Tactile Sensitivity, a scientific insight into why we have it

Somatosensory cortex functional connectivity abnormalities in autism show opposite trends, depending on direction and spatial scale.

Not very readable, right?

Let’s try and translate that out of the language known only to neuroscientists and into something the rest of us can access (with a bit of help from this article here ).

Sensory information comes in through the nerves, be it through the retinal nerve in our eyes, the nerves that detect movement of the eardrum in our ears, the nerves that detect touch or temperature on the skin, and so on. They’re relayed to the brain, where we process the information. This study primarily concerns tactile sensory input, or touch, because they know which parts of the brain process that. We process touch in two different parts of our brain, which communicate with each other. They’re called the Primary and Secondary Somatosensory Cortex, or S1 and S2.

The touch information goes through S1 first, which then forwards it onto S2. When the touch information enters a somatosensory cortex, it begins sending its own short-range signals to surrounding areas. S2 also sends signals back to S1, and eventually all of these signals get so noisy that they have a dampening effect on the original information, the touch information.

This is how neurotypical brains filter out irrelevant information after a while.

In this study, we found direct evidence of increased long-range feedforward functional connectivity between S1 and S2 in ASD, using passive vibrotactile stimulation. We also found reduced local functional connectivity in both S1 and S2 in ASD, using the same paradigm.

In autistic brains, the short-range internal signals aren’t as strong, and the long-range signals are stronger. This means that the information coming into our somatosensory cortices is much stronger than in a neurotypical person. We’re having to deal with a much greater intensity of signal that we have to process. And we have to keep processing it, because our brains don’t generate a strong enough signal to block it out.

So how much can we trust these results? You’d need to talk to a mathematician to determine whether their statistics are up to scratch, but they do provide reasoning for each of the methods they use, and they look a fair bit better than a preference for simplicity (a la Brian Hooker, check out Harpocrates for a description of why simplicity isn’t always best).

I’d like to see a bigger and more diverse sample size, the study used 20 neurotypical 15 autistic subjects, all male and right-handed, aged 8–18.

The results work with things we’ve known for a long time:

  • That we feel things more keenly than neurotypical people do
  • That we can’t ignore or block out some sensory information

Now we’ve pinned down exactly what’s going on, what are the practical applications?

It’s unlikely we’re just going to “grow out of it”. The study’s authors reported that they saw no difference in results based on the age of the participant (8 to 18).

It may be that now we know the mechanism for tactile sensitivity, treatments can be attempted to allow our brains to produce those signals that dampen the sensory input. I’m no neuroscientist, so I’ve no idea how that would work, but would be inclined to guess that it would involve either training the brain to produce weaker feed-forward signals or stronger feedback signals, or it would involve some kind of technology that would help us by performing the dampening for us.

One thing’s for sure, we’re not going to “get over it” by force of willpower. We’re not intentionally sensitive and not making a decision to have sensory processing difficulties. With any luck, this will provide enough information to stop ABA focused on preventing reactions to tactile sensitivity.

Think of it like pain. You can train a person not to show a response to pain (up to a certain point). You can train them to manage their breathing, facial expression, and you can train them not to make any noise. What you cannot train them to do is stop feeling the pain. Even if you succeed in changing the pain response behaviour, even if you train them to laugh at pain, you have not trained away the experience of pain. Similarly for painful sensitivities, you can train a person to behave differently, but you are not taking away their discomfort.

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