Where are you now? Look around you; what can you see? Close your eyes and think of a loved one – do you see their face? Stretch out a hand; what can you feel with your fingertips, your palm, the soft underside of your wrist? What can you hear – nearby and far away?
The information you receive from your senses makes up your world. But that world does not exist. What we perceive to be the absolute truth of the world around us is a complex reconstruction, a virtual reality created by the complex machinations of our minds in tandem with the wiring of our nervous systems. But what happens if that wiring goes awry? What happens if connections falter, or new and unexpected connections are made? Tiny shifts in the microbiology of our nervous systems can cause the world around us to shift and mutate, to become alien and unfamiliar.
Professor Guy Leschziner is one of the world’s foremost clinical neurologists, and in his new book The Man Who Tasted Words, he explores the secrets of our senses, and how people with extraordinary sensory disturbances can teach us more about our own sensory experience.
In this interview, I speak to Prof. Guy Leschziner about how our senses work, what we need to know about our senses, and how the science of sense is opening questions of philosophy, and about who we are.
Q: How do our senses define our reality?
[Guy Leschziner]: Our senses are the conduit between the external world and our interior. When we’re born, we have some wiring, but essentially a very limited experience of the exterior. To really understand the world we inhabit, we need to try and observe it. In order to function in the world, we need to have a model of the world upon which we base predictions. That model evolves through observation of the world we inhabit – there are of course questions about how real our observed reality is, but it seems our ability to interact with the world, to eat, sleep, socialise, work and every act in between – is entirely dependent on our sensory interactions.
Q: Do we all experience the same reality?
[Guy Leschziner]: As neuroscientists, we know that there are individuals out there, with essentially normal brains, without any diseases or disorders, who experience the world in very, very different ways. Sometimes we see this visibly in the general population- for example- the meme where people could see a dress in different colours. There are other people, with synesthesia, who have a merging of the senses and experience reality in a very different way from ourselves. There are genes – and variants of genes – that influence whether we can smell particular smells, or taste the bitterness of vegetables too – so it’s clear that there are significant differences between us in terms of ‘how’ we sense the same things.
The difficulty is in characterising those differences- if you see red, and I see red, do we see the same ‘red’ – the honest answer is that we still don’t know.
Perhaps these differences explain the diversity of beliefs. If our senses are really how we understand the world, and there are differences in those sensory windows, then our internal world will be different.
Q: To what extent can we trust our senses?
[Guy Leschziner]: We are constantly making assumptions about what we sense and that includes vision. Our senses have to deal with significant ambiguity. They have to deal with issues of bandwidth – it’s impossible to construct our sensory world second by second, so we live slightly in the past – so, by the time we ‘see’ something (perceptually), we’re a fraction of a second behind ‘real-time.’ Our brains are constantly taking shortcuts to inform us about the world and this introduces an intrinsic error which our brains are filling in. We all have blind-spots in our vision for example. We have a big blind-spot in the centre of our vision (relating to the anatomy of the eye). It’s where the nerve that leads out of the eye conveys information, and there’s no retina there. Yet, we are completely unaware of it for the most part.
We sometimes experience these errors and inconsistencies more vividly using psychedelic drugs, or through conditions like psychoses – but everyone has to be aware that there are significant distinctions between what we perceive to be reality and the cold, hard, molecular world we inhabit. The reality is, we have no idea about the world that we inhabit and that what the brain is doing is really creating an entire shortcut that enables us to understand the world without being able to physically really understand the reality in which we inhabit, which is a mind-blowing concept.
Q: What is life like for people with sensory conditions such as synesthesia?
[Guy Leschziner]: Synesthesia is a merging of two or more senses. The most striking examples include individuals for whom words, or thoughts about words, trigger senses-or where music triggers visual phenomena and sensations. Some synesthetes will associate particular letters or numerals with colours or personalities. Some have a crossover between time and space, so they may experience days, weeks or months as particular areas of an ellipse around them. These are very difficult concepts for non-synesthetes to understand.
I remember working with a musician who associated different keys of music with different colours – she literally saw colours in the periphery of her visual field that are associated with the keys and chords she was playing. The experience was also remarkably consistent. D was always, for example, green
From a rather dispassionate, clinical perspective, and if you remove the awful consequences that people experience when something does go wrong, you can see conditions like synesthesia as nature’s experiments. We can learn a lot about the underlying functioning of our nervous system and bodies from studying when things go wrong!
I’m a clinical neurologist. I see patients day in, day out, and my area of expertise is epilepsy and sleep disorders. Epilepsy, at its core, is an abnormal sensation in the cerebral cortex. The seizures demonstrate that many of our experiences are derived from the brain rather than reality. People who have seizures in the visual part of the brain will often experience visual hallucinations. People who have seizures in the sensory part of the brain will experience sensory experiences. In our general neurology clinic, we often see patients with a whole range of sensory disturbances, and each one teach us something more about our own senses.
Q: How does our body adapt to a lack of senses?
[Guy Leschziner]: As with many neurological conditions, it depends on the age at which you lose a particular sense as to how well (or not) you adapt. Our brains become less adaptable as we get older. Indeed, there are people who have adapted extraordinarily well to a lack of a particular sense because they lost it in young age and were able to adapt. There is a young man in the United States who is blind, who has developed an echolocation technique where he clicks his tongue repeatedly and is able to map out his environment using those clicks and how they bounce back to his ears. Imaging of his brain revealed that parts of the brain would be responsible for vision were now stimulated by his auditory system.
Q: Is there a hierarchy of emotions, as far as our brain is concerned?
[Guy Leschziner]: For most of our senses, there is a barrier between what we’re sensing and the brain. Smell is an outlier. The way smell works is that the brain essentially sent out a little tentacle into the world, those nerve fibres are the only contact between the central nervous system and the external world. This is the point at which there is no barrier between the brain and the outside world – and if you look at where smell is regulated, it’s very closely aligned with the areas of the brain that are related to emotion and memory. We think that smell, perhaps above all other senses, has a direct involvement in emotion, emotional memory, processing and has links with depression.
Q: What are the biggest mysteries yet to be solved about our senses?
[Guy Leschziner]: Despite our huge scientific advances, we’re still very-much at the early stages of discovery. Many of our great questions are also stepping into the realms of philosophy…. Do we all see the same way? Do we all perceive the same way? Understanding the senses will be key to understanding the differences between us. It’s a hidden frontier.