Sensitivity of H-Reflexes and Stretch Reflexes to Presynaptic Inhibition in Humans

Abstract

The sensitivity of soleus H-reflexes, T-reflexes, and short-latency stretch reflexes (M1) to presynaptic inhibition evoked by a weak tap applied to the biceps femoris tendon or stimulation of the common peroneal nerve (CPN) was compared in 17 healthy human subjects. The H-reflex was strongly depressed for a period lasting up to 300-400 ms (depression to 48 +/- 23%, mean +/- SD, of control at a conditioning test interval of 70 ms) by the biceps femoris tendon tap. In contrast, the short-latency soleus stretch reflex elicited by a quick passive dorsiflexion of the ankle joint was not depressed. The soleus T-reflex elicited by an Achilles tendon tap was only weakly depressed (92 +/- 8%). The H-reflex was also significantly more depressed than the T-reflex at long intervals (>15 ms) after stimulation of CPN (H-reflex 63 +/- 14%, T-reflex 91 +/- 13%; P < 0. 01). However, the short-latency (2 ms) disynaptic reciprocal Ia inhibition evoked by stimulation of CPN was equally strong for H- and T-reflexes (H-reflex 72 +/- 10%, T-reflex 67 +/- 13%; P = 0.07). Peaks in the poststimulus time histogram (PSTH) of the discharge probability of single soleus motor units (n = 53) elicited by an Achilles tendon tap had a longer duration than peaks evoked by electrical stimulation of the tibial nerve (on average 5.0 ms as compared with 2.7 ms). All parts of the electrically evoked peaks were depressed by the conditioning biceps femoris tendon tap (average depression to 55 +/- 27% of control; P < 0.001). A similar depression was observed for the initial 2 ms of the peaks evoked by the Achilles tendon tap (69 +/- 48%; P < 0.001), but the last 2 ms were not depressed. Conditioning stimulation of the CPN at long intervals (>15 ms) also depressed all parts of the electrically evoked PSTH peaks (n = 34; average 65%; P < 0.001) but had only a significant effect on the initial 2 ms of the peaks evoked by the Achilles tendon tap (85%; P < 0.001). We suggest that the different sensitivity of mechanically and electrically evoked reflexes to presynaptic inhibition is caused by a difference in the shape and composition of the excitatory postsynaptic potentials underlying the two reflexes. This difference may be explained by a different composition and/or temporal dispersion of the afferent volleys evoked by electrical and mechanical stimuli. We conclude that it is not straightforward to predict the modulation of stretch reflexes based on observations of H-reflex modulation.

Web-based neuromuscular simulator applied to the teaching of principles of neuroscience

“…When the conditioning stimulus is applied to the CPN, the H-reflex amplitude decreases by ~40% of the control value (see black curves in Figure 7B). This amount of inhibition is compatible with experimentally observed values for humans (Morita et al, 1998). The lower panels in Figure 7B show the raster plots of active MNs for a single trial in control (left graph) and RI (right graph) conditions (in this case less MNs fired due to the reciprocal inhibition).…”

Reflex responsiveness of a human hand muscle when controlling isometric force and joint position

“…The absence of task differences in mechanically elicited responses might therefore be explained by diminished sensitivity of the stretch reflex to presynaptic inhibition. For example, human (Morita et al, 1998) and animal (Enriquez-Denton et al, 2002) experiments suggest that the nearly synchronous afferent volleys produced by electrical stimulation are less influenced by previous activation of Ia afferents compared with the temporally dispersed volleys produced by mechanical stretch. This difference results in greater sensitivity of the H-reflex to presynaptic effects.…”

Differential Modulation of Spinal and Corticospinal Excitability During Drop Jumps

“…Thus if a strong contribution of ⌱a-afferents to muscular activity was present during the entire stance phase, this would probably interfere with such a flexible modulation of the "voluntary" component. However, it has to be mentioned that other factors than changes in the ⌱a-transmission may have influenced the size of the H-reflex: muscle length was shown to affect the H-reflex size (Norlund et al 2002;Patikas et al 2004) as well as activity in upper leg muscles like the biceps femoris or the rectus femoris (Izumi et al 2001;Knikou and Conway 2002;Morita et al 1998). Furthermore, cutaneous afferent input can also alter the excitability of the H-reflex (Knikou 2007).…”