Cortical excitability is modified in schizophrenia  but the effect of antipsychotic drugs has been disputed. In particular, patients receiving olanzapine and risperidone showed less cortical disinhibition compared to untreated schizophrenic subjects . However, despite the observed increase, the Resting Motor Threshold (RMT) remained inferior to the RMT in normal controls, and the Transcallosal Conduction Time (TCT) did not change.
There is no comparative study of the effect of clozapine, an effective antipsychotic with proconvulsant properties.
We studied cortical excitability by transmagnetic stimulation in stabilized schizophrenic patients treated by clozapine (n=10), olanzapine (n=10) compared to healthy volunteers (n=10).
The aim of this study was to extend previous research into inhibitory deficits in schizophrenia and to compare the effect of clozapine and olanzapine on neurophysiological parameters such as RMT, Intracortical Inhibition (ICI), Intracortical Facilitation (ICF), Cortical Silence Period (CSP) and Transcallosal Inhibition (TI).
In clozapine treated patients, the RMT and ICI were significantly lower (p<0.05) compared to olanzapine treated and healthy subjects. TCT was longer in schizophrenic patients without difference in treatment subgroups.
The trend toward normalization of RMT and ICI with antipsychotic treatment seems to be independent of the magnitude of therapeutic effect.