Wednesday, June 26, 2013

Electrically Shocking Your Brain Enhances Cognition, Somehow

For those of us wishing to improve our cognitive abilities without having to deal with a concomitant host of unpleasant hobgoblins, including patience, perseverance, industry, toil, thrift, caloric restriction, abdominal exercises, and master cleansing, science has once again come to the rescue. In place of the boredom and the loneliness and the indignity of solitary study, we can instead improve our minds by zapping localized patches of cerebral cortex with small electrical currents, which to me seems conceptually similar to sticking a fork in an electrical socket. This technique is known as transcranial magnetic stimulation, or TMS.

There is a TMS facility at my university, although I have only observed it done to others. From what I could tell, the real payoff occurred when the experimenter was able to position the TMS coils just right so that when the unit was turned on, the subject's finger moved a couple of centimeters, as though jerked by an invisible string. I didn't fully appreciate its significance at the time, although I later learned how it could be used to establish which regions were necessary to carry out specific processes, and how disruption of activity in one area of the brain could either up- or down-regulate functions in other areas.

However, far from being only used to disrupt neural communication, several experiments have shown that TMS can be used to enhance neural functioning, and, by extension, possibly improve skill acquisition and memory retention. Although TMS is designed to depolarize neurons and induce neural firing, different frequencies of TMS can lead to markedly different results; and even within the same frequency, different results can be induced from applying the same frequency to different regions and during different tasks. For example, a 5 Hz TMS pulse over the dorsolateral prefrontal cortex disrupts performance in a delayed match-to-sample task, while the same frequency applied to the midline parietal cortex increased performance.

One theoretical framework for how TMS can improve performance is that of addition-by-subtraction, in which cognitive functioning is enhanced through disruption of competing cognitive processes. For example - and to use extremely simplified cortical representations - let's say that a participant is shown a series of emotional and fearful men's and women's faces and is asked to categorize each face as male or female. TMS is then used to disrupt the emotional part of the brain (again, extremely simplified example), which prevents the processing of extraneous, competing emotional information to interfere with the task. The participant thus becomes faster and more efficient at categorizing the face by gender.

An excellent review of these techniques and other issues related to TMS can be found in the new issue of Neuroimage in an article by Luber & Lisanby, found here. Obviously, it is only a small series of steps before we install public TMS facilities that look like huge futuristic salon hairdryers which can be used for an array of cognitive enhancing techniques, such as mathematical reasoning, crossword puzzle solving, and remembering your girlfriend's birthday.

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