title: Callosal effects of transcranial magnetic stimulation (TMS): the influence of gender and stimulus parameters.
abstract: 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.
authors.affiliation: Dipartimento di Psicologia, Sezione di Neuroscienze, Università di Roma La Sapienza, Via dei Marsi 78, 00185 Rome, Italy. luigi.degennaro@uniroma1.it
authors.forename: Luigi
authors.initials: L
authors.lastname: De Gennaro
authors.forename: Mario
authors.initials: M
authors.lastname: Bertini
authors.forename: Flavia
authors.initials: F
authors.lastname: Pauri
authors.forename: Riccardo
authors.initials: R
authors.lastname: Cristiani
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Curcio
authors.forename: Michele
authors.initials: M
authors.lastname: Ferrara
authors.forename: Paolo Maria
authors.initials: PM
authors.lastname: Rossini
mesh_terms: 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