Search PubMed⌕ Search

Biomedical subjects

J C Rothwell

Publications and source records attributed to J C Rothwell.

342 records · Page 19Linked to original sources
PubMed1980

Anticipatory postural reflexes in Parkinson's disease and other akinetic-rigid syndromes and in cerebellar ataxia.

We have examined anticipatory postural responses in calf muscles (triceps surae) in response to a small pull to the arm in standing subjects. This stimulus normally evokes a brisk automatic compensatory contraction of the calf muscles. This is not due to calf muscle stretch, for leg movement occurs after the response has appeared. It appears to be driven centrally by input produced by the pull to the arm. Such anticipatory postural responses were present in every one of the 50 normal subjects studied, but were absent or greatly reduced in many patients with Parkinson's disease when compared to age-matched normal subjects, particularly in those exhibiting postural instability. However, a normal anticipatory postural response was elicited in four patients with progressive supranuclear palsy and in a single patient with an akinetic rigid syndrome due to cerebrovascular disease. Cerebellar truncal ataxia only depressed the response in severe cases. We conclude that although these responses may not be necessary to maintain balance, they may be employed in fine adjustment of posture.

Cerebellar Ataxia↗
PubMed1980

A grab reflex in the human hand.

The effect of stretching or unloading flexor pollicis longus indirectly has been investigated by altering the force on the wrist while the subject tracked a moving spot on a cathode ray oscilloscope by flexing the top joint of the thumb against a fixed stiff lever. A radialward pull on the wrist, which lifted the thumb off the lever, thereby indirectly unloading flexor pollicis longus, caused a burst of EMG activity about 50 to 60 ms later, rather than the silent period seen at the same latency when the muscle was unloaded directly. A similar burst of activity occurred in the long finger flexors. Letting the wrist go, which caused the thumb to hit against the lever thereby indirectly stretching flexor pollicis longus, produced an initial burst of EMG activity about 50 ms later, as occurred when the thumb was stretched directly; but this was terminated prematurely after about 10 ms by a paradoxical silent period. The response of flexor pollicis longus to indirect unloading was not altered by anaesthetizing the skin of the wrist under the chain pulling it, nor by anaesthesia of the thumb, so was not due to cutaneous stimuli. Nor was it affected by motor point anaesthesia of flexor pollicis longus, so it was unlikely to be due to changes in spindle input from that muscle. However, it was reduced considerably by bracing the arm, suggesting that it arose as a result of movement proximally at the shoulder. The response to indirect unloading of flexor pollicis longus by a pull on the wrist did not occur if the subject held the lever free in his hand, indicating that it was dependent on and adapted to the task. A similar response to a pull on the wrist occurred if the subject was asked merely to hold his thumb and fingers adjacent to a full sherry glass. In these circumstances wrist release also caused a thumb flexion. Such an automatic flexion response or 'grab reflex' helps the subject to maintain contact of his digits with an object when his hand is displaced from it, provided that is his intent. Although the response occurs too early to be voluntary, it depends on the nature of the task and the subject's prior instruction.

Electromyography↗
PubMed1980

A patient with reflex myoclonus and muscle rigidity: "jerking stiff-man syndrome".

A patient with progressive muscular rigidity associated with reflex myoclonus is described. The muscular rigidity was predominantly axial, and the myoclonic jerks affected axial and leg muscles. Jerks occurred either spontaneously, or in response to touch to the perioral region, or to stretch of head and neck muscles. Physiological investigations suggested that the myoclonus originated in the medulla and was mediated by fast-conducting pathways upwards through the brainstem and down the spinal cord. The relationship of this condition to other types of muscular rigidity with and without myoclonus is discussed.

Adult↗
PubMed1979

Effect of thumb anaesthesia on weight perception, muscle activity and the stretch reflex in man.

1. We have confirmed the results of Gandevia & McCloskey (1977) on the effect of thumb anaesthesia on perception of weights lifted by the thumb. Weights lifted by flexion feel heavier and weights lifted by extension feel lighter. 2. The change in size of the long-latency stretch reflex in flexor pollicis longus or extensor pollicis longus after thumb anaesthesia cannot explain the effect on weight perception by removal or augmentation of the background servo assistance to muscular contraction. 3. During smooth thumb flexion, thumb anaesthesia increases e.m.g. activity in flexor pollicis longus and extensor pollicis longus for any given opposing torque. 4. During smooth thumb extension the opposite occurs: e.m.g. activity in both extensor and flexor pollicis longus decreases. 5. Clamping the thumb at the proximal phalanx to limit movement solely to the interphalangeal joint reduces or abolishes the effect of anaesthesia on both weight perception and e.m.g. activity during both flexion or extension tasks. 6. Gandevia & McCloskey's findings on the distorting effects of thumb anaesthesia on weight perception cannot be used to support the hypothesis of an efferent monitoring system of the sense of effort. Our results emphasize the close functional relationship between cutaneous and joint afferent information and motor control.

Anesthesia, Local↗
PubMed1979

Primary writing tremor.

We describe a patient who complained of jerking of the right forearm on writing. Active pronation of his arm produced several beats of pronation/supination tremor. A burst of tremor also could be elicited by tendon taps to the volar surface of the wrist, to the finger extensors, and to pectoralis major, and by forcible supination of the wrist delivered by a torque motor. The subject's writing difficulty and tremor were temporarily abolished by partial motor point anaesthesia of pronator teres. We conclude that the tremor was caused by an abnormal response to muscle spindle input from pronator teres.

Adult↗
PubMedDate not supplied

The corticomotoneurone connection is normal in Parkinson's disease.

