A meta-analysis of cortical inhibition and excitability using transcranial magnetic stimulation in psychiatric disorders

ObjectiveTo evaluate transcranial magnetic stimulation (TMS) measures of inhibition and excitation in obsessive–compulsive disorder (OCD), major depressive disorder (MDD) and schizophrenia (SCZ).MethodsParadigms included: short-interval cortical inhibition (SICI), cortical silent period (CSP), resting motor threshold, intracortical facilitation, and motor evoked potential amplitude. A literature search was performed using PubMed, Ovid Medline, Embase Psychiatry and PsycINFO 1990 through April 2012.ResultsA significant Hedge’s g was found for decreased SICI (g = 0.572, 95% confidence interval [0.179, 0.966], p = 0.004), enhanced intracortical facilitation (g = 0.446, 95% confidence interval [0.042, 0.849], p = 0.030) and decreased CSP (g = −0.466, 95% confidence interval [−0.881, −0.052], p = 0.027) within the OCD population. For MDD, significant effect sizes were demonstrated for decreased SICI (g = 0.641, 95% confidence interval [0.384, 0.898], p = 0.000) and shortened CSP (g = −1.232, 95% confidence interval [−1.530, −0.933], p = 0.000). In SCZ, a significant Hedge’s g was shown for decreased SICI (g = 0.476, 95% confidence interval [0.331, 0.620], p = 0.000).ConclusionInhibitory deficits are a ubiquitous finding across OCD, MDD, SCZ and enhancement of intracortical facilitation is specific to OCD.SignificanceProvides a clear platform from which diagnostic procedures can be developed.

► Motor cortex inhibitory and excitatory transcranial magnetic stimulation paradigms were quantitatively assessed in severe psychiatric illnesses.
► Inhibitory deficits are a ubiquitous finding across obsessive–compulsive disorder, major depressive disorder and schizophrenia, by contrast, enhancement of intracortical facilitation is specific to obsessive–compulsive disorder.
► Limitations of transcranial magnetic stimulation studies are reviewed and potential future applications are discussed.