P40-F The relationship between age and SICI parameters obtained with threshold tracking TMS

Background Recently developed threshold tracking TMS (TT-TMS) paired pulse techniques have been shown to be of benefit in clinical diagnostic practice. Reduced Short Interval Cortical Inhibition (SICI) with increasing age has been shown in several studies using conventional paired-pulse TMS techniques. However, TT-TMS SICI parameters did not correlate to age in healthy subjects in a previous study (Shibuya et al., 2016). We aimed in this study to present the preliminary results of our normal material on TT-SICI and the relationship between SICI measurements and age. Material and methods Thirty-three healthy subjects (mean age: 51.06 ± 2.48, range: 23–77) were included. Paired-pulse TT-TMS was undertaken using a 90 mm figure-of-eight coil applied to the motor cortex, with currents generated by BiStim system controlled by Qtrac software. The motor evoked potential (MEP) response was recorded over the first dorsal interosseus (FDI). MEP amplitude was set to a target value of 0.2 mV, and the changes in the intensity of the test stimulus required to generate this target MEP were measured. The relationship between age and SICI measurements were analyzed using regression analysis. Results Resting motor threshold (RMT) (MSO, %) (mean: 54.43 ± 2.41) and SICI (%) at 1 ms (12.01 ± 1.86), 2.5 ms (11.02 ± 1.65), 3 ms (8.20 ± 1.69) and 1–7 ms (5.93 ± 1.12) on TT-TMS were analysed. RMT increased with increasing age (r = 0.45, p = 0.08), while age had an inverse relationship with SICI on 1 ms (r = −0.49, p = 0.003), 2.5 ms (r = −0.45, p = 0.008), 3 ms (r = −0.41, p = 0.019) and 1–7 ms (r = −0.41, p = 0.017). Conclusions SICI parameters closely relate to age for TT-TMS similar to previously reported conventional. Further studies are required with large groups of healthy subjects.