Sol H-reflex Research Articles

Cumulative vibratory indices and the H/M ratio of the soleus H-reflex: a quantitative study in control and spastic subjects

Suppression of the soleus (Sol) H-reflex recruitment curve by Achilles tendon vibration and the ratio of maximum Sol H-reflex (H max) to maximum M-response (H/M ratio) have been studied by means of computer processing on the basis of peak-to-peak (P-P) and area values in 46 controls and in 16 spastic patients. The ‘classical’ vibratory index (VI) has been compared with a new cumulative VI (CVI), which is defined as the quotient of the surface under the recruitment curve obtained with vibration and the one obtained without vibration up to an equal intensity level. Statistical analyses were performed from threshold to 3 different intensity levels. Tendon vibration is found to be less effective at higher intensity levels. Mean values with S.D.s of CVIs at H max intensity are significantly lower than those of the ‘classical’ VIs. VIs increase with age while H/M ratios decline. Stepwise discriminant analyses showed that area CVI at H max intensity yielded the best distinction between controls and patients. Additional differential contribution is obtained by P-P H/M ratio. A canonic variable derived from these two variables correctly classified 44 out of 46 controls and 15 out of 16 patients. The methods presented improve the specificity of the quantitative neurophysiological measure of spasticity by means of Sol H-reflex recordings.

Changes in presynaptic inhibition of Ia fibres to soleus motoneurones during voluntary dorsiflexion of the foot.

Variations of presynaptic inhibition in heteronymous Ia fibres projecting to soleus motoneurones were studied during the first 250 ms of phasic voluntary isometric contractions of the antagonist tibialis anterior muscle in human subjects. During the first 60-80 ms of TA e.m.g activity, presynaptic inhibition was often more marked than at rest, but not in all experimental sessions. After 60-80 ms, presynaptic inhibition was always increased compared to rest and to the onset of TA e.m.g. activity. A "rebound" in femoral nerve induced Ia facilitation was often observed between 90-150 ms. The early increase in presynaptic inhibition was widespread and non specific since it was observed at the onset of extensor carpi radialis contractions of maximal strength. The "rebound" in heteronymous Ia facilitation was interpreted as a relative decrease in presynaptic inhibition to which nonspecific suprasegmental and cutaneous effects contributed. The late increase in presynaptic inhibition in Ia fibers to soleus motoneurones was considered as reciprocally inhibiting the Sol H-reflex, thus counteracting the phasic stretch of the antagonist muscle during TA contraction.

Voluntary muscle release is not accompanied by H-reflex inhibition in patients with upper moto neuron lesions

Changes in excitability of the soleus (Sol) monosynaptic reflex are were investigated in spastic subjects, affected by amyotrophic lateral sclerosis (ALS), upon voluntary relaxation of tonic contraction of triceps surae muscle. Force and electromyograms (EMG) were recorded during triceps release, performed in response to an acoustic signal, in a reaction-time (RT) situation. Sol H-reflex was evoked at random during the task, and its amplitude was referred in time to the end of Sol EMG. At variance with the results for the same task in normal subjects, it was found that in ALS patients the RTs of the termination of EMG were longer than those of the beginning of the EMG, the decrease in force was prolonged and perturbed owing to intercurrent clonus-like EMG activity, and the H-reflex did not undergo the expected profound inhibition. It is suggested that the absence of the activation of presynaptic inhibitory mechanisms by the descending command to release brings about major disorders in voluntary muscle relaxation.

Excitability of reciprocal and recurrent inhibitory pathways after voluntary muscle relaxation in man.

We studied the potential contribution of postsynaptic mechanisms to the depression of reflex excitability which occurs immediately after a voluntary release from tonic muscle contraction. The excitability of the Soleus (Sol) motor pool was tested at rest and after voluntary muscle relaxation. In both cases the Sol H-reflex was conditioned by a single shock to the peroneal nerve, in order to activate the Ia interneurones (INs) mediating the reciprocal inhibition via a peripheral input, or by a short-lasting voluntary contraction of the Tibialis Anterior (TA) muscle, to activate the Ia INs via a central command. Changes in excitability of Renshaw cells were also tested at rest and after release, to assess the role of recurrent inhibition in the release-induced inhibition of the Sol H-reflex. It was demonstrated that: the excitability of the INs mediating the reciprocal inhibition was only slightly enhanced in comparison with resting conditions; the H-reflex of the antagonist muscle (TA) evoked after Sol release was not consistently facilitated with respect to rest; the command to contract the TA muscle reduced the H-reflex of the Sol muscle during rest but not after Sol release; recurrent inhibition did not increase its effect in the post-release period. Such features suggest that recurrent and reciprocal post-synaptic inhibitions do not play a major role in reducing the reflex excitability of a relaxing muscle; rather, the command to release prevents the reciprocal inhibitory effect which accompanies the contraction of the antagonist muscle.(ABSTRACT TRUNCATED AT 250 WORDS)