Evidence that a transcortical pathway contributes to stretch reflexes in the tibialis anterior muscle in man

Abstract

In human subjects, stretch applied to ankle dorsiflexors elicited three bursts of reflex activity in the tibialis anterior (TA) muscle (labelled M1, M2 and M3) at mean onset latencies of 44, 69 and 95 ms, respectively. The possibility that the later of these reflex bursts is mediated by a transcortical pathway was investigated. The stretch evoked a cerebral potential recorded from the somatosensory cortex at a mean onset latency of 47 ms in nine subjects. In the same subjects a compound motor‐evoked potential (MEP) in the TA muscle, evoked by magnetic stimulation of the motor cortex, had a mean onset latency of 32 ms. The M1 and the M2 reflexes thus had too short a latency to be caused by a transcortical pathway (minimum latency, 79 ms (47 + 32)), whereas the later part of the M2 and all of the M3 reflex had a sufficiently long latency. When the transcranial magnetic stimulation was timed so that the MEP arrived in the TA muscle at the same time as the M1 or M2 reflexes, no extra increase in the potential was observed. However, when the MEP arrived at the same time as the M3 reflex a significant (P < 0.01) extra‐facilitation was observed in all twelve subjects investigated. Peaks evoked by transcranial magnetic stimulation in the post‐stimulus time histogram of the discharge probability of single TA motor units (n= 28) were strongly facilitated when they occurred at the same time as the M3 response. This was not the case for the first peaks evoked by electrical transcranial stimulation in any of nine units investigated. We suggest that these findings are explained by an increased cortical excitability following TA stretch and that this supports the hypothesis that the M3 response in the TA muscle is ‐ at least partly ‐ mediated by a transcortical reflex.

Modulation of reflex responses in activated ankle dorsiflexors differs in healthy young and elderly subjects

“…Recently, Obata et al (2010) also investigated the latency of the tibialis anterior stretch reflex during weak contractions (*10% MVC) and did not observe any significant difference between elderly (66 ms) and young (60 ms) adults. Such long latencies for the tibialis anterior, however, are surprising when compared with our data (*38 and 41 ms in young and elderly subjects, respectively) and those reported for young adults (Petersen et al 1998;Zuur et al 2009). Regardless of the discrepancy between studies, the increase in reflex latency with advancing age should be related to the slowing in synaptic transmission and conduction velocity due to degenerative changes affecting sensory and motor fibres (Desmedt and Cheron 1980;Doherty et al 1994).…”

“…3). Results from previous studies combining transcranial magnetic stimulation and stretch reflexes recording, suggest a transcortical pathway for LL 2 in the tibialis anterior (Petersen et al 1998;Zuur et al 2009), indicating that the greater LL 2 area in elderly adults observed in the present study may involve supraspinal mechanisms (Kawashima et al 2004;Lin and Sabbahi 1998;Obata et al 2010). The increase of the long-latency reflex component may be an adaptatory mechanism to changes occurring with advancing age.…”

“…The reflex response is composed of a short-latency component involving a spinal pathway (Pierrot-Desseilligny and Burke 2005) and a longlatency component involving a supraspinal pathway, at least in upper limb muscles (Matthews 1991) and in the tibialis anterior (Petersen et al 1998). Studies investigating the effect of ageing reported contradictory results as the size of the short-latency stretch reflex either decreased (Corden and Lippold 1996) or did not change in elderly adults (B70 years; Kawashima et al 2004;Lin and Sabbahi, 1998;Obata et al 2010).…”

Changes in predictive motor control in drop-jumps based on uncertainties in task execution

“…At 50 ms before ground contact, the time to successfully change the muscular pattern was expected to be too short. The conduction time of the fastest corticospinal fibers activated by the motor areas of the neocortex to contract the muscles of the lower leg is approximately 30 ms (e.g., Petersen, Christensen, Morita, Sinkjaer, & Nielsen, 1998). This leaves the insufficient time of 20 ms to perceive the auditory cue, change the motor command and process this information to the motor output areas.…”

Early compensatory and anticipatory postural adjustments following anterior cruciate ligament reconstruction

“…Such a difference between patients with ACLR and healthy participants might be due to surgery-related neural adaptations of either peripheral or central origin, or to a combination of both. An efficient reaction to unexpected postural perturbations would depend on a feedback control system where an error signal, which is carried by sensory afferences, is processed to restore a given set point (Marsden et al 1983;Matthews 1991;Pruszynski and Scott 2012;Petersen et al 1998). Muscle spindles and joint receptors should be the main sources of sensory signals informing the brain on the onset of leg fall.…”