Genki Futatsubashi

Gain modulation of the middle latency cutaneous reflex in patients with chronic joint instability after ankle sprain

OBJECTIVE To investigate the neural alteration of reflex pathways arising from cutaneous afferents in patients with chronic ankle instability. METHODS Cutaneous reflexes were elicited by applying non-noxious electrical stimulation to the sural nerve of subjects with chronic ankle instability (n=17) and control subjects (n=17) while sitting. Electromyographic (EMG) signals were recorded from each ankle and thigh muscle. The middle latency response (MLR; latency: 70-120 ms) component was analyzed. RESULTS In the peroneus longus (PL) and vastus lateralis (VL) muscles, linear regression analyses between the magnitude of the inhibitory MLR and background EMG activity showed that, compared to the uninjured side and the control subjects, the gain of the suppressive MLR was increased in the injured side. This was also confirmed by the pooled data for both groups. The degree of MLR alteration was significantly correlated to that of chronic ankle instability in the PL. CONCLUSIONS The excitability of middle latency cutaneous reflexes in the PL and VL is modulated in subjects with chronic ankle instability. SIGNIFICANCE Cutaneous reflexes may be potential tools to investigate the pathological state of the neural system that controls the lower limbs in subjects with chronic ankle instability.

A common neural element receiving rhythmic arm and leg activity as assessed by reflex modulation in arm muscles

Neural interactions between regulatory systems for rhythmic arm and leg movements are an intriguing issue in locomotor neuroscience. Amplitudes of early latency cutaneous reflexes (ELCRs) in stationary arm muscles are modulated during rhythmic leg or arm cycling but not during limb positioning or voluntary contraction. This suggests that interneurons mediating ELCRs to arm muscles integrate outputs from neural systems controlling rhythmic limb movements. Alternatively, outputs could be integrated at the motoneuron and/or supraspinal levels. We examined whether a separate effect on the ELCR pathways and cortico-motoneuronal excitability during arm and leg cycling is integrated by neural elements common to the lumbo-sacral and cervical spinal cord. The subjects performed bilateral leg cycling (LEG), contralateral arm cycling (ARM), and simultaneous contralateral arm and bilateral leg cycling (A&L), while ELCRs in the wrist flexor and shoulder flexor muscles were evoked by superficial radial (SR) nerve stimulation. ELCR amplitudes were facilitated by cycling tasks and were larger during A&L than during ARM and LEG. A low stimulus intensity during ARM or LEG generated a larger ELCR during A&L than the sum of ELCRs during ARM and LEG. We confirmed this nonlinear increase in single motor unit firing probability following SR nerve stimulation during A&L. Furthermore, motor-evoked potentials following transcranial magnetic and electrical stimulation did not show nonlinear potentiation during A&L. These findings suggest the existence of a common neural element of the ELCR reflex pathway that is active only during rhythmic arm and leg movement and receives convergent input from contralateral arms and legs.

Regionally distinct cutaneous afferent populations contribute to reflex modulation evoked by stimulation of the tibial nerve during walking

During walking, cutaneous reflexes in ankle flexor muscle [tibialis anterior (TA)] evoked by tibial nerve (TIB) stimulation are predominantly facilitatory at early swing phase but reverse to suppression at late swing phase. Although the TIB innervates a large portion of the skin of the foot sole, the extent to which specific foot-sole regions contribute to the reflex reversals during walking remains unclear. Therefore, we investigated regional cutaneous contributions from discrete portions of the foot sole on reflex reversal in TA following TIB stimulation during walking. Summation effects on reflex amplitudes, when applying combined stimulation from foot-sole regions with TIB, were examined. Middle latency responses (MLRs; 70-120 ms) after TIB stimulation were strongly facilitated during the late stance to mid-swing phases and reversed to suppression just before heel (HL) strike. Both forefoot-medial (f-M) and forefoot-lateral stimulation in the foot sole induced facilitation during stance-to-swing transition phases, but HL stimulation evoked suppression during the late stance to the end of swing phases. At the stance-to-swing transition, a summation of MLR amplitude occurred only for combined f-M&TIB stimulation. However, the same was not true for the combined HL&TIB stimulation. At the swing-to-stance transition, there was a suppressive reflex summation only for HL&TIB stimulation. In contrast, this summation was not observed for the f-M&TIB stimulation. Our results suggest that reflex reversals evoked by TIB stimulation arise from distinct reflex pathways to TA produced by separate afferent populations innervating specific regions of the foot sole.

Side-to-side difference in dynamic unilateral balance ability and pitching performance in Japanese collegiate baseball pitchers

[Purpose] To evaluate the side-to-side difference in dynamic unilateral balance ability and to determine the correlation of the balance ability with pitching performance in collegiate baseball pitchers. [Subjects and Methods] Twenty-five Japanese collegiate baseball pitchers participated in this study. Dynamic balance ability during a unilateral stance was bilaterally evaluated using the star excursion balance test (SEBT). The pitchers threw 20 fastballs at an official pitching distance; the maximal ball velocity and pitching accuracy (the number of strike/20 pitches × 100) were assessed. Side-to-side difference in scores of SEBT was assessed using a paired t-test. Correlations between SEBT scores and pitching performance were evaluated for both legs using a Pearson’s correlation analysis. [Results] The pivot side showed significantly higher score of the SEBT in the anteromedial direction than the stride side. On the other hand, the SEBT scores in the pivot and stride legs did not have significant correlations with maximal ball velocity and pitching accuracy. [Conclusion] These findings suggest that marked side-to-side difference does not exist in the dynamic unilateral balance ability of collegiate baseball pitchers and that the dynamic unilateral balance ability of each leg is not directly related to maximal ball velocity and pitching accuracy.

P31-24 Follow-up study of changes in cutaneous reflex in the peroneus longus after acute ankle sprain

MEPs remained above 50% of baseline in all of 23 patients and no patients had postoperative vagus nerve deficits. Conclusions: Reliable facial and vagus nerve MEPs could be recorded throughout the procedure during skull base procedures. CB MEP monitoring can circumvent difficulties of standard EMG monitoring techniques, provide ongoing evaluation of facial and vagus nerve function and predict outcome with sufficiently useful accuracy.

P13-2 Modulation of cutaneous reflexes during preparation of the contralateral finger movement

Hereditary neuropathy with liability to pressure palsies is an autosomal dominant disorder due to a 1.5 Mb deletion in chromosome 17p11.2p12 resulting in reduced expression of the PMP22 gene, the same gene that is duplicated in CMT1A. HNPP generally presents with an increased susceptibility to pressure palsies although phenotype within one family is variable. Nerve conduction studies show prolonged distal latencies and histopathologically dysmyelination, with characteristic tomaculi, is seen. The underlying pathophysiology of the disorder however is still not well understood. Methods: Axonal excitability studies were performed on four patients with genetically and biopsy proven HNPP. All subjects had been symptomatic on at least one occasion. Excitability testing of motor axons was performed by stimulating the median nerve at the wrist and elbow and recording from the thenar muscles and forearm flexors respectively. Excitability studies were performed using the TROND protocol of QTRACs. Comparisons were made with seven age-matched control subjects. Results: Motor thresholds were significantly greater in all HNPP patients and strength duration time constants were longer for HNPP subjects. Studies stimulating the median nerve at the wrist showed fanning out of the threshold electrotonus graph with a notch in the depolarising direction. These changes in threshold electrotonus were not present with stimulation at the elbow. Conclusion: There are changes in axonal excitability in HNPP, some of which resemble those observed in CMT1A. The changes are not uniform along the nerve.