Short-term memory performance with magnetic stimulation of the motor cortex

Whether transcranial magnetic stimulation of the motor cortex has an influence on memory was investigated. In a first experiment with 21 healthy volunteers six pronounceable nonsense words were visually presented, immediately followed by a magnetic stimulus. There were three blocks of stimulation with field intensities of 60, 80 and 100% (referring to a maximal intensity of 2 Tesla), each block comprising six magnetic stimuli and six nonsense words. After each block there was a free recall test and at the end another free recall trial as well as a multiple-choice recognition test for all 18 words. Eighteen subjects served as controls, undergoing the same procedure, except that the field intensity was zero. A significant but small reduction of short-term memory performance was observed only for 100% field intensity. In a second experiment with 16 subjects who had not participated in experiment I, the effect of 100% intensity cortical magnetic stimulation was compared with a control stimulation over the cervical spine. There was no difference in free recall or in the multiple-choice test between the sites of stimulation, suggesting that the difference in the 100% intensity block in experiment I was not due to a specific cortical effect of the magnetic field on memory function. With respect to the effect on memory functions, transcranial magnetic stimulation of the motor cortex is thought to be a safe method.