Callosal effects of transcranial magnetic stimulation (TMS): the influence of gender and stimulus parameters.
Transcranial magnetic stimulation (TMS) of the motor cortex of one hemisphere (conditioning stimulus, CS) inhibits EMG responses evoked in distal hand muscles by a magnetic stimulus given at appropriate interval later over the opposite hemisphere (test stimulus, TS). The common interpretation attributes this effect to an inhibition produced at cortical level via a transcallosal route. The variability of cortical excitability as measured by the interhemispheric paired-pulse (PP) technique has been assessed in healthy subjects in order to compare sub- and supra-threshold intensity of CS (80% versus 120% of individual motor threshold, MT). Within- and between-subject variability relating, respectively, to interhemispheric and gender differences were also assessed. Results point to an efficacy of a magnetic CS on one hemisphere in inhibiting EMG responses of the abductor digiti minimi (ADM) stimulated by a TS delivered over the opposite hemisphere in a range of intervals centered at 12ms. These reductions were produced by the 120% suprathreshold CS, while the 80% subthreshold CS did not affect EMG responses. Females showed a higher transcallosal inhibition than males, suggesting gender differences in interhemispheric connectivity that concern the anterior half of the trunk of the corpus callosum.
De Gennaro
Luigi
L
Dipartimento di Psicologia, Sezione di Neuroscienze, Università di Roma La Sapienza, Via dei Marsi 78, 00185 Rome, Italy. luigi.degennaro@uniroma1.it
Bertini
Mario
M
Pauri
Flavia
F
Cristiani
Riccardo
R
Curcio
Giuseppe
G
Ferrara
Michele
M
Rossini
Paolo Maria
PM
D000328:Adult; D000704:Analysis of Variance; D003337:Corpus Callosum / Q000502:physiology*; D004574:Electromagnetic Fields; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D012727:Sex Characteristics