Impaired motor cortical facilitatory-inhibitory circuit interaction in Parkinson’s disease

Abstract

OBJECTIVE\nMotor cortical (M1) inhibition and facilitation can be studied with short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF). These circuits are altered in Parkinson s disease (PD). The sensorimotor measure short latency afferent inhibition (SAI) is possibly altered in PD. The aim was to determine if the manner in which these circuits interact with each other is abnormal in PD.\n\n\nMETHODS\nFifteen PD patients were studied at rest in ON and OFF medication states, and were compared to 16 age-matched controls. A triple-stimulus transcranial magnetic stimulation paradigm was used to elicit a circuit of interest in the presence of another circuit.\n\n\nRESULTS\nSICF was increased in PD OFF and PD ON conditions compared to controls. SICI facilitated SICF in controls and PD ON, but not in PD OFF. SICF in the presence of SICI negatively correlated with UPDRS-III scores in OFF and ON medication conditions. SAI showed similar inhibition of SICI in controls, PD OFF and PD ON conditions.\n\n\nCONCLUSIONS\nThe facilitatory effect of SICI on SICF is absent in PD OFF, but is restored with dopaminergic medication.\n\n\nSIGNIFICANCE\nImpaired interaction between M1 circuits is a pathophysiological feature of PD.