Cortical excitability in schizophrenia

Abstract

Abnormalities in brain plasticity, including abnormal information processing by disturbed cortical inhibition and facilitation in schizophrenia, have been described several times in the past. Transcranial magnetic stimulation (TMS) provides a neurophysiological technique for the measurement of cortical excitability, especially of the motoneural system. With TMS it is possible to explore important aspects of the pathophysiological mechanisms underlying schizophrenia using recently developed paradigms (paired pulse method, cortical silent period). This review summarizes the results of available diagnostic TMS studies in schizophrenia. Studies investigating the efficacy of therapeutic repetitive magnetic stimulation in patients with treatment resistant hallucinations or predominantly negative symptoms were not considered. The reviewed studies support the assumption of reduced cortical inhibition, probably caused by GABAergic deficit, in schizophrenia. Factors influencing the study results, the limitations of this promising technique in schizophrenia, and further research options are discussed.

The impact of NMDA receptor hypofunction on GABAergic neurons in the pathophysiology of schizophrenia

“…Electrophysiological findings provide additional support for a link between NMDA and GABA in schizophrenia, as reduced NMDAR-dependent inhibitory drive results in the increased excitability that characterizes schizophrenia (Wobrock et al, 2007). In the cortical slice preparation, exposure to MK-801 reduces inhibitory post-synaptic currents (IPSCs) on pyramidal neurons (Li et al, 2002).…”

Veränderung der kortikalen Inhibition und Fazilitation bei Patienten mit einem Risikostadium für eine Schizophrenie im Vergleich mit Schizophrenie-Ersterkrankten und gesunden Kontrollprobanden.

“…Der Wert wird in Prozent angegeben und entspricht der geringsten Reizstärke, die benötigt wird, um ein motorisch evoziertes Potential (MEP) mit einer Amplitude ~ 50 µV in mindestens fünf von zehn Reizen auszulösen(Rossini et al 2015; Siebner und Ziemann 2014). Die motorische Schwelle lässt sich auf zwei Wegen bestimmen: die RMT (resting motor threshold), die im ruhenden Zustand ermittelte Schwelle, sowie die AMT (active motor threshold), die im voraktivierten (mit etwa 5 -10% der maximalen Kraft) Muskel abgeleitet wird(Wobrock et al 2007). Triggs et al berichten 1999 über Unterschiede zwischen beiden Hemisphären.…”