The inhibitory connection between both primary motor cortices (M1), which is discussed to be mediated by corpus callosum pathways, was found to be deficient in schizophrenia patients [5]. One further study supported the idea of an altered interhemispheric connection, revealing a selectively impaired facilitatory connectivity between the left dorsal premotor cortex and the right M1 [34]. As a third disrupted interhemispheric pathway, the connection between right cerebellum and left M1 was shown to be deficient in schizophrenia patients [6], indicating a disrupted direct cerebellar-M1 connection or an abnormal cerebellar inhibitory output. A disturbed intrahemispheric connectivity between the right posterior parietal cortex (PPC) and the right M1 in schizophrenia patients has been reported, too [28]. Finally, a dysfunctional interhemispheric connection between the right premotor and left M1 was discovered with a plasticity inducting repetitive TMS [33].
