Biomedical subjects

H C Kwan

Publications and source records attributed to H C Kwan.

At least 19 recordsLinked to original sources

PubMed1991

Automatic end-expiratory air sampling device for breath hydrogen test in infants.

An automatic electronically operated end-expiratory air sampler has been developed for use in small infants. Upon expiration, which is detected by a hot-wire sensor, a small portion of the end-expiratory air is automatically collected into a syringe mounted on a syringe driver. The sampler obtained 87% of the end-expiratory air sample. Additionally, highly reproducible and consistent results were obtained for the respiratory gases (O2, N2, CO2). The sampler has been applied for studying breath hydrogen excretion to detect lactose malabsorption. It may also be applicable to study other expiratory gases in infants.

Breath Tests↗

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

Neural network control of simple limb movements.

It is possible to embed the control and computation of a simple single-joint movement at different speeds by a small non-linear network of neuron-like elements. The network "learns" by appropriate adjustment of the strengths of interconnection, or synaptic weights, between the neuron-like elements. The learning of a few movement trajectories is generalized to the learning of a family of unlearned trajectories. These observations are in support of our hypothesis that relaxation of a network from an initial state to a final equilibrium state is both causal and computational to movement generation and control.

Electromyography↗

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↗

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

Detection of feedback in the central nervous system using system identification techniques.

An analysis method to detect the presence of feedback between biological signals, particularly those associated with the central nervous system, is presented. The technique is based on recent results in the system identification literature involving the concept of a feedback free process. It may be applied to volume conducted signals such as EEG and EMG, as well as to neuronal spike trains through the use of a data transformation procedure. The utility of the technique is then demonstrated in a study of the relationship between Parkinsonian tremor and certain tremor cells found in the thalamus of Parkinsonian patients, using data collected during thalamotomies. The results obtained suggest that feedback mechanisms may be an important factor contributing to Parkinsonian tremor.

Biofeedback, Psychology↗

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↗

PubMed1987

Interaction between neurons in precentral cortical zones controlling different joints.

The relationship of the strength of interaction between precentral cortical neurons and their distance of separation during active reaching movements was studied in adult primates. Chronic unit recording experiments with two independent microelectrodes were performed in the left precentral forearm area of monkeys trained to execute reaching movements with the right arm in response to a visual cue. Neurons were identified by the joint actions produced by intracortical microstimulation. Cross-correlation analysis was employed to assess the strength of interaction between units. Unit pairs which exhibited the highest strength were recorded by the same electrode. For unit pairs derived from separate electrodes, the incidence and strength of interaction fell as the separation between the units was increased. Neurons identified by intracortical microstimulation as controlling the same or contiguous joints tended to interact with each other with much higher probability than did those neurons identified as controlling non-contiguous joints. When the direction of flow of information was assessed, these was a preferential flow from neurons controlling proximal joints to those controlling distal ones. These results are consistent with recent findings of tight kinematic coupling between contiguous joints and the observation of proximal-to-distal sequence of activation at the neuronal and electromyogram levels during voluntary movement.

Animals↗

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↗

PubMed1986

Measurements of human forearm viscoelasticity.

In human subjects, stiffness of the relaxed elbow was measured by three methods, using a forearm manipulandum coupled to a.d.c. torque motor. Elbow stiffness calculated from frequency response characteristics increased as the driving amplitude decreased. Step displacements of the forearm produced restoring torques linearly related to the displacement. The stiffness was very similar to that calculated from natural frequencies at amplitudes above 0.1 rad. Thirdly, elbow stiffness was estimated from brief test pulses, 120 ms in duration, by mathematically simulating the torque-displacement functions. Stiffness values in the limited linear range (under +/- 0.1 rad) were higher than in the linear range of the first two methods. A major component of elbow stiffness appears to decay within 1 s. The coefficients of viscosity determined from the simulation were, however, very similar to those calculated from the frequency response. Test pulse simulation was then used to determine joint impedance for different, actively maintained elbow angles. Joint stiffness and viscosity increased with progressive elbow flexion.

Adult↗

PubMed1985

Properties of visual cue responses in primate precentral cortex.

