You can learn a lot about the brain by working with zombies…

The Walking Corpse Syndrome

This remarkable case of Cotard Syndrome that was reported recently got me thinking about how much studying zombies can teach us about the brain.

There’s no good reason for anyone reading this to have heard about this rare and bizarre syndrome before, so I’ll briefly summarize for those up the back. Jules Cotard was a late 19th century French neurologist who described the delusion of negation. This was defined as the implacable belief that one has died or otherwise doesn’t exist. The index patient for Cotard’s délire de négation was presented as Mademoiselle X, who apparently denied the existence of parts of her body, and felt no need to eat. This unfortunate lady went on to develop the belief that she could no longer die a natural death, since she was already non-existent and eventually died of starvation. Other sufferers of Cotard Syndrome have acted in bizarre fashion in accordance with their deluded belief that they have died or do not exist, including living in graveyards, refusing to eat and drink and in one extreme case believing that they can transform into a dog.

Experiencing the belief that one is dead while indisputably alive seems to occur specifically in cases of severe brain dysfunction. It has been reported in cases of psychiatric illness such as bipolar disorder and severe depression, as well as major brain damage from hypoxic brain injury, stroke, neurosurgery and dementia. The dysfunction seems to need to involve parts of the brain that serve to identify externally perceived objects as part of the self. The case reported in the news story above was from this journal article which identified him as having remarkably low brain metabolism activity. With recovery from the brain injury, I am pleased to report his delusion improved.

A possibly related condition is the equally oddball Capgras Syndrome in which the sufferer develops the belief that someone they know well has been replaced by an identical double. There is usually a paranoid flavour to the delusional explanation of who has done this and why. I met a patient with newly diagnosed Capgras Syndrome when I was a student. He believed his wife had been abducted by aliens and replaced with an android who looked and acted like her in all respects. He had agreed to go along with the aliens’ deception and be assessed by a psychiatrist as he was concerned that they might abduct and replace his daughter as well if he let on that he had figured them out.

In both Cotard and Capgras Syndrome, there are no apparent disorders of perception. The person can see, hear and sense the world perfectly clearly, and can potentially function well in other respects when not acting on the delusions, so the problem is not with how they are perceiving external reality. It seems to be that the ability to identify, that is to associate a particular person with a face, body part or other perception is lost. In Cotard Syndrome, the hypothesis is that this loss extends to one’s own body parts, to the extent that the only explanation that makes intuitive sense of the situation is that one must be dead, or non-existent in some way. The brain’s ability to confabulate, or fill in gaps with made up stuff, is well recognised when studying memory and other cognitive processes. It is also seen in split-brain patients with fascinating consequences.. Studying the so-called ‘walking corpse syndrome’ and other similar rare problems will continue to give us useful insights into the stunning complexity of brain function.

More about zombies in medicine…

In pain medicine, there is an ongoing philosophical debate as to whether pain is a quale. Qualia could be described as properties of sense-states or consciousness which are internally experienced in a way that is not accessible to any other being. You’ll have to take it from me that this is important in trying to understand and maybe measure someone’s pain, as the full philosophical argument is too long for a blog post like this.

As briefly as I can put it, some philosophers have proposed that it is possible to imagine that a creature they call a philosophical zombie or p-zombie for short, might conceivably exist. A p-zombie looks, acts and responds in all respects like a real person, except that they have no conscious awareness. Poke a p-zombie with a stick, he will bruise and say ‘ouch’ but can he be said to actually experience pain? The above link about quales contains a discussion about the pros and cons of p-zombie arguments that is worth reading (if very jargony). I’m going to focus on just one small aspect of the issue of p-zombies as they relate to my daily job.

There is a school of thought that holds if you can’t measure it, it doesn’t exist. This idea goes by many names, including reductionism, materialism and others. The sheer hubris of purporting to measure a quale with the puny tools of science worries many people, since it would potentially mean that the whole edifice of pain science is like Monty Python’s castle built on the swamp. Similarly, the whole justification for using animal models to generate insight into human pain becomes irrelevant if pain can only be truly judged or measured as a quale, ie a non-reproducible non-communicable sentient experience. We would have to work out which animals could experience pain as a quale, and use them for research.

Fortunately while the philosophical debate rages, it does appear that conceding that human pain may well be a quale, we can make progress with the tools of reductionist research while we are waiting to figure out whether p-zombies are conceptually possible. It isn’t necessary for me to fully understand and experience every aspect of your pain to know that 5mg of drug X is likely to help alter that experience to make it less intense or to reduce its impact on your ability to have a satisfying life. The items in our psychological toolbox that we use in practice admittedly rely on the presumption that pain patients are fully conscious and not zombies. We seemed to be able to measure abstract quantities as quality of life and level of disability well enough for our purposes. I’ve not come across any definite p-zombies in the clinic, but if I do I will certainly make them a cuppa and ask them exactly what they are feeling!