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Biomedical subjects

N M Murray

Publications and source records attributed to N M Murray.

At least 55 records · Page 3Linked to original sources
PubMed1987

Excitability of the human motor cortex is enhanced during REM sleep.

A conspicuous feature of rapid eye movement (REM) sleep is atonia of postural muscles due to a powerful brainstem inhibitory effect on spinal motoneurones. However, small myoclonic jerks occur during REM sleep and increased activity of cortical neurones is suggested by the EEG. Transcranial cortical stimulation with magnetic pulses has been used to investigate motor excitability during sleep in man. Motor responses were evoked during sleep using stimuli identical to those used in wakefulness. Response amplitudes were depressed during slow wave sleep (SWS) and enhanced or the same during REM sleep. These findings suggest that the susceptibility of the human motor cortex to stimulation is enhanced during REM sleep.

Electric Stimulation↗
PubMed1987

Magnetic brain stimulation: central motor conduction studies in multiple sclerosis.

Central motor conduction (CMC) was evaluated in 32 normal subjects and 83 patients with multiple sclerosis, and the findings were correlated with clinical signs and evoked potential data. CMC time was obtained from the latency difference in responses from the abductor muscle of the little finger to magnetic stimulation of the motor cortex and electrical stimulation at the C-7/T-1 interspace. Mean CMC time in normal subjects was 6.2 msec (SD 0.86 msec), and amplitudes of responses to cortical stimuli were at least 18% of those obtained with stimuli at the wrist. CMC was abnormal in 60 patients with multiple sclerosis (72%); this correlated well with brisk finger flexor jerks (p less than 0.005). CMC was abnormal in 79% of patients with weakness of the abductor muscle of the little finger and in 54% with a normal muscle. Neurological examination was normal in 7 arms with abnormal CMC. Visual evoked potentials were abnormal in 67%, somatosensory evoked potentials in 59%, and brainstem auditory evoked potentials in 39% of those tested. For each procedure more subjects had abnormal CMC and normal evoked potentials than the reverse. The technique is of value for demonstrating and documenting central motor pathway lesions in multiple sclerosis, especially when physical signs are equivocal.

Action Potentials↗
PubMed1987

Chronic demyelinating peripheral neuropathy associated with multifocal central nervous system demyelination.

A series of 6 cases is described in which a chronic demyelinating neuropathy was associated with a relapsing multifocal CNS disorder, the clinical features of which resembled multiple sclerosis. Multifocal CNS lesions were demonstrated by CT and MR imaging and the presence of CNS demyelination was indicated by prolonged central conduction times. These cases are discussed in relation to the occurrence of combined peripheral and central demyelination in chronic relapsing experimental allergic encephalomyelitis and neuritis.

Action Potentials↗
PubMed1987

Trigeminal sensory neuropathy. A study of 22 cases.

The clinical and electrophysiological findings in 22 patients with chronic trigeminal sensory neuropathy are described. The main clinical feature was slowly evolving unilateral or bilateral facial numbness sometimes associated with pain and paraesthesiae and commonly with disturbed taste. Nine patients had either systemic sclerosis or mixed connective tissue disease. Of the 13 other patients, 9 had either organ or nonorgan specific serum autoantibodies. Blink reflex latencies were recorded in 17 patients, the commonest abnormality being an 'afferent' defect with modest prolongation of latency. Trigeminal sensory evoked responses were recorded in 14 cases, 6 showing mild prolongation of latencies. It is suggested that the lesion in this type of trigeminal neuropathy is in the trigeminal ganglion or in the proximal part of the main trigeminal divisions. This conclusion is supported by limited pathological data.

Adult↗
PubMed1987

Magnetic and electrical transcranial brain stimulation: physiological mechanisms and clinical applications.

