One of the reporters for Wired took part in an experiment that combines several key neuroscience technologies to pinpoint a brain area, switch it off, and measure the effects.
TMS is a technique that allows parts of the brain to be safely and temporarily shut down or stimulated for a few hundred milliseconds. It’s particularly useful because it allows you to be sure that the function of a brain area is involved in causing a particular behaviour.
Brain scans only allow you to see if an area is associated with a behaviour. The brain area might be reliably active when something important is in progress, but like a car radio, it might not actually be driving the outcome.
However, if you guess that an area is part of the cause, you can use TMS to change its function while the behaviour is in progress. If the behaviour changes, you know the brain area is involved.
Often, the brain area is chosen because it is commonly associated with that behaviour. The trouble is, each person varies slightly.
Doing an fMRI brain scanning experiment first will tell you exactly where activity occurs, so later on, you can use TMS to target the spot more precisely in each individual.
While using TMS to alter the function of a brain area, researchers can also use EEG to see the physiological effect of the stimulation. As well as seeing the behavioural outcome, you can also see it’s effect on the wider brain networks.
Combining these techniques is becoming increasingly common in cognitive neuroscience.
Some recent studies have even used TMS when people are lying in fMRI scanners using magnetic coils made of non-ferrous materials so as not to be dangerous in the powerful scanner magnet.
My favourite one is a recent study where they used TMS to trigger ‘movement’ in a phantom limb by stimulating the motor cortex. They then measured the brain activity linked to movement in the non-existent hand.