Application of TMS for pathophysiology of psychiatric diseases

Abstract

Several transcranial magnetic stimulation (TMS) techniques are able to examine human cortical excitability and intracortical inhibitory/excitatory mechanisms which are assumed to be mediated by neurotransmitters including GABA and acetylcholine. The late part of the cortical silent period is thought to represent GABA-B-receptor-mediated intracortical inhibition in the motor cortex, and was reported to be inversely associated with negative symptoms in schizophrenia and show different responses depending upon antipsychotics. Short interval intra-cortical inhibition (SICI) measured by using paired-pulse TMS is linked to the function of GABA-A-receptor-mediated cortical interneurons. SICI was reported to be disturbed in schizophrenia, and can be a tool to examine the hypothesis of GABA neurotransmission abnormalities in schizophrenia. Short-latency afferent inhibition (SAI) is related mainly to the function of central cholinergic circuits, and is reduced in cholinergic forms of dementia including Alzheimer disease and dementia with Lewy bodies, but is not reduced in non-cholinergic forms of dementia. SAI can be a useful tool to predict effectiveness of cholinergic drugs in treating demented patients.