Abstract
Both active and passive rhythmic limb movements reduce the amplitude of spinal cord Hoffmann (H-) reflexes in muscles of moving and distant limbs. This could have clinical utility in remote modulation of the pathologically hyperactive reflexes found in spasticity after stroke or spinal cord injury. However, such clinical translation is currently hampered by a lack of critical information regarding the minimum or effective duration of passive movement needed for modulating spinal cord excitability. We therefore investigated the H-reflex modulation in the flexor carpi radialis (FCR) muscle during and after various durations (5, 10, 15, and 30 min) of passive stepping in 11 neurologically normal subjects. Passive stepping was performed by a robotic gait trainer system (Lokomat®) while a single pulse of electrical stimulation to the median nerve elicited H-reflexes in the FCR. The amplitude of the FCR H-reflex was significantly suppressed during passive stepping. Although 30 min of passive stepping was sufficient to elicit a persistent H-reflex suppression that lasted up to 15 min, 5 min of passive stepping was not. The duration of H-reflex suppression correlated with that of the stepping. These findings suggest that the accumulation of stepping-related afferent feedback from the leg plays a role in generating short-term interlimb plasticity in the circuitry of the FCR H-reflex.
Highlights
Part of the neuronal coordination between the fore- and hind-limbs observed in quadrupedal locomotion is preserved in humans (Dietz, 2002a; Zehr and Duysens, 2004; Sakamoto et al, 2007; Zehr et al, 2009; Meyns et al, 2014)
EMG activities of the flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps femoris (BF), rectus femoris (RF), and tibialis anterior (TA) were essentially inactive during passive stepping while small but rhythmic EMG activity was visible in several stepping phases in the SOL
We demonstrated that passive stepping using a robotic device elicits prolonged suppression of monosynaptic reflex excitability in forearm muscles
Summary
Part of the neuronal coordination between the fore- and hind-limbs observed in quadrupedal locomotion is preserved in humans (Dietz, 2002a; Zehr and Duysens, 2004; Sakamoto et al, 2007; Zehr et al, 2009; Meyns et al, 2014). A recent study we conducted revealed that robot-assisted passive stepping with a driven gait orthosis (DGO) induces forearm H-reflex suppression (Nakajima et al, 2011; Domingo et al, 2014). These interlimb interactions are partially regulated through presynaptic inhibition of group Ia afferent terminals in the H-reflex circuit (Frigon et al, 2004; Nakajima et al, 2013b). Steppingrelated afferent feedback from the legs may contribute to a decrease in transmission from Ia afferents to motoneurons (MNs) innervating forearm muscles
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
