Why you can't TICKLE yourself and what it has to do with Chronic STRESS

Have you ever wondered why you can’t tickle yourself, no matter how hard you try? It’s one of those fascinating peculiarities of human biology that has puzzled scientists for decades.

While the simple answer might be that your brain knows what’s coming, the full story delves deeper into the mechanisms of predictive processing, a foundation of how our brains make sense of the world.

But what if this mechanism starts to falter? And what could chronic stress have to do with it? Let’s get curious.

The science of tickling

Tickling is a universal experience found not only in humans but in primates as well. It often evokes uncontrollable laughter or squirms of discomfort as we wriggle to get free of our tickler. Scientists have classified it into two types

- knismesis (a light, itching sensation) and

- gargalesis (the laughter-inducing tickling).

However, the real intrigue lies in why we can’t stimulate the same reaction by tickling ourselves.

Research has revealed that the answer lies in how the brain predicts and processes sensory input. Yes, that’s right, people have actually studied this in experiments!

When another person tickles us, the sensation is unexpected and unpredictable, which makes it funny or uncomfortable. But when we attempt to tickle ourselves, the brain’s predictive mechanisms dampen the response. These predictions are generated by what neuroscientists call the "efference copy," a neural signal that allows the brain to anticipate the sensory consequences of our own movements.

Essentially, your brain knows you’re about to tickle yourself and filters out the sensation as unimportant.

In studies by researchers like Sarah-Jayne Blakemore and others, it’s been shown that the suppression of self-tickling involves areas of the brain such as the cerebellum and somatosensory cortex. These findings highlight how predictive processing not only makes tickling a social experience but also plays a vital role in how we perceive and interact with the world.

What is predictive processing?

Predictive processing is a theory of brain function that suggests the brain is essentially a prediction machine. At its core, the brain continuously generates predictions about incoming sensory information based on past experiences. These predictions are compared to the actual sensory input, and any mismatch (known as a "prediction error") prompts the brain to update its model of the world.

This process happens at lightning speed and governs everything from recognising faces to catching a ball. For example:

• When you hear footsteps behind you, your brain predicts their source based on the context.
• When you reach for a cup, your brain predicts the sensory feedback of holding it.
• Even your ability to understand speech depends on the brain predicting the words as they are spoken.

Predictive processing allows us to navigate the complexities of daily life with remarkable efficiency. It minimises sensory overload by filtering out expected information and highlighting unexpected inputs that may require attention.

The impact of chronic stress on predictive processing

While predictive processing is a marvel of the evolution of our brain, it is not immune to disruption. Chronic stress, a far too common condition in today’s society, can significantly impair this delicate system. Stress floods the brain with cortisol, a hormone that, in excessive amounts, can damage neural circuits involved in prediction and error correction.

Here are some ways chronic stress affects predictive processing

1. Reduced accuracy - Chronic stress can impair the brain’s ability to generate accurate predictions. This might lead to sensory overload or misinterpretation of stimuli, making the world feel more chaotic and less predictable. (Cue chronic stress loop)
2. Heightened Sensitivity - Stress often heightens sensitivity to sensory inputs, as the brain shifts into a hyper-vigilant state thanks to cortisol and its friend adrenaline. This can amplify everyday annoyances or create a sense of unease.
3. Difficulty in adaptation - Stress hinders the brain’s capacity to update predictions when confronted with new information, resulting in rigid thinking or increased anxiety when things don’t go as planned.
4. Emotional dysregulation - The emotional brain regions, such as the amygdala, become overactive under stress, disrupting the balance between prediction and emotional responses. This can lead to feelings of being overwhelmed or out of control.

Could self-tickling be a warning sign?

Now, here’s what got me curious.

What if you started being able to tickle yourself? Could this be a subtle indicator that something is off with your predictive processing machinery?

While there’s no definitive research linking self-ticklishness to stress, it’s worth considering how predictive processing failures manifest in everyday life.

If the brain’s ability to filter self-generated sensations becomes impaired, it might suggest that chronic stress or other factors are disrupting normal neural functioning.

This hypothetical connection might prompt us to reflect on our mental health. If you find yourself more easily startled, overly sensitive to stimuli, or even able to tickle yourself, it might be time to assess your stress levels and take steps to manage them.

Managing stress to support brain health

Fortunately, there are many ways to reduce stress and support the brain’s predictive abilities and there are loads of peer reviewed studies on the effectiveness of the following methods.

• Mindfulness practices - Techniques like meditation can help calm the mind and improve the brain’s ability to process sensory information.
• Physical activity - Exercise reduces cortisol levels and strengthens neural connections.
• Adequate sleep - Sleep is essential for memory consolidation and prediction updating.
• Diet - A balanced diet supports optimal brain function and reduces inflammation.
• Therapeutic interventions - Cognitive-Behavioural Therapy (CBT) can help retrain the brain’s predictive models by addressing negative thought patterns.

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It’s important to acknowledge that we are all neurodiverse. Each of us processes information and predicts the world in slightly different ways. This diversity is not a flaw but a strength, fostering creativity, innovation, and resilience.

While predictive processing is a universal brain function, its nuances vary from person to person. Embracing these differences allows us to better understand ourselves and others, creating a richer, more inclusive society.

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The inability to tickle yourself is more than an odd biological fact, it’s a window into the incredible predictive machinery of the brain.

By understanding how predictive processing works and how stress can disrupt it, we can gain some valuable insights into the interplay between mental health and sensory perception.

So, the next time you laugh uncontrollably at someone else’s tickles, remember…

Your brain is working exactly as it should. And if you ever start to tickle yourself, perhaps take it as a gentle reminder to check in on your mental well-being. After all, a healthy brain is the key to a curious and fulfilling life.

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Stay Curious!

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Mark