Keeping hope alive: Brain activity in vegetative state patients

Thirteen year-old Jahi McMath went into Oakland Children’s Hospital on December 9 for a tonsillectomy. Three days later she was declared brain-dead. Severe complications from the surgery resulted in cardiac arrest and the eventual tragic demise of Ms. McMath; and while neurologists and pediatricians at the hospital have declared Jahi brain-dead, her family refuses to accept the doctors’ diagnosis, fighting to keep her on life support.

This heartrending battle between hospital and family is sadly not a new one, and there is often little that can be done to compromise the two sides. However, neuroscientific research in recent years has made substantial developments in more empirically determining if there are still signs of consciousness in vegetative state patients, which can either bring hope to a desperate family, or provide stronger footing for doctors trying to do the more difficult but often more humane thing.

In 2010, researchers at the University of Cambridge published a groundbreaking study in the New England Journal of Medicine looking at brain activity in minimally conscious or vegetative state patients using fMRI. These patients were placed in the scanner and asked to imagine themselves in two different scenarios: in the first, they were instructed to envision themselves playing tennis and swinging a racket, which would activate a motor region of the brain. In the second, they were told to think of a familiar place and mentally map or walk around the room. This would then light up the parahippocampal gyrus, an area involved in spatial organization and navigation.

Five of the patients (out of 54) were able to consistently respond to the researchers’ requests, reliably lighting up either the supplementary motor cortex or parahippocampal gyrus with each instruction. Even more amazing, one of the patients was able to turn this brain activation into responses to yes or no questions. The patient was asked a series of autobiographical questions, like “Do you have any siblings?”. If the response to the question was yes, they were instructed to “play tennis”, while if the answer was no, they should take a mental stroll around the room. Remarkably, this individual was able to accurately respond to the researchers’ questions just using these two symbolic thought patterns.

Building on this study, a new report released in November of this year in NeuroImage used EEG to measure electrical activity in the brain in an attempt to better assess consciousness in the same group of vegetative state patients.

A certain type of EEG brain wave, the P300, is generated when we are paying attention; and just as there are different kinds of attention (i.e. concentration, alertness, surprise), there are different P300 responses associated with each type. An “early” P300 burst in activity in the parietal lobe (P3a) is externally triggered, such as when something surprising or unexpected grabs our attention. Conversely, delayed P300 waves in the frontal cortex (P3b) are more internally generated and are activated when we are deliberately paying attention to something.

To test this, Cambridge researchers hooked up the same group of minimally conscious patients to an EEG machine and made them listen to a string of random words (gown, mop, pear, ox). Sprinkled throughout these distractor stimuli were also the words “yes” and “no”, and patients were instructed to only pay attention to the word “yes”. Typically, when a participant hears the target word (yes) they experience a burst in delayed P300 activity, signifying they were concentrating on that word. However, upon hearing the word “no”, participants often show early P300 activity, as they were not explicitly paying attention for this stimulus, but given its association with the target it still attracts their attention.

As in the first study, four of the participants showed brain activity indicating they were successfully distinguishing the target from the distractor words, with the expected P300 firings for each stimulus. This suggests that not only are these patients still aware and able to process instructions, they can also perform the attention task and spontaneously produce the typically expected brain activity. Three of these four individuals also successfully showed the appropriate activation during the tennis test listed above. However, it’s important to remember that in both of these studies only a very small minority of the patients were able to respond; the vast majority showed no evidence of consciousness during either task.

For the McMath family, studies such as these provide hope that their daughter is still somewhere inside herself, still able to interact with the outside world. But doctors fear this research may be misleading as these results are by far the exception. Additionally, there is no evidence that this type of activity will result in any change in the patient’s prognosis. Finally, and most relevant for the current controversy, complete brain death – as in the case of young Jahi – is very different from vegetative state or minimal consciousness; there is never any recovery from brain death. Advancements in neuroscience have gotten more and more incredible in the last decade, and our knowledge of the brain has grown exponentially, but there is still more that we don’t know than what we do, and we are a long long way off from being able to bring back the dead.

Dana Smith

PhD student in Experimental Psychology at the University of Cambridge