It’s not been a good few weeks for Adrian Owen and his team of Canadian neurologists.
Over the past few years, Owen’s made numerous waves, thanks to his claim that some patients thought to be in a vegetative state may, in fact, be at least somewhat conscious, and able to respond to commands. Remarkable if true, but not everyone’s convinced.
A few weeks ago, Owen et al were criticized over their appearance in a British TV program about their use of fMRI to measure brain activity in coma patients. Now, they’re under fire from a second group of critics over a different project.
The new bone of contention is a paper published in 2011 called Bedside detection of awareness in the vegetative state. In this report, Owen and colleagues presented EEG results that, they said, show that some vegetative patients are able to understand speech.
In this study, healthy controls and patients were asked to imagine performing two different actions: moving their hand, or their toe. Owen et al found that it was possible to distinguish between the ‘hand’ and ‘toe’-related patterns of brain electrical activity. This was true of most healthy control subjects, as expected, but also of some – not all – patients in a ‘vegetative’ state.
The skeptics aren’t convinced, however. They reanalyzed the raw EEG data and claim that it just doesn’t prove anything.
This image shows that in a healthy control, EEG activity was “clean” and generally normal. However in the coma patient, the data’s a mess. It’s dominated by large slow delta waves – in healthy people, you only see those during deep sleep – and there’s also a lot of muscle artefacts which can be seen as ‘thickening’ of the lines.
These don’t come from the brain at all, they’re just muscle twitches. Crucially, the location and power of these twitches varied over time (as muscle spikes often do).
This wouldn’t necessarily be a problem, the critics say, except that the statistics used by Owen et al didn’t control for slow variations over time i.e. of correlations between consecutive trials (non-independence). If you do take account of these, there’s no statistically significant evidence that you can distinguish the EEG associated with ‘hand’ vs ‘toe’ in any patients.
However, in their reply, Owen’s team say that:
their reanalysis only pushes two of our three positive patients to just beyond the widely accepted p=0.05 threshold for significance – to p=0.06 and p=0·09, respectively. To dismiss the third patient, whose data remain significant, they state that the statistical threshold for accepting command-following should be adjusted for multiple comparisons… but we know of no groups in this field who routinely use such a conservative correction with patient data, including the critics themselves.
I have to say that, statistical arguments aside, the EEGs from the patients just don’t look very reliable, largely because of those pesky muscle spikes. A new method for removing these annoyances has just been proposed… I wonder if that could help settle this?
Goldfine, A., Bardin, J., Noirhomme, Q., Fins, J., Schiff, N., and Victor, J. (2013). Reanalysis of “Bedside detection of awareness in the vegetative state: a cohort study” The Lancet, 381 (9863), 289-291 DOI: 10.1016/S0140-6736(13)60125-7