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Biomedical subjects

J C Rothwell

Publications and source records attributed to J C Rothwell.

At least 325 records · Page 18Linked to original sources
PubMed1984

On the significance of giant somatosensory evoked potentials in cortical myoclonus.

Four patients with cortical myoclonus were studied. All had reflex muscle jerking and grossly enlarged somatosensory evoked responses (SEPs) following electrical stimulation of the digital nerves. In addition, three of the patients had spontaneous or action-induced myoclonus. Back-averaging the EEG from these spontaneous muscle jerks showed a large positive wave over the contralateral somatomotor cortex which preceded the jerk by about 20 ms. Administration of lisuride (0.1 mg iv) reduced the severity of the reflex and spontaneous myoclonus, but had no effect on, or increased the size of the SEP. Two of the patients also received 1 mg clonazepam iv. As with lisuride, the severity of myoclonic jerking was reduced although the size of the SEP was increased. It is concluded that the usual association between giant SEPs and reflex muscle jerking can be abolished by acute administration of lisuride and clonazepam in patients with cortical myoclonus.

Adult↗
PubMed1983

Transmission in the spinal reciprocal Ia inhibitory pathway preceding willed movements of the human wrist.

Transmission in the Ia inhibitory pathway from wrist extensor muscles onto flexor motoneurones was investigated in the 160 ms period prior to a willed movement in 6 human subjects. H-reflexes were evoked in flexor muscles at various times before the onset of electromyographic activity. Disynaptic inhibition of the H-reflex was produced by low intensity stimulation of the antagonist radial nerve. Prior to a wrist flexion movement, transmission in the inhibitory pathway was diminished. Prior to an extension movement it was facilitated. The findings are consistent with the notion that the command to the agonist motoneurones acts also on a specific population of Ia inhibitory interneurones.

Afferent Pathways↗
PubMed1983

Interaction between the long-latency stretch reflex and voluntary electromyographic activity prior to a rapid voluntary motor reaction.

The size of the long-latency component of the stretch reflex has been examined in the time interval between a signal to move and the required rapid voluntary contraction of triceps and flexor pollicis longus in 8 normal subjects. Bilateral movements of the elbow and thumb were made following an auditory signal. In 50% of the trials a torque pulse was applied unilaterally in order to elicit a stretch reflex response in one arm. The voluntary response in the contralateral arm was uncorrupted by a stretch reflex response, so was used as an indicator of voluntary reaction time. Control experiments, using an electrical stimulus to the fingers rather than muscle stretch, verified that both arms reacted almost simultaneously to the auditory cue, even when the reaction time was shortened by the presence of a unilateral electrical stimulus. Similarly, an interposed muscle stretch stimulus considerably reduced the reaction time to the audio signal. Because of this, the start of the voluntary EMG response frequently 'over-lapped' the end of the long-latency stretch reflex. Failure to take this shortening of voluntary reaction time into consideration can lead to the erroneous conclusion that reflex gain is increased prior to a rapid movement. If the 'overlap' of EMG responses is accounted for, very little change in the size of the long-latency stretch reflex is evident prior to activation of the muscles responsible for the movement of either the elbow or the thumb.

Acoustic Stimulation↗
PubMed1983

Cortical reflex myoclonus responds to intravenous lisuride.

Six patients with myoclonus were given 0.1-0.15 mg lisuride i.v. All patients had stimulus-sensitive myoclonus and an increased size of somatosensory evoked potentials, and in three there was electrophysiological evidence of a cortical event time-locked to the jerks. All subjects showed a considerable diminution of spontaneous, action- and stimulus-evoked jerking. Lisuride has potent central dopaminergic and serotonergic actions. Administration of the dopamine agonists levodopa or apomorphine had no effect on myoclonic jerking in any of the six patients. Detailed pharmacological analysis of the myoclonus in one patient showed that levodopa, apomorphine, and haloperidol had no effect, and that haloperidol did not prevent the therapeutic action of lisuride. 5-Hydroxytryptophan abolished the myoclonus, and methysergide prevented the beneficial effect of lisuride, although it did not alter spontaneous myoclonus. These observations suggest that lisuride improves some types of reflex, stimulus-sensitive cortical myoclonus by a serotonin agonist action.

Adult↗
PubMed1983

The function of the antagonist muscle during fast limb movements in man.

