Slow transcranial magnetic stimulation, long-term depotentiation, and brain hyperexcitability disorders.

OBJECTIVE Many clinical syndromes in neuropsychiatry suggest focal brain activation. Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a method for selectively altering neural activity. METHOD Studies assessing effects of "slow" rTMS, administered up to once per second, in normal people and in those with pathological conditions are reviewed. The findings are compared with those of animal studies examining long-term depression and long-term depotentiation through direct electrical stimulation of cortical tissue. RESULTS Data suggest that slow rTMS reduces cortical excitability, both locally and in functionally linked cortical regions. Preliminary studies of patients with focal dystonia, epileptic seizures, and auditory hallucinations indicate symptom reductions following slow rTMS. Long-term depotentiation exhibits many features congruent with those of slow rTMS, including frequency dependence, spread to functionally linked cortical regions, additive efficacy, and extended duration of effects. CONCLUSIONS Slow rTMS offers a new method for probing and possibly treating brain hyperexcitability syndromes. Further studies linking slow rTMS to animal models of neuroplasticity are indicated.