Saturday, 23 March 2013

Acquired savantism: can tDCS make you a genius?


Allan Snyder's THINKING CAP

The real 'Rain Man'

The extraordinary abilities of 'savants' became part of popular culture thanks to the film 'Rain Man'.  Dustin Hoffman's character was inspired by Kim Peek, who was born without the corpus callosum (which connects the left and right hemispheres).

Peek was able to read two pages of a book simultaneously (one page with each eye) in eight seconds, and commit them to memory with 98% accuracy. He could recall more than 12,000 books in their entirety, and he accurately summed columns of phone numbers from the phone book.

Peek was not mentally retarded or autistic, but was unable to master basic life skills. A technical consultant on 'Rain Man', Darold Treffert, MD, researched this condition for nearly 50 years, developing the theory that savant syndrome characteristically consists of left-hemisphere dysfunction combined with right-hemisphere emergence. In other words, without the restrictions imposed by the left-brain, the right-brain is free to dazzle.


Acquired Savant Syndrome

Thirty-odd cases of acquired savant syndrome are known, where neurologically normal people suddenly exhibit prowess in art, mathematics, or memory after suffering brain damage.   Jason Padgett,  beaten by muggers, can now draw fractals (the only person in the world with this ability), and claims to have discovered a mistake in Pi. Jon Sarkin, a 35-year-old chiropractor who suffered a brain hemorrhage and stroke , became obsessed with creating art: his work typically sells for five-figure sums.

 Dr Bruce Miller  noticed that some of his elderly dementia patients displayed a gradual improvement in new artistic skills as their neurological decline progressed. He noted that the damaged regions were associated with linguistic and higher-order processing, and social norms. These elderly people shared with born-savants a compunction to exercise their particular skill, as well as marked deficiencies in social and language behaviours.

Miller examined autistic savants using single-photon-emission computed tomography (SPECT) and discovered that the impairment of the anterior temporal lobes of the left hemisphere in these scans was the exactly the same as the scans of his fronto-temporal dementia patients.

Miller concluded that the areas of the brain that are damaged have been inhibiting 'latent abilities' that were always present. Kapur (1996) used the term "Paradoxical functional facilitation", noting that "in normal subjects, inhibitory and excitatory mechanisms interact in a complex harmony. ... The role of inhibitory processes may be critical in mediating specific restorative paradoxical functional facilitation effects".

The Thinking Cap

Allan Snyder, neuroscientist at the University of Sydney, used transcranial direct current stimulation (tDCS) to temporarily impair the area of the brain that was damaged in Miller's savant-like dementia patients. He found that 40% the volunteers were able to solve the 'nine dots problem' after receiving the tDCS, where none of them had been able to solve it before.

Snyder maintains that the results confirm the left-brain dominance hypothesis, that abilities are able to emerge when the brain areas that are normally controlled by the brain region that filters sensory input into pre-existing categories (schema that have been learned) have become 'unfettered'.

Or is it chemistry?

Berit Brogaard, a neuroscientist and philosophy professor at the Center for Neurodynamics at the University of Missouri-St Louis, thinks that dying brain cells release neurotransmitters that rewire parts of the brain, creating new neural pathways into previously unreachable regions:

"Our hypothesis is that we have abilities that we cannot access. Because they are not conscious to us, we cannot manipulate them. Some reorganization takes place that makes it possible to consciously access information that was there, lying dormant."

Brogaard's work with Jason Padgett (the man who draws Pi) revealed damage in the visual cortex areas associated with detecting motion and boundaries. She found hyperactivity in the parietal cortex (regions associated with new visual images, mathematics, and action planning), areas adjacent to those that had suffered the damage, and able to benefit from the neurotransmitters that had been released from the damaged cells.


Reference
Kapur, N. (1996) Paradoxical functional facilitation in brain-behaviour research. A critical review. Brain, 119, 1775-1790


1 comment:

  1. We've all heard the pseudoscience claim that we only use 10% (or some other small amount) of our brain. The best answer I heard to that was to ask the person making the claim which part of his/her brain they were willing to have removed? In any case, doesn't the remarkable abilities of some of these people make you wonder how it is that they had such amazing abilities that were totally unknown to them until they were revealed by a freak accident?

    There's a fascinating account of what it's like to have your corpus callosum severed here:

    http://www.ted.com/talks/jill_bolte_taylor_s_powerful_stroke_of_insight.html

    Given this woman's credentials I take her insights very seriously - and they are truly awesome. Her "trip" where she zoned in and out normal consciousness seems to confirm the availability of normally unknown perception where she claimed to have experienced nirvana. When I was 9 I almost drowned and I distinctly remember the moment when I thought I was going to die - at that moment I felt the exact same release, but none of her universal consciousness.

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