Wednesday, 10 December 2014

Trans-Cranial Magnetic Stimulation and the Curled-Cat and Bristly-Scottie Drawings of Allan Snyder's Subjects

I thought I'd say some more about trans-cranial magnetic stimulation (TMS) and drawing, which I mentioned here. The paper that got me interested is "Savant-like Skills Exposed in Normal People by Suppressing the Left Fronto-Temporal Lobe", Journal of Integrative Neuroscience, 2, 2, 2003, by Allan Snyder and colleagues. The cat and dog drawings shown at the top of page 4 excited me, and I'll explain why next.

Many art teachers say that novices draw objects "symbolically", usually showing the object's main parts, from a point of view that makes them instantly recognisable. Novices often draw objects "flat" as well, side-on or face-on. Well-known examples are spectacles drawn as a pair of circles, and trees drawn as a trunk with branches sticking out flat on either side.

That's true of the non-TMS cats drawn by Snyder's subject N.R. and the dogs drawn by A.J. But what excites me is that under TMS, N.R.'s cat changed from side-on to curled round on itself. That's a complicated posture that many novices probably wouldn't be able to recall, and wouldn't dare to draw even if they could. Was the TMS somehow causing N.R. to access a previously inacessible memory?

Likewise with A.J.'s dogs. Because of foreshortening, a dog's muzzle is difficult to draw face-on. But something has prompted A.J. to do so under TMS, and perhaps even to draw the bristles around the muzzle receding back into the distance.

What has this to do with TMS? Snyder hypothesises that savants' remarkable skills are innate, rather than arising through intensive practice or greater development of parts of the brain. These skills, he says, work by accessing low-level information that's in everyone's brains — in the case of drawing savants such as Stephen Wiltshire, an analogue representation of the visual field. Normal people can't access such information, but savants can because of their brain impairments, so if we can simulate these impairments via TMS, perhaps we can induce savant skills in normal people.

Snyder doesn't go into detail about the neural mechanisms, and some neuroscientists I've spoken to have criticised him for this. But I think this research needs to be regarded in the same way as the discovery of drugs such as opium and digitalis. The mechanisms may not be known, but it's obvious that something interesting and useful is happening, and that it's worth working out how to enhance it.

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