Ragged Clown

It's just a shadow you're seeing that he's chasing…


Jul
7
2022

Does that make sense?

When most people think about how vision works, they think of the eyes as being like a camera that sends pictures into the brain which tries to make sense of what the eyes are seeing. In this paradigm, the brain is a passive recipient of the information from the senses. But the latest theories from neuroscience give the brain a much more active role in vision and the other senses.

The prevailing theory, known as predictive coding, is that the brain constructs a model of the world and it continuously sends messages to the visual cortex to ask “Is my model accurate?”. Is there still a dog chasing the ducks? Is the woman walking down the street still walking down the street? Is the ball still heading towards the goal? The visual cortex responds that yes, the dog is still chasing ducks and yes, the woman is still crossing the street and yes, the ball is still headed towards the goal.

No ducks to chase today?

The predictions made by the brain help us to know that the dog is still chasing the ducks even when the dog runs behind an object that hides it briefly and the brain is able to predict when the dog will emerge from the other side. Most things that happen in the world have a certain predictability: objects usually don’t vanish for no reason and a ball on a certain path will usually continue on that path unless something intervenes. If the visual cortex has information that contradicts the brain’s model — if the dog did not emerge from behind the object — the brain gets a little surprise and tries to figure out a new hypothesis for what is happening. It updates its model and makes new predictions.

I don’t know much about how the olfactory cortex works but I imagine it’s not too different to the visual system. If you suddenly smell dog treats, the brain decides there must be dog treats nearby and continually asks the olfactory cortex to confirm “Do you still smell dog treats?”… “How about now?” When the smell goes away, the brain updates its model and stops asking about the dog treats.

Now, consider that something went wrong in the brain and it reports that it can smell dog treats all the time. How would we explain this?

One possible explanation is that the olfactory cortex — or the part of the insular lobe that integrates smells into the brain’s model of the world — is experiencing a seizure. Seizures are sudden bursts of electrical activity in the brain that temporarily affect how it works. A seizure in the olfactory cortex might magic up the idea of the smell of dog treats and tell the brain, “We smell dog treats!” even if there are no dog treats within smelling distance.

Lovely smelling dog treats

Another possible explanation is that the brain’s olfactory model of the world says “Hey! We were smelling dog treats before. Are we still smelling them?” And the olfactory cortex says “I dunno. I have a glioma. Could be anything!” And the brain says “Probably still dog treats then.” Or maybe the dog-treat-detector is just stuck in the on position.

I smell dog treats ALL THE TIME. My coffee smells of dog treats. My salmon smells of dog treats. Sometimes the smell changes: on Sunday, I had liquorice tea all day; last week, it was dry-roasted peanuts. I guess it’s possible that I am experiencing epileptic seizures — sudden bursts of electrical activity — ALL THE TIME but I think it’s more likely that my olfactory cortex is failing to update my brain’s olfactory model because it has been damaged in some way by the tumour that is growing inside.

I wish there were some kind of diagnostic test to tell whether or not my brain is experiencing seizures.

My epilepsy nurse says that I should continue taking the anti-seizure meds and see if the seizures stop (narrator: the seizures have not stopped) and add another anti-seizure medication to see if that makes them stop (narrator: the seizures have still not stopped). Today she suggested adding a third anti-seizure medication. I said I’d rather not add any more medications until I have some indication that I am actually having the seizures that they are intended to treat. I wish I knew more about neuroscience so that I could argue my case more confidently.

My textbook — Principles of Neural Science — arrives tomorrow.

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7 responses to Does that make sense?

Georgina July 7, 2022

I’m going to read that book too.

Claire ATX July 7, 2022

Dredging up information in my brain that is forty years old so take caution…

There are twelve cranial nerves.

The olfactory nerve has very little processing of the olfactory information it receives before the information reaches the brain. Many people say that a smell can trigger old memories instantaneously. A professor used to say, Straight to the brain.

The auditory nerve has a number of synapses at various levels of the brain as the information travels from the ear to the brain. At each level some aspect of the auditory information is processed.

Not sure that helps in any way with sorting out olfactory seizures. How I wish I knew more..

Robin Martinez July 7, 2022

I too wish we knew more! I like your characterization of the problem. I know the neurosurgeon won’t go for that or for my picture version:

Ever see those movies – sometimes adventures, sometimes comedies – where people are put in a control area with unlabeled buttons and they have to push the right button? “Make it stop! Make it start! Is it working? I have no idea!”

That’s how I picture the glioma interacting with the olfactory cortex. The glioma is an untrained operator misusing normal controls because it happens to be in the same room with them. Phantom smells = normal signals misplaced or mistimed.

Whether you get burnt toast or dog treats or roses is a random button. Sometimes the glioma stops or changes buttons. (But it’s not pushing more than one button at once. That’s how I’d characterize a seizure.)

A side note: Did you know Catholics regard an unexplained scent of roses as signaling the presence of Mary?
https://blog.familyrosary.org/mother-mary-and-the-scent-of-roses

What actually is going on in there?

Robin Martinez July 8, 2022

Kevin and Georgina – wow, that’s an impressive book to tackle! Just the table of contents is daunting.

Claire ATX July 8, 2022

Just in case you haven’t checked out Wikipedia…..

Here’s what Wikipedia has to say about the book, Principles of Neural Science:

“It has been hailed as the “Bible of Neuroscience” having been co-written by the 2000 Nobel Prize winner Eric Kandel.[3]”

Chapter 5 on Perception May be the chapter to begin with…

Claire ATX July 9, 2022

I just have to chuckle with delight at Mr. and Mrs. Clown. Their thinking: Neuroscience? How tough can it be?

I admire your intellectual tenacity to get the answers to your questions. Well done.

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