Repetitive TMS applied to the motor cortex can reproducibly increase or decrease cortical excitability, as measured by thumb muscle movement amplitude.

“And the other group right upstairs at the National Institute for Neurological Diseases and Stroke, NINDS, they were looking at using TMS, which had been around for 10 years, and repetitively stimulating in motor cortex. And what they found was, gosh, we can get a readout in thumb muscle movement amplitude that's really reproducible across people. It's like, you know, universally reproducible. And if we do certain stimulation approaches, they are biologically active to either increase excitability, IE the thumb motion, and a set intensity goes up, the amount of amplitude goes up, or inhibitory or depotentiating, it goes down with other biological stimulation approaches.”