Schematic diagram outlining the possible neural pathways for integration of cutaneous reflex pathways inputs from different nerves of foot during arm and leg remote rhythmic movement (ARM&LEG).

<p>At the center is a simplified interneuronal (IN) reflex pathways in tibialis anterior muscles. Inputs from the sural and tibial nerves have connections onto shared INs (dashed black lines). Excitability of common INs and motoneurons (MNs) are regulated by central commands and peripheral feedback related to LEG (blue square) and ARM (green square) movement. It is possible that individual input arising from each LEG and ARM movement converge “in parallel” onto these putative reflex pathways (dashed lines of blue and green squares) during ARM&LEG movement. TIB n.: tibial nerve. SUR n.: sural nerve. MNs: motoneurons.</p

Convergence effect of simultaneous sural and tibial nerve stimulation on TA cutaneous reflex amplitude during ARM&LEG movement.

<p>(A) Full-wave rectified and averaged EMG in TA muscle following simultaneous combined stimulation of sural and tibial nerves (TIB&SUR, red trace), sural alone (SUR, green trace) and tibial alone (TIB, Blue trace) obtained from a single subject. Dashed gray trace: the mathematical summation of EMG traces for individual TIB and SUR nerves stimulation (Algebraic SUM). (B) Grand means (± SD) of the magnitudes of early-latency reflex responses (45–80 ms after stimulation onset) following simultaneous combined stimulation of sural and tibial nerves (Red bar), sural alone (Green bar) and tibial alone (Blue bar) obtained from 12 subjects. Hatched gray bar: mathematical summation of reflex amplitude for individual nerve stimulation (TIB+SUR). * <i>p</i><0.001. Calibration bar = 10 µV.</p

Typical recordings of EMG activities in AD, VL, MG and TA muscles during ARM&LEG movement for a single subject.

<p>Gray vertical line: stimulation position of ipsilataral side. Dashed lines: flexion phase of movement. Thick lines: extension phase of movement.</p

Effect of conditioning the <i>flexor carpi radialis</i> H-reflex with superficial radial nerve stimulation during leg cycling and static activation obtained from 11 subjects.

<p>Format and abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076313#pone-0076313-g002" target="_blank">Figure 2</a>.</p

Effect of superficial radial nerve conditioning on <i>flexor carpi radialis</i> (FCR) H-reflex amplitudes during leg cycling.

<p>(A) Rectified and averaged FCR EMG and H-reflex waveforms following superficial radial (SR) nerve stimulation [1.0× radiating threshold (RT)] obtained from a single subject. (B) Conditioning effect of FCR H-reflex with weak radial nerve stimulation (0.51×RT) during static and cycling tasks. (C) EMG responses following weak SR nerve stimulation (0.51×RT; just above perceptual threshold) during static activation and leg cycling. Please note that <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076313#pone-0076313-g005" target="_blank">figures 5A, B, and C</a> were obtained from same subject. (D) Grand means (± SEM) of H-reflexes (upper panel), M-waves (middle panel), and pre-stimulus EMG levels (lower panel) in the FCR muscle during SR nerve conditioning obtained from 9 subjects. * <i>p</i><0.01 significantly different from the unconditioned values of each tasks. +<i>p</i><0.01 significantly different from the unconditioned static values. Format and abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076313#pone-0076313-g004" target="_blank">Figure 4</a>.</p

Experimental set-up for leg cycling on the ergometer.

<p>Nerve stimulation was delivered during cycling and static trials at the 12'clock position of the right pedal crank (thick lines of red). Green lightning bolt: median nerve stimulation (test stimulation for evoking the H-reflex). Blue lightning bolt: superficial radial nerve stimulation (conditioning stimulation to reduce Ia PSI and facilitate <i>flexor carpi radialis</i> (FCR) H-reflex amplitudes) Red lightning bolt: radial nerve stimulation (conditioning stimulation to increase Ia PSI and suppress FCR H-reflex amplitudes).</p

Schematic diagram outlining the possible neural pathways for integration of inputs arising from leg cycling and somatosensory conditioning stimulation on the presumed Ia presynaptic inhibitory pathway.

<p>At the center is a simplified H-reflex pathway illustrating group Ia afferents synapsing with alpha motoneurons (MNs) of the <i>flexor carpi radialis</i>. Ia PSI and excitability of MNs are regulated by central commands and peripheral feedback related to leg cycling (black square). Inputs from the radial (red lightning bolt) and superficial radial nerves (blue lightning bolt) have excitatory and inhibitory connections onto Ia PSI interneurons (gray circle), respectively. The square with dashed line is a possible shared presynaptic pathways integrating locomotor-related inputs and somatosensory conditioning volleys during locomotion. Green lightning bolt: median nerve stimulation (test stimulation for evoking the FCR H-reflex).</p

Effect of conditioning the <i>flexor carpi radialis</i> H-reflex with radial nerve stimulation during leg cycling and static activation.

<p>(A) Typical averaged recordings of conditioned (black lines) and unconditioned (gray lines) H-reflex waveforms during static (upper traces) and cycling (lower traces) tasks obtained from a single subject. Grand means and SEM of magnitudes of the pre-stimulus EMG (B), H-reflex (C) and M-wave (D) during conditioned (black bars) and unconditioned (gray bars) trials. *<i>p</i><0.01 significantly different from the unconditioned values for each task. +<i>p</i><0.01 significantly different from the unconditioned static value.</p