I once had a t-shirt that I really wanted to like. It was a souvenir from a trip to Hawaii. The color, the material, the fit, the design–all perfect. It would have been my favorite new shirt, except for one thing.
It had a tiny thread in the collar that scratched my neck. A thread so small that I couldn’t see it. I’d cut out the offending tag and all of the visible stitching holding the tag in place, but that one little thread refused to go.
So I decided that I was going to get used to it. I was going to pretend that evil remnant of plastic thread didn’t exist. If it was too small to see, surely I could ignore it.
I tried. I really did.
I put the shirt into my summer t-shirt rotation and wore it at least once a week. The material got softer with each washing, which only made me want to love it more. It was one of the most comfortable shirts I owned. It would have been that most elusive of things–the perfect shirt–except for that microscopic thread.
I developed seriously mixed feelings about the shirt. I was determined not to let the thread win. It became A Thing. Some days I would wear it all day, doggedly ignoring how the thread jabbed at the back of my neck when I moved this way or that way. Other days I’d only make it to early afternoon before tossing the shirt in the laundry and changing–with a sigh of relief–into a more comfortable shirt. One with the tag cut cleanly out.
This went on for years. I wore the shirt in spite of how it made my neck itch and burn, in spite of the way it made me unconsciously pull at my collar all day long. I wore it right up until the day I admitted to myself that I was never going to get used to that thread. Putting my Hawaii shirt in the donation bag felt like a defeat. A thread–so small it was invisible–had gotten the better of me.
As you can probably guess from my willingness to torture myself with that shirt for several years, I can put up with a high level of physical discomfort. I can push myself through the fatigue and pain of running long distances. I can squeeze out another set in the gym or go at a heavy bag until I’m breathing so hard that I’m lightheaded.
But that thread–that was something else entirely.
It wasn’t until I learned about sensory sensitivities and sensory processing disorder that I understood why I couldn’t desensitize myself to the feel of the thread. Or to the tags in my clothes or lacy trim or any of a long list of tactile sensitivities. More importantly, I learned that I didn’t have to.
The Basics of Sensory Gating
Our brains are blessed with a function called sensory gating or sensory filtering. I like the visual metaphor that sensory gating evokes. At any given time, some “gates” are open to admit relevant sensory data; the rest are closed to keep out irrelevant sensory input. Which gates are open or closed is constantly being adjusted by our brains. For example, while I’m sitting here typing, the sound of the dog down the hall barking, the sirens out in the street, the rain hitting the window and the cars driving over that darn metal plate in the road are all irrelevant to me. Most people’s brains would note the lack of relevance and close those “gates”, preventing the unwanted sound from being a distraction.
In fact, a typical person would have had to stop typing and actively listen for those background noises to list them. My autistic brain, on the other hand, isn’t filtering any of them out so as I’m writing this post my brain is going “oh, it’s raining . . . wow, that dog is annoying . . . more traffic than usual going over the plate this morning . . . is that a fire truck or a police car or an ambulance.”
While I’m writing! Not between sentences or intermittently, but a constant stream of thought chugging along on a parallel cognitive track. Kind of amazing, isn’t it? And people say we can’t multitask.
And that’s just one set of sensory inputs. We’re also constantly being bombarded by the relevant and irrelevant data via our eyes, nose, mouth and skin. We receive millions of pieces of sensory data per second. A typical brain filters this incoming data, limiting the pieces of relevant information entering the brain for processing to the low thousands.
The processing of sensory data in the brain is complex and not entirely well understood, especially in the autistic brain, but here’s a simple explanation: After a piece of sensory data is allowed through the initial gate, it’s passed off to other areas of the brain for analysis and response. The sensory filtering system can pass on a piece of sensory data to either the prefrontal cortex, which is responsible for decision making and complex behavior, or the limbic system, which is often called the emotional brain and is also responsible for the “fight or flight response” to imminent danger.
The sensory filtering system, the decision-making part of the brain and the emotional brain work in concert, sending and receiving messages to each other to fine tune how our sensory filtering and processing system works. (More on how that works in a later section.)
The autistic brain filters incoming data, but we seem to have a relevancy problem. The sensory data that gets passed on for processing in our brain is a cacophony of relevant and irrelevant. Somehow, our brains not only allow irrelevant data through the gate and flag it for processing, they also fail to correctly prioritize a lot of what gets through. The result is things like background noise sounding just as loud (or louder than) a conversation we’re trying to have.
Atypical Sensory Processing
Most autistic people experience some form of atypical sensory processing. The DSM-5 acknowledged this by including hyper- or hypo-reactivity to sensory input in their revised criteria for ASD diagnosis.
Why atypical sensory processing happens isn’t entirely clear. We know what typical and atypical sensory processing look like, but we don’t know exactly why the two are different. There is strong evidence that the differences are neurological, meaning that the brains of people with atypical sensory processing are literally wired differently.
I have no idea how things in my brain are wired differently when it comes to sensory input. I can’t tell if it’s a problem with gating or with inhibition or with processing or prioritizing or filtering or feedback. The more I read about the neurological workings of the sensory system, the more places I find for things to go wrong.
But I do know how it feels to be wired differently.
From what I understand, typical people have a sensory processing system that operates like a fancy shower head. They can adjust the temperature and pressure and how the water flows until it’s just right. People with atypical sensory processing, on the other hand, have a fire hydrant valve where that shower head should be. We get lots of data, all at once, all the time. Adjusting the flow of data ranges from difficult to impossible to totally unpredictable.
And that’s why, no matter how hard I tried or how determined I was, I couldn’t get used to that thread in my shirt. That single thread was like a sensory fire hydrant and no amount of subjecting myself to it was going to change that.