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Biomedical subjects

B L Day

Publications and source records attributed to B L Day.

At least 91 records · Page 5Linked to original sources
PubMed1988

Percutaneous electrical stimulation of lumbosacral roots in man.

High voltage percutaneous electrical stimulation over the lumbosacral spinal column was used to assess conduction in the cauda equina of 13 normal subjects. Electromyographic activity elicited by such stimulation was recorded from various muscles of the lower limbs. The stimulating cathode was placed over the spinous process of each vertebral body and the anode kept on the iliac crest contralateral to the studied limb. Shifting the cathode in a rostro-caudal direction shortened the response latency in quadriceps, tibialis anterior and extensor digitorum brevis muscles. At moderate intensities (60% maximum), this occurred abruptly when the cathode was placed at levels corresponding to the exit sites from the spinal canal of the roots innervating these muscles. At these intensities, the size of the response in each muscle was largest when the cathode was placed over the conus medullaris or at or below the exit of the motor roots from the spine. Latencies were always equal to or shorter than those obtained with F-wave measurements, suggesting that peripheral motor axons, rather than intraspinal structures were activated by the stimulus. Collision experiments demonstrated that activation occurred at two sites: near the spinal cord and at the root exit site in the vertebral foramina. Recordings made from soleus indicated that larger diameter proprioceptive afferent fibres also could be activated. This technique might have useful clinical applications in the study of both proximal and distal lesions of the cauda equina and provide a non-invasive method of localising such lesions electrophysiologically.

Adult↗
PubMed1987

Modulation of the long-latency reflex to stretch by the supplementary motor area in humans.

Surface-recorded, electromyographic responses to 200-ms ramp stretches were studied in the wrist flexor muscles from both arms of a patient with clinical and radiographic evidence of infarction in the right supplementary motor area (SMA). They were compared with those from 8 age-matched control subjects. The latencies of the spinal component of the stretch reflex were slightly longer than normal in both arms of the patient (normal subjects: 28.5 +/- 2.6 ms; patient: 35 ms, right arm and 32 ms left arm). However, the amplitude and duration of the short-latency response were identical in both arms. The onset of the long-latency response to stretch was symmetrical in both the patient's arms and was slightly later than normal (normal subjects 55.5 +/- 4.0 ms, patient: 72 ms right arm and 70 ms left arm); however, its duration was considerably prolonged in the arm contralateral to the SMA lesion (normal subjects: 44.8 +/- 6.0 ms; patient: 48 ms right arm. 105 ms left arm). These results are consistent with the hypothesis that the long-latency stretch reflex is mediated via a transcortical loop.

Adult↗
PubMed1987

Different sites of action of electrical and magnetic stimulation of the human brain.

The latency of the surface recorded electromyographic response to either an electrical or magnetic stimulus applied to the scalp has been measured in the first dorsal interosseous and abductor pollicis brevis muscles of 3 subjects. In the contracting muscle the response latency to the magnetic stimulus was longer by 1.4-2.7 ms compared to the electrical stimulus. Poststimulus time histograms of the firing of single motor units of first dorsal interosseous muscle were studied in 4 subjects. The first period of increased probability of firing of the single motor units showed a similar latency difference (mean 2.8 ms) to the two modes of stimulation. It is concluded that the extra delay to magnetic stimulation is consumed in central motor pathways. This implies that the two modes of stimulation activate the brain at different sites. It is suggested that the magnetic stimulus excites the corticospinal neurones transynaptically, whereas the electrical stimulus excites these neurones directly.

Brain↗
PubMed1987

Examination of motor function in lesions of the spinal cord by stimulation of the motor cortex.

Electrical stimulation of the motor cortex was performed in 3 patients with cervical cord trauma and in 3 with cervical myelopathy caused by cervical spondylosis. Abnormal conduction in central motor tracts was demonstrated in 5 of the 6 patients; yet in 4 of these, cortical somatosensory evoked potentials from the same limb were of normal latency. In the remaining patient who had normal motor latencies, the somatosensory evoked potentials were delayed on one side. Electrophysiological examination of the motor pathways by cortical stimulation may therefore be of considerable value in the assessment and management of patients with traumatic and compressive disease of the spinal cord.

Adult↗
PubMed1987

The Bereitschaftspotential, L-DOPA and Parkinson's disease.

