The neuroscience of Autism Spectrum Disorder: Amygdala

The last few posts in this series have been laying down a groundwork by establishing what Autism Spectrum Disorder is, and how it is caused. With that information behind us, we can get into the fun stuff. Let’s take a look inside an Autistic brain.

There are multiple brain regions that scientists have found differences in when studying Autism Spectrum Disorders. To discuss all of them in one post would probably make it too long to read in a single sitting, so I’ll break it up into different sections. This post, we will cover the autistic amygdala.

Amygdala

The amygdala is a fascinating region. Like most things in the brain there are two of them, one on each side. It is a small, round structure way out near the edge of your brain. Place your fingers on your temples, and imagine a region about the size of an almond just a few inches beneath your skull. The amygdala only accounts for about 0.3% of your total brain, but despite being small its role is huge. There are studies linking it to lots of different functions such as fear, your sense of smell, sexual behavior, and even memory. Don’t kill yourself trying to think about what those traits have in common.

The main reason I want to talk about the amygdala today is because of the job it does processing social and emotional information, since those are the main deficits associated with Autism Spectrum Disorders. The amygdala is needed for tasks like recognizing emotion in faces, deciding if someone should be feared or trusted, and it is the brain region that gives us a sense of “personal space”. Have you ever been standing around, minding your own business, and someone walked up and stood way, way too close to you? When you get that intense feeling that you really want to step back, that’s your amygdala!

Autism researchers have always eyed the amygdala with suspicion simply because we know it plays a big role in recognizing facial emotions, something people with Autism struggle to do. And it turns out there are differences in the amygdala in Autism Spectrum Disorder brains, but those differences were not exactly what people expected. Since you need your amygdala to recognize facial emotions and carry out other social and emotional processing, it was assumed that people with an Autism Spectrum Disorder would have a damaged, or smaller or somehow inadequate amygdala. Makes sense, right? But when they started taking measurements, they actually found that toddlers with an Autism Spectrum Disorder have a much larger amygdala compared to normal toddler brains. Then, as children age this pattern reverses. In the normal children the amygdala grows larger and larger over time, but in children with autism this growth doesn’t seem to take place. In fact, by the time they are young teenagers the amygdala in normal brains has caught up with or even surpassed those in the autistic brains. What is going on here?

As is always the case when you’re talking about the human brain, things are more complicated than originally thought. Scientists think what is happening is the amygdala initially grows wrong getting much too big. We generally think that bigger is better (for example, see Texas), but the brain is more like Goldielocks; too small is bad, too large is bad, everything needs to be just right. So if the amygdala in an Autistic child’s brain is too large, that might mean that it is not connecting or functioning the way it is supposed to with the rest of the brain. That’s bad because it needs to be connected properly to grow and mature into a highly efficient adult amygdala. Since the young amygdala is too big and possibly not connected normally to other brain areas, as the child gets older it doesn’t grow and mature like it is supposed to.

What does that have to do with the specific deficits seen in Autism Spectrum Disorders? One possibility is the role the amygdala plays in fear. As we encounter objects in the world, the amygdala is responsible for assessing how risky each object is to us. So, if you walk up to a wooden chair, the visual information of the chair is sent to the amygdala, and the amygdala is quiet because the chair is pretty harmless. If you walk up to a grizzly bear, that visual information will generate a gigantic response from the amygdala which will make you feel terrified and immediately want to run away as fast as you can. Perhaps if you were born with an amygdala that was not processing information normally, it could register things that are supposed to be neutral as scary and make you avoid them. This could explain why autistic children avoid eye contact with people, perhaps each time they make eye contact their amygdala registers a threat and they look away to avoid that fear. It makes sense, but is there any evidence to support this possibility?

A recent study by Dr. Kleinhans and his labmates used an fMRI brain scanner to look at how the amygdala of normal or Autistic children responded when they were shown pictures of faces. The pictures were of adults with a neutral expression on their face. The children were shown these pictures over and over and over. In a normal brain, the amygdala will initially react to a stranger’s face, but as these faces keep appearing over and over, the reaction gets smaller and smaller. You can see the results from their brain scan below. The blue dots represent areas where there was significantly less brain activity to the last few pictures of faces compared to the first pictures.

Fig1b

Those blue dots are right on the amygdala. That means that as these brains looked at pictures of faces, the amygdala got quieter and quieter. Now, what about Autistic brains?

Amygdalafig1

Again, the blobs (this time they’re red instead of blue) are areas where there was less brain activity to the last few faces compared to the first few. You can see that there is not very much reduction in the Autistic brains compared to the normal ones. This means, that every face picture is still getting a big activation from the amygdala.

What does this mean? Remember that the amygdala’s job is to assess whether or not what we’re looking at is a big threat. Normally when you suddenly see a stranger’s face right in front of you, the amygdala reacts. A stranger appearing out of nowhere right in front of your face could be a big threat. Stranger danger! But, as the stream of faces keeps going, your amygdala realizes these are non-threatening and it calms down. In the autistic children, this calming never takes place suggesting that the amygdala keeps tagging each and every face as a potential threat. Could this amygdala be tagging other faces as dangerous too? Like the faces of the child’s mother and father and brother and sister? Imagine how you might behave if every time you looked at your mom or dad’s face you got the same feeling as when you see a stranger walking down a dark street. Thinking of it this way can really help understand why people with Autism act the way they do. They essentially live in a world where socially important signals are tagged as dangerous all the time.

It is important to note that the differences in amygdala are not the full story of what is going on in Autism Spectrum Disorder. Over the next couple of posts, I will be getting into other brain systems that are different in Autism. In the mean time, I hope this post helps you get inside what it must be like to have an Autism Spectrum Disorder. We all experience what it feels like when a stranger stands too close to us, or when we are alone on a dark street with a stranger. Imagine how distressing it would be if you got those feelings every time you were around any human being no matter how kind and gentle they were.

Politicus Cerebri

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