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Biomedical subjects

R R Tasker

Publications and source records attributed to R R Tasker.

At least 109 records · Page 6Linked to original sources
PubMed1983

What happened to VIM thalamotomy for Parkinson's disease?

A prospective review of 75 of 190 parkinsonian patients undergoing unilateral thalamotomy was displayed with a computer graphics technique examining three equal consecutive groups from the pre-, early, and late L-dopa eras. Histograms for average function and scattergrams of individual patient's performance preoperatively and up to 2 years postoperatively were prepared. No ipsilateral effects or consistent iatrogenic deterioration of any function were identified. 2 years after surgery, 82% had no tremor in the contralateral fingers or hand and 7% had almost no tremor; contralateral tremor elsewhere was infrequent. Rigidity and manual dexterity improved less strikingly, the latter only reflecting abolition of tremor; locomotion, speech, facial movement and handwriting did not improve. There was no mortality, but 8% had persistent significant complications. VIM thalamotomy remains the treatment of choice for severe drug-resistant parkinsonian tremor.

Adult↗
PubMed1983

Ruptured berry aneurysm of the anterior ethmoidal artery associated with bilateral spontaneous internal carotid artery occlusion in the neck. Case report.

A unique case is described of subarachnoid hemorrhage from a ruptured berry aneurysm of the right anterior ethmoidal artery, and its pathogenesis is discussed. The literature suggests an increased incidence of posterior circulation aneurysms in moyamoya disease, of contralateral anterior circulation aneurysms in agenesis of the carotid artery, and of aneurysms at various sites in spontaneous and iatrogenically acquired obstructions of the internal carotid artery. In addition to congenital anomalies of the vessel wall and systemic hypertension, increased regional blood flow should be regarded as an important factor in the generation of berry aneurysms.

Aged↗
PubMed1983

Electromyographic response to displacement of different forelimb joints in the squirrel monkey.

The electromyographic (EMG) reflex response evoked in muscles stretched by imposed angular joint displacement has previously been studied in a variety of muscles and species. In most muscles studied, the EMG response consists of an initial burst of activity at latencies comparable to tendon tap responses followed by one or more bursts of EMG activity occurring at latencies less than somatosensory reaction time. The longer latency bursts or peaks of activity have often been assumed to be of similar origin in functionally diverse muscles. The present experiments were performed to examine the EMG response to imposed joint displacement in several different muscles of the squirrel monkey forelimb. The EMG was studied in muscles stretched by elbow, wrist, and metacarpophalangeal joint extension. Early (M1) and long (M2) latency peaks of activity could be observed in the EMG responses of short head of biceps (SHB), flexor carpi ulnaris (FCU), and flexor digitorum profundus (FDP), at latencies which are similar to those reported in other primate species allowing for differences in the size of the animals. The intervals between these peaks did not correspond to the period of oscillations in tension which occurred after the onset of the joint extension. The M2 peak consistently occurred later in SHB than in FCU and FDP. The M1 peak was smaller in distal than in proximal muscles and was frequently absent in FDP at resting levels of EMG activity. The ratio of M1 to M1 + M2 activity for different muscles revealed that proximal muscles had prominent early with less prominent long latency activity, whereas distal muscles had minimal early latency activity with prominent long latency activity. The onset of EMG activity approached tendon tap latencies in FCU at high base line EMG levels but in most cases occurred at approximately twice tendon tap latencies in FDP at high base line EMG levels. The results demonstrate the presence of significant differences between the EMG response to joint displacement in the proximal-distal series of forelimb flexors. Differences in the reflex response to joint displacement are discussed in view of twitch times and motor unit composition of the muscles studied.

Animals↗
PubMed1983

The effect of cortical lesions on the electromyographic response to joint displacement in the squirrel monkey forelimb.

The extent of participation of supraspinal structures in the generation of the long latency (M2) electromyographic (EMG) response to imposed joint displacement may be reflected in the effect of lesions of the central nervous system. M2 activity has been reported in a variety of studies to be either present or absent following supraspinal lesions. Since other studies have shown different characteristics of long latency activity in proximal as compared to distal upper limb muscles in primates, the present experiments were conducted to determine the effect of motor cortical (area 4) lesions on reflex activity generated in a proximal versus a distal upper limb muscle. Chronic experiments were performed on squirrel monkeys with unilateral lesions of the forelimb motor cortex (area 4) which was mapped with the aid of electrical stimulation. Input-output relationships were determined between torque motor-imposed joint rotation and the EMG response in the stretched muscles (flexor digitorum profundus (FDP) and short head of biceps (SHB)). The EMG responses were reported as a percentage of maximum EMG output and controlled for base line EMG level. The "gain" (slope of EMG response versus torque load) for FDP M2 activity was markedly decreased in the limb contralateral to the area 4 lesion as compared to the opposite limb. This decrease was independent of base line EMG levels. In SHB, early latency (M1) EMG activity was significantly increased, but M2 activity appeared unaffected on the side contralateral to the lesion. The results demonstrate that the central and peripheral mechanisms generating M2 activity in FDP differ from those in SHB in terms of motor cortical dependency.