The human brain can be stimulated by electric shocks or by brief intense magnetic fields. The latter cause only a trivial scalp sensation. Stimuli exciting the motor cortex cause contralateral muscle responses, but the threshold for excitation is markedly reduced by slight voluntary contraction of the target muscle. For small hand muscles, the overall latency from scalp to muscle is shorter by 1.8 ms when electrical stimuli are used than when stimuli are magnetic. Central motor conduction time (CMCT) can be estimated by stimulating over the scalp and then over the cervical area. In healthy subjects, the CMCT is 6.1 +/- 0.8 (SD) (n = 29). Physiological studies have shown that the facilitation of responses in hand muscles produced by voluntary contraction is also present when contralateral muscles are used, but not when a leg muscle is contracted. The mechanism of facilitation may involve neural activity at both spinal and cortical levels. Single motor units can be caused to discharge by threshold brain stimuli. These motor units are the same ones activated first during weak voluntary contractions. Clinical studies have shown that the CMCT may be greatly prolonged in patients with multiple sclerosis and that subclinical motor pathway lesions can be detected. Central conduction may also be abnormal in patients with motor neuron disease and cervical myelopathy. Side effects have not been encountered with either type of stimulator.

Electric Stimulation↗
PubMed1987

Responses in small hand muscles from magnetic stimulation of the human brain.

1. The magnetic field generated by a brief current in a 9 cm diameter flat circular coil varies rapidly with time and when applied over the human scalp it is capable of exciting motor structures subserving the small hand muscles. With a peak magnetic field at the centre of the coil of 0.9-1.6 Tesla, single scalp stimuli produced twitches in the right abductor digiti minimi (a.d.m.), first dorsal interosseous (f.d.i.) and adductor pollicis muscles. Compound muscle action potentials (c.m.a.p.s) and single motor units from these muscles were recorded. 2. The twitch force and corresponding c.m.a.p. were greatly enhanced by voluntary background contraction of the muscle and depended on the direction and intensity of the magnetic field. Response amplitude was maximal with the stimulating coil centred near the vertex but precise coil position was not critical. 3. When the orthodromic volley set up in the peripheral nerve by magnetic stimulation of the brain collided with a maximal antidromic volley set up by stimulation at the wrist, remaining electromyographic (e.m.g.) activity gave evidence of multiple firing of some spinal motoneurones, provided that the muscle exerted a slight voluntary background contraction and the stimulus intensity was above threshold for relaxed muscle. 4. When the muscle changed from total relaxation to a slightly contracted state the onset latency of the c.m.a.p. was shortened by about 3 ms without further change when the background contraction increased. In slightly contracted muscle, c.m.a.p. onset latency was little affected over a wide range of stimulus intensities and was unaffected by the position of the stimulating coil within an area of 6 X 6 cm over the vertex. 5. Single motor units, recorded with needle electrodes in the a.d.m. or f.d.i. muscle, could be caused to discharge at a constant latency by threshold brain stimuli. Different single motor units had latencies varying from 22.4 to 32.1 ms. The same motor unit was activated from different coil positions up to 7 cm apart. These motor units had the lowest thresholds for voluntary activation. Stronger stimuli caused the same motor unit to discharge 1.5 ms earlier. 6. The threshold for excitation of pathways to the a.d.m. muscle was reduced by voluntary contraction of the contralateral a.d.m. and by contraction of the ipsilateral f.d.i. muscles. Using these procedures, the c.m.a.p. of totally relaxed a.d.m. muscle showed a more than 2-fold amplitude increase, a shortening of onset latency to a similar degree as with contraction of the muscle itself, and single motor units in the a.d.m. muscle discharged 1.5 ms earlier.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

McArdle's sign in multiple sclerosis.

A patient with multiple sclerosis is reported in whom neck flexion produced a reversible deterioration in gait and an increase in the degree of pyramidal weakness of the lower limbs. The name McArdle's sign is proposed.

Female↗
PubMed1986

Magnetic stimulation of the human brain: facilitation of motor responses by voluntary contraction of ipsilateral and contralateral muscles with additional observations on an amputee.

