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Biomedical subjects

H C Kwan

Publications and source records attributed to H C Kwan.

At least 55 records · Page 3Linked to original sources
PubMed1979

Differential effects of reciprocal wrist torques on responses of somatotopically identified neurons of precentral cortex in awake primates.

The present study was undertaken to investigate the functional significance of previous observations that both reciprocal and bidirectional responses are found in the forelimb area of precentral cortex following oppositely directed torques delivered about a single forelimb joint. Extracellular unit recordings were made in the contralateral precentral cortex of awake monkeys. These units were classified, according to their responses to passive somatosensory stimulation and to the effects of local intracortical microstimulation (ICMS), as being functionally coupled to single joints. Both joint- and cutaneous-sensitive neurons were included. The responses of such classified neurons to oppositely directed torques were then studied. All of the joint-sensitive wrist (flexion-extension) units responded reciprocally to the oppositely directed torques. In contrast reciprocally and bidirectionally responsive neurons were found in the cutaneous-sensitive wrist population and in both the joint- and cutaneous-sensitive non-wrist (F-E) populations. These results are discussed in terms of the expected receptor actions of the applied torques, and are consistent with other evidence that a correlation exists between activities of precentral neurons which respond to sensory events at or about a single forelimb joint, and voluntary movement about the same joint.

Animals↗
PubMed1979

Activity of precentral neurons during torque-triggered hand movements in awake primates.

In monkeys performing a handle-repositioning task involving primarily wrist flexion-extension (F-E) movements after a torque perturbation was delivered to the handle, single units were recorded extracellularly in the contralateral precentral cortex. Precentral neurons were identified by passive somatosensory stimulation, and were classified into five somatotopically organized populations. Based on electromyographic recordings, it was observed that flexors and extensors about the wrist joint were specifically involved in the repositioning of the handle, while many other muscles which act at the wrist and other forelimb joints were involved in the task in a supportive role. In precentral cortex, all neuronal responses observed were temporally correlated to both the sensory stimuli and the motor responses. Visual stimuli, presented simultaneously with torque perturbations, did not affect the early portion of cortical responses to such torque perturbations. In each of the five somatotopically organized neuronal populations, task-related neurons as well as task-unrelated ones were observed. A significantly larger proportion of wrist (F-E) neurons was related to the task, as compared with the other, nonwrist (F-E) populations. The above findings were discussed in the context of a hypothesis for the function of precentral cortex during voluntary limb movement in awake primates. This hypothesis incorporates a relationship between activities of populations of precentral neurons, defined with respect to their responses to peripheral events at or about single joints, and movements about the same joint.

Animals↗
PubMed1979

Control of stiffness by the medium latency electromyographic response to limb perturbation.

It is hypothesized that the medium latency electromyographic (EMG) response (ML) to limb perturbation functions to preset limb stiffness to a constant initial level. Three predictions are derived from this hypothesis: Firstly, in the presence of an instruction calling for opposition to limb perturbation, a control signal, ML, will be observed and will lead to the establishment of a constant level of limb stiffness. Secondly, in the absence of an instruction to oppose, no control signal will be observed and correspondingly a constant stiffness will not be generated. Thirdly, the latency of onset of stiffness control will covary with the latency of onset of ML. These predictions were tested in experiments involving perturbation of the human forearm about the elbow joint, with surface EMG measurements and computation of the limb stiffness function. The results are in accord with these predictions, and support the hypothesis that ML functions in the feedforward control of limb stiffness.

Adult↗
PubMed1979

Patterns of early and late discharges in somatotopically identified precentral neurons in awake monkeys in response to somatic inputs.

Extracellular recordings were made of single neurons in precentral cortex of awake monkeys. These neurons were somatotopically identified with respect to their responses to inputs from single joints or their somatic surround. Many of these neurons exhibited early (less than 50 ms) and late (greater than 50 ms) discharges in response to flexion or extension torques delivered about the wrist. With the monkey in a mode requiring opposition to the injected torque, all responsive neurons showed a parallel excitatory or inhibitory modification in the early and late discharges. This was true both for cells identified as wrist (flexion-extension) neurons and those identified as nonwrist (flexion-extension) neurons. These findings indicate that the reflex and voluntary components of percentral discharge invariably show a congruent functional response to a torque disturbance, for this particular instruction set.

