P 104. Transcranial direct current stimulation reveals overshooting LTP-like motor cortex plasticity in schizophrenia: A study in antipsychotic-free patients

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Background In schizophrenia, dysfunctional long-term potentiation (LTP) like plasticity has been demonstrated using paired associative stimulation (PAS), transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) of the motor cortex (Hasan et al., 2011). However, the majority previous studies have investigated patients receiving antipsychotic medication, and psychopharmacological treatment may significantly alter motor cortex excitability (Nitsche and Paulus, 2011). Thus, this pilot study investigates tDCS-induced non-focal plasticity in schizophrenic patients who are free of antipsychotic medication. Methods A combined tDCS-motor evoked potential (MEP) paradigm was used to measure non-focal neuronal plasticity in 15 patients with schizophrenia (DSM-IV) compared to 15 healthy subjects matched for age and gender. All patients were free of psychotropic drugs apart from benzodiazepines. Anodal tDCS (2mA, 20min) was applied over the left M1 area with the cathode placed over the right supraorbital region. MEPs were recorded at baseline and for further 120min following tDCS. All patients underwent antipsychotic treatment and were followed by a second measurement at week 4. Results Repeated measures ANOVA revealed increased MEP amplitudes (df=1, F =5.93, p =0.021) following anodal tDCS. At week 4, this difference was even more pronounced (df=1, F =12.04, p =0.002). Moreover, significant correlations were found between MEP amplitudes and negative symptoms as measured with the Positive and Negative Syndrome Scale (PANSS) as well as the duration of inpatient treatment. Conclusion Non-focal motor cortex plasticity was altered in schizophrenic patients compared to healthy subjects-also in patients undergoing four weeks of antipsychotic pharmacotherapy. However, our findings differ from previous studies and replication trials are warranted to clarify this discrepancy which may not only be due to the lack of concomitant antipsychotic medication in the current study.