The muscle silent period: variability in normal man

SUMMARY The muscle silent period was measured in 11 patients with moderate to severe rigidity associated with Parkinson's disease. The determinations were made under conditions of maximum disability for each patient, since all medications had been withdrawn before testing. The duration of the EMG silence, produced by small and large electrical twitch contractions of the adductor pollicis muscle, fell within a range of values previously determined for normal individuals. Major alleviation of the rigidity and bradykinesia with chronic oral L-dopa therapy was not accompanied by any change in the silent period. It was concluded that in untreated Parkinsonism, and also after its treatment with L-dopa, the functioning of the muscle spindles and local inhibitory reflexes remains normal.Previous investigators (Angel, Hofmann, and Eppler, 1966), utilizing the unloading reflex, demonstrated that the electromyographic (EMG) silent periods in four patients with Parkinsonian rigidity were similar to those obtained in normal individuals. The present investigation, using 11 patients, demonstrated normal silent periods under conditions which provide additional insight into the reflex behaviour in Parkinsonism. The silent period was obtained by an electrically induced contraction of a single muscle (adductor pollicis). During maximal stimulation the early portion of EMG silence was a manifestation of inhibitory actions, while events related to muscle spindle function were identifiable in the termination of the silence (Granit, Kellerth, and Szumski, 1966; Higgins and Lieberman, 1968a, b). METHODThe technique of obtaining the silent period of the adductor pollicis muscle has been described previously (Merton, 1951; Higgins and Lieberman, 1968a, b). Two modifications were made to simplify the recording procedure.The first modification was that two skin surface electrodes with silver-silver chloride junctions (Beckman Bio-potential electrodes; diameter 2 mm) were used for EMG recording instead of needle electrodes. The active Identical silent periods were observed in the surface and needle electrode recordings obtained from a normal individual. The second modification was that stimulation of the ulnar nerve at the wrist and recording of EMG and tension responses were accomplished with a HewlettPackard Electromyograph (Model 1510A) equipped with a storage cathode ray tube and Polaroid camera.The ulnar nerve was stimulated at several intensities in order to compare the degree of inhibition associated with maximal and minimal isometric contractions. The stimuli occurred at equal or unequal intervals between I and 5 sec. Isometric tension was recorded with a Grass strain gauge (Model FT-10), as previously described. The amplified DC output of this gauge was applied directly to the vertical amplifier of the second recording channel of the electromyograph, by-passing the AC preamplifier.As in previous investigations of this type, close attention was given to the maintenance of steady tension and EMG levels before each electrical stimul...

Section: Resultssupporting

confidence: 73%

Section: Resultssupporting

confidence: 57%

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Muscle silent period in Parkinson's disease

Higgins

Haidri

Wilbourn

1971

“…The duration of the SP was taken as the interval between the onset (0) of the silence and the beginning of the uninterrupted voluntary activity (X). The latency time was measured from the stimulus (S) to the onset of the silence (Higgins and Lieberman, 1968;McLellan, 1973). In the patients, furthermore, the blink and jaw reflexes, recorded by the methods reported elsewhere (Ongerboer de Visser and Goor, 1974), and masseter EMGs were investigated.…”

Section: Methodsmentioning

confidence: 99%

Cutaneous silent period in masseter muscles: a clinical and electrodiagnostic evaluation.

Visser¹,

Goor²

1976

SYNOPSIS In 35 normal subjects electromyographic silent periods were constantly evoked bilaterally in the masseter muscles during maximal contraction after unilateral electrical stimulation over the infraorbital or mental nerve. Findings in this study and data obtained in 30 patients suffering from trigeminal (26) and facial (four) nerve lesions suggest that the silent period evoked according to our methods is cutaneous in origin. The trigeminal sensory root forms the afferent limb of the silent period reflex. Its central pathway is thought to pass both crossed and uncrossed through the pons. Determination of the cutaneous silent period might be of value for the demonstration of trigeminal nerve lesions and to supplement results concerning other brain-stem reflexes.The electromyographic silent period (SP) refers to a transitory, relative or absolute decrease of EMG activity evoked in the midst of an otherwise sustained contraction (Shahani and Young, 1973). The term SP should be reserved for reflex pauses following a stimulus of some kind -for example, an electrical shock-to peripheral nerves and the skin overlying them; phasic reflex contractions-for instance, a tendon tap; or sudden decreases in the load against which a muscle is contracting (unloading reflex). Several factors are involved in the SP, including recurrent inhibition of motoneurones (Renshaw inhibition), Golgi tendon organ inhibitory activity, a pause in muscle spindle input, cutaneous factors, and descending impulses from subcortical or cortical areas, as well as other mechanisms yet to be described (Shahani and Young, 1973;Struppler, 1975).In the masseter muscles SPs have been observed after acoustic stimuli, a tap on the chin, and stimulation applied to the surface of the tongue and to the masseter muscle belly (Hoffman and Tonnies, 1948;Struppler et al., 1960;

“…Series of 10 consecutive recordings were then averaged by the computer; the averaged traces were displayed on the storage tube of the computer and photographed. The length of the silent period was taken as the interval between the stimulus and the onset of uninterrupted voluntary activity, or the S-X interval (Higgins and Lieberman, 1968a).…”

mentioning

confidence: 99%

The electromyographic silent period produced by supramaximal electrical stimulation in normal man

McLellan

1973

SUMMARY The electromyographic silent period produced by supramaximal electrical stimulation of the median nerve was recorded in the abductor pollicis brevis muscle of four normal subjects during maximal isometric voluntary contraction. Except for an inconstant F response, electrical silence could usually be induced in the muscle from the twitch potential until the reappearance of uninterrupted voluntary activity. The silent period produced by stimulation at the wrist was approximately 25 msec longer than that produced by stimulation at the elbow and was independent of muscle tension. Further shortening of the muscle during the twitch contraction did not significantly alter the length of the silent period. A silent period in the abductor pollicis brevis muscle was also obtained after stimulation of the ulnar nerve, at the wrist and at the elbow. The onset of this period of silence was delayed, but it ended at the same time after the stimulus as the corresponding silent periods produced by median nerve stimulation. It is concluded that the end point of the silent period produced by supramaximal electrical stimulation of a mixed peripheral nerve is determined by an inhibitory spinal reflex, afferent impulses travelling in slowly-conducting fibres that are directly activated by the stimulus. Under these conditions the length of the silent period gives no indication of spindle activity in the muscle.