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R R Tasker

Publications and source records attributed to R R Tasker.

At least 19 recordsLinked to original sources
PubMed1992

Central pain in the absence of functional sensory thalamus.

Since the pioneering publication by Dejerine and Roussy, the thalamus has been commonly implicated in the pathogenesis of central pain. It is well known that cerebral lesions that spare the thalamus as well as both small and large ones within that structure produce similar pain syndromes, but could such pain develop if the thalamus were completely destroyed? CT scans of our patients suggested that it could. Moreover, exhaustive physiological explorations of the thalamus with macro- and microstimulation and microelectrode recordings in 2 more patients in whom CT scans suggested thalamic preservation despite massive suprathalamic infarcts, for the purpose of carrying out deep brain stimulation (DBS), revealed no evidence of ascending or descending diencephalic function. Their sensory examinations were similar to those of patients with congenital hemiatrophy who had undergone hemispherectomy. In 1 case, microstimulation of periaqueductal grey-periventricular grey (PAG-PVG) on the unaffected side of the brain induced the spectrum of responses correctly associated with these areas and during acute stimulation nearly abolished the patient's allodynia and hyperpathia. These observations suggest that processes occurring at a subdiencephalic level (or possibly ipsilaterally) may be involved in the generation of pain. Stroke-induced central pain remains a therapeutic dilemma for the pain surgeon, and the mechanisms underlying this pain state remain a mystery.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Arteries↗
PubMed1992

A comparison between magnetic resonance imaging and computed tomography for stereotactic coordinate determination.

The spatial accuracy of magnetic resonance imaging (MRI) has not been established for stereotactic surgery. Magnetic susceptibility artifacts may lead to anatomical distortion and inaccurate stereotactic MRI coordinates, especially when targets are in regions of the brain out of the center of the magnetic field. MRI-guided stereotactic localization, however, provides better multiplanar target resolution than is available with computed tomographic (CT) scanning. Therefore, we compared the accuracy of stereotactic coordinates determined by MRI and CT studies in 41 patients (53 targets). Coordinates were measured in each plane and as vector distances between the target and the center of the stereotactic frame on axial or coronal MRI studies. Absolute axial plane MRI and CT distances varied an average of 2.13 +/- 1.59 mm. The mean difference in measurements in the X (left-right) dimension was 1.19 mm and 1.55 mm in the Y (anterior-posterior) dimension. Central targets (located less than 2 cm from the frame center) had a mean MRI-CT difference of 2.09 +/- 1.79 mm; peripheral targets (greater than 2 cm from the frame center) differed by 2.17 +/- 1.3 mm. The voxel volumes were calculated for all compared images. Although differences between the physical properties of data acquisition with each imaging modality could explain the observed CT-MRI discrepancies, a 1-pixel difference in target selection could account totally for all the variance observed. MRI field strength (0.5 vs. 1.5 T) did not correlate with coordinate determination accuracy. We conclude that MRI-guided stereotactic localization can be used with confidence for most diagnostic, functional, and therapeutic stereotactic procedures.

Artifacts↗
PubMed1992

Intractable pain of spinal cord origin: clinical features and implications for surgery.

The clinical features and types of pain affecting 127 patients with central pain caused by lesions in the spinal cord were studied and correlated with the results of surgical procedures performed on 103 of them. The surgical procedures consisted of percutaneous cordotomy in 39 cases, cordectomy in 12, dorsal root entry zone (DREZ) surgery in four, dorsal cord stimulation in 35, and brain stimulation in 13. The three most common types of pain in the 127 patients were characterized as: steady in 95% of cases, intermittent (usually shooting) in 31%, and evoked (allodynia, hyperpathia, or hyperesthesia) in 45%. Steady pain was usually causalgic (74.8%) or dysesthetic (27.6%). The only obvious clinical correlation with pain type was the association of intermittent pain with lesions at the T10-L2 vertebral level. Destructive surgery (cordotomy, DREZ surgery, or cordectomy) affected the three chief types of pain differently from treatment with cord or brain stimulation. Destructive surgery resulted in reduction of steady pain in 26% of affected cases, of intermittent pain in 89%, and of evoked pain in 84%, while stimulation resulted in pain reductions in 36%, 0%, and 16% of cases, respectively. The differential effect of destructive surgery on steady and intermittent pain is consistent with published experience. These observations suggest differing mechanisms for the three types of pain.

