10/24/17: Your Predictive Brain…

…or Why You Can’t Tickle Yourself

Something you probably don’t know is that the technical terms for tickles were coined by two psychologists back in 1897. Knismesis is the prickly feeling you get when something (such as a loose thread or an insect) lightly brushes your skin. The sensation prompts you to brush or scratch the spot to get rid of whatever is causing it. The other type of tickling, gargalesis, is the one that causes you to laugh out loud, sometimes uncontrollably. The jury is still out on the evolutionary benefits of laughter as a response to gargalesis, but not for lack of studying the effect.

Tickling of either kind functions as an alert that lets you know something is touching your body. The reason you can’t tickle yourself is that one part of the brain involved in the tickling response, the cerebellum, is on to you. It knows what your own movements are, so it predicts the sensation.

According to Sarah-Jayne Blakemore, a research fellow at the Institute of Cognitive Neuroscience at University College London, the prediction of the cerebellum cancels the response of other brain areas. You don’t need to be alerted when you yourself are initiating the action.

Surfing Uncertainty

The main job of your brain is to make sure you survive. So it is wired to reduce risk by diminishing uncertainty. And it does that by working overtime to predict what’s going to happen next and determine how you should respond to it. Andy Clark, author of Surfing Uncertainty, says that our primary contact with the world…is via our expectations about what we are about to see or experience.

This is an efficient way to function in the world. If your brain wasn’t predictive, it would be completely preoccupied with trying to figure out what’s going on (what’s happening, what it means, and what you should do about it). There wouldn’t be much brainpower left for anything else. However, on the plus (?) side, with so much of your attention deployed elsewhere, you might have a better chance of being able to tickle yourself.


In its attempt to diminish uncertainty, your brain doesn’t waste resources responding to completely predictable stimuli. It focuses instead on novel—or unpredictable—stimuli.

Your brain generates multiple possible representations of what to expect in the environment. The representation with the smallest prediction error is selected. —Dirk De Ridder, Jan Verplaetse, and Sven Vanneste, Frontiers in Psychology, 4/30/13

Of course your brain doesn’t have access to all the information in the world. But it has to base the representations it generates on something. So how does your brain come up with its predictions? Well, the first thing it looks to is the model of the world it maintains of what is normal for you. Your mental model is the lens through which you (and your brain) view the world, and your brain updates it according to the accuracy of its predictions.

But your brain also takes two other sets of factors into consideration: interoceptive (internal) and exteroceptive (external) information. Interoception is sensitivity to stimuli originating inside your body, including blood sugar level, temperature, hunger, and thirst. Interoception gives your brain a feeling for how things are with you. Exterocepion is sensitivity to stimuli in the environment, such as where you are, who you’re with, what you see, and the speed at which you’re operating your vehicle. Exteroception provides your brain with information about what’s happening around or to you.

How things are with you can influence the type of information your brain seeks to get from the external world. If you’re traveling and you’re hungry, it will pay more attention to restaurants because where and when to eat is salient to you in the moment. If you’re traveling and you just finished a meal, eating won’t be salient. Vice versa, if you’re in a restaurant, your brain will consider how hungry you are—among other things—to predict what you’re going to order.

Your brain is constantly weighing and calculating multiple internal and external factors to arrive at its predictions—all within the context of what is normal for you—and then preparing your response. What are you going to do next? You might be the last to know.

At the next MONTHLY MEETING OF THE MIND (& BRAIN), we’ll uncover how having a predictive, rather than a reactive, brain makes life as you know it—both good and bad—possible. If you’re in the area and can join us, please do.

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