We have examined fast flexion movements of the human thumb and fast extension movements of the elbow over three different distances at a variety of speeds in order to elucidate the function of the antagonist muscle in these circumstances. All movements were of such a velocity that they showed the typical bi- or triphasic pattern of muscle activation in agonist and antagonist. Slower movements, with continuous agonist activity, were not analysed. For movements made through the same angle at different velocities, there was a linear relationship between the amount of antagonist activity needed to halt the movement and the peak velocity. However, the slope of this relationship was a function of the distance moved. Movements made through large angles showed less antagonist activity than those made through small angles at the same speed. The timing of the antagonist activity also changed as a function of both distance and speed. Fast, small movements showed earlier onset of antagonist activity than slow, large ones. Movements which were halted mechanically with the subject's prior knowledge had little or no antagonist activity, since it was no longer necessary in these conditions. The complexity of these relations indicates that the triphasic pattern of muscle activity underlying these movements can no longer be regarded as a simple immutable 'programme'. The size and timing of the bursts of muscle activity are subtly adjusted to the precise nature of the task.

Action Potentials↗
PubMed1983

The behaviour of the long-latency stretch reflex in patients with Parkinson's disease.

The size of the long-latency stretch reflex was measured in a proximal (triceps) and distal (flexor pollicis longus) muscle in 47 patients with Parkinson's disease, and was compared with that seen in a group of 12 age-matched normal control subjects. The patients were classified clinically into four groups according to the degree of rigidity at the elbow or tremor. Stretch reflexes were evaluated while the subject was exerting a small force against a constant preload supplied by a torque motor, and the size of the reflex response was measured as fractional increase over basal levels of activity. When stretches were given at random intervals by increasing the force exerted by the motor by a factor of 2 or 3, there was a clear trend for the more severely affected patients to have larger long latency responses in the triceps muscle, although there was no change in the size of the short-latency, spinal component of the response. In contrast, there was no change in the size of the long-latency response of the flexor pollicis longus in any group of patients with Parkinson's disease. Despite any differences in reflex size, the inherent muscle stiffness of both muscles appeared to be normal in all groups of patients with Parkinson's disease, since the displacement trajectory of the limb following the force increase was the same as control values in the short (25 ms) period before reflex compensation could intervene. In 20 of the patients and in seven of the control subjects, servo-controlled, ramp positional disturbances were given to the thumb. Up to a velocity of 300°/s, the size of the long-latency stretch reflex was proportional to the log velocity of stretch. This technique revealed, in both moderately and severely rigid patients, increases in the reflex sensitivity of the flexor pollicis longus, which had not been clear using step torque stretches alone. However, whether using ramp or step displacements, long latency stretch reflex gain was not closely related to rigidity; reflex size was within the normal range in many patients with severe rigidity. Enhanced long latency stretch reflexes thus contribute to, but may not be solely responsible for, rigidity in Parkinson's disease.

Electromyography↗
PubMed1983

Postanoxic symptomatic oscillatory myoclonus.

Two young patients with a history of birth anoxia and cerebral palsy developed paroxysmal irregularly oscillating muscle jerks at rest and during voluntary movement. Electrophysiologic studies revealed short bursts of alternating activity at 4 to 6 Hz in antagonist muscles. The absence of time-locked EEG discharges suggests a subcortical origin for this unusual form of myoclonus. A comparison is made between this and previously reported conditions with a similar paroxysmal burstlike nature.

Child↗
PubMed1983

Myoclonic dystonia.

We studied 14 patients who had a combination of idiopathic torsion dystonia and myoclonic jerks. In many cases, the same muscles were involved in both the myoclonus and the dystonia. This made observation of the crucial dystonic postures difficult and led to misdiagnosis of other dyskinesias. The jerks usually were brief (50 to 200 msec) and occurred irregularly, often showing cocontraction in antagonist muscles. Frequently, they were superimposed upon sustained dystonic contractions in the same or distant muscles. We found no time-locked EEG event before the jerks. The myoclonus probably arises from a subcortical focus, and the visible jerks probably are part of the spectrum of involuntary movements that accompany torsion dystonia.

Adolescent↗
PubMed1982

Manual motor performance in a deafferented man.

We have studied manual motor function in a man deafferented by a severe peripheral sensory neuropathy. Motor power was almost unaffected. Our patients could produce a very wide range of preprogrammed finger movements with remarkable accuracy, involving complex muscle synergies of the hand and forearm muscles. He could perform individual finger movements and outline figures in the air with high eyes closed. He had normal pre- and postmovement EEG potentials, and showed the normal bi/triphasic pattern of muscle activation in agonist and antagonist muscles during fast limb movements. He could also move his thumb accurately through three different distances at three different speeds, and could produce three different levels of force at his thumb pad when required. Although he could not judge the weights of objects placed in his hands without vision, he was able to match forces applied by the experimenter to the pad of each thumb if he was given a minimal indication of thumb movement. Despite his success with these laboratory tasks, his hands were relatively useless to him in daily life. He was unable to grasp a pen and write, to fasten his shirt buttons or to hold a cup in one hand. Part of hist difficulty lay in the absence of any automatic reflex correction in his voluntary movements, and also to an inability to sustain constant levels of muscle contraction without visual feedback over periods of more than one or two seconds. He was also unable to maintain long sequences of simple motor programmes without vision.

