Abstract
This study examined the effects of joint angle and passive movement direction on corticospinal excitability. The subjects were 14 healthy adults from whom consent could be obtained. We performed two experiments. In Experiment 1, we measured motor evoked potential (MEP) amplitude, F-wave and M-wave at 0° and 20° adduction during adduction or abduction movement, in the range of movement from 10° abduction to 30° adduction. In Experiment 2, MEPs were measured at static 0° and 20° adduction during passive adduction from 10° adduction to 30° adduction and static 20° adduction. MEP, F-waves and M-waves were recorded from the right first dorsal interosseous (FDI) muscle. Experiment 1 revealed significantly increased MEP amplitude at 0° during passive adduction compared to static 0° (p < 0.01). No other significant differences in MEP, M-wave and F-wave parameters were observed. In Experiment 2, MEP amplitude was significantly higher at 20° adduction during passive adduction compared with static 0° (p < 0.01). Based on these findings, it appears that fluctuations in MEP amplitude values during passive movement are not influenced by joint angle, but rather it is possible that it is due to intracortical afferent facilitation (AF) dependent on afferent input due to the start of movement and interstimulus interval (ISI) of transcranial magnetic stimulation (TMS).
Highlights
Passive movement is known to alter the excitability of sensorimotor cortex
Many studies have reported that the primary somatosensory cortex (S1) and primary motor cortex (M1) are activated during afferent input from the periphery associated with passive movement (Xiang et al, 1997; Carel et al, 2000; Reddy et al, 2001; Onishi et al, 2013; Shriver et al, 2013)
There were significant differences in motor evoked potential (MEP) amplitude and MEP/M ratio during passive movement compared with the static position (MEP: F(4,52) = 6.334, p = 0.000, partial η2 = 0.328; MEP/M ratio: F(4,52) = 4.515, p = 0.003, partial η2 = 0.258)
Summary
Passive movement is known to alter the excitability of sensorimotor cortex. Many studies have reported that the primary somatosensory cortex (S1) and primary motor cortex (M1) are activated during afferent input from the periphery associated with passive movement (Xiang et al, 1997; Carel et al, 2000; Reddy et al, 2001; Onishi et al, 2013; Shriver et al, 2013). An examination of the relationship between joint angle and MEP amplitude during passive movement of the wrist revealed that MEPs decrease immediately after the start of extension (Lewis et al, 2001). It was reported that MEPs do not decrease immediately after passive index finger adduction from the abduction position but do decrease at 0◦ (mid-position; Edwards et al, 2002, 2004). The relationship between joint angle and MEP amplitude during passive
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