Evidence Suggesting a Transcortical Pathway from Cutaneous Foot Afferents to Tibialis Anterior Motoneurones in Man

Abstract

Stimulation of the superficial peroneal or the sural nerve (3 shocks, 3 ms interval, 1 ms duration, 2.5 × perception threshold) evoked a reflex activation of the tibialis anterior muscle at a latency of approximately 70–95 ms in all of nine healthy human subjects. Stimulation of the medial plantar nerve only rarely produced similar effects. The possibility that a transcortical pathway contributes to these late reflex responses was investigated by combining the cutaneous stimulations and a transcranial magnetic stimulation of the contralateral motor cortex. A significant facilitation of short‐latency peaks in the post‐stimulus time histogram of single tibialis anterior motor units evoked by the transcortical magnetic stimulation was observed in eight out of nine subjects following stimulation of the superficial peroneal or sural nerves at the latency of the long‐latency reflex. In contrast such a facilitation was only rarely seen when the medial plantar nerve was stimulated. With the same timing for the stimuli, the superficial peroneal and sural nerve stimulations also produced a significant increase in the short‐latency, presumed monosynaptic, facilitation of the tibialis anterior H reflex produced by the brain stimulation. Similar facilitatory effects of the cutaneous stimuli could not be demonstrated when the magnetic stimulation of the cortex was replaced with electrical stimulation, implying that cortical excitability is affected by a conditioning cutaneous stimulation. It is suggested that the long‐latency reflexes in the tibialis anterior muscle evoked by activation of cutaneous afferents from the human foot are, at least partly, mediated by a transcortical pathway.

Altered timing of postural reflexes contributes to falling in persons with chronic stroke

“…Postural reflex onset latencies of healthy older adults in response to similar platform translations range from 100-115 ms (Marigold et al 2004). Studies using transcranial magnetic stimulation have suggested that reflex responses after 80-90 ms may be partially mediated by a transcortical reflex loop (Nielsen et al 1997;Petersen et al 1998;van Doornik et al 2004). Therefore, the greater postural reflex delay in the Faller group may represent a greater deficit in cortical functioning, which was exhibited by the lower functional scores in this group.…”

Modulation of ankle muscle postural reflexes in stroke: influence of weight-bearing load

“…controls or stroke), the timing of the observed postural reflexes in response to platform translations suggests long-latency reflexes that receive supraspinal input and may utilize a transcortical loop (Nielsen et al, 1997). Although others (Berger et al, 1988;Dietz and Berger, 1984;Di Fabio, 1987;Di Fabio et al, 1986) have reported slower postural reflex onset latencies on the paretic side, it was not possible to determine if this was simply due to the reduced load on the paretic limb since load was not monitored during the perturbation.…”

Task-related modulation of crossed spinal inhibition between human lower limbs

“…However, the reflex latency ranged from 70 to 100 ms, suggesting mediation through a transcortical loop (Nielsen et al 1997;). More recently, new evidence for spinal crossed reflex action has been found by stimulating the posterior tibial nerve (PTN), producing inhibition in contralateral soleus (cSol) motoneurons with shorter latency (37-41 ms) mediated by proprioceptive afferents, probably of group I and group II origin (Stubbs and Mrachacz-Kersting 2009;Stubbs et al 2011a).…”