Search PubMed⌕ Search

Biomedical subjects

W G Tatton

Publications and source records attributed to W G Tatton.

At least 73 records · Page 4Linked to original sources
PubMed1983

Postnatal dendritic development in motoneurons: evaluation by a Monte Carlo technique.

A Monte Carlo method was used to quantitate the dendritic characteristics of horseradish peroxidase-injected lumbar motoneurons (MNs) from kittens 44 to 73 days old (during the postnatal interval when motor cortical input/output linkages mature) and compared with those from adults. All of the 6 MNs analyzed were within the same range of somal sizes (40-61 micron) and dendritic domain volumes. However, two-dimensional distributions of dendritic diameter versus distance from the soma revealed that in the youngest MNs' (44 and 51 days) most dendritic processes (82 and 84%) were less than 2 micron in diameter, and had no dendrites greater than 5 micron. The adult MNs had large dendrites (20 and 24% were greater than 5 mu), while the kittens of intermediate age (66 and 73 days) exhibited both adult-like (6 and 13% greater than 5 micron) and immature (48 and 73% less than 2 micron) characteristics. "Hit probabilities" calculated from the Monte Carlo data suggest that immature MNs' dendrites may present denser targets per unit volume for ingrowing growth cones than adult MNs, and may facilitate the probability of contact with appropriate afferent axons.

Animals↗
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

Long latency reflexes to imposed displacements of the human wrist: dependence on duration of movement.

Reflex EMG responses to angular displacements of the wrist joint were recorded from 12 normal human volunteers. A mechanical stop was used to suddenly arrest displacements at varying times following the onset of the stimulus. With unrestricted movement of the handle, the EMG response consisted of an early component (M1) with a latency of 30-35 ms and a long-latency component (M2-3) beginning 55-65 ms after the onset of the displacement. When the displacements were arrested prior to a critical time occurring between 40 and 50 ms after the onset (mean of 44 ms), the M2-3 component of the response was not present. Increasing the duration of the displacement beyond this time resulted in a rapid increase in the size of M2-3. Facilitation provided by volitional intent to oppose the perturbation was not sufficient to generate an M2-3 response to either a brief, low velocity displacement produced by the torque motor or to a phasic, high velocity stretch produced by a tendon tap. The timing relationships between the onset latency of M2 and the minimum duration of displacement required to generate an M2-3 response are not easily reconciled with the notion that the segmentation of the EMG responses into components is mediated by repeated activation of the same central reflex pathway by phasic afferent bursts. Two mechanisms that could account for these results are either inhibition in response to the sudden stop of phasically-active "linking" interneurons which are part of the long latency pathway, or the loss of an essential convergent facilitatory input which serves to monitoring the continuation of the movement.

Adult↗
PubMed1981

Descending projections to the cervical spinal cord in the developing kitten.

The distribution of neurons filled by retrograde axonal transport of horseradish peroxidase from the cervical enlargement is described in kittens prior to and following the time of appearance of mature alpha-motoneuron responses to motor cortical stimulation (at 107-111 days gestational age; about 41 days postnatally). Cortex and brainstem reconstructions of the distributions of filled neurons demonstrate a well-defined, discrete projection from cortical area 4 to spinal cord segments C3 to C8, both in mature and immature (20 and 24 days postnatal) animals. In addition, appropriate rubrospinal, reticulospinal and vestibulospinal projections were present at all ages studied.

Animals↗
PubMed1981

Postnatal histogenetic death of rat forelimb motoneurons.

