A recent study combining TMS with simultaneous EEG also showed intriguing network pathology in schizophrenic patients (Ferrarelli et al., 2008). The authors applied single TMS pulses to the right premotor cortex, and assessed differences in the resulting TMS-evoked potential between schizophrenic patients and healthy controls. They found that the total brain activation evoked by TMS, as measured via the global mean-field power, was significantly decreased for schizophrenic patients between 12 and 100ms after each stimulus pulse, with the maximum decrease occurring at the peaks of two TMS-evoked gamma oscillations, 22 and 55 ms after the TMS pulse. In schizophrenic patients, the amplitude of these peaks was significantly reduced in a subset of frontocentral electrodes (Figure 11). The authors then demonstrated that this decrease was due to both decreased amplitude and decreased phase-locking of the TMS-evoked gamma activity. Using source analysis techniques the authors demonstrated that in healthy subjects, the current maxima shifted rapidly from premotor cortex to right sensorimotor cortex and then left premotor and sensorimotor regions, whereas, in schizophrenic patients, cortical activation was more localized, shifting slowly between premotor
