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R R Tasker

Publications and source records attributed to R R Tasker.

At least 37 records · Page 2Linked to original sources
PubMed1989

Thalamic stimulation and recording in patients with deafferentation and central pain.

Thalamic exploration was carried out in 39 patients with central or deafferentation pain. Several patients were explored more than once or bilaterally; therefore, 52 explorations were carried out. In 16 cases, microelectrode recording and microstimulation were employed. In the deafferented thalamus, a phenomenon of central allodynia was identified, in which patients with hyperpathia experience pain on stimulation rather than the usual sensations. With microrecording, a distinct unit firing in bursts can be identified and classified into three types. In several patients, the thalamic somatotopic map is found to be altered, and this reorganization can be classified into four types.

Afferent Pathways↗
PubMed1988

Single-unit analysis of the human ventral thalamic nuclear group: somatosensory responses.

1. We have studied the functional and somatotopic properties of 531 single mechanoreceptive thalamic neurons in humans undergoing stereotactic surgery for the control of movement disorders and pain. The majority of these somatosensory cells had small receptive fields (RFs) and were activated in a reproducible manner by mechanical stimuli applied to the skin or deep tissues. These neurons, which we termed "lemniscal," could be further classified into those responding to stimulation of cutaneous (76% of lemniscal sensory cells) or deep (24%) structures. 2. The incidence of neurons having cutaneous or mucosal RFs in the perioral region, thumb, and fingers (66%) was much higher than that of neurons having RFs elsewhere on the body. Most of the deep cells were activated by movements of and/or mechanical stimuli delivered to muscles or tendons controlling the elbow, wrist, and fingers. 3. Sequences of cells spanning several millimeters in the parasagittal plane often exhibited overlapping RFs. However, RFs changed markedly for cells separated by the same distances in the mediolateral direction. This suggests that the cutaneous somatotopic representation of each region of the body is organized into relatively thin sheets of cells oriented in the parasagittal plane. 4. By comparing neuronal RFs in different parasagittal planes in thalamus of individual patients we have identified a mediolateral representation of body surface following the sequence from: intraoral structures, face, thumb through fifth finger to palm, with forearm and leg laterally. 5. Along many trajectories in the parasagittal plane the sequence of cells with overlapping RFs was interrupted by another sequence of cells with RFs corresponding to a different body region. The RFs of the intervening sequence characteristically represented body regions known to be located more medially in thalamus (see 3 above). These findings could be explained if the lamellae postulated above were laterally convex. 6. Cells responding to deep stimulation (deep cells) could be further classified into those responding to joint movement (63%), deep pressure (15%), or both (22%). Deep cells were found usually at the anterior-dorsal border and sometimes at the posterior border of the region containing cells responding to cutaneous stimuli. Although there was some overlap in the RFs, deep cells representing wrist were found medial to those representing elbow, and both of these were found medial to cells representing leg.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1988

Methods for microstimulation and recording of single neurons and evoked potentials in the human central nervous system.

An apparatus and technique are described for microstimulation and recording of both slow wave and single neuron (single unit) activities during functional stereotaxic procedures. This method facilitates microstimulation and evoked potential and single unit analysis which, in combination, provide optimum definition of stereotaxic targets in the treatment of functional disorders of the human central nervous system.

Brain↗
PubMed1988

Single unit analysis of the human ventral thalamic nuclear group: correlation of thalamic "tremor cells" with the 3-6 Hz component of parkinsonian tremor.

Although cells firing at tremor frequency, called "tremor cells" (Guiot et al., 1962), have often been recorded in the thalamus of parkinsonian patients, the extent of correlation between these spike trains and tremor has rarely been assessed quantitatively. This paper describes spectral cross-correlation functions calculated between the activity of "tremor cells" and electromyogram (EMG) signals recorded from several muscles in the contralateral arm. The power occurring in the spike train at tremor frequency was described in absolute terms by the spike autopower, and in relation to the average for all spectral components by the spike autopower signal-to-noise ratio (spike autopower SNR). The probability of significant cross-correlation between the thalamic spike train and EMG at tremor frequency was assessed by the coherence at tremor frequency. Autopower spectra of the activity of many of these cells exhibited a concentration of power at tremor frequency, indicated by spike autopower SNRs as high as 18. Of the EMG signals studied, signals recorded from finger flexors were most often significantly correlated at tremor frequency. Significant correlation between the thalamic spike train and finger flexor EMG activity was found in 34% of cells analyzed. Tremor frequency coherence was significantly correlated with tremor frequency spike autopower (r = 0.46, p less than 0.0001) and spike autopower SNR (r = 0.533, p less than 0.0001). The proportion of cells with a spike autopower SNR greater than 2 that were significantly correlated with finger flexor EMG activity was greater than that of cells with a spike autopower SNR of less than 2 (p less than 0.001; chi-square). Therefore, cells exhibiting a large amount of power at tremor frequency were those best correlated with EMG activity during tremor. Some of these cells may be involved in the generation of tremor.

Action Potentials↗
PubMed1988

Thalamotomy in generalized dystonia.