An intense rapidly changing magnetic field generated in a coil over the scalp can excite motor pathways to hand muscles. With a suprathreshold stimulus, the amplitude of the muscle action potential of the abductor digiti minimi is increased: by weak contraction of the muscle itself, by weak contraction of the ipsilateral first dorsal interosseus, by stronger contraction of the contralateral abductor digiti minimi, but not by contraction of the contralateral first dorsal interosseus, nor by the ipsilateral quadriceps muscle. This facilitation of response to brain stimulation may occur by two mechanisms, one related to the focussing of attention onto a particular hand, the second involving a rise in excitability of homologous motor pathways.

Amputation Stumps↗
PubMed1986

Measurement of central motor conduction in multiple sclerosis by magnetic brain stimulation.

Central motor conduction time (CMCT) to abductor digiti minimi was measured in 18 healthy subjects and in 15 patients with multiple sclerosis. A novel percutaneous magnetic stimulator was used to stimulate the motor cortex painlessly and CMCT was calculated by subtracting the onset latency of muscle responses obtained by electrical stimulation over the C7/T1 interspace from that obtained from stimulation over the scalp. In healthy subjects CMCT was 6.0 +/- 0.76 ms. In multiple sclerosis patients with pyramidal signs in the arms, CMCT was almost always prolonged, the longest conduction time being 39 ms. In 10 patients CMCT was prolonged despite normal strength in the muscle.

Action Potentials↗
PubMed1986

Electrical stimulation over the human vertebral column: which neural elements are excited?

Supramaximal percutaneous electrical stimuli applied over the human cervical vertebral column produce maximal compound muscle action potentials (CMAPs) in abductor digiti minimi. It is important to know which neural elements are excited by these stimuli and experiments were performed to answer this question. With stimulating electrodes placed progressively lateral to the midline, submaximal CMAPs with the same latency are produced. With shocks over the cervical vertebrae in the midline, the threshold for excitation of arm muscles is much lower than for excitation of leg muscles. Comparison of conduction time from the cervical column to more distal sites on the ulnar nerve by direct measurement and by F wave latency determination shows that the latter exceeds the former by 1.6 msec. Collision experiments in which paired shocks were given at the wrist and Erb's point or the wrist and cervical column showed that recovery from blocking as interstimulus interval lengthened was similar for the two sites, and that it was possible to detect F waves from the proximal stimulus. The latency of CMAPs evoked from midline surface stimuli was identical to that from a needle stimulus near the C8 root. It is concluded that electrical stimuli applied over the cervical vertebrae in the midline excite the motor roots at their exit from the spinal canal. This finding has implications for clinical studies of pyramidal tract and proximal peripheral nerve conduction.

Action Potentials↗
PubMed1986

Neurophysiological evaluation of associated demyelinating peripheral neuropathy and multiple sclerosis: a case report.

A case of combined multiple sclerosis and demyelinating neuropathy is presented. Percutaneous electrical stimulation of the cortex and spinal cord has shown that pyramidal tract conduction time was prolonged and conduction velocity in the cord was 4 m/s. Motor conduction velocity in proximal segments of peripheral nerves was slowed to the same extent as in distal segments.

Evoked Potentials↗
PubMed1985

Corticospinal tract conduction time in multiple sclerosis.

Anodal shocks of 400 to 700 V from a low-output impedance stimulator applied percutaneously over the motor cortex evoke muscle action potentials in partially voluntarily activated contralateral muscles. Cathodal shocks from the same device applied to the cervical spinal cord produce maximal ipsilateral muscle action potentials in a relaxed limb. This technique was used to study the central motor pathway in 15 healthy subjects and 8 patients with clinically definite multiple sclerosis. As stimuli were applied in the axilla, over the C7 vertebral level, and over the arm area of the motor cortex, recordings were made of muscle action potentials of forearm flexor muscles. In controls, cord-to-axilla conduction time was 4.1 +/- 0.61 ms, and cortex-to-cord time was 4.4 +/- 0.75 ms. In patients, cord-to-axilla conduction times were normal, while central conduction times were either markedly prolonged (6.4 to 31 ms) or absent. This technique is a potentially powerful tool for the investigation of central motor pathways in healthy subjects and patients with neurological disease.

