Intracortical excitatory and inhibitory phenomena to paired transcranial magnetic stimulation in healthy human subjects: differences between the right and left hemisphere

Intracortical inhibition (ICI) and facilitation (ICF) to paired magnetic st imuli reflect the activation of interneuronal circuits within the motor cor tex. Intersubjects physiological variability of these phenomena, partly lim its the usefulness of such method. Therefore, interhemispheric ICI/ICF diff erences might represent a more sensitive and less variable neurophysiologic al parameter to test the motor cortex excitability. Motor evoked potentials from the hand muscles were recorded in ten healthy subjects in a paired-pu lse paradigm. Interstimulus intervals (ISIs) from 1 to 50 ms were used. The time course of ICI and ICF in the two hemispheres is consistent with minim al interhemispheric asymmetries. The interhemispheric differences of ICI an d ICF could be a valuable neurophysiological marker for the diagnosis, prog nosis and follow-up of neurological diseases characterized by monohemispher ic damage and lateralized motor deficits. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.