That Neuroscience Guy - Neuroscience Bites - Charles Bonnet Syndrome

Episode Date: April 13, 2024

In today's Neuroscience Bite, we discuss Charles Bonnet syndrome - a rare disorder where people suffer extreme hallucinations related to top-down control over a damaged visual system. 

Hi, my name is Olaf Kregolsen and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to another neuroscience bite. This one came up randomly in conversations with colleagues and I was thinking about that top-down processing episode. So what I'm going to tell you about quickly is something called Charles Bonnet syndrome. And it's a very interesting phenomenon. Basically, people with Charles Bonnet syndrome have visual hallucinations. And it's caused usually because of significant vision loss. So whether that's happening through aging or it's happening through trauma,

typically in the elderly, it's just through aging. And it can be eye conditions that affect sight, like macular degeneration, for instance. But it can happen in younger people who have had trauma to the visual systems, say a car accident, and all of a sudden their visual system is disrupted. And what happens is these people see visual hallucinations. And I mean like really extreme hallucinations. One of the examples that I read about when I was doing my research for The Bite was someone who basically saw cartoon characters in the real world. So some of us think that would be the best thing that could ever happen. But this poor person would see like Daffy Duck walking down the street. And people with

Charles Bonnet syndrome, they take a long time to report these things because the hallucinations tend to be very extreme. So that they tend to be embarrassed about them. You know, like who wants to tell their doctor that you see Daffy Duck walking around because typically they might jump to a conclusion about mental illness. Like I said, the cause is very simple. It's damage to the vision system, but it can be damage to the eyes or it can be damage to the actual visual cortex. It's not really known how many people actually have Charles Bonnet syndrome because with all of these neural disorders that you have to appreciate that there's levels to them. So some people have very extreme Charles Bonnet syndrome, which would be seeing Daffy

Duck functioning in the world, but other people would have mild Charles Bonnet syndrome where they just might seem something that's out of place, but it's not completely unbelievable. Typically with people with Charles Bonnet syndrome, they have no control over the hallucinations. So they're not able to stop them. They see them and there's nothing they can really do about it. And typically you find examples like if they close their eyes and they open their eyes again, even if they hold their eyes closed for say 30 seconds, they can still see that illusion. What's equally weird with it is these people are aware that the hallucinations aren't real for the most part, especially in the extreme cases, because they know that Daffy Duck isn't walking down the street, right? So they know that they're hallucinating,

but there's nothing they can do about it. It's almost impossible to treat unless you do something to improve the visual system. So if it was due to a car accident, you might just heal over time. If it's due to a vision loss, maybe through treating that vision loss through new glasses or something like this. And people can see very simple things like just a pattern that doesn't belong there or it can be something complex like the Daffy Duck example. And these images typically tend to be anything, these hallucinations. They can come in color or black or white. They can be like a photograph. So static, but they can be moving like the, like the thing they're seeing is interacting with the world.

They can be life-sized or tiny. I read about one woman who only saw very small things that weren't real. Uh, and then other people say their real life, they can be realistic. So you might see a lion in your living room, but they can also be fantastic, right? So you see a dragon or something like Daffy Duck that doesn't exist. Sometimes they can be pleasant. People can laugh at seeing them. Sometimes they can be frightening. Sometimes they're very brief. They only happen for a few minutes, but sometimes they persist for a few hours.

Like the one person that saw Daffy Duck basically spent the day walking around with Daffy Duck. They're typically meaningless. They're just random things that are popping in from your brain. And they typically, they're different every time, but some people do have repetitive images. So that's Charles Bonnet syndrome. Damage to the visual system, either the eyes or the primary visual areas in the brain,

causes you to have these hallucinations where you see things that aren't really there. Hopefully you found that interesting. Don't forget the website, thatneuroscienceguy.com. There's links to Etsy and Patreon. Of course, send us ideas on threads or X at thatneuroscienceguy or email us at thatneuroscienceguy at gmail.com. And of course, thank you for listening to the podcast. Please subscribe.

My name's Olive Craig Olson, and I'll see you soon.