P 5. Motor cortical excitability in psychiatric disorders probed by transcranial magnetic stimulation: A systematic review

Abstract

Introduction Since many years, transcranial magnetic stimulation (TMS) has been used to probe cortical physiology in awake humans. In particular, single-and paired-pulse TMS-protocols applied to the human motor cortex allowed the exploration of various intracortical inhibitory and facilitatory networks. In psychiatry, TMS offers the possibility to access motor-cortical excitability and to link the findings to possible neurotransmitter alterations with regard to the investigated disorder. However, little is known about general patterns of cortical excitability across psychiatric disorders. Objectives We aimed to review the evidence for impaired cortical excitability in psychiatric disorders using TMS. Methods A systematically literature research for this review was conducted via the internet database PubMed (1985–2012) using predefined search-algorithms. This search offered 684 publications in total. After screening of the abstracts and careful review of the content by two independent researchers with regard to the objectives of this review, a number of 82 publications was considered to be suitable. Results Most studies (n = 20) investigated the effects of TMS in patients with schizophrenia. Remarkably, all major psychiatric disorders were investigated by TMS: dementia (n = 19), attention deficit hyperactivity disorder (n = 13), Tourette syndrome (n = 6), cocaine dependence (n = 5), depression (n = 4), alcohol dependence (n = 3), cannabis-dependence (n = 3), nicotine dependence (n = 2), obsessive compulsive disorder (n = 2), borderline personality disorder (n = 1), bipolar disorder (n = 1), posttraumatic stress disorder (n = 1), altered personality traits (n = 1) and subjects at risk to develop psychosis (n = 1). In general, psychiatric illness can be linked to reduced cortical inhibition and in parts to enhanced cortical facilitation, resulting in a motor-cortex hyperexcitability. Detailed descriptions and exceptions will be presented and discussed at the conference. Conclusion Our results show that motor-cortex TMS is currently not suitable as a general diagnostic tool for psychiatric disorders. The disease state, different phenotypes of the same diseases and the influence of neuroactive medication can be discussed as major confounding factors. While it seems to be possible to hypothetically transmit results from motor-cortex TMS to other cortical and subcortical structures, further investigations are needed to understand the meaning of alterations in motor-cortex excitability in psychiatric disorders.