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At least 19 recordsLinked to original sources
PubMed1976

Audio-spinal influence in man studied by the H-reflex and its possible role on rhythmic movements synchronized to sound.

An investigation was made of the time course of audio-spinal influences in man using the H-reflex technique and non-startling sounds. It was found that in all subjects the sound potentiated the H-reflex at a central latency of 80 msec, the peak facilitation (185%) being attained at 110--130 msec. The mean duration of this facilitation was 200 msec ranging from 120 to 460 msec. No inhibition was seen to follow the excitatory period. An habituation study showed a significant drop in peak facilitation after exposure to ten conditioning stimuli but a constant increase of the H-reflex above control level even after 60 presentations. The time course of this audiospinal facilitation was superposed over the EMG events during hopping to a simplified musical stimulus. In this situation, landing occurred some 50 msec prior to the ON beat or strong beat of the music. With this mode of synchronization, the timing of the ON and OFF beats of the musical stimulus would be suitable to potentiate the EMG events related respectively to the peak upwards acceleration determining the take-off and to the landing. It is inferred that during synchronized stereotyped movements to repetitive auditory stimuli, the motor events are timed to make best use of a potential audio-spinal facilitation.

Adolescent↗
PubMed1979

Effects of H-reflex conditioning upon the contralateral alpha motoneuron pool.

H-reflex recovery curves have been elicited by subliminal conditioning stimuli applied to the ipsilateral and contralateral posterior tibial nerves in 10 healthy female subjects. In both types of recovery curve there was clear evidence of a period of facilitation in the ipsilateral soleus motoneuron pool 75-250 msec after the conditioning stimulus. These results indicate the bilateral nature of the facilitation and show it to be most probably produced by stimulus-evoked inputs as opposed to twitch-evoked inputs. If the facilitation is produced by descending long-loop reflex influences, then complementary evidence is provided for previous electromyographic data showing the bilaterality of long-loop reflexes evoked by percutaneous electrical stimulation. It is impossible, however, at the present time, to rule out the possible involvement of cutaneous afferent discharges or other stimulus evoked inputs in the late facilitation.

Adult↗
PubMed1979

Assessment of the H-reflex excitability curve using a cubic spline function.

A procedure for modeling H-reflex recovery curve data is described. The procedure involves fitting a cubic spline function to the recorded data points in such a way that the goodness of fit is determined by the standard error of the mean of each point. The cubic spline function possesses numerous advantages over other subjective and objective procedures for extracting information from the excitability curve.

H-Reflex↗
PubMed1975

Startle responses recorded in the leg of man.

The EMG pattern of startle reactions in the leg was studied in man using a 100 msec, 1 kc/sec squre wave tone burst of 114 dB as the auitory stimulus. At rest, 74 responses were recorded in the ankle flexor tibialis anterior (TA) and 23 in the ankle extensor gastrocnemius (G) with a significantly different mean latency of 151 and 123 msecrespectively. During tonic extension or flexion of the ankle, the EMG response in TA or G consisted in a burst of activity superimposed on the voluntary EMG at a latency of approximately 150 msec after the onset of the tone burst and followed, at 200 msec, by a period of EMG silence lasting close to 100 msec. Similar periods of silence also occurred as the sole EMG modulation in response to sound. Although predominant in flexors, startle reactions are significant in extensors during or after tonic ankle extension suggesting that audiospinal influences may be channelled to one or the other group depending on their functional state. The silent period of EMG following an excitatory startle or appearing on its own suggests an important inhibitory component in audiospinal mechanisms particularly related to startle since it had not been disclosed in a previous study of the modulation of the H-reflex by non-startling auditory stimulus. From the distribution and EMG pattern of startle, it is inferred that audiospinal influences may be meaningfully integrated through the reticulospinal system in sound guided behaviour.

Acoustic Stimulation↗
PubMed1978

Stretch and Hoffmann reflexes during phasic voluntary contractions of the human soleus muscle.

Measurements were made of EMG responses in human soleus muscle, following torque disturbances of the foot during phasic voluntary plantarflexions. These were compared with measurements of the Hoffmann reflex during identical voluntary movements. We observe that stretch adequate to evoke a stretch reflex in the relaxed limb often fails to evoke any response during a phasic contraction until about 120 msec after the onset of the stimulus. During this period the H-reflex is facilitated. These findings are discussed in terms of the servo-theory of stretch reflex function and the concept of trans-cortical stretch reflexes.

Adult↗
PubMed1976

Occurrence of the H reflex and the F wave in the rat.

In adult rats the tibial nerve was stimulated at the ankle and the evoked EMG of the foot muscles was recorded. A low threshold reflex discharge was elicited that was subsequently depressed by stronger stimuli eliciting the direct (M) wave. This discharge was abolished by cutting the dorsal roots (except for 1-3% postulated to be due to recurrent discharge). It had a central latency of about 2 msec, was depressed by stimulation rates above 0.3/sec and showed posttetanic depression, all of which are also properties of the rats's monosynaptic reflex. By analogy it is assumed to be an H reflex.

Animals↗
PubMed1976

Excitability of human motoneurones after discharge in a conditioning reflex.

