Full transcript of neuroscientist Paul Fletcher’s TEDx Talk on Psychosis: Bending Reality to See Around the Corners @ TEDxCambridgeUniversity conference.
Listen to the MP3 audio: Psychosis_ Bending Reality to See Around the Corners by Paul Fletcher @ TEDxCambridgeUniversity
Paul Fletcher – Neuroscientist
I am going to talk about psychosis.
This is an experience or a phenomenon that’s associated with a number of psychiatric, neurological, and physical illnesses. But it’s something more than that, and it’s something that I want to persuade you is actually highly related to the way in which we process the world day-to-day trying to make sense of its complexities.
Psychosis is a much misunderstood, much misused, much criticized term. It’s actually a description, a broad description, not a diagnosis. And it refers to a loss of contact with reality, whatever reality may be.
The textbooks say that there are two key characteristics. The first is hallucinations. People may hear, see, touch, taste, feel things that aren’t apparently there. The other phenomenon is the delusion, a seemingly irrational belief that arises without good evidence.
And it’s held in a way that seems to be impervious to evidence that contradicts it. So that’s the dry textbook definition.
My first experience with psychosis really came when I was a young medical student on my first psychiatry attachment in an inpatient ward in the Hackney Hospital, North East London. And I spent a long time talking to a young man, who described to me in great detail the experience that he’d had of being sent messages from television, film, and radio, and newspapers. Messages in verbal, and visual, and even telepathic forms that were highly critical of him, very unpleasant, very threatening. They even instructed him to harm himself with a knife.
I was deeply disconcerted, but also baffled by this, because he was a young man, who was articulate, intelligent, insightful, and yet, though we seem to inhabit the same world, the reality that he had was very, very different to my own.
And there’s no easy way of applying a simple loss of functional derangement or dysfunction model to understanding that.
Now, I’d like to argue that in order to begin to understand this, to get a glimmer of understanding, we need to take a step back and look at the way that the normal, healthy person in the world processes that world in order to try and make some sense out of its complexities, its ambiguities, and its uncertainties.
And I think through looking at that, we get a glimmer of the possibility that actually, many of us are in a pretty much psychotic state all the time. Primarily, the brain needs to be able to predict the world, to be successful, and to survive.
And in order to do that, it needs to build an internal model of that world outside. And this is where the difficulty starts, because we don’t have direct contact with that world outside.
We have the illusion of direct contact. We have the illusion of reality. This was put very nicely by Vernon Mountcastle, who was a neuroscientist, and he said in 1976, “Each of us lives within the universe or the prison of their own brain. Projecting from it, are millions of fragile sensory nerve fibers, arranged in groups uniquely adapted to sample the energetic states of the world: heat, light, force, chemical composition. That’s all we can know of it directly. Everything else is logical inference.”
Now, this is a profound statement, because it’s telling us that we are actually bringing something to the act of perceiving reality. And it’s worth considering the nature of that inference.
Hermann Von Helmholtz, a 19th century scientist, thought a lot about perception, perceiving and experiencing the world as an inferential, logical process. And in fact, he said that it’s an act of imagination. He said, “Objects are always imagined as being present in the field of vision as would have to be there in order to create the same impression of the nervous mechanism.”
What he was saying here was that we have impressions, experiences on our nervous system just as Mountcastle suggested. And we then have to imagine what could have caused those.
We back project to the cause of the sensations that we do have. This is a form of inference, and it’s a form of inference that this chap here, Charles Peirce, an early 20th century philosopher, referred to as abductive inference or abduction.
Abductive inference really refers to reasoning backwards from evidence to the causes of those evidence. So we have the evidence in our senses, we need to reason backwards. And Peirce pointed out that actually this is one of the shakiest, most fragile, most tenuous forms of logical inference that you could have. He referred to it as guessing.
And the reason is guessing is that for any given sensory experience that we have, there is a myriad, multiple, infinite number of possible causes that could have given rise to that. And we are stuck with having to make a decision about what could have been that cause. As Peirce put it, he said, “The whole fabric of our knowledge is a matted felt of pure hypothesis.”
But we seem to get by. We do manage. And the reason that we manage is actually captured in a theorem that was developed by this 18th century Presbyterian minister Thomas Bayes. Many of you’ll have heard of Bayes’ theorem. You certainly come across it more and more in neuroscience nowadays. And Bayes pointed out, and in fact, Bayes, although he didn’t use the term, was talking about this form of abductive inference, about working out the causes based on the evidence.