Hack5.Transcranial Magnetic Stimulation: Turn On and Off Bits of the Brain

Hack 5. Transcranial Magnetic Stimulation: Turn On and Off Bits of the Brain

Stimulate or suppress specific regions of the brain, then sit back and see what happens.

Transcranial magnetic stimulation (TMS) isn't an imaging technique like EEG [Hack 2] or fMRI [Hack #4], but it can be used along with them. TMS uses a magnetic pulse or oscillating magnetic fields to temporarily induce or suppress electrical activity in the brain. It doesn't require large machines, just a small device around the head, andso far as we knowit's harmless with no aftereffects.

Neurons communicate using electrical pulses, so being able to produce electrical activity artificially has its advantages. Selected regions can be excited or suppressed, causing hallucinations or partial blindness if some part of the visual cortex is being targeted. Both uses help discover what specific parts of the brain are for. If the subject experiences a muscle twitching, the TMS has probably stimulated some motor control neurons, and causing hallucinations at different points in the visual system can be used to discover the order of processing (it has been used to discover where vision is cut out during saccades [Hack #17], for example).

Preventing a region from responding is also useful: if shutting down neurons in a particular area of the cortex stops the subject from recognizing motion, that's a good clue as to the function of that area. This kind of discovery was possible before only by finding people with localized brain damage; now TMS allows more structured experiments to take place.

Coupled with brain imaging techniques, it's possible to see the brain's response to a magnetic pulse ripple through connected areas, revealing its structure.

1.6.1. Pros

• Affects neural activity directly, rather than just measuring it.

1.6.2. Cons

• Apparently harmless, although it's still early days.

1.6.3. See Also

• "Savant For a Day" by Lawrence Osbourne (http://www.nytimes.com/2003/06/22/magazine/22SAVANT.html or http://www.cognitiveliberty.org/neuro/TMS_NYT.html, an alternative URL), an article in the New York Times, which describes Lawrence Osborne's experience of TMS, having higher-level functions of his brain suppressed, and a different type of intelligence exposed.

Myles Jones & Matt Webb