Gait acts as a gate for reflexes from the foot

Abstract

During human gait, electrical stimulation of the foot elicits facilitatory P2 (medium latency) responses in TA (tibialis anterior) at the onset of the swing phase, while the same stimuli cause suppressive responses at the end of swing phase, along with facilitatory responses in antagonists. This phenomenon is called phase-dependent reflex reversal. The suppressive responses can be evoked from a variety of skin sites in the leg and from stimulation of some muscles such as rectus femoris (RF). This paper reviews the data on reflex reversal and adds new data on this topic, using a split-belt paradigm. So far, the reflex reversal in TA could only be studied for the onset and end phases of the step cycle, simply because suppression can only be demonstrated when there is background activity. Normally there are only 2 TA bursts in the step cycle, whereas TA is normally silent during most of the stance phase. To know what happens in the stance phase, one needs to have a means to evoke some background activity during the stance phase. For this purpose, new experiments were carried out in which subjects were asked to walk on a treadmill with a split-belt. When the subject was walking with unequal leg speeds, the walking pattern was adapted to a gait pattern resembling limping. The TA then remained active throughout most of the stance phase of the slow-moving leg, which was used as the primary support. This activity was a result of coactivation of agonistic and antagonistic leg muscles in the supporting leg, and represented one of the ways to stabilize the body. Electrical stimulation was given to a cutaneous nerve (sural) at the ankle at twice the perception threshold. Nine of the 12 subjects showed increased TA activity during stance phase while walking on split-belts, and 5 of them showed pronounced suppressions during the first part of stance when stimuli were given on the slow side. It was concluded that a TA suppressive pathway remains open throughout most of the stance phase in the majority of subjects. The suggestion was made that the TA suppression increases loading of the ankle plantar flexors during the loading phase of stance.

Modulation of Cutaneous Reflexes From the Foot During Gait in Parkinson's Disease

“…Indeed, in patients with spinal cord injury some elements of the modulation of these responses are largely preserved (Jones and Yang 1994;Knikou et al 2009). Lesions in the corticospinal tract do not eliminate the phase-dependent modulation but mostly cause an overall reduction in the amplitude of the responses (Duysens et al 2004b). Inversely, activation of the cortex through transcranial magnetic stimulation facilitates the reflex responses, indicating that there is convergence of the corticospinal tract and the reflex pathways involved in these responses, in confirmation of evidence obtained in cat studies (Bretzner and Drew 2005).…”

“…3. modulation is regulated at other levels of the CNS. Phasedependent modulation of cutaneous reflexes persists in patients with a damaged corticospinal tract (Duysens et al 2004a) and it was argued that most of the phase-dependent modulation of cutaneous reflexes could be due to spinal mechanisms supplemented by cortical input (Duysens et al 2004b). If so, one would expect little change in patients with intact spinal cord and motor cortex but deficient substantia nigra (such as seen in PD).…”

“…This TA activity is part of the ankle muscle coactivation frequently seen when subject are walking while feeling unstable. For example, under conditions that resemble limping, TA activity was observed during the stance phase of the more stable leg in both healthy subjects (Dietz et al 1994;Duysens et al 2004b) and patients with PD . Under stable conditions, however, there is usually no extra TA activity during the stance phase (Cioni et al 1997;Dietz et al 1981Dietz et al , 1995Dietz et al , 1997Lewis et al 2000;Mitoma et al 2000; for exceptions see Cioni et al 1997;Dietz et al 1995).…”

Dual task effects for asymmetric stepping on a split-belt treadmill

“…A few studies have considered the information processing involved at cortical and subcortical levels for split-belt walking. Duysens et al [17], looking at specific mechanisms of muscle control over such loading coordination using split-belt walking, have shown cortical involvement over the complex sensori-motor integration of ankle muscles. In addition, two papers looking at the ability to adapt to split-belt asymmetric speeds in persons with stroke [18] and with cerebellar deficits [19] have suggested that inter-limb coordination adaptation is mediated specifically by cerebellar influence through brainstem circuits.…”

Temporal and spatial organization of gait-related electrocortical potentials

“…Jain et al also found a strong correlation between the ensemble-averaged EEG activity at Cz and activity of transition muscles during pedaling, indicating some cortical control over these muscles [12]. One of the first to suggest the involvement of the motor cortex in driving muscle activity during walking has been made by [8]. They indicated that the background activity in TA at end stance is due to CPG activity, while at end swing, it is generated by the cortex.…”