Rapid rate transcranial magnetic stimulation – a safety study

Abstract

We assessed the safety of repeated short trains (4 stimuli) of rapid-rate transcranial magnetic stimulation (rrTMS) over the left motor cortex 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 intensity of 5–10% above active motor threshold. We monitored EEG, and assessed aspects of neurological (balance, gait, two-point discrimination, blood pressure, pulse rate), cognitive (attention, memory, executive function) and motor function (speed of movement initiation and execution and manual dexterity) before and after the two blocks of rrTMS. EMG was also recorded from a number of hand, forearm and arm muscles contralateral to the site of stimulation. Two blocks of repeated rrTMS at 20 Hz and 5–10% above active motor threshold did not produce any adverse effects. Measures of neurological, cognitive and motor function showed no change following rrTMS. From the EMG recording there was evidence of increase in the amplitude of the motor evoked potentials (MEPs) recorded from the biceps in one subject during the first block of rrTMS, but this did not occur in the second block. A similar magnification of MEPs was also observed in another subject only during the second block of stimulation. When applied using parameters falling within published guidelines (Pascual-Leone et al., 1993; Pascual-Leone et al., 1994), 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 for the study of cognitive function as well as sensory or motor function.