The Neuroscience of Autism Spectrum Disorder: Insula Cortex

In this chapter of the Neuroscience of Autism Spectrum Disorder series, I want to talk about changes in a brain region called the insula cortex. And just like that we have moved to our first structure in the cortex. The cortex is the thin layer on the outer surface of the brain. And even though the cortex is only about an inch thick, it is mostly this region that sets humans apart from other animals. The cortex is what allows for really complex intelligence, and not surprisingly its functions are very complex and mysterious. In humans, the cortex has grown so large that it won’t even fit on the top of our brains anymore, so instead it is wrinkled up. That’s why when you see a picture of a human brain you see a wrinkly mess. The bigger the cortex, the more wrinkles there are.

But even though all we can see when we look at a human brain is lots and lots of cortex regions, you still can’t see the insula cortex. That’s because it folds inwardly and gets covered up by the other lobes. The only way to see it is to cut a brain in half and look at the folds from the inside, as shown in the picture below. In this picture the insula cortex has been colored green, brown, and blue, and you can see how it has folded inside the brain whereas the rest of the cortex wrinkles up on the surface.

Human_brain_frontal_(coronal)_section_description2

The insula cortex is still one of the most mysterious brain regions. It is really hard to say that it does this job or that job. Just to show you what I mean, there are studies linking the insula to the feeling of awareness of your body, your sense of taste, hand-eye coordination, swallowing, speaking articulately, and increasing your heart rate and blood pressure when you start exercising.

But one of the most interesting functions of the insula cortex is its job in emotional and social processing. The insula is one of the biggest players in the brain when it comes to emotions. In fact, this one region is thought to be responsible for your feelings of love, anger, happiness, sadness, trust, and it is also highly involved in sexual arousal. I usually like to familiarize each brain region when I talk about it, and this one is easy. The experience of having an orgasm comes from the insula.

So we know that the insula cortex processes really complex social and emotional information, and we know that Autism Spectrum Disorder is characterized as a decrease in social and emotional processing. It probably won’t surprise you then that the insula cortex shows some pretty big differences in people with an Autism Spectrum disorder.

The most apparent difference is that the insula is smaller in patients with Autism compared to the rest of the population. But size of the region is not the only difference. One study put subjects into an fMRI brain scanner and then showed them pictures of eyes. With each set of eyes the scientists showed two emotional words and asked the subjects to decide which emotion the person in the photograph was feeling from just their eyes. It’s a pretty difficult task. Here are two examples from their article, so you can see how tough this can be.

Baron-Cohen_et_al-1999 Fig 1

The correct answers are “concerned” and “sympathetic”.

By just showing the eyes, they were hoping to make each person think about the emotions really hard. What they found is that most people show a big activation in their insula cortex while they’re trying to decide the emotions behind the eyes. But people with Autism showed a lot less activation in their insula cortex. Interestingly, the Autism subjects showed more activation in a different region (the superior temporal gyrus) that is involved in processing faces and eyes. It’s as if the insula wasn’t doing its job properly, so the autism patients were trying to use other brain regions to compensate!

Another study showed that it isn’t just other people’s emotions that autistic brains struggle with. Participants in this study were shown a series of pictures while they were in an fMRI scanner, and as each picture came up they were asked to rate how the picture made them feel: negative, positive or neutral. So this time people had to decide how the picture made them feel, instead of trying to figure out how the person in the picture felt. You can see some examples of the pictures they chose below.

Silani Figure

They then compared the brain activity that occurred when participants were considering how an unpleasant photo made them feel compared to how a neutral one made them feel. They found that in normal people there was a big activation in the insula cortex when people thought about feeling negatively towards the unpleasant photos. However, there was much less activation in the insula of autism patients.

These studies suggest that autism patients have a smaller and less functional insula cortex. This makes it more difficult to figure out how other people are reacting emotionally based on their facial expressions and it also makes it more difficult to understand how they themselves feel emotionally. Understanding these differences in insula cortex function can help you imagine what it must feel like to live with an Autism Spectrum Disorder. Imagine how confusing it would be if you couldn’t recognize other people’s emotions by looking at their faces. How often would you misunderstand what they said because you couldn’t detect the underlying emotional context? Now imagine how confusing it would be to have emotions boiling to the surface but not understanding what those emotions were, where they came from, or why you were feeling them. This is the world people with Autism Spectrum Disorders face every day.

Politicus Cerebri

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