Do you know why you can't tickle yourself, Dave? Kind of. Surprise is a part of it, right? That we don't know when it's going to happen and for how long. You know, if we could actually tickle ourselves, how crazy would it be to accidently tickle myself and start laughing hysterically. Oh man, that would be weird.

So, you're right, surprise is lost when we touch ourselves, but also, our brains reduce the sensitivity we feel in that patch of skin. Strange, right? Yeah. And in this study, healthy volunteers were asked to lay in an fMRI machine which can record images of brain activity. People either stroked their own arms or were stroked by researchers in the same way and brain images would reveal if the brain processed them differently.

With self-touch, activity in several parts of the brain was reduced compared to touch by someone else. And amazingly this difference in reactions started in the spinal column even before the brain had processed the signals. That's similar to our ability to process what we see as soon as an image hits the retina. This study supports a theory in brain research that suggests the brain tries to predict the sensory consequences of our actions.

So, here the brain seems to play down sensory perceptions from our own bodies and play up its expectation of the sensation from someone else. For example, in another experiment, a person's arm was touched with filaments of varying thickness while self-stroking or being stroked by someone else. Again, the brain played down sensations of self-stroking.

So now if your kids ask why they can't tickle themselves you have some answers, although they're likely to roll their eyes sometime partway into your explanation.