Adult↗
PubMed1981

Gating of somatosensory evoked potentials during different kinds of movement in man.

1. Somatosensory evoked potentials from electrical stimulation of the digital nerves of the right thumb have been recorded during the performance of various motor tasks in eight normal subjects. 2. The N20-P30 primary cortical response is only moderately affected by task context, while the P45-N55 secondary response is markedly 'gated' by movement of the stimulated digit. The late N140 vertex is variable. 3. In most subjects, active and passive movements are about equally effective in suppressing the secondary complex; but in one, passive movement has come to be rather less effective than active. 4. Secondary response suppression occurs in proportion to the velocity of the movement of the thumb, up to a velocity of 20 deg/s. 5. Secondary response suppression is unrelated to load in the range 0 to 0.16 Nm. 6. When the stimulus is timed to occur at various points in movement, secondary complex suppression occurs at all stages; but there is little or no suppression when stimulation is timed at 200 ms before the start of or 500 ms after the end of a movement. 7. Secondary response suppression is maximal when the same digit is both moving and shocked. When the right index or little finger are moved instead, the right thumb being stimulated, suppression is less; when the left thumb moves, no suppression is seen. 8. Secondary response suppression is reduced but not lost if the skin and interphalangeal joint of the thumb are anaesthetized distal to the stimulating electrodes. 9. Secondary response suppression is unimpaired when the radial nerve is anaesthetized, paralysing the finger extensors. 10. In an attempt to identify the course taken by the afferent volley between the primary and secondary responses, and to identify the gating site, we recorded the responses in six patients with Parkinson's disease who had undergone thalamotomy. Their secondary responses were present, and gated in the normal way. 11. We are unable to confirm whether the secondary response represents the re-arrival at cortical level of a volley that has traversed the cerebrocerebellar loop. 12. We confirm that the secondary complex is located a little anterior to the primary cerebral response. 13. We conclude that a gating action is exerted in the brain on somatosensory afferent activity, after it first reaches the cortex, and that this gating action associated with movement is controlled by other afferent signals from the stimulated limb, and particularly from the stimulated digit.

Adult↗
PubMed1981

Reliability and efficacy of the long-latency stretch reflex in the human thumb.

1. The amount of positional compensation afforded by the long-latency reflex in the flexor pollicis longus has been investigated in ten normal human subjects. 2. The interphalangeal joint of the thumb was extended by between 2 and 40 degrees at up to 900 deg/s by suddenly increasing the standing force applied to the lever against which the subject was pressing with the pad of the thumb. 3. Electromyographic (e.m.g.) responses at spinal-latency were very small or absent for stretches of this magnitude. The long-latency stretch reflex produced an average positional correction of about 50% for disturbances in the range of 5-25 degrees. The response began to saturate for disturbances of greater than 25 degrees. 4. The e.m.g. response was pulsatile, lasting only some 50 ms, even during continuously increasing disturbances; frequently it terminated despite a remaining positional error. 5. There was a large variation from subject to subject in the average amount of positional correction provided by the stretch reflex. Examination of single responses to the same stretch in individual subjects showed an even greater variation from trial to trial. 6. Variation in the compensation produced by the long-latency stretch reflex from trial to trial could not be explained by the slight variation in size or maximum velocity of the individual stretches.

Adult↗
PubMed1981

Simple tics in Gilles de la Tourette's syndrome are not prefaced by a normal premovement EEG potential.

EEG events prior to simple tics have been examined in six patients with Gilles de la Tourette's syndrome, and compared to EEG changes occurring when the same subjects voluntarily mimicked their own tics. Voluntary jerks were prefaced by a premovement negative potential commencing about 500 ms prior to the muscle EMG discharge and reaching an amplitude of about 7 muV. No such premovement potential was evident in the EEG prior to spontaneous tics in five of the six patients; a very small event was seen in the sixth patient but it was only about one-tenth of the size of the premovement potential seen prefacing voluntary jerks in the same subject. These data indicate that simple tics in Gilles de la Tourette's syndrome are physiologically distinct from normal self-paced willed movements.

Action Potentials↗