Bereitschaftspotentials (BPs) prior to extension movements of the index finger were studied in normal subjects and in patients with Parkinson's disease. In both, BPs were studied before and after L-DOPA therapy; in addition, the normal subjects were studied after dopamine antagonists. In both patients and normal subjects, L-DOPA caused an increase in the amplitude of the early part of the BP and of the point of peak negativity, just prior to EMG onset (N1) but it did not cause an increase of the late lateralized part of the BP (NS' of Shibasaki); in normal subjects dopaminergic antagonists caused a decrease in the amplitude of the N1. Control experiments suggested that the change caused by L-DOPA was not the result of slower movement or poorer triggering when OFF drugs. For patients with Parkinson's disease there was no correlation between the change in their peak BP negativity (N1) after L-DOPA and their change in clinical mobility; in addition, there was no difference in the peak BP negativity of patients OFF therapy and that of age-matched normals, though there was a slight decrease in the amplitude of the early part of the BP for the patients with Parkinson's disease; this was the same part that had been enlarged by L-DOPA therapy. These findings suggest that the N1 is not affected by Parkinson's disease and that the effect of dopaminergic drugs on the N1 is mediated by actions on dopaminergic mechanisms elsewhere than in the striatum, perhaps in the cerebral cortex itself. The effect of L-DOPA will need to be taken into account in subsequent studies of the BP in Parkinson's disease.

Adult↗
PubMed1987

The interpretation of electromyographic responses to electrical stimulation of the motor cortex in diseases of the upper motor neurone.

The complexities of interpreting results of electrical stimulation of the motor cortex in pathological states are discussed and illustrated by reference to results from a variety of patients with diseases affecting the upper motor neurone (multiple sclerosis, cervical spondylosis and myelopathy, motor neurone disease, hemiparesis due to cerebral infarction, and hereditary spastic paraplegia). The abnormalities of the electromyographic (EMG) responses after anodal cortical stimulation consisted of delay in the latency to onset, dispersion or reduction in response size or even absence of EMG responses. These changes were not confined to any specific condition or pathology. Previous work has suggested that the sequence of events that follow anodal cortical stimulation involves repetitive excitatory inputs to spinal motoneurones and transmission across at least one central synapse. Accordingly, delayed latencies may not exclusively indicate slowing of motor conduction, while the absence of any response may not indicate complete failure of conduction in corticomotoneurone pathways.

Adult↗
PubMed1987

Disturbance of sequential movements in patients with Parkinson's disease.

The following sequences of two single movements were examined in 10 patients with Parkinson's disease and compared with the performance of 9 normal subjects of similar age. Isometric opposition of thumb and fingers to a force of 30 N ('squeeze'), followed by isotonic elbow flexion ('flex') through 15 degrees with the same arm. 'Squeeze' with the left hand followed by 'flex' with the right elbow. Isotonic opposition of thumb and fingers ('cut') through 90 degrees followed by isotonic 'flex' with the same arm. Isotonic elbow 'flex' followed by isometric 'squeeze' with the same arm. All movements were self-paced. Subjects were given instructions to move as rapidly as possible and to start the second movement immediately after the end of the first. Patients were slower than normal when each single movement was performed separately. There was a further decrease in speed when two movements were executed sequentially. This was due to an increase in movement duration of each of the component movements, especially the second, and to an increase in the pause between the first and second movements. In both normals and patients, there was no correlation between the times taken to perform the first and second movements of any of the four sequences that were studied. Because of this we suggest that the two components of the sequence remained under the control of two separate motor programs. When performing the sequential tasks, normal subjects automatically chose an interval between the onsets of the two separate movements of about 230 ms, even in tasks in which the duration of the first movement was less than 200 ms. If normal subjects were instructed to begin the second movement with an interonset interval of less than 200 ms, the speed of the second movement was much slower. Patients with Parkinson's disease automatically chose a much longer interonset interval of 400-500 ms. In addition, they exhibited difficulty in switching from the first to the second movement in the sequence. We suggest that the problems exhibited by patients with Parkinson's disease when they try to perform two rapid sequential movements can be seen as a deficit in the capacity to switch from one motor program to another within an overall motor plan.

Adult↗
PubMed1987

Motor cortex stimulation in intact man. 1. General characteristics of EMG responses in different muscles.

This paper is the first of two papers describing our five-year experience with the technique of electrical stimulation of the human motor cortex. In this first paper we illustrate the basic distribution and behaviour of electromyographic responses in limb muscles to anodal stimulation of the motor cortex in intact, awake human subjects. These responses may be recorded at short latency, with estimates of conduction velocities from the brain to the spinal cord suggesting transmission in rapidly conducting pathways, such as the corticomotoneuronal component of the corticospinal tract. The site at which the stimulus activates these motor pathways to produce responses at such short latency is likely to be at, or adjacent to the origin of these major descending motor pathways in the cerebral cortex. The best stimulating sites for activation of arm or leg muscles corresponds to the known somatotopic arrangement of the cerebral cortex. The electromyographic response characteristics are different in the contracting, as compared with the relaxed muscle; the EMG response latency shortens, its size becomes larger and its threshold is lowered when the muscle is voluntarily made to contract. The mechanisms that are responsible for these characteristics are examined in the following paper.

