Modulation of input-output curves by low and high frequency repetitive transcranial magnetic stimulation of the motor cortex.
OBJECTIVE
Exploring the modulatory effects of different frequencies of repetitive transcranial magnetic stimulation (rTMS) on the excitability of the motor cortex as measured by the input-output curve technique (I-O curve).


METHODS
Sixteen healthy subjects participated in this experiment. On two different sessions, conducted 1 week apart, rTMS was applied either at a frequency of 20 or 1 Hz at 90% of individual motor threshold (MT) for a total of 1600 pulses each. Before and after rTMS, the cortical excitability was assessed by measuring MT and the size of motor evoked potentials (MEPs) collected at different intensities of stimulation.


RESULTS
The analysis on the whole population showed a significant decrease of cortical excitability after 1 Hz rTMS and an increase after 20 Hz rTMS. A subsequent cluster analysis pointed out the presence of two distinct groups of subjects with opposite responses at the same frequency of stimulation. Significant variations on MT were found for both groups only for the facilitatory effect irrespective of the frequency of stimulation.


CONCLUSIONS
The results provide further insight into interindividual differences in the effects of rTMS and suggest the existence of subpopulations with specific patterns of response to rTMS.
Laboratory for Magnetic Brain Stimulation, Division of Behavioral Neurology, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Massimo
M
Gangitano
Antoni
A
Valero-Cabré
José Maria
JM
Tormos
Felix Manuel
FM
Mottaghy
Jose Rafael
JR
Romero
Alvaro
A
Pascual-Leone
D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation