Friday, 9 June 2006

Rare counting ability induced by temporarily switching off brain region

A minority of people with autism have one or more extraordinary intellectual talents, such as the rapid ability to calculate the day of the week for a given date, or to count large numbers of discrete objects almost instantaneously - they're often called 'autistic savants' or 'idiot savants'. Now Allan Snyder and colleagues have shown that by placing a pulsing magnet over a specific area of the brain, these kind of abilities can, to some extent, be induced in people who aren’t autistic.

Twelve healthy participants were given several chances to estimate, from 50 to 150, how many blobs appeared on a computer screen. The blobs appeared for just 1.5 seconds, and the number of blobs changed on each attempt. Remarkably, the performance of ten of the subjects improved drastically after Snyder’s team applied 15 minutes of low frequency transcranial magnetic stimulation (TMS) to their left anterior temporal lobe, a brain region that’s been implicated in autistic people with rare counting and calcluating abilities.

For example, before the TMS, one participant had 20 goes at estimating the number of blobs onscreen, and each time she was more than 5 away from the true figure. Yet immediately after receiving the TMS, she made 6 out of 20 guesses that were within 5 blobs of the true figure. Before TMS, another participant scored 3 estimates out of 20 that were within 5 of the true figure, compared with 10 out of 20 immediately after the TMS.

The enhanced ability was gone within an hour, and moreover, no such improvements followed application of a sham version of the TMS that made all the same noises, but was applied only weakly over a different brain region. In fact, the participants’ performance deteriorated slightly in this condition.

The researchers think that by temporarily inhibiting activity in the left anterior temporal cortex, the TMS allowed the brain’s number estimator to act on raw sensory data, without it having already been automatically grouped together into patterns or shapes. In other words, they believe it caused the 'normal' brain to function more like an autistic 'savant' brain. “We argue that it removes our unconscious tendency to group discrete elements into meaningful patterns, like grouping stars into constellations, which would normally interfere with accurate estimation”, the researchers said. “By inhibiting networks involved in concepts, we may facilitate conscious access to literal details, leading to savant-like skills”.

Snyder, A., Bahramali, H., Hawker, T. & Mitchell, D.J. (2006). Savant-like numerosity skills revealed in normal people by magnetic pulses. Perception, 35, 837-845.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Update: Not all people who show the rare counting and calculating abilities discussed in this report are autistic. However, according to the source paper, most are.