Animals↗
PubMed1982

Identification of pain processing systems by electrical stimulation of the brain.

Much can be learned about the brain's function in pain processing through electrical stimulation. The spinothalamic tract which is conceived to be the chief pathway for nociceptive pain and whose interruption induces dissociated sensory loss can be recognized from the anterolateral columns of the spinal cord to the posterior thalamus by the induction of feelings of chiefly contralateral, somatotopographically organized, warm, cool, or cold sensations, less often burning and rarely pain. The spinoreticulothalamic tract, whose function in normal pain processing is controversial and whose interruption produces no clinically detectable sensory loss, is normally silent to stimulation. However, in patients with deafferentation pain, it appears to become sensitive to electrical stimulation, both in the anterolateral columns and in midbrain and medial thalamus, giving rise to chiefly contralateral, non-somatotopographically organized, burning or painful sensations which often reproduce fairly accurately the patient's pain. This phenomenon, which does not appear to occur in patients with nociceptive pain, may reflect denervation neuronal hypersensitivity which is a possible pathophysiological mechanism explaining deafferentation pain. The dorsal column/lemniscal system can be recognized by electrical stimulation from the spinal cord to the somatosensory cortex by the induction of paraesthesiae. Its chronic stimulation at the level of the dorsal column, the ventrocaudal nucleus or the internal capsule appears capable of suppressing deafferentation pain. The arc of neuronal tissue extending from the septal area through hypothalamus and periventricular grey to the periaqueductal grey, which acts as a receptor area for opiates and endorphins, thereby exerting an inhibitory effect on access to the spinothalamic tract, can also be exploited through chronic stimulation for the control of pain. Stimulation of the periventricular area gives rise to feelings of warmth, comfort and relaxation, of the hypothalamus, horror and autonomic effects while that of the periaqueductal grey induces discomfort, distress, anxiety and weeping, and of the septal area flushing, paraesthesiae, nausea, nystagmus and a feeling of warmth. Thus four brain systems involved in pain signalling can be recognized by electrical stimulation, one which conveys nociceptive pain to consciousness, another that suppresses it, one that may undergo denervation neuronal hypersensitivity and bring deafferentation pain into consciousness, possibly by establishing novel connectivity and one that is presumably capable of suppressing that hyperactivity.

Afferent Pathways↗
PubMed1980

Visual phenomena evoked by electrical stimulation of the human brain stem.

19 visual effects have been elicited out of 9,383 sites during stimulation mapping for physiological localization during stereotactic surgery. It is proposed that three visual pathways can be recognized during subcortical electrical stimulation in man. The optic tract and geniculocalcarine pathway, projecting to area 17, are recognizable by the production of contralateral coloured phosphenes. The tectopulvinar pathway projecting to areas 18 and 19 is recognizable by the eliciting of contralateral or bilateral colourless phosphenes or 'negative' visual effects, the latter presumably reflecting inhibitory collicular influences. Finally, deep responses, consisting of apparent movement of the visual fields, intermingled with 'negative' visual and oculomotor effects, suggest activation of a visual-oculomotor coordinating system.

Brain Mapping↗
PubMed1980

Deafferentation and causalgia.

The concept of deafferentation pain has been developed as an entity distinct from somatic pain which can arise in the course of both cancerous and nonmalignant disease. Its distinctive clinical features and responses to diagnostic and therapeutic manipulations have been reviewed. Evidence is marshalled to show that it results from gradually developing alterations in the central nervous system, which, once established, persist despite removal of the original stimulus. Evidence is presented that the mesencephalic tegmentum may be part of a reticulothalamocortical system undergoing denervation hypersensitivity following deafferentation, whose stimulation by electric impulses, and, presumably, naturally occurring neural inputs, can result in a painful conscious experience reproducing the patient's pain in a manner similar to that whereby stimulation of temporal-parietal association cortex elicits recall of past events.

Anesthetics, Local↗
PubMed1978

Vestibulothalamic projections in man--a sixth primary sensory pathway.