Previous workers have reported a five fold decrease in motoneuron numbers occurring from birth to adulthood in the rat. It has also been reported that forelimb muscles receive connections from motoneurons in both ventral horns prior to day 14 of life in the rat and that the contralateral cells subsequently degenerate completely by day 21. In the present study, postnatal changes in motoneuron number and distribution within the ventral horn were studied in the rat using the technique of retrograde horseradish peroxidase (HRP) transport following intramuscular infusion of HRP into biceps brachii (BB). Peripheral nerves other than those to BB were sectioned and ligated to control for HRP diffusion. The spatial organization of BB motoneurons was compared in animals 9-14 days old and adult animals using computer 3-D reconstruction. This allowed observations of the BB motoneurons from a variety of perspectives in relationship to a number of spinal cord landmarks and avoided the necessity for transverse and horizontal sectioning of the cords in alternate animals. A decrease of 50-75% in the number of HRP filled motoneurons number was found from birth to adulthood (adults 98-150, neonates 172-243). The spatial arrangement of the BB motoneurons with regard to the root entry zones and other landmarks such as the dorsolateral convexity of the ventral horn, remains constant from birth to adulthood. No evidence was found to support the existence of inappropriate connections from motoneurons in either the ipsi or contralateral ventral horns of neonate rats. It is suggested that the comparatively small decreases in motoneurons postnatally could be a continuation of the histogenetic processes of cell death begun in utero and is related to the postnatal development of the central and peripheral connections of motoneurons.

Aging↗
PubMed1981

Comment: a schema for the interactions between motor programs and sensory input.

In this overview we utilize and extend a model, originally developed for "command interneuron" control of the generation of motor programs, to discuss the roles sensory inputs play in movement control. To provide a conceptual framework, we present a modular schematic of the motor control and sensory processing apparatus of an hypothetical nervous system. In the schematic, "subroutines" (basic units of motor programs) are seen as "playing out" through switching and sequencing networks to "driver neurons." The "driver neurons" then activate motoneurons to execute the programmed movements. Five modes of interaction between motor programs and sensory input are considered using examples from invertebrate and vertebrate neuronal circuitry. These modes of interaction occur at the following locations: (1) the "program selector," to initiate a motor program; (2) the "motor subroutine directory," advancing the program to the next subroutine; (3) the "driver neurons" and motoneurons, where the "gain" of subroutine instructions can be modulated; (4) the "motor programmer," which monitors programs in progress and provides for program development and updating; and (5) the "driver neurons" themselves, which control sensory processing by "selecting" the appropriate sensory inputs for the program in progress. Mode 5 is illustrated in more detail through a consideration of the modification of stretch receptor input by "extensor" and "flexor" command interneurones in the circuitry controlling postural movements of the crayfish abdomen.

Humans↗
PubMed1980

Synchronous development of motor cortical output to different muscles in the kitten.

Previous observations indicate that the output linkages from motor cortex (area 4) to triceps brachii motoneurons develop relatively late in the postnatal kitten. Responses in multiple, simultaneously-recorded EMG's from facial, forelimb and proximal hindlimb musculature to intracortical microstimulation appear over gestational days 107-111 (about 41 days postnatally). Thus, output from the motor cortex to alpha motoneurons develops in a synchronous, rather than a sequential manner across the area 4 homunculi.

Aging↗
PubMed1980

Sequential output-input maturation of kitten motor cortex.

Average response histograms of the responses of single cortical neurons to imposed forelimb displacements in the kitten were utilized to quantify: (1) Background activity, (2) excitatory response latency, (3) percentage responding neurons, and (4) synaptic effectiveness. Motor cortical neuronal responses to the input did not attain adult values until 55--65 days of age, while adult-like responses were found in somatosensory cortical neurons as early as 9 days postnatally. Motor cortical output to alpha-motoneurons innervating triceps brachii, as tested by intracortical and subcortical microstimulation, first appeared over an interval ranging from 37--45 days postnatally. Thus, motor cortical responses to forelimb mechanoreceptors develop after completion of the output linkages from motor cortex to forelimb motoneurons and, though the motor cortex can output at 45 days, motor cortical functions requiring somatosensory feedback cannot be operative until about 60 days. This system provides a discrete and "late" maturing model in which to study the postnatal development of neuronal networks underlying normal and abnormal motor behavior.

Afferent Pathways↗
PubMed1979

Motor unit responses in muscles stretched by imposed displacements of the monkey wrist.

