Jay Leschner: “Reality is entirely a construct of our nervous system” | Neurology

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Jay Leschner is a Consultant Neurologist at Guys and St. Thomas Hospitals. His areas of specialization are epilepsy and sleep disorders. He has presented two BBC radio series, one on sleep and one on the neuroscience of our sensory world. His latest book is The Man Who Tasted Words, which explores the relationship between our sensory perception and the reality it constructs.

A common phrase in cognitive neuroscience is “perception is nothing more than a controlled hallucination.” What exactly does that mean what we think of as hallucinations is an experience that is devoid of reality or far from reality. The term “controlled hallucinations” indicates that our experiences are generated by the brain. As I point out in the book, sometimes we perceive it to be a very different reality from the cold, harsh reality or what we assumed was the cold, harsh reality around us. So it basically emphasizes the point that what we call reality is entirely a construct of our nervous system.

There is a debate in neuroscience between the orthodox view that our sensory system is a kind of defective means of perceiving reality and those who suggest that it is designed to obscure reality. What are your thoughts on those discussions? Intuitively as a human being, and not as a neurologist, I find it very difficult to understand those views that our brains are designed to hide reality. I am intrigued by these theories. Do I in my heart like to kiss them? No, I don’t. I am more comfortable with the view that there is some connection between the world we live in and what we experience rather than completely removing them from each other.

The title of your book refers to a man with synesthesia, in which one synesthesia leads to the other. He can taste the words while someone else sees the colors in the music. What does this tell us about our sensory system? The most prevalent statistic regarding the prevalence of synesthesia is that it affects about 4-5% of individuals. The thing it’s really telling us is that there are people with essentially normal brains – these are not individuals with pathology, not people with trauma or brain damage – who experience reality in a very different way than most of us. It highlights that our perception of reality is determined by how our brains work and shows that it depends entirely on our nervous system.

Sleep is one of your areas of expertise. Neuroscientist David Eagleman argues that the brain is a Darwinian battleground between neurons and that dreaming is a way to preserve vision when we sleep. What do you think that? It is true that humans have evolved to be more dependent on their vision rather than other senses. But there are a lot of theories as to why we dream. The thing I particularly like is that in order for our nervous system to function properly, and in order to understand the world, we constantly need to make predictions. In order to make predictions, we need some kind of internal model of the world as we understand it. And the dream may represent an integration of our experiences throughout the day and, in fact, over the course of our lives in this model. And this dream sleep is that stage of our lives each night where we adjust this internal model of the brain.

The issue of pain features prominently in your book. No one experiences any pain at all. Why do you think pain is so painful? We know that pain has many components. A key component is sensory perception, which tells you where the pain is in the body. Another feature that everyone will recognize is the so-called emotional component of pain. Plus knowing I hit my finger with a hammer, that kind of overwhelming hatred, that dread of pain. I think this is a very important evolutionary mechanism. Pain is a very powerful motivator to avoid self-harm.

It is not often recognized that smell is a very important means of communication

You’re touching on Covid-19, especially in terms of loss of smell. Do you expect research into Covid will yield neurological findings? For many people, this is the first time they have encountered their own mortality. But it also appears that there is a physical or biological component to it. From a neurological perspective, one recent study looked at individuals with Long-Covid brain fog. What they clearly showed in this group of individuals is that 70% of them had cerebrospinal fluid abnormalities. I think what we will discover is that there are a combination of factors that lead to the spread of Covid. And it might be a mistake to group them into one case.

If you had a billion pounds to spend on medical research, where – from a neurological perspective – would you like to go? From a completely selfish perspective, my academic background is epilepsy and sleep deprivation. Sleep was the topic of my first book. And I think because we spend a third of our lives sleeping and yet we don’t fully understand the impact of what sleep does, I think this is an area that is still being researched and may have far-reaching implications for all of us.

In a sense, it asks the reader to re-evaluate the senses, especially the overlooked senses of taste and smell. How you rank the senses in order of importance to you, I would say first seeing, then hearing, then touch, then smelling and then tasting. By the end of writing the book, I’m not sure it’s changed much, but I certainly appreciate the scent so much more. It has far-reaching implications in terms of memory, in terms of emotion, in terms of a lot of the subtle aspects of our lives, for example, the attraction towards another individual. I think the fact that smell is a very important means of communication has not been underestimated.

In the time you’ve been exercising, what medical breakthrough has had the biggest impact on your patients? When I was a medical student, neurology was said to be the specialty with 1001 diagnoses, but only one treatment. This treatment was steroids. While our understanding of immunology, in particular, has caused an explosion in terms of available treatments for some very serious conditions such as multiple sclerosis or other autoimmune diseases that cause devastating neurological damage. This is a major therapeutic step forward.

The Man Who Tasted Words by Guy Leschziner is published by Simon & Schuster (£16.99). To support Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply

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