P2-36. Short-interval intracortical inhibition and facilitation in Parkinson’s disease

Abstract

It is still controversial whether short-interval intracortical inhibition (SICI) is abnormal in Parkinson’s disease (PD). In the healthy population, a research indicated that short-interval intracortical facilitation (SICF) is contaminated when testing SICI (Peurala et al., 2008), and provided methodological caution in SICI. In this study, therefore, we aimed at investigating inhibitory process within the primary motor cortex in PD by combination of SICI and SICF. In addition to usual SICI and SICF, we tested SICF with SICI, which we previously reported reflects intracortical inhibition (Shirota et al., 2010). SICI was tested using three interstimulus intervals (ISIs) of 2, 3, and 4 ms. For SICF, ISI was varied from 1.5 to 5.0 ms in 0.5 ms steps to cover three peaks of SICF. In SICF with SICI, SICI at 3 ms was combined with the SICF (triple-pulse paradigm). SICF was significantly enhanced, whereas SICI tended to be decreased in PD. Importantly, SICF under the influence of SICI lacked its second peak at 3.0 ms both in PD and healthy volunteers, suggesting that inhibitory process similar to that tested by SICI was preserved in PD. Apparently decreased SICI in PD might be caused by contamination of enhanced SICF.