1. Responses suggesting activation of the vestibular system, elicited by electrical stimulation of the human thalamus during 22 routine stereotaxic neurosurgical procedures, were examined in a retrospective study to determine the possible existence of vestibulothalamo-cortical projections in man. 2. Such responses were most frequently described as sensations of movement through space and were associated with two distinct vestibulothalamic projections: a) an anterior relay was situated ventral to the medial lemniscus, passing lateral to the red nucleus and dorsal to the subthalamic nucleus prior to terminating in the nucleus ventrointermedius (Vim) (comparable to VPLo in primates); b) a posterior relay associated with the auditory pathway (lateral lemniscus and brachium of the inferior colliculus) projected to the medial geniculate body. 3. The production of sensations of motion in conscious patients by stimulating areas that are similar to those reported constituting vestibulothalamic pathways in cats and primates implies a distinct primary sensory cortical projection for processing information from the vestibular receptors pertaining to the recognition of spatial movements.

Brain Mapping↗
PubMed1978

Computerized graphic display of physiological data collected during human stereotactic surgery.

An on-line computerized graphic display has been developed for use during stereotactic operations. This depicts in the form of figurine charts and alph-numeric symbols, appropriately oriented on saggital brain diagrams, the results of serial threshold stimulation of the brain. The display facilitates choice of target sites and the data can be stored in a tape library from which search-and-plot programs can be activated for any type or combination of types of response.

Brain↗
PubMed1977

Computerized graphic display of results of subcortical stimulation during stereotactic surgery.

An on-line computer programme is described and illustrated which is capable of displaying graphically in the form of Woolsey-type figurine charts stimulation-induced responses obtained during stereotactic surgery. Not only can these data then be optimally utilized for lesion localization but also the programme includes facilities for a variety of types of analysis of the tape-stored data pooled from all patients studied.

Computers↗
PubMed1976

Computer mapping of brain-stem sensory centers in man.

A computer program is described for use on-line with a two--stage stereotaxic technique in man. It has four capabilities. It transposes coordinates between a brain atlas and a stereotaxic frame, simultaneously adjusting for variations in individual brain dimensions. Corrections for electrode trajectories, and for any irregularities of placement of the stereotaxic frame in the head are also made. It plots an operative template that shows electrode trajectories and the sites from which physiological data are collected appropriately oriented upon a sagittal diagram of the brain. It graphically displays physiological data in the form of a Woolsey-type figurine chart that indicates threshold in milliamperes and, through the use of coded symbols, the quality of response and certain other data. It stores all this data in a tape library together with the locations of any lesions made. This makes it possible to replot any individual patient's operative data at any time. It also permits scanning of the stored protocols from all patients for any particular type of data either by itself or in combination with other data. This retrieved information is plotted on appropriate sagittal brain diagrams corrected for individual variations in brain size. Illustrations of the capabilities of the program are presented particularly with reference to the primary afferent pathways of the upper brain stem.

Afferent Pathways↗
PubMed1975

Decorticate spasticity: a re-examination using quantitative assessment in the primate.

Decorticate spasticity in the squirrel monkey was chosen as a convenient laboratory model of spasticity capable of quantitative assessment upon which to evaluate various currently popular clinical spasmolytic measures. The effects of a wide variety of cortical lesions were studied involving primary and supplementary motor, premotor and parietal cortex unilaterally and bilaterally, measuring muscle tone with the evoked integrated E.M.G. technique. Measurable spasticity resulted only if primary motor cortex was ablated bilaterally usually but not always preferentially involving biceps brachii and quadriceps. Resulting postures were variable offering no justification for the term "decorticate posture". The integrated evoked E.M.G. was proportional to rate of stretch and chiefly phasic in type as in hemiplegic man. Stereotactic dentatectomy resulted in profound ipsilateral reduction in this spasticity, but was without effect in intercollicular or anemic decerebrate cats. The mechanism of the spasticity and of the cerebellar effects are discussed.

Animals↗
PubMed1975

Neurological concepts of pain management in head and neck cancer.

The physiological basis, historical evolution, and our own practice of stereotactic surgery for the relief of cancer pain are briefly described. Thirty-nine procedures have been performed on 33 patients, 27 for pain due to cancer. Lesions have been made both in the specific neospinothalamic pathway of midbrain and thalamus and in the non-specific reticulothalamic system with an overall five per cent mortality and five per cent morbidity. Initial pain relief was achieved in 90 per cent of patients with relief till death in 74 per cent. Lesions were more successful in releiving pain when the specific pain system was involved but only if the analgesia produced by the lesion "covered" the patient's pain. On the other hand, dysesthesia occurred only with lesions of the specific system, especially if they involved the thalamus.

Brain↗