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It’s All in Your Mind: The feeling of ‘wetness’ is an illusion

This article is featured in this year's edition of 'The Best Australian Science Writing 2015', which can be purchased here.

Everything you experience is an illusion to some extent.

The light from your screen, the sound of your breathing, the ambient temperature of a room — you cannot experience these things directly because you are your brain, and your brain is currently housed in a bony isolation chamber with no contact to the outside world.

Your brain is in stark darkness inside your skull, yet you still see the light from your screen because of the light receptors in your eyes. Similarly, hairs in your ears help you to hear, and temperature receptors in your skin help you to detect temperature. Using these types of information, your body has evolved detection kits to help sense the outside world, to feed the brain accurate information about the environment.

There are temperature receptors all over your skin, although, they are more common on the hairy parts of your body. And all over your skin there are also ‘movement’ receptors to help you detect changes in pressure and texture (these are more concentrated in your hands and feet, non-hairy skin).

But what about the feeling of wetness? This seems to be a different case entirely, for there are no ‘wet’ receptors.

We can all agree on how important wetness/humidity is. Humidity governs the health of our skin, our lungs, and maybe our joints. Being wet can mean a sudden change in body temperature. And being wet is what sweating is all about; that is your body stopping itself from cooking to death.

A recent study published in the Journal of Neurophysiology discovered that humans cannot truly feel wetness. Since ‘wet receptors’ never evolved along our line in the family tree, our brains must compensate with other clever tricks.

The researchers used cold-wet, cold-dry, warm-wet, and warm-dry treatments on participants who had various receptor nerves blocked. The study found that the brain integrates information about temperature and contact with the skin in order to infer wetness.

They discovered that participants were more likely to feel wet if the liquid was cold than if it were warm. And if the participants had nerve blockers reducing movement sensitivity, they could only detect cold liquids as wet, not warm ones.

Once we process these two stimuli (heat and touch), we can cross-reference those feelings with past experiences to determine that we are indeed getting wet.

Even completely fabricated perceptions such as 'being wet' can feel so real that we'd never thought to question them before. Researchers point out that a nose-bleed, where the liquid is at body temperature, can go undetected till we are informed. And, dare I say it, the slow compression of hairs can be what alerts us to a pants wetting incident. Not that any of us can remember what that feels like, right?

 

Originally published at thinkinc.org.au on the 10th of April 2014

Feature photograph: Roswitha Siedelberg/Flickr/CC BY-NC-SA 2.0

Story source: Science Daily

Research paper: D. Filingeri, D. Fournet, S. Hodder, G. Havenith. Why wet feels wet? A neurophysiological model of human cutaneous wetness sensitivityJournal of Neurophysiology, 2014; 112 (6): 1457 DOI: 10.1152/jn.00120.2014