I'll be darned.

How did that get discovered? It's like tapioca.

I read about this just a month or so ago on the Internet (can't remember the source, alas). The reason has to do with the wiring of the spinal cord. The complex set of impulses required to make either extremity (hand or foot) rotate can travel by only one pathway down the spinal cord. When you make your right hand rotate counter-clockwise by making the numeral "6," you're sending a "counter-clockwise rotate" message down the spinal cord, which overrides the "clockwise rotate" message being sent to the right foot.

I'll be darned, too.

I think the conflict resides in the motor cortex, not in the spinal cord. There are separate spinal nerves that innervate motor neurons of the arm and leg; the motor cortex where these commands are generated is not so segregated. But the point made by Christopher is still valid in one respect: The motor command in the cortex is an isomorphic representation of the physical motion. In other words, the collective neural activity there does travel from cell group to cell group in a clock- or counter-clockwise fashion.

A similar phenomenon is seen when you attempt to rub the tummy and pat the head at the same time. Motor commands, made of spatially isomorphic activity in the cortex, conflict with each other and make the task difficult. Its a lot easier, though, for someone whose corpus callosum (the bundle of nerve fibers between the brain's hemispheres) has been severed. Then, their hands can move independently of each other.

"...and there's nothing you can do about it."

(Is this proof that there may well be a gay gene, oj?)

By the way, it's even harder with the left hand/leg---but might that be because I'm right-handed/footed?

Wjy? Do their feet rotate the other way?

An experiment would take a half-dozen infants(say, less than 18-mos old.) Have them try this task as an exercise, comparable to throwing a ball or twisting a rotary handle, over a 2-3 yr period. They may develop the capacity. We typical adults have never diligently tried this, and it may be akin to the kittens who cannot see "45-degree-angled" straight lines because they were careful kept unexposed to such a scene during a critical developmental stage (for the case of the kittens, I seem to recall that unexposure at something like 30-to-40 days old.... would cause this sight deficiency.