Abstract
Up to now relatively little is known about interlimb reflexes (ILR). Especially it is not well known whether ILR may habituate or not to subsequent stimuli. The main aim of the present investigation was to explore the short term habituation behavior of ILR. The electromyogram was recorded over the tonically active biceps brachii (BB) muscle in 11 healthy subjects contralateral and ipsilateral to supramaximum electrical stimuli (9–12 mA) that were delivered at 1.0 and 0.4 Hz over the left sural nerve. In addition, a selective averaging method was used to investigate the influence of preceding stimuli on the ILR. Thus, 30 blocks of 3 subsequent stimuli were used. All 1st ILR of each block were averaged together. Averages were also obtained for 2nd and 3rd ILR. While ILR amplitudes gained significantly both ipsilateral and contralateral to the stimulus (p < 0.05) after train stimuli as compared with single stimuli, ILR amplitudes showed a significant decrease at 1.0 Hz versus 0.4 Hz stimuli. ILR amplitudes decreased significantly after the 2nd and 3rd stimulus relative to the 1st (p < 0.05). ILR can be recorded bilaterally remote from the stimulus site. Furthermore, ILR show clear short term habituation behavior.
Highlights
After electrical limb nerve stimuli, different motor responses can be recorded, such as e.g., H-reflex or the so called long latency reflex (LLR)
interlimb reflexes (ILR) were seen over the biceps brachii (BB) on either side in all 11 subjects when trains of 3 stimuli were delivered at a rate of 0.4 Hz (Figure 1, 6th trace from top, Figure 2C)
When trains of 3 stimuli were given at a rate of 1 Hz, ILR amplitudes were significantly lower as compared to the 0.4 Hz condition (p < 0.005 both ipsilateral and contralateral to the stimulus site; Figure 1, traces 3 and 6 from top; Figure 2C)
Summary
After electrical limb nerve stimuli, different motor responses can be recorded, such as e.g., H-reflex or the so called long latency reflex (LLR). In contrast to LLR, interlimb reflexes (ILR) can be obtained contralateral to the stimulated site and even in the legs when the stimulus was placed over an arm nerve and vice versa (Zehr et al, 2001; Butler et al, 2016). An important feature to discriminate reflex responses is whether they show short term habituation or not. The motor response obtained over the biceps brachii (BB) muscle contralateral to an arm nerve stimulus has been shown to habituate (Alaid et al, 2012a). Our previous results of arm muscle response habituation to contralateral stimuli have been interpreted to be a startle response. The main aim of the present study was to clarify whether ILR in general would habituate and could eventually be correlates of startle responses
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