Transcranial brain stimulation in schizophrenia: targeting cortical excitability, connectivity and plasticity

Transcranial magnetic stimulation (TMS) is a very popular tool used within neuroscience. This and other associated techniques allow the in vivo investigation of cortical excitability, cortical connectivity and cortical plasticity. Schizophrenia is a brain disorder and various theories other than the dopamine hypothesis have been developed to describe its underlying neurobiology. Supported by animal and post mortem studies, findings from TMS studies indicate that schizophrenia is a disease of reduced cortical inhibition and impaired intra- and intercortical connectivity. Further studies using repetitive TMS and other plasticity-inducing techniques have shown that cortical plasticity is altered in schizophrenia patients, supporting the recently discussed plasticity deficiency theory of schizophrenia. This review gives an introduction to the most frequently applied techniques, describes findings in schizophrenia patients and discusses these findings with regard to the neurotransmitters and associated receptors involved. In summary, there is emerging evidence of an important pathophysiological interplay between reduced inhibition, impaired connectivity and reduced plasticity in schizophrenia patients. Gamma-aminobutyric-acid-receptors and glutamtergic N-Methyl-D-aspartic-acid-receptors are most likely to be involved in this complex interplay, which may reflect a disturbed signal-to-noise ratio in schizophrenia patients. This review will discuss this issue with regard to the available treatment options and will give implications for future research and therapeutic strategies regarding disinhibition and neuroplasticity in schizophrenia.