Last week I attended a conference on the science of consciousness in Helsinki. While there, I attended a very interesting session on the Minimally Conscious State (MCS). This is a state that follows severe brain damage. Those diagnosed as MCS are thought to have some kind of conscious mental life, unlike those in Vegetative State. If that is right – so say many bioethicists and scientists – then the moral implications are profound. But what kind of conscious mental life is a minimally conscious mental life? What kind of evidence can we muster for an answer to this question? And what is the moral significance of whatever answer we favor? One takeaway from the session (for me, at least): it’s complicated.
In his contribution to the session, the philosopher Tim Bayne pointed out that there are various routes to a diagnosis of MCS. Patients are put through a series of tests and receive a score that sums performance in a series of categories – auditory function, visual function, motor function, verbal function, communication, and arousal are measured. In order to be diagnosed as in the MCS, a patient must receive a high enough score on one of the scales. For example, looking solely at the visual function scale, a patient must exhibit fixation as opposed to visual startle.
Visual startle is tested by presenting a ‘visual threat’ – in this case, passing a finger 1 inch in front of the patient’s eye. Visual startle is demonstrated when the patient’s eyelid ‘flutters’ or when a blink follows, on at least 2 out of 4 trials.
Fixation is tested by presenting a brightly colored or illuminated object 6-8 inches in front of the patient’s face, and then moving the object to various quadrants of the visual field. Fixation is demonstrated when the patient’s ‘eyes change from initial fixation point and refixate on the new target for more than 2 seconds.’ Over 4 trials, 2 instances of fixation are required.
The functional difference between fixation and visual startle is subtle, and there are of course many reasons why patients with varying degrees of residual cognitive function might fail either test. Misdiagnoses in this area are common.
The diagnostic difficulties here were underscored by Rachelle Gibson in her interesting contribution. Gibson discussed a paper by her and others in Adrian Owen’s lab exploring the use of neuroimaging and EEG as ways into a better understanding of the mentality of severely injured patients (Gibson, R.M., Fernandez-Espejo, D., Gonzalez-Lara, L.E., Kwan, B.Y., Lee, D.H., Owen, A.M. and Cruse, D. Multiple tasks and neuroimaging modalities increase the likelihood of detecting covert awareness in patients with Disorders of Consciousness, Frontiers in Human Neuroscience, doi: 10.3389/fnhum.2014.00950, 2014). Gibson’s study used 6 participants – 4 diagnosed as vegetative, 2 as minimally conscious. These participants were asked to perform two tasks. The first was a task involving the production of motor imagery, which was assessed by EEG and by fMRI. The second was a spatial navigation task assessed by fMRI. Interestingly, one patient diagnosed as in VS showed signs of completing the motor imagery task as assessed by both fMRI and EEG. Another VS patient showed signs of spatial navigation, but not motor imagery. One MCS patient showed signs of motor imagery as assessed by EEG, but not of motor imagery as assessed by fMRI nor of spatial navigation. The other MCS patient only showed evidence of spatial navigation. In other words, the existence of capacities Gibson et al. tested did not map cleanly onto a behavioral diagnosis of VS or MCS.
Charles Weijer’s interesting contribution emphasized the importance of collaboration between ethicists and neuroscientists in the construction and design of research programmes. Weijer and colleagues are working closely with Adrian Owen’s lab on a number of issues, e.g.: how best to think about the welfare of these patients, whether results should be shared with families, what the impact of neuroimaging and EEG studies on families might be, whether and at what point patients should be allowed to make their own treatment decisions, and what role there ought to be for neuroimaging in intensive care – or even in diagnosis. Weijer is right to emphasize the importance of collaboration on these questions. It looks like close collaboration between ethicists and scientists will be critical for sorting through practical issues. And it looks like collaboration between philosophers and scientists could be critical for sorting through the closely associated theoretical issues.