RAPID RATE TRANSCRANIAL MAGNETIC STIMULATION - A SAFETY STUDY

We assessed the safety of repeated short trains (4 stimuli) of rapid-r ate transcranial magnetic stimulation (rrTMS) over the left motor cort ex in 6 healthy normal subjects. rrTMS involved two separate blocks of 50 consecutive trains of 4 stimuli at a frequency of 20 Hz and an int ensity of 5-10% above active motor threshold. We monitored EEG, and as sessed aspects of neurological (balance, gait, two-point discriminatio n, blood pressure, pulse rate), cognitive (attention, memory executive function) and motor function (speed of movement initiation and execut ion and manual dexterity) before and after the two blocks of rrTMS. EM G was also recorded from a number of hand, forearm and arm muscles con tralateral to the site of stimulation. Two blocks of repeated rrTMS at 20 Hz and 5-10% above active motor threshold did not produce any adve rse effects. Measures of neurological, cognitive and motor function sh owed no change following rrTMS. From the EMG recording there was evide nce of increase in the amplitude of the motor evoked potentials (MEPs) recorded from the biceps in one subject during the first block of rrT MS, but this did not occur in the second block. A similar magnificatio n of MEPs was also observed in another subject only during the second block of stimulation. When applied using parameters falling within pub lished guidelines (Pascual-Leone el al., 1993; Pascual-Leone et al., 1 994), repeated rrTMS is a relatively safe technique in healthy normal subjects. As rrTMS allows disruption of cortical function for a longer period, it has the potential of becoming a particularly useful tool f or the study of cognitive function as well as sensory or motor functio n. (C) 1997 Elsevier Science ireland Ltd.