Adult↗
PubMed1987

Motor cortex stimulation in intact man. 2. Multiple descending volleys.

Using an isometric strain gauge, we measured the twitch force produced in the first dorsal interosseous (FDI) muscle by a single anodal shock to the contralateral scalp. At high intensities of stimulation this twitch can greatly exceed the force produced by supramaximal stimulation of peripheral nerve. This indicates that a single cortical shock can cause repetitive firing of some or all FDI motoneurons. Such repetitive firing was demonstrated using a collision technique in which a supramaximal ulnar nerve stimulus was given at the wrist shortly after a cortical shock. The antidromic volley from the peripheral nerve stimulation failed to obliterate completely the response to cortical stimulation. Additional EMG activity was visible in the normally silent period between ulnar M and F waves. This activity must have been due to the presence of repetitive volleys of activity set up in spinal motoneurons by the cortical shock. Such activity summates with the twitch produced by the ulnar M wave to produce a very large force twitch of the muscle. Multiple firing of some motoneurons can be observed in some individuals at cortical stimulation intensities below that necessary to evoke activity in all the motoneurons in the FDI pool. Multiple firing probably was caused by repetitive excitatory inputs impinging on spinal motoneurons. These could be demonstrated using poststimulus time histogram techniques on single motor units. Low intensities of cortical stimulation produced a single short duration (mean 1.8 ms) peak of increased motor unit firing 20 to 30 ms after the shock. At high intensities, this was followed by extra peaks some 4 to 5 ms later. H reflex testing showed that the threshold of the initial descending volley, produced by the cortical stimulus was uninfluenced by a voluntary contraction. These results are discussed with reference to the D and I waves recorded from pyramidal tract after anodal stimulation of the exposed cortex in animals.

Biomechanical Phenomena↗
PubMed1987

Some experiences of techniques for stimulation of the human cerebral motor cortex through the scalp.

Stimulation of the motor cortex transcranially has shown a rough somatotopy of stimulation sites on the scalp corresponding to the homunculus and preferential activation of contralateral hand muscles, as well as very short latencies of signals in the cervical spinal cord. The responses are also facilitated by background activation of the muscles. We are reporting a set of patients studied using electrical and magnetic stimulation transcranially. We observed that the latency of electromyogram activation is much shorter in active than contracting muscles and that the muscle twitch produced by cortical stimulation can exceed the force produced by supramaximal stimulation of the peripheral nerve. Our findings suggest that this may be due to multiple firing of motor neurons. Another observation is that magnetic stimulation is not as subject to a reduction in the response latency with facilitation, and response latencies with magnetic stimulation were 2 ms longer than with electrical stimulation. The implications of these findings are discussed.

Adult↗
PubMed1987

Evidence favouring presynaptic inhibition between antagonist muscle afferents in the human forearm.

1. A single motor-threshold electrical stimulus to the radial nerve in the spiral groove produced three phases of inhibition in the H reflex of relaxed wrist and finger flexor muscles. The first phase of inhibition occurred with a conditioning-test interval of -1 to 3 ms and represents disynaptic Ia reciprocal inhibition of flexor motoneurones by afferent input from extensor muscles. The second phase occurred with a conditioning-test interval of 5-40 ms. The characteristics of the second inhibitory phase have been investigated in the present study. 2. The threshold intensity of radial nerve stimulation required to produce the second phase of inhibition was 0.7 X motor threshold and was the same as that required to produce the first (disynaptic) phase of inhibition. 3. The time course of the effect of a radial nerve stimulus on the size of e.m.g. response to transcranial electrical stimulation of the motor cortex also was studied. The results were compared to those obtained with H reflex testing. The time course and depth of the first phase of inhibition were identical with both test inputs. The second phase of inhibition, however, was seen only with the H reflex test stimulus. When the corticospinal volley was timed to arrive at the cervical cord 30 ms after the radial nerve afferent volley, the flexor muscle response was facilitated rather than inhibited. 4. A single stimulus (2-3 X sensory threshold) to the superficial (cutaneous) branch of the radial nerve at the wrist failed to produce inhibition of the flexor H reflex. Instead, the H reflex was facilitated when the median nerve Ia volley (for the H reflex) was timed to arrive at the cervical cord between 30-40 ms after the radial nerve cutaneous afferent volley. In contrast to results using mixed nerve stimulation in the spiral groove, there was no difference between the effect of this cutaneous input on the cortically evoked e.m.g. response and the H reflex. 5. We conclude that the second phase of flexor H reflex inhibition is produced by activity in large-diameter (group I) extensor muscle afferents which acts on the H reflex pathway at a premotoneuronal site.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Simple and complex movements off and on treatment in patients with Parkinson's disease.