Adolescent↗
PubMed1985

Epileptic psychosis: an evaluation of PSE profiles.

Data are presented on 24 patients with epilepsy and psychosis whose clinical presentation was rated using the Present State Examination (PSE). Seventeen had complex partial seizures and a diagnosis of temporal lobe epilepsy, seven had generalised epilepsy. An association between a CATEGO category of nuclear schizophrenia (NS) and a lesion of the left side was noted. No clear link between depressive symptoms and a right-sided focus was discovered. Affective disorders were noted in both groups of epileptic patients, although paranoid psychoses were commoner in the temporal lobe group. There was also a tendency for the latter to have more delusions of persecution, ideas of reference, and special features of depression. The group rated as NS appear less likely to show evidence of intellectual deterioration than the other psychotic patients; in addition, the interval between the onset of their epilepsy and the onset of their psychosis is shorter. Radiological assessment by CAT reveals few differences between groups, but the psychotic samples do show higher than expected values on a number of variables, in particular the bilateral septum-caudate distance and the size of the third and fourth ventricle.

Adult↗
PubMed1984

A comparison of concentric needle electromyography, quantitative EMG and single fibre EMG in the diagnosis of neuromuscular diseases.

Conventional concentric needle electromyography, quantitative electromyography using automatic analysis (Quant-EMG) and single fibre electromyography (SFEMG) were compared in the right biceps muscle of 10 patients with anterior horn cell disease and 20 patients with primary muscle disease. Abnormalities were demonstrable by all 3 techniques in the majority of cases irrespective of whether the biceps was weak. SFEMG was found to be more sensitive than Quant-EMG in neurogenic cases and it also provided an indication of disease activity. In cases of myopathy Quant-EMG was of more diagnostic help and was easier to perform than SFEMG. Large amplitude potentials found in some cases of myopathy were associated with increase in the mean amplitude on Quant-EMG and these probably emanate from hypertrophied muscle fibres.

Adult↗
PubMed1984

A clinical study of Gilles de la Tourette syndrome in the United Kingdom.

The clinical features of 53 British-born patients with Gilles de la Tourette syndrome are described. The mean age at onset of body tics was seven years and for vocalisations 11 years. Coprolalia was present in 39%, copropraxia in 21%, echolalia in 46% and echopraxia in 21%. Complicated antics and mannerisms were also common, often involving the compulsive touching of objects or self-injurious behaviour. Forty-six per cent of cases had a family history of tics in a single close relative and in two individuals a further member of the family had Gilles de la Tourette syndrome. Focal dystonia was present in four patients who had never received neuroleptics drugs and chorea was seen in two other untreated patients. In three patients acoustic startle consistently induced brief eye blink followed by a whole body jerk or jump. Rapid repetitive movements of the hands increased the frequency and severity of tics in 13 patients, but the performance of mental arithmetic under time pressure had a much more unpredictable effect. Electroencephalographic abnormalities occurred in eight (13%) but no definite CT brain scan abnormalities were detected. The incidence of left handedness did not differ from that in the general population and no evidence to suggest organic impairment was found on neuropsychological testing. This study provides no support for the notion that Gilles de la Tourette syndrome is a degenerative disorder of the central nervous system but provides some evidence for heterogeneity.

Adolescent↗
PubMed1984

Deliberate alteration of the visual evoked potential.

Seven out of 12 normal subjects could deliberately produce abnormal pattern-reversal visual evoked potentials (VEPs) which simulated disorders of the anterior visual pathways without detection. In six the mechanism was near-point accommodation and in one eccentric fixation. If voluntary suppression of the VEPs is suspected various modifications to the recording technique may be of value. These include the use of a large check size and stimulus field and binocular stimulation.

Adult↗