that the imaging technique might be useful for distinguishing the 2 conditions (and that, perhaps, the definition of minimally conscious state should include fMRI-dependent findings) and for establishing communication in patients with reproducible fMRI responses.
* Ropper also concludes his NEJM editorial with a groan-inducing pun that should not be reproduced.
Image of Berkeley’s fMRI machine from Wikipedia.