The performance of a 15 degrees elbow flexion and a 30N hand squeeze was studied in nine normal subjects and in five patients with Parkinson's disease. The patients were studied when immobile after 12-18 hours withdrawal from antiparkinsonian drug therapy (OFF) and when more mobile after drugs (ON). Subjects performed each movement separately (simple movements) and both movements either simultaneously or sequentially (complex movements). The duration of both movements and the time between the onset of each movement in the sequential task (interonset latency) were measured. The patients OFF therapy had longer movement times than normal for both movements; these improved after levodopa but still were not normal. When the patients performed complex movements there was an extra slowness, over and above that seen for simple movements, in both movements of the simultaneous task and in the second movement of the sequential task. In addition, the interonset latency in the sequential task was longer than normal. After levodopa there was a more striking improvement in the movement times of complex movements than there had been for simple movements. The interonset latency in the sequential task was shorter than before therapy though still was not the same as in normal subjects. It is suggested that the basal ganglia are not only involved in the execution of simple motor programmes, but also play some role in the superimposition and sequencing of motor programmes.

Adult↗
PubMed1986

The physiology of orthostatic tremor.

This article describes the physiological findings in a patient with orthostatic tremor. The tremor primarily affected the legs, was alternating between antagonist muscle groups, and had a remarkably rapid frequency of 16 Hz. It was present only during certain postures and appeared to be of central origin. A tremor of the same frequency was also recorded in the arms during particular movements, but was cocontracting. We suggest that orthostatic tremor may be generated by spontaneous oscillation in those central structures responsible for organizing the motor programs for standing.

Electromyography↗
PubMed1986

Electrophysiology of the corticomotoneurone pathways in patients with movement disorders.

The corticomotoneurone pathways were examined in 21 patients with movement disorders, using the technique of percutaneous electrical stimulation of the motor cortex. Conduction in these pathways was assessed by measuring the latency to onset of electromyographic activity in the muscles of the upper limb after cortical stimulation. In all patients [five with primary (idiopathic) torsion dystonia and two with secondary (symptomatic) hemidystonia, seven with Huntington's disease, four with essential tremor, and three with Parkinson's disease] central motor conduction was normal. This and other evidence suggests that the origin of the disorder of movement in these conditions lies in the delivery of abnormal motor commands to a normal corticomotoneuronal system.

Adult↗
PubMed1986

Simple and complex movements in a patient with infarction of the right supplementary motor area.

The role played by the supplementary motor area (SMA) in the higher-level organization of motor behaviour (motor programming) has been highlighted by the study of cerebral blood flow during voluntary movements in normal humans. We present a detailed physiological investigation from a patient with a right SMA lesion and show that the right SMA plays a role in programming simultaneous and sequential movements in both arms, though the contralateral arm was the more severely impaired. In addition, we obtained evidence to suggest that the precentral motor cortex may be more responsive to peripheral perturbations when the modulating influence of the SMA is absent. In view of the similarity of the physiological findings in this subject to those in patients with Parkinson's disease, we suggest that the defect of motor programming in Parkinson's disease is likely to reflect functional deafferentation of the SMA.

Aged↗
PubMed1986

Habituation and conditioning of the human long latency stretch reflex.

The effects of stretch repetition rate, prior warning stimuli and self administered stretch were examined on the size of the short and long latency components of the stretch reflex electromyographic EMG response in flexor pollicis longus and the flexor muscles of the wrist and fingers. Stretches of constant velocity and extent were given every 10 s, 5 s, 2 s, or 1 s to either the wrist or thumb during a small background contraction of the flexor muscles. The size of the long latency component of the stretch reflex (measured as the area under the averaged rectified EMG responses) declined dramatically at faster repetition rates, especially in the wrist and finger flexors. The size of the short latency component was relatively unaffected. The size of the electrically elicited H-reflex in forearm muscles also failed to habituate under the same conditions. If each individual trial of a series was examined, the long latency component of the stretch reflex EMG could be seen to decrease in size over the first three to six stretches if stretches were given every 1 s, but not if stretches were given every 10 s. When stretches were given every 5 s to either wrist or thumb, an electrical stimulus applied to the digital nerves of the opposite hand 1 s before stretch reduced the size of the long latency component of the reflex EMG response. The short latency component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