In 2011, a very exciting study came out in the medical journal, the Lancet, that claimed to use electroencephalography (EEG) to detect unexpected levels of brain activity in a small sample of vegetative patients, suggesting that they were still capable of voluntary, perhaps even conscious, thought. The research garnered attention from the New York Times as a potential bedside tool for determining the status of non-responsive patients. However, a new, independent analysis of the study is calling the results into question.
"We showed that their method is invalid for their patient data," says Andrew Goldfine, a rehabilitation neurologist at the Burke Rehabilitation Hospital in White Plains, NY and an author on the new study.
In the original research, cognitive scientists gave a verbal command to patients with traumatic brain injury, asking them to listen for a tone and then respond by imagining movement in either their right hand or the toes on their right foot. With EEG, they looked for brain activity that would indicate processing of motor imagery and compared these results to those collected in healthy subjects. Of the 16 patients they tried this with, three seemed capable of completing the task.
Goldfine and his colleagues, who have also used EEG to detect residual activity in non-responsive patients, were at first stunned by the results. "We were really impressed because here they had done something simlilar to us," says Goldfine. "Then we learned about what their task was. And their task was much harder than ours."
Funded by a grant from the James S. McDonnell Foundation, which supports data-sharing and collaboration in brain trauma rehabilitation research, Goldfine undertook a fresh analysis of the data, performing the same statistical analysis that he does on his own results. When given access to the raw data, he found that the researchers had run many trials in succession, analyzing them as independent data points in a way that was inappropriate according to Goldfine. When the trials were run again as blocks of data, the reponses that jumped out in the original results disappeared and the brain activity looked completely random. "In the EEG before the beep and after the beep there was no signal change at all," he says.
Moreover, Goldfine determined that the observations reported in the original results were most likely due to twitching muscles rather than command-driven brain activity. EEG is a crude imaging device designed to pick up neuronal firing at the surface of the brain using electrodes pasted to the scalp. But a lot of noise gets mixed in with the data. Tiny movements in the muscles around the electrodes put out their own electrical signal. And this is most likely what the researchers observed in their original paper. "As a clinician, I have the expertise to say 'well that is muscle activity on top of very low brain activity,'" says Goldfine.
In recent years, doctors have been using fMRI to get much more reliable evidence of residual brain activity in vegetative patients. Most recently, it was shown that Ariel Sharon, who has been unconscious since a stroke in 2006, could respond to audio recordings of his son's voice.
But not every hospital has an fMRI machine, and the procedure is too expensive and inconvenient to use on a regular basis. "The problem is that fMRI isn't really practical. You can't bring someone to an fMRI machine everytime you want to ask them something," says Goldfine. EEG, would be a much more portable tool.
Neither of these techniques can be used to conclusively state whether a patient is capable of conscious thoughts. Nor do they predict whether patients will emerge from their vegetative states. However, if perfected, they could help families make difficult end-of-life decisions. Although it looks like the claims made in the Lancet in 2011 may have been too hasty, other less publicized studies continue inching toward the goal of using EEG as a bedside tool. A similar one from 2008, for example, stands un-refuted. And so, the question is whether more research with EEG will result in more reliable results.
"Absolutely," says Goldfine.
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