Humans↗
PubMed1991

Neurones with epileptiform discharge in the central nervous system and chronic pain. Experimental and clinical investigations.

Epileptiform discharge was recorded from neurons in the thalamic nuclei of chronic pain patients during stereotactic surgery. Hyperactive neurons showed regular firing of 3-5 trains of epileptic-like group discharges with a frequency of 4 to 5 Hz. As described by Lombard et al. (1979), we operated on the dorsal root unilaterally, sectioning C5 to Thl in male Wistar rats. One to three months after the operation, hyperactive neurons were examined in the contra-lateral thalamic nuclei (VP, zona incerta), and lemniscus medialis. The firing patterns and distribution of hyperactive neurons in these animals was very similar to those of humans. The hyperactive neuron was unaffected by electrical stimulation of the nucleus raphe dorsalis (NRD) and locus ceruleus (LC). Administration of phenytoin and diazepam reduced the firing. However, no effect was seen with valproic acid. During spreading depression of the sensorimotor cortex, a remarkable reduction was seen on the firing of thalamic hyperactive neurons. This suggested that hyperactive neurons of the thalamic nuclei received facilitory effects from the sensorimotor cortex with little influence from adrenergic or serotoenergic systems.

Animals↗
PubMed1991

Computerized tomography (CT) is just as accurate as ventriculography for functional stereotactic thalamotomy.

Eighty-three consecutive functional stereotactic procedures (56 thalamotomies, 1 medial thalamotomy, and 26 chronic brain stimulatory electrode introductions) were done using CT to identify the three-dimensional coordinates of anterior and posterior commissures. The three-dimensional locations of the tactile relay in ventrobasal complex for manual digits were then determined as the first step in physiological corroboration of target site using single-cell recordings and microstimulation. The measured location of this structure was then compared with that predicted by the Schaltenbrand and Bailey atlas. There was no discrepancy in the mediolateral plane in 62.7%, in the dorsoventral plane in 63.9%, and in the anteroposterior plane in 44.6% of the cases. Over 2 mm deviation occurred in 10.8, 12.0, and 19.2% of the cases in these three planes, respectively. This precision of localization is better than that reported with ventriculography. Many of the larger discrepancies occurred in patients who had suffered from stroke, multiple sclerosis, severe head injury, or after craniotomy.

Brain Diseases↗
PubMed1990

Somatosensory neurons in human thalamus respond to speech-induced orofacial movements.

As part of stereotactic surgery, microelectrode recordings of somatosensory neurons in thalamus were obtained in 5 patients. Neurons with receptive fields on the lips and tongue were consistently activated when these structures were involved in production of speech sounds. The magnitudes of these responses were similar to those elicited by experimentally applied mechanical stimuli, suggesting that speech-induced somatosensory inputs are not suppressed at the thalamic level.

Action Potentials↗
PubMed1990

Correlation of CT and MR with impedance monitoring and histopathology in stereotactic biopsies.

Magnetic Resonance Imaging (MR) and Computer Assisted Tomography (CT) guided stereotaxis combined with intraoperative impedance monitoring and multiple sequential biopsies provides the opportunity to correlate the results of radiologic imaging with impedance and histopathology. The authors present the methods used and preliminary results obtained from 30 stereotactic biopsies with complete correlation in 12 cases. Impedance changes correlate accurately with lesion margins as defined by histology. CT images of enhancing lesions correlate quite closely to the histopathologic lesion margins whereas the appearance of the lesion on MR images is often larger than subsequently identified by either impedance or at pathologic examination. Impedance monitoring is a useful adjunct to stereotactic biopsy as it helps to accurately define lesion margins and can help direct the choice of biopsy sites.

