Effect of transcranial magnetic pulses on cortical network connectivity in schizophrenia

Transcranial magnetic stimulation (TMS) pulses applied to the cortex induce dynamic changes in brain network activity. These changes are useful for the in vivo study of functional connectivity, which may be characterized with the application of network parameters to the pre-stimulus (i. e., baseline) and the post-stimulus (i. e., response) of TMS-mediated electroencephalographic (EEG) recordings. These measures may be altered in schizophrenia, so we hypothesized a basal hyperactive network associated to hypomodulation with TMS in patients.

Twenty-six schizophrenia patients and 26 healthy controls were subjected to TMS pulses during an EEG recording in order to assess the effect on connectivity strength (CS), a parameter summarizing the global EEG synchrony of the cortical network at baseline and its TMS-evoked modulation.

Patients showed a higher baseline CS in all bands except gamma. In controls, TMS increased CS in all bands, more notably on beta and gamma. In comparison to controls, patients showed a lower baseline-to-response multiband activity increase of CS, and significantly lower CS modulation values in the gamma band with TMS pulses. No relationships were found between these measures and antipsychotic dose or other clinical and cognitive variables.

In the context of evidence supporting an inhibitory deficit in schizophrenia, these results may reflect the functional consequences of an inhibitory/GABAergic deficit in the cortex in this syndrome.