Paired-pulse measures

This article reviews the physiology and application of the currently available paired-pulse protocols. Paired-pulse transcranial magnetic stimulation (TMS) techniques study the modulation of human motor cortical excitability. Paired-pulse experiments are designed to give insight into the nature of the cortical circuitry activated by TMS. Changes in motor cortical excitability produced by the conditioning pulse are estimated by changes in the size of the conditioned motor-evoked potential (MEP). It is possible to identify specific abnormalities in the balance between inhibitory and facilitatory processes, even if the pathology lies in abnormal afferent signalling to the motor cortex rather than in the motor cortex itself. The conclusion that emerges from the studies on interhemispheric interactions is that it is now possible by means of TMS protocols to chart long-range functional interhemispheric connectivity of remote areas of the human brain.