Monkeys were trained to perform a visuomotor task involving the alignment of a cursor over a vertical target line on a videomonitor by flexion or extension movements of the wrist. The forelimb area of the contralateral precentral cortex was thoroughly explored during the task. Intracortical microstimulation was employed to classify the forelimb region into wrist flexion--extension and non-wrist flexion--extension populations. Unit recording revealed an initial response to the cue for movement, viz. the appearance of the cursor and target line on the videomonitor, while visual signals not related to the task failed to evoke any response. The mean latency of these visual cue responses was approximately 150 ms. A great majority of the responses (96%) were bidirectional in character, in that they did not correlate with the directional information embedded in the visual cue, nor were they good predictors for the direction or timing of the subsequent movement. They were uniformly distributed in both the wrist and non-wrist regions of the forelimb area; the non-forelimb areas were devoid of the cue response. Further, when the variability of response to the visual cue for the wrist and non-wrist populations was compared, no significant difference was observed. These observations are consistent with an interpretation that the visually triggered cue responses provide a generalized activation over the task-related area of precentral cortex, paving the way for later and more specific activations leading to the execution of the task.

Animals↗

PubMed1985

Cross correlation studies in primate motor cortex: synaptic interaction and shared input.

Awake, unrestrained monkeys were trained to reach out with the forelimb and touch a button. Extracellular spike trains were recorded from pairs of neurons in contralateral precentral cortex with the same or separate microelectrodes. The neurons were located in the same or different functional columns as defined by intracortical microstimulation and passive sensory stimulation. Cross correlation analysis showed patterns consistent with synaptic excitation and/or inhibition between members of the cell pairs during the voluntary movement. The strength of correlation was inversely related to distance between columns, with the strongest correlations found between cells within the same column. Inhibitory correlations were virtually restricted to cell pairs within a single column. Temporal analysis showed that direct synaptic interaction and shared input patterns could be clearly distinguished in this physiologic setting. Spatial analysis indicated that shared input was concentrated among columns in the same and adjacent joint controlling zones as well as within a single column. No directional preference of shared input was present, a finding which was consistent with the observed nested organization of the forelimb area.

Action Potentials↗

PubMed1985

Cross correlation studies in primate motor cortex: event related correlation.

Simultaneous extracellular unit recordings were made from each cell of 237 pairs in two awake monkeys, during a voluntary reaching movement of the forelimb. The cells were located in contralateral precentral cortex and functionally coupled to single forelimb joints, as indicated by intracortical microstimulation and passive sensory stimulation. Cross correlation analysis showed that 72 of these pairs exhibited significant event-related correlation over periods of up to 780 ms, comparable to and coincident with the forelimb movement. Spatial analysis showed that such correlation extended across contiguous portions of all four forelimb joint zones of precentral cortex, over distances up to 3.5 mm. No preferred direction of correlation was observed. The data confirm the previously described nested organization of the forelimb area of precentral cortex. Findings are discussed in terms of mechanisms by which columns of neurons in motor cortex participate in the reaching movement.

Animals↗

PubMed1985

Sequential activation of neurons in primate motor cortex during unrestrained forelimb movement.

We trained monkeys to perform an unrestrained, reaching movement of the arm. Electromyogram (EMG) recordings of forelimb muscles revealed sequential activation, proximal to distal, of muscle groups involved in the task. The delay in onset of EMG activity between proximal (shoulder and elbow) and distal (wrist and finger) muscles was approximately 60 ms. We identified the neurons in the forelimb area of the contralateral motor cortex as controlling particular joints by previously defined criteria involving responses to somatosensory stimulation and effects of intracortical microstimulation. Many cells discharged prior to the onset of EMG activity acting on the appropriate joint, whereas others began firing at a later phase of the movement. The population of all proximal cells altered discharge patterns approximately 60 ms earlier than the population of distal cells. A small percentage of cells showed an initial inhibitory change in discharge frequency, and this inhibition typically occurred prior to the excitatory changes seen in the majority of cells. The results are discussed in terms of the "nested-zone" model of the forelimb motor cortex. The data support one of the predictions of this model, namely that discharges of identified cells within the cortical zones are causally related to voluntary movement at appropriate forelimb joints.

Animals↗

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↗

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↗