Fig. 2: Monitoring corticospinal and corticocortical excitability with TMS protocols.
Cortical excitability data were analyzed using mixed-factorial ANOVAs with repeated measures (see Table 1). a Global corticospinal excitability monitored by MEP amplitudes at different TMS intensities via the I–O curve protocol. ECs showed significantly higher corticospinal excitability in the morning than in the evening (t130% = 3.19, P = 0.004; t150% = 5.054, P < 0.001), and compared to the same time in LCs (t130% = 3.05, P = 0.007; t150% = 4.67, P < 0.001), and LCs display enhanced excitability in the evening (t130% = 2.64, P = 0.026; t150% = 3.248, P = 0.004), and compared to the same time in ECs (t130% = 2.78, p = 0.017; t150% = 3.63, p = 0.004) at higher TMS intensities. b Intracortical inhibition and facilitation measured by the SICI-ICF paired-pulse (pp)TMS protocol. Significantly higher cortical inhibition in the evening and morning were observed for ECs (tISI2 = 3.09, p = 0.006; tISI3 = 3.13, p = 0.005) and LCs (tISI2 = 2.57, p = 0.031; tISI3 = 1.80, p = 0.217), respectively. In contrast, cortical facilitation was significantly enhanced in the morning, and evening for ECs (tISI10 = 5.09, P < 0.001; tISI15 = 4.79, P < 0.001) and LCs (tISI10 = 4.71, P < 0.001; tISI15 = 5.23, P < 0.001), respectively. c I-wave facilitation for monitoring GABA-dependent intracortical inhibition. Cortical excitability was significantly facilitated for early, middle, and late ISIs in the morning for ECs (tearly = 3.84, P = 0.009; tmiddle = 3.70, P = 0.001; tlate = 2.992, P = 0.018) and in the evening for LCs (tearly = 3.92, P = 0.007; tmiddle = 3.85, P = 0.009; tlate = 3.214, P = 0.009), indicative for less cortical inhibition. d Inhibitory effect of peripheral nerve stimulation on motor cortical inhibition, as measured by SAI. ECs showed more prominent cortical inhibition in the evening (tISI20 = 4.76, P = 0.001; tISI40 = 4.99, P < 0.001), whereas LCs showed more cortical inhibition in the morning (tISI20 = 5.50, P < 0.001; tISI40 = 3.56, P < 0.001). All pairwise comparisons were calculated using Bonferroni-corrected t tests (two-sided). n = 32 (16 per group). Data are presented as mean values ± SEM (standard error of means). Filled symbols represent a significant difference of MEP amplitudes compared to the respective test pulses (for SICI-ICF, I-wave, SAI) or MEP at RMT intensity (for I-O curve). Asterisks [*] represent statistically significant comparisons of each outcome measure across time of day for each group. ECs early chronotypes, LCs late chronotypes, MEP motor-evoked potential, RMT resting motor threshold, ms milliseconds; I–O curve input–output curve, ISI interstimulus interval.