Imposed angular displacements of monkey's wrist produce three major peaks of activity (terms M1, M2, and M3 peaks) in the averaged gross EMG activity ot the stretched muscles. The displacements were imposed on monkey's wrist by computer controlled step loads (range 60--540 g). Gross EMG was recorded simultaneously with the activity of single motor units (SMUs) in the stretched muscles. SMUs were identified and separated using a computer "shape-fitting" program. Average response histograms (ARHs) were constructed for each SMU's responses to randomly presented repetitions of up to five different step loads. Eighty-three percent of the SMUs showed a single excitatory response peak that was limited to a time interval corresponding to that of only one of the gross EMG peaks. Despite marked differences in the time courses of the imposed displacements, the time courses of the SMU excitatory responses were maintained. By increasing the background load and hence the tonic firing of the individual SMUs, the histograms show that the long latency of the M2 peak is not due to an inhibitory-excitatory sequence. The SMUs responding at longer latencies (M2 and M3 SMUs) show firing characteristics in keeping with those reported for fast twitch motor units while those of M1 SMUs correlate with those found for slow twitch units. These results establish that the M1, M2, and M3 peaks do not merely represent synchronized oscillatory activity of the motoneurons but largely result from the reflex excitation of separately responding motoneuron "subpopulations", each of which contributes to the generation of only one of the gross EMG peaks.

Afferent Pathways↗
PubMed1979

Input-output properties of motor unit responses in muscles stretched by imposed displacements of the monkey wrist.

Reflex responses are "servo-like" where the output is graded with the input or are "triggered" where the output is independent of input once an input threshold is exceeded. Imposed displacements of monkey or human upper limb joints result in prolonged EMG output in the muscles stretched by the displacements. The longer-latency portions of the prolonged output have been variously reported to be servo-like or to be triggered in nature. In monkeys and humans, angular wrist displacements imposed by step loads result in three peaks (M1, M2 and M3) in the gross EMG recorded from the stretched muscles. Each gross EMG peak largely results from the firing of a separately-responding subpopulation of single motor units (SMUs). We studied the responses of SMUs to loads that were presented to the monkeys in a random order as to magnitude, duration and onset time. Average response histograms were constructed for the SMU responses for individual step load magnitudes. Averages were also constructed for the simultaneously-recorded gross EMG responses for each step load magnitude. The input parameters used were the initial velocity of displacement or the magnitude of step load, while the output was taken as the probability of firing/millisecond/presentation above baseline for the SMUs or the area under the response peaks above baseline for gross EMG. The results establish: 1) That it is not possible to unambiguously determine the input-output properties of the responses to imposed displacements utilizing the analysis of gress EMG activity due to the response characteristics of the various subpopulations of motor units contributing to the gross response. 2) That the SMU activity during all of the peak intervals is monotonically graded with increases in magnitude of the step load or the initial velocity of displacement. Hence, the long-latency portions of the EMG responses are servo-like in nature and are not preprogrammed or triggered responses. 3) That the gain (output/input) of the gross EMG responses almost entirely reflects the variation in the number of motoneurons recruited by changes in magnitude of the step loads rather than variation in the firing rates of motoneurons during the reflex responses.

Animals↗
PubMed1979

Dynamics of a long-latency reflex pathway in the monkey.

Angular wrist displacements in the monkey result in a short-latency (20--25 ms) "reflex" response of motor cortical cells in area 4 and separate peaks of activity in the gross EMG of the stretched muscles. Frequency domain analysis was carried out between (1) wrist position as input and motor cortical neuron response as output, (2) position as input and EMG response as output, and (3) motor cortical neuron response as input and EMG response as output. The results show that the dynamics of primary spindle afferents characterize the dynamics of the pathway to the motor cortex and that of the reflex loop. Results are discussed in terms of "long-loop" reflexes.

Animals↗
PubMed1975

Nerve-impulse patterns: a quantitative display technique for three neurons.

A scatter diagram is described that displays the relative timings of nerve impulses in 3 simultaneously monitored neurons. The technique is a generalization of the cross-correlation histogram for two impulse trains. The time intervals between impulses in different neurons are plotted on triangular coordinates to yield a Joint Impulse Configuration Scatter Diagram. The resulting 'snowflake' plot shows a pattern of spots and lines, which is interpretable in terms of the functional circuitry among teh neurons. Illustrations are given of the snowflakes produced by a variety of three-neuron circuits, which may serve as a preliminary catalog of snowflake types for interpretation of experimental data.

Computers↗