Transcallosal inhibition and motor conduction studies in patients with schizophrenia using transcranial magnetic stimulation

Background Transcranial magnetic stimulation of the motor cortex may not on ly elicit excitatory responses in hand muscles contralateral to the stimula ted hemisphere, but may also suppress tonic voluntary electromyogram activi ty in muscles ipsilateral to the stimulation. This inhibition is mediated b etween the motor cortices via the corpus callosum. Aims To investigate motor excitability and interhemispheric (transcallosal) connections in patients with schizophrenia. Method Transcallosal inhibition and motor conduction parameters were invest igated in ten patients with schizophrenia and in ten age- and gender-matche d healthy subjects. Results Transcallosal conduction time (TCT) and duration of the inhibition were significantly longer in patients with schizophrenia (mean (s.d.)):TCT, 12.4 (2.9) ms in normal subjects and 15.3 (2.6) ms in patients(P=0.03); me an duration, 34.1 (4.9) ms in normal subjects and 51.9 (16.8) ms inpatients (P=0.01). Conclusions Magnetic motor conduction parameters are unaltered in schizophr enia, but transcallosal inhibition is significantly delayed and prolonged. This may indicate abnormal function of the corpus callosum in these patient s. Declaration of interest Grants received from the Deutsche Forschungsgemeins chaft and the University Hospital, Aachen, Germany.