Voluntary movements in Parkinson's disease are initiated and executed slowly. It is assumed that the motor cortex and its output pathway are intact and that bradykinesia is due to abnormal motor commands delivered to a normal corticospinal system. We have tested this assumption using electrical stimulation of the motor cortex through the scalp in three patients with severe Parkinson's disease, studied during fluctuations from relatively normal mobility when receiving drugs (ON) to severe bradykinesia when not receiving drugs (OFF). Thresholds and latencies for motor cortex stimulation to excite thumb flexor muscles and the resulting fast mechanical responses were the same in both ON and OFF conditions, even though the patients were unable to execute fast thumb flexion movements voluntarily when OFF. We conclude that the excitability and conduction velocity of the corticospinal motor pathways are normal in Parkinson's disease.

Adult↗
PubMedDate not supplied

Low intensity strength training for ambulatory stroke patients.

PURPOSE: To investigate feasibility and effectiveness of an individually-directed, group strength-training programme on knee muscle strength after stroke. METHOD: Ten volunteers (62 +/- 11 years, mean +/- SD), 6 - 12 months after first-ever unilateral stroke, walking independently with or without aids were recruited. Using an A1-B-A2 design, 3 sets of baseline measures were taken at 2 weekly intervals; volunteers then attended twice weekly sessions of low intensity progressive strengthening exercises and were assessed after each series of 8 sessions to a maximum of 24 sessions; post training, measures were repeated after 4 - 6 weeks. Measures included isometric and concentric knee extensor muscle strength and 10 m walking velocity. RESULTS: Strength of knee extensor muscles was improved after training (ANOVA, p < 0.05). On cessation of training, isometric strength increased by 58 +/- 19% and concentric strength at 30 degrees /s by 51 +/- 14%; walking velocity quickened from 0.47 +/- 0.06 m x s-1 to 0.57 +/- 0.08 m x s-1 (t = -3.31, p < 0.01). These gains were maintained 4 - 6 weeks after completion of training. CONCLUSIONS: These findings support the use of low intensity strength training after stroke and confirm published evidence. It was feasible for one therapist to deliver the training programmes for 4 - 6 participants at a time; an important feature when resources are limited.

Aged↗
PubMedDate not supplied

[Changes of muscle excitability of the hand contralateral to a task performing one: a transcranial magnetic stimulation study].

It used to be considered that unilateral movements of distal limb parts are associated only with contralateral motor cortical activity. Recent neuroimaging studies, however, suggest that the motor cortex ipsilateral to a task-performing hand is also activated, and that motor patterns in one hand affect the degree of the activity of the ipsilateral motor cortex. If so, muscles of the hand contralateral to a task-performing one may change those excitability depending on types of tasks. We studied eight subjects who performed three different finger tasks by one hand: (a) pinch, (b) sequential finger opposition, and (c) tactile discrimination. Transcranial magnetic stimulation was delivered by a figure eight coil over the hemisphere ipsilateral to a task-performing hand. Motor evoked potentials and background electromyographic activities were recorded from the opponens pollicis muscle contralateral to the stimulated hemisphere. On average, the motor evoked potentials were larger during tactile discrimination task than those at rest in either hand (p < 0.01). Background electromyographic activities in the left hand increased significantly during right hand tactile discrimination task (p < 0.01), whilst those in the right hand did not change during the left hand performance (p > 0.05). These findings suggest the followings: (1) the hand muscle contralateral to a task performing one changes its excitability depending on types of tasks; and (2) increment of excitability of the left hand muscle associated with right hand tactile discrimination is greater than that of the right hand one in association with the same task by the left hand, thus supporting the idea that there is a functional asymmetry between the right and left motor cortex in respect of motor performance.

Adult↗
PubMedDate not supplied

Brainstem myoclonus.

In brainstem myoclonus, muscle jerks arise from activity in neuronal centres within the lower brainstem. The most common forms probably use the same circuitry as used by the normal startle reflex, which may be related to that described in animal experiments as the spino-bulbo-spinal reflex. In man, the jerks are generalized with long-lasting electromyographic bursts (greater than 100 ms), and may be provoked by many different types of sensory stimuli, although cutaneous taps around the nose and face are particularly effective. The neural activity spreads down from the brainstem via a relatively slowly conducting spinal efferent motor pathway. The cranial nerve nuclei are activated by rapid spread up the brainstem. Other forms of brainstem myoclonus may also exist, and these are characterized by more rapid conduction in spinal efferent pathways and greater sensitivity to muscle stretch rather than cutaneous input.

Animals↗
PubMedDate not supplied

Reduced late component of exteroceptive reflex in patients with Parkinson's disease.

The exteroceptive reflexes in the masseter muscles in patients with Parkinson's disease (PD) were examined. The reflex produced by 3 Hz mental nerve stimulation consisted of four negative peaks and three positive peaks in the unrectified recordings. The latencies of the peaks in patients with PD were the same as those in control subjects, except for the P2 component in the right masseter muscle. The amplitudes of N3-P3 and P3-N4 were smaller in patients with PD than those in control subjects. Interpeak latency of N3-N4 was shorter in PD patients. Exteroceptive suppression in the masseter muscles was also examined. The early component (ES1) of so-called exteroceptive suppression was normal in patients with PD. The duration and degree of the late component (ES2) of exteroceptive suppression decreased in patients with PD. According to the latencies, N1 and N2 speaks seem to be the onset and end of ESI; N3 and N3 peaks the onset and end of ES2, respectively. The early component did not show any significant abnormality. Reduced late component of exteroceptive reflex in patients with PD might be related to the abnormal motor control system of the facial muscles.

Electric Stimulation↗