A prospective long-term semiquantitative evaluation of the results of ventral intermediate-posterior ventral oral nucleus thalamotomy on the different aspects of dystonia was made in 29 patients with secondary disease, 12 with nonfamilial, eight with (non-Jewish) familial, and seven with atypical DMD. The effect of disease progression, even in secondary patients, on surgical outcome was reviewed. Thalamotomy resulted in a long-term improvement in limb function of more than 25% to 50% in 23% of the patients, over 50% in 34% of patients, but midline features responded poorly. Manual dexterity was little changed in secondary cases because of underlying paralysis but improved 38% in cases of DMD. Involvement of neck and trunk, of three to four limbs, and progressive disease prognosticated for a poorer result, but phasic and tonic, familial, and nonfamilial dystonia respond equally well and age at surgery made no difference. Significant complications in 29 secondary cases included one death 31 days postoperative, one case of worsened hemiparesis, two cases of worsened dysarthria, two cases of worsened locomotion, one case of hydrocephalus requiring shunting, and one case of need for permanent tracheotomy. In 27 cases of typical and atypical DMD, there were two instances of hemiparesis, two of significant speech deterioration, three of hand ataxia, one of postoperative seizures, and one of hydrocephalus requiring shunting for an overall significant morbidity rate of 21%. The limiting factor in treating secondary dystonia is the underlying spastic paralysis but that in DMD is the relentless postoperative progression. The overall results of this study are remarkably similar to those of other published series: a quarter of the patients improved by 25% to 50%, a quarter to a third by more than 50%. The analysis of effect on specific features of the disease may be useful in the future for predicting outcome in a particular patient.

Dystonia↗
PubMed1987

Long-latency reflex activity in squirrel monkeys with occlusion of the middle cerebral artery.

The primate middle cerebral artery (MCA) preparation has been studied as an animal model of human spasticity resulting from stroke. MCA occlusion in 3 squirrel monkeys was accomplished through a transorbital approach and animals were evaluated by 'clinical' examinations and studies of EMG responses to torque motor imposed joint displacement. Animals were transiently hemiparetic but not spastic postoperatively, although all were found to have a large infarct in MCA territory on post-mortem examination. The electromyographic (EMG) response of biceps in normal animals to torque motor imposed elbow extension consisted of both early (M1) and late (M2) components (Tatton et al. 1975). These components were unchanged following MCA occlusion. The EMG response to metacarpophalangeal joint extension in finger flexors or normal animals consisted solely of a long-latency (M2) component (Lenz et al. 1983a). Following MCA occlusion the M2 component in this muscle was decreased or absent, but a short-latency (M1) component appeared.

Animals↗
PubMed1987

Microelectrode techniques in localization of stereotactic targets.

Although physiological corroboration of the target is essential in functional stereotactic surgery, the collected data can also be used for the offline study of normal and abnormal brain function. Such studies have the advantage of being made in actual clinical states with the unique opportunity of communicating with the patient. Correlations were made between microelectrode recordings and microstimulation at the same thalamic site with the same microelectrode in 'normal' patients, in those with tremor and in those with central and deafferentation pain. Human somatosensory organization is similar to that of subhuman primates. Five types of tremor cells have been identified-unresponsive nonsynchronous, unresponsive synchronous, kinaesthetic, voluntary, and voluntary with receptive field. While the last two qualify in latency and connectivity as tremor pacemakers, system analysis suggests an important element of long loop feedback as well. In the pain patients, five features were identified-somatotopic reorganization, altered firing in reorganized cells, bursting cells induction of burning widespread in thalamus and reproduction of the patient's pain by microstimulation-possibly a 'central allodynia' found in deafferented somatosensory thalamus particularly in patients with allodynia or hyperpathia. All but the latter effects may be merely the consequence of deafferentation and were seen in a 'control' stroke patient with dystonia, sensory loss but no pain.

Brain Mapping↗
PubMed1987

Selection of the optimal lesion site for the relief of parkinsonian tremor on the basis of spectral analysis of neuronal firing patterns.

Techniques for quantitatively describing the firing properties of neurons have been used to identify thalamic cells with a firing pattern which is correlated with EMG activity during tremor. By locating these cells relative to the anterior border of the somatosensory nucleus and the anterior commissure-posterior commissure line, it may be possible to select the optimal lesion site for the relief of parkinsonian tremor on a rational rather than an empirical basis.

Humans↗
PubMed1987

Thalamic microelectrode recording and microstimulation in central and deafferentation pain.

Microelectrode recording and microstimulation (in 1 case macrostimulation) were used to localize stereotactic targets in 8 patients with central and deafferentation pain and 1 'deafferented control' patient without pain. Off-line study revealed two features commonly proposed as potential physiological factors for such pain, but they were present in both pain and control patients--somatotopographic reorganization and the presence of bursting cells. In all patients in whom stimulation induced pain referred to deafferented parts of the contralateral body, hyperpathia or allodynia were present instead of normal paraesthetic, sensorimotor or thermal responses.

Electric Stimulation↗
PubMed1987

Spinal meningioma en plaque. Report of two cases.

Two cases of spinal meningiomas exhibiting en plaque patterns of growth are presented, one of which is reviewed more fully with emphasis on the radiographic and histological characteristics. The difficulties in diagnosis of this unusual tumor, its surgical management, and its postoperative course are discussed.

Aged↗
PubMed1985

Cross-correlation analysis of thalamic neurons and EMG activity in parkinsonian tremor.

Bursting activity in cells cross-correlated with electromyographic (EMG) activity during parkinsonian tremor. Statistically significant evidence of cross-correlation was found for 49% of cells located at the lesion target for relief of tremor. Statistically significant correlation was found for 90% of cells having tremor frequency power greater than twice 'average power' at nontremor frequencies. This population of cells may be involved in the generation of parkinsonian tremor.

Electromyography↗
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↗