Biopsy↗
PubMed1990

Single unit analysis of the human ventral thalamic nuclear group. Activity correlated with movement.

During neurosurgical operations for the relief of movement disorders, single thalamic neurons (n = 107) were identified with activity which was related to verbally cued active movements (movement-related cells). The activity of each neuron was examined during different contralateral movements in order to determine the movement which was associated with the most consistent and pronounced change in firing rate (the optimal response). The optimal response was determined by analysis of histograms of neuronal activity which were constructed by using the onset of EMG activity to synchronize successive repetitions of the active movement. Movement-related cells exhibited optimal responses associated with such movements as making a fist, extension or flexion of the wrist, flexing or extending the elbow, pointing with the entire upper extremity, extending the tongue and lifting the leg. Most movement-related cells recorded in a single parasagittal plane in an individual patient had optimal responses related to movements involving the same part of the body. Movement-related cells were classified into those that were activated in response to somatosensory stimulation (combined cells, n = 20) and those which were not (voluntary cells, n = 87). Combined cells were activated in advance of EMG activity during active movement and so could be distinguished from cells responding only to sensory stimulation (sensory cells). Movement-related cells (combined and voluntary cell types) were located anterior to sensory cells and tended to show a mediolateral somatotopic organization parallel to that of sensory cells with cutaneous receptive fields. Combined cells responded to somatosensory stimulation of the same part of the body as that involved in the active movement related to the optimal response of the cell. Combined cells responding to passive movements of a joint always had their optimal response during active movement about the same joint. The activity of combined cells during parkinsonian tremor may clarify the role of sensory feedback in tremor.

Electric Stimulation↗
PubMed1990

Thalamic single-unit activity occurring in patients with hemidystonia.

Lesions of the ventrolateral complex of the human thalamus may relieve abnormal movements in patients with dystonia. We have now recorded the thalamic single-unit activity and the electromyographic (EMG) activity in the upper extremity during the physiologic localization which is required prior to thalamotomy for hemidystonia. The activity of thalamic single units was correlated with the EMG signal by spectral methods. Results of this analysis indicate that a group of thalamic cells show a concentration of activity, occurring at the same frequency as the EMG activity during dystonia. In many cases, there was statistically significant correlation between thalamic and EMG signals at the frequency of dystonia. The activity of these cells may be involved in the generation of dystonic movements.

Dominance, Cerebral↗
PubMed1990

Microstimulation for stereotactic neurosurgery.

840 microstimulations were done in 21 patients with movement disorders and chronic pain. Paresthesia was the most common response and occurred in 53.3% of cell responses, since the present study was performed mainly in the nucleus ventrocaudalis (Vc). Sensorimotor responses were noted in 8.3%, mainly from the Vc, but they were also noted from the nuclei intermedialis (Vim) and oralis posterior (Vop). Motor responses were noted in 3.6%, mainly from the Vim and Vop nuclei. Pain sensation was elicited in 3.8% and no response was seen in 22.6% of cells after stimulation.

Chronic Disease↗
PubMed1990

The relationship of documented destruction of specific cell types to complications and effectiveness in thalamotomy for tremor in Parkinson's disease.

Microstimulation and single unit recording techniques were used to explore the thalamus prior to performance of 18 thalamotomies in 13 patients. Identified tactile, kinesthetic and tremor-synchronous cells were mapped to scale. Lesion sizes were determined experimentally from lesions made in rat thalami and superimposed on the human maps. Effectiveness and complications were evaluated vis-à-vis documented destruction of tactile kinesthetic and tremor-synchronous cells.

Brain Mapping↗
PubMed1990

Gauze-induced granuloma ("gauzoma"): an uncommon complication of gauze reinforcement of berry aneurysms.