Action Potentials↗
PubMed1978

Factors affecting serum IgA antibody to Epstein-Barr viral capsid antigens in nasopharyngeal carcinoma.

Irrespective of the ethnic origin of the patient, nasopharyngeal carcinoma (NPC), appears to stimulate the production of IgA antibodies against VCA. These antibodies are detected at high frequency and titres in sera from NPC patients but only rarely from control subjects. A majority of relapse-free survivors tested 1-12 years after radiotherapy (RT) sustain a detectable level of IgA anti-VCA. Serum titres of IgA anti-VCA remain relatively unchaged in individual NPC patients after RT, regardless of the disease evolution. These antibodies were detected in serum from one individual 9 months before NPC and the titre rose concomitantly with its clinical onset. Titres of IgA anti-VCA in multiple serum specimens from individual NPC patients, and in sera from different NPC patients, do not correlate with titres of IgG anti-VCA or with Serum IgA. It thus seems possible that the IgA anti-VCA in the sera of NPC patients might be largely derived near NPC. Apparently healthy individuals showing detectable IgA anti-VCA tend to aggregate in families of NPC patients. The distribution of siblings of these families who have the IgA anti-VCA reaction shows the binomial distribution expected for an autosomal recessive trait, implying the involvement of an autosomal recessive gene in the IgA anti-VCA response.

Antigens, Viral↗
PubMed1978

Immunohistochemistry of local immunoglobulin production in nasopharyngeal carcinoma.

Immunohistochemical investigations by the immunoperoxidase method have been carried out on sections of biopsy specimens obtained from the primary tumour sites of patients with nasopharyngeal carcinoma (NPC). It was found that, in many of the sections thus examined, there was an accumulation of plasma cells, particularly of the IgA type, in the connective tissues surrounding nests of NPC cells. Similar accumulation of plasma cells in the subepithelial connective tissues was likewise observed in a case of choanal polyp. Plasma cells were rarely observed in the section of a biopsy specimen of non-neoplastic oropharyngeal mucosa. These results indicated that the nasopharynx may be a site for the local production of IgA, but the antigenic specificity of these molecules is, however, not known. The possibility that the nasopharynx is a site for the local production of antibodies to the Epstein-Barr virus (EBV)-related antigens was discussed.

Humans↗
PubMed1978

An intracortical microstimulation study of output organization in precentral cortex of awake primates.

We investigated the output organization of the forelimb control area in primate precentral cortex by using low-current (less than 30 microamperemeter) intracortical microstimulation (ICMS). Movement about a joint was selected as the index of response. Penetrations perpendicular to the cortical surface and deep into the rostral bank of the central sulcus were made in two awake unanesthetized monkeys (Macaca arctoides). Cortical areas were designated by the joint about which movements occurred. 1. ICMS loci which produced movements about finger joints were found to tightly cluster in a central zone, and were surrounded by loci controlling movement about the wrist. This wrist zone was in turn approximately encircled by an elbow zone, which itself was enclosed by a shoulder zone. 2. Appreciable overlap between these zones controlling movements about contiguous joints was observed. 3. The observations indicate a nested-ring organization of the forelimb output zones of precentral cortex, such that a cortical zone controlling movement of a more distal joint is partly encircled by the zone controlling a more proximal joint.

Animals↗
PubMed1977

Simple probe for localized cryogenic blockade in the brain.

The construction of a simple probe utilizing an air-space thermal insulation and circulating coolant for localized cooling of brain tissue is described. Results of isotherm studies in the cerebellum and electrophysiological observations in the motor cortex are presented indicating the effectiveness of localized cooling by the probe.

Animals↗