A new method of exploring the H reflex excitability cycle is proposed which permits the exploration of motoneurones that discharged in response to the conditioning shock. This is made possible by using a test stimulus supramaximal for the alpha motor fibres of the nerve, which causes a collision in the alpha fibres between the orthodromic conditioning reflex volley and the antidromic motor volley. As a result of this collision, a test reflex contraction appears in the EMG, due to motoneurones that have already discharged in the conditioning response. This method permits studies in human subjects of the poststimulus refractory period of motoneurones as well as the early inhibitory phenomena related to the conditioning stimulus and response. It is shown that during the initial period of the classical H reflex excitability cycle, the test shock explores only alpha motoneurones corresponding to a fringe of cells subliminally excited by the conditioning stimulus. The difference between the populations of motoneurones tested by the two methods explains the differences between the features of the cycles obtained.

Evoked Potentials↗
PubMed1976

The relation between monosynaptic spinal reflex amplitudes and some EEG alpha activity parameters.

Some investigators have found that in normal human subjects the amplitudes of repetitively evoked tendon reflexes decrease as the number of evoked reflexes progresses. The question whether this decrement is a spinal phenomenon or that it can be ascribed to supraspinal influences that are related to the degree of cortical activation was investigated in two experiments designed to test whether a relation exists between the Hoffmann (H) and Achilles tendon (T) reflex amplitudes and EEG alpha activity parameters during a rest condition. The principal results can be summarized as follows: 1. A constant alpha index was accompanied by stable reflex amplitudes. 2. A decreasing alpha index was accompanied by decreasing reflex amplitudes. 3. A positive relation was found between H and T reflex amplitudes. 4. A positive relation was found between alpha index and alpha amplitude. 5. No circumscribed relation was found between the alpha wave period on the one side and the alpha index and amplitude on the other side. Apparently these relations are dependent on the state of activation of the subject. 6. The relations between the reflex amplitudes and the alpha parameters showed great interindividual differences.

Adult↗
PubMed1976

Extinction of the Hoffmann reflex by antidromic conduction.

We have shown that one cause of the extinction of the Hoffmann reflex by antidromic conduction in the alpha motor axons must be a relative refractoriness of the motoneuron pool. A hypothesized collision between the H-wave and the antidromic M-wave component is not disproved but it (and the incumbent assumptions about relative afferent and efferent conduction velocities) is shown to be unnecessary. A montonic variation of the M-wave with tonic soleus contraction (M-wave increasing with contraction) is observed but not explained.

Evoked Potentials↗
PubMed1977

[Somatosensory evoked potentials and Hoffmann reflex in acute spinal cord lesions; physiopathological and prognostic aspects].

Twenty-four patients with recent and acute spinal cord lesions were examined. The somatosensory cerebral evoked potential (SEP) following stimulation of the peroneus communis nerve tested spinal conduction, whereas the H reflex showed spinal excitability belowe the lesion. After complete spinal cord section, the SEP was always abolished and the H reflex was absent in most cases tested in the first 24 hours. Into other patients, the recruitment curve and the recovery cycle of the H reflex displayed some abnormalities which progressively disappeared. With partial lesions, SEP could occasionally be altered. Some abnormalities of the H reflex recovery cycle, of the same type as those seen in the late stage of complete sections, were also observed. These data give nre information on the physiopathology of spinal shock; they lead to the distinction of several evolutionary stages after acute spinal lesions and also have prognostic disgnificance.

Adolescent↗
PubMed1978

[Electrophysiological study of latent neuropathies induced by perhexiline].

The aim of this study was to estimate the frequency of latent perhexiline-induced neuropathy in man. Several electrophysiological parameters were recorded and compared between a control group and a group of treated patients, without clinical evidence of neuropathy. The Hmax/Mmax amplitude ratio of the soleus H reflex was decreased in 2/3 of the patients. The H reflex latency was increased in 1/3 of them. The distal motor latencies of ulnar and popliteal nerves were increased in 1/4 of them. Only 1/3 of the patients treated did not show any electrophysiological abnormality. The validity of these results and the possible mechanisms involved are discussed.

Adult↗
PubMed1979

Hyperbaric hyperreflexia: tendon-jerk and Hoffmann reflexes in man at 43 bars.

Tendon jerk (TJR) and Hoffmann (H) reflexes of the soleus muscle were studied in two men during a 26-day simulated oxygenhelium dive to a maximum pressure of 43 bars. The amplitude of the TJR response was observed to increase markedly after compression and also at the end of decompression. This biphasic pattern of enhanced reflectivity was reproduced by synchronised but much smaller variations in H reflex response. The positive facilitatory effects of applying Jenkdrassik's manoeuvre were reduced and the negative effects increased during hyperbaric exposure. Excitability cycles (twin-pulses methods) revealed modifications in one subject similar to those observed in clinical hyperreflexia, namely a shortening of Phase III and an enhancement of Phase IV. The other subject exhibited a notable depression of Phase IV. Abnormal EMG recordings are described including randomly-triggered slow wave potentials with no mechanical effects, and fixed, long latency late responses of a reflex nature with a definite mechanical effect. The contention that alterations in vestibulo-spinal relations may result in the release from tonic presynaptic inhibitory control of myotatic reflex arc excitability is discussed as a partial explanation for these and related findings.

Adult↗