Incompletely and even adequately clipped berry aneurysms are often reinforced with finely shredded gauze. In seven female patients this practice led to a series of events including headache, pyrexia, seizures, cranial nerve deficits, endocrinopathy, cerebrospinal fluid pleocytosis, and an enhancing mass demonstrated by computerized tomography at the aneurysm site. One patient with blindness, hydrocephalus, and panhypopituitarism died and was examined at autopsy. Three additional female patients have been identified in the literature with similar case histories. It is suggested that in these patients the gauze induced a foreign-body granuloma, accompanied by progressive occlusion of neighboring small arteries. It would seem prudent to reserve gauze reinforcement for aneurysms that cannot be securely obliterated surgically.

Adult↗
PubMed1990

Thalamotomy.

Despite astounding progress in the biochemical management of Parkinson's disease in particular and of other movement disorders, there are still patients disabled by severe tremor and not by bradykinesia in whom thalamotomy remains the treatment of choice. Though the irreducible complications of surgery must be taken into account, the problems of prolonged multiple drug therapy should not be ignored. The same rationale applies to selected patients with essential or familial tremor. For some patients with ataxic tremor caused by multiple sclerosis and other brain lesions, or with dystonia or, rarely, other movement disorders, thalamotomy may offer limited though significant relief from an otherwise intractable disability. Indications for the use of stereotactic destructive lesions in the treatment of nociceptive pain in those cases where cordotomy and intraspinal morphine infusion are unsuitable have contracted with the introduction of lower-risk alternatives such as intraventricular morphine instillation. When destructive lesions are indicated, the choice will lie between mesencephalic tractotomy, with its higher success rate but irreducible mortality and morbidity, and medial thalamotomy, which, though less risky, is also less effective. For central and deafferentation pain, the same two procedures may be considered. However, destructive lesions are seldom effective for the treatment of the most common element of these pain syndromes: steady burning or dysesthetic pain. They may be more promising, though, for the intermittent, often shooting pain and the evoked elements (hyperpathia and allodynia) of central and deafferentation pain. Even so, it is advisable first to carry out a trial of VC and PVG stimulation before considering a destructive lesion, which should be a last resort.

Follow-Up Studies↗
PubMed1989

Characteristics of the bursting pattern of action potentials that occurs in the thalamus of patients with central pain.

Neurons in the somatosensory thalamus of patients with central pain following spinal cord injury fire in bursts of action potentials more frequently than do similar neurons in patients without pain. Furthermore, the characteristic firing pattern within these bursts is similar to that which is shown to be associated with the occurrence of calcium spikes in intracellular studies of thalamic nuclei. This finding may have significant implications for the etiology and treatment of central pain states.

Action Potentials↗
PubMed1989

Recordings of abnormal activity in patients with deafferentation and central pain.

We have performed a single-unit analysis of the spontaneous activity of cells in 9 patients with central and deafferentation pain and 4 patients without pain. These studies have concentrated on the analysis of cells firing in bursts, which are particularly prevalent in pain patients. These cells were found to fire typically at interspike intervals of 1-2 ms and interburst intervals of 50 ms. Such cells occurred throughout nucleus ventralis caudalis, nucleus ventrocaudalis parvocellularis and possibly nucleus ventralis intermedius and are different in terms of firing characteristics and locations from bursting cells found in non-pain patients.

Afferent Pathways↗
PubMed1989

Evoked potentials from the human thalamus: correlation with microstimulation and single unit recording.

During stereotactic surgery, intrathalamic single unit recordings and summated evoked potentials (Th-SEP), evoked by percutaneous electrical median nerve stimulation and intrathalamic microstimulation, were done using the same microelectrode at the same site. Potentials evoked by natural and electrical stimulation were compared. The format of Th-SEP varied in anteroposterior, mediolateral and dorsoventral directions in the ventrocaudal nucleus (Vc). The positive response peak latency was shortest from the caudal part of Vc and longest from the anterior part of Vc.

Electric Stimulation↗