Sometimes, following a brain injury, patients have periods of wakefulness but can't communicate with those around them. Might they still be feeling pain, pleasure or discomfort? Could it be that they still understand when loved ones speak to them, even if they can't respond? Doctors and families alike find themselves asking these questions, unable to answer them with any confidence.
Authors
- Mona-Marie Wandrey
PhD Candidate in Philosophy of Science, University of Cambridge
- Jonathan Birch
Professor of Philosophy, London School of Economics and Political Science
Despite the lack of certainty, doctors are still expected to make a diagnosis. They follow established procedures, looking for signs of "purposeful behaviour" at the bedside. If a patient can follow commands or interact with their surroundings in seemingly purposeful ways (for example, by squeezing a doctor's hand or following an object with their eyes) they are said to be in a "minimally conscious state".
Some patients, by contrast, don't show any purposeful behaviour during wakefulness. Traditionally, the term "vegetative state" has been applied to these patients, though this term has been criticised as dehumanising . Increasingly, "unresponsive wakefulness syndrome" is used instead.
These patients are not completely expressionless. They sometimes grimace, cry or yawn, but these actions are usually seen by their doctors as mindless reflexes. For a long time, it was believed these patients simply couldn't have any conscious experiences.
In the past two decades, researchers have realised that this assumption is often false. One problem is that bedside diagnosis is unreliable. It is not easy to distinguish purposeful behaviour from reflexes, and standard medical exams can miss subtle signs of awareness in around 40% of cases .
Recent studies have also suggested that as many as 25% of outwardly unresponsive patients are trying to respond. The evidence comes from measures of brain activity. For example, when asked to clench their right fist, the patient's hand will not move, but their brain activity will show a response, suggesting an attempt to clench their fist. These patients may well be hearing and understanding the commands, a condition called "covert consciousness".
Even patients who can't follow commands in this way often show brain activity in networks linked to consciousness. For example, more than a third of patients have activity in the cerebral cortex: the outer layer of the brain responsible for functions like thinking, planning and processing complex information. This suggests that parts of their brain involved in consciousness may still be working.
Yet researchers disagree on whether a cerebral cortex is needed for conscious experience. Some evidence suggests that the midbrain , an area at the top of the brainstem, might be enough to support a state of "primary consciousness" involving basic feelings such as fear and pain.
Some midbrain activity must remain in all patients who cycle between periods of sleep and wakefulness because the midbrain regulates these cycles. So, even if neither behavioural exams nor measurements of brain activity reveal any signs of consciousness, we are still not in a position to rule out the possibility of continuing experience.
Precautionary attitude
We therefore need to take a precautionary attitude towards these patients. Instead of drawing sharp lines between conscious and unconscious patients, we need to take seriously the possibility that all patients in a state of unresponsive wakefulness might be capable of some forms of experience, including pain and pleasure.
Taking this possibility seriously does not mean underplaying the extent of the brain injury, nor does it mean assuming that patients will one day regain the ability to communicate. Sometimes this never happens. Doctors should separate diagnosis from prognosis and be honest with relatives in cases where the prognosis is bleak. But they should never assume experience is absent.
Doctors' guidelines for diagnosing "disorders of consciousness" (the medical term for conditions in which behavioural signs of consciousness are reduced or absent) should reflect this need for precaution. The European guideline recommends that doctors should not only look for signs of purposeful behaviour but also assess patients' brain activity whenever possible. While this is a step in the right direction, current methods mostly focus on the cortex and overlook the possibility of conscious experience without cortical activity.
The UK guidelines include a more general precautionary recommendation. They stress that signs of pain or discomfort should be treated appropriately in all patients with disorders of consciousness. But guidelines should go further. At the very least, doctors need to explain to patients what is happening to them and why, in case they can hear and understand.
More fundamentally, though, doctors should not be expected to draw sharp lines between "minimally conscious" and "vegetative state" patients. We are not sure enough to make that call. Instead, we should use the broader term "prolonged disorder of consciousness" and tailor care to each patient's needs, while working on more detailed classification systems drawing on the latest scientific evidence.
Jonathan Birch receives funding from the European Research Council, Open Philanthropy and the Navigation Fund.
Mona-Marie Wandrey does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
