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Biomedical subjects

W T Thach

Publications and source records attributed to W T Thach.

At least 37 records · Page 2Linked to original sources
PubMed1995

Cerebellar outflow lesions: a comparison of movement deficits resulting from lesions at the levels of the cerebellum and thalamus.

Previous work has shown that lesions in the lateral cerebellum involving the dentate nucleus impair both reaching and pinching movements in humans and monkeys. This study addressed the question of whether disruption of the cerebellar-thalamo-cortical pathway at the level of the thalamus would produce behavioral deficits similar to those seen after dentate damage. We compared the performance of both reaching and pinching movements in patients with lateral cerebellar lesions and in patients with discrete lesions of the ventrolateral thalamus. The patients with thalamic lesions had minimal or no sensory loss and no corticospinal signs, suggesting that the abnormal movements were due to disruption of the cerebellar projection to the thalamus. We found that lesions of the ventrolateral thalamus resulted in impaired pinching movements, but remarkably normal reaching movements with the exception of a slight tremor. This is in contrast to the profound pinching and reaching impairments of patients with lateral cerebellar lesions involving the dentate nucleus. Implications about the functional organization of cerebellar output are discussed.

Adult↗
PubMed1995

Nonclock behavior of inferior olive neurons: interspike interval of Purkinje cell complex spike discharge in the awake behaving monkey is random.

1. Complex spikes of cerebellar Purkinje cells recorded from awake, behaving monkeys were studied to determine the extent to which their discharge could be quantified as periodic. Three Rhesus monkeys were trained to perform up to five different tasks involving rotation of the wrist in relation to a visual cue. Complex spike activity was recorded during task performance and intertrial time. Interspike intervals were determined from the discharge of each of 89 Purkinje cells located throughout lobules IV, V, and VI. Autocorrelation and Fourier transform of the autocorrelation function were performed on the data. In addition, the activity from one cell was transformed so that the discharge occurred on the beat of a 10-Hz clock, and in a further transformation, on the beat of a noisy 10-Hz clock. These transformed data were then analyzed as described above. 2. Fourier transform of the autocorrelogram function of the data that had been transformed to a 10-Hz clock, and that of the noisy 10-Hz clock, both showed a prominent peak at 10 Hz. However, the autocorrelograms and the Fourier transforms of the autocorrelogram functions failed to reveal a prominent periodicity for the actual discharge of any of cells, at any frequency up to 100 Hz: the discharge appeared random with respect to the interspike interval. The discharge was not random with respect to behavior. Complex spike activity was commonly time locked to the start of wrist movement. We examined this discharge to see whether oscillatory discharge could be seen after alignment of the data on the start of wrist movement, or after alignment of the data on the complex spike occurring peri-start of wrist movement. No oscillation was seen for either alignment. 3. The inferior olive, which sends its climbing fibers to the cerebellum, has been implicated in such different activities as 1) pathological tremor of the soft palate, 2) physiological tremor, 3) the normal initiation of all bodily movement, and 4) motor learning. Previous work in pharmacologically or surgically treated animals has shown that, under some conditions, the discharge of these neurons is periodic and synchronous. This firing pattern has been interpreted to support a role in the first two activities. But measurements reported here in the awake monkey show just the opposite: the discharge is aperiodic to the extent of being random. As such, the inferior olive cannot be a "motor clock" in the general role that has been proposed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Basal ganglia intrinsic circuits and their role in behavior.

There have been significant recent advances in the understanding of basal ganglia circuitry and its role in behavior. Important areas of work in the past year include, firstly, the role of striatal neurons in early phases of movement and, secondly, further characterization of the intrinsic circuitry with emphasis on the importance of the subthalamic nucleus and its connections. A conceptual model of basal ganglia inhibition of competing motor programs is discussed.

Animals↗
PubMed1993

Preserved simple and impaired compound movement after infarction in the territory of the superior cerebellar artery.

A patient with an infarct in the distribution of the right superior cerebellar artery was studied with regard to his ability to make simple movements (visually triggered, self-terminated ballistic wrist movements), and compound movements (reaching to a visual target and precision pinch of a seen object). Movements on the right side of the body alone were affected. Control movements were made by the normal left upper extremity. Wrist movement on the right side was normal in reaction time, direction, peak velocity, and end-point position control as compared to the left. By contrast, both reaching and pinching movements on the right were impaired. Reaching movements showed marked decomposition of the compound elbow-shoulder movement into seriatim simple movements made alternately at elbow and shoulder. Pinching movements were not made, and instead winkling movements (a movement of index alone) were substituted. These results are compared to similar results of controlled inactivation of the cerebellar dentate nucleus in monkeys. We conclude that one function of the cerebellum may be to combine elements in the movement repertoires of downstream movement generators. When that ability is lost, a strategy may be voluntarily adopted of using the preserved simple movements in place of the impaired compound movements.

Arteries↗
PubMed1993

Cerebellar nuclei: rapid alternating movement, motor somatotopy, and a mechanism for the control of muscle synergy.

Monkeys were trained to make rapid alternating flexion and extension movements seriatim at each of five body parts--foot (toe grasp and release), shoulder, elbow, wrist, and thumb. "Facial movements"--mouth, tongue, jaw and pharynx--were also made to drink the fruit juice reward. Movement at a given joint could be performed simply by alternate activation of the prime mover muscle groups, and EMG analysis indicated that these primary muscles were active during movement of that joint. No muscle within any one large body part (leg or arm) was strongly active in relation to movement of another body part. Yet, within a body part (arm), synergist muscles were often more active than the primaries during movement of a given joint, only to become less active during movement of the joint at which their action was primary. Neurons in dentate and interpositus discharged in relation to these movements. In the antero-posterior dimension of both dentate and interposed nuclei, there was a significant tendency for neural modulation to be somatotopically arranged according to the preferred movement: hindlimb anteriormost, forelimb in the middle, and head posteriorly. In the medio-lateral dimension, no such localization was seen for the different movements of the upper limb. Like muscle activity, neural discharge modulation usually occurred in strong relation to a number of movements in a single body part (arm), but not to the movements of different body parts (leg, face). Lesion of the middle third of dentate and of a portion of lateral interpositus had little effect upon the movements at the single joints, and thus upon the prime movers. However, the pattern of activity of agonist, antagonist, and synergist muscles was changed. These results are consistent with the view that the dentate controls muscle synergy and movement coordination more than the prime movers per se.

Animals↗
PubMed1992

The cerebellum and the adaptive coordination of movement.

Based on a review of cerebellar anatomy, neural discharge in relation to behavior, and focal ablation syndromes, we propose a model of cerebellar function that we believe is both comprehensive as to the available information (at these levels) and unique in several respects. The unique features are the inclusion of new information on (a) cerebellar output--its replicative representation of body maps in each of the deep nuclei, each coding a different type and context of movement, and each appearing to control movement of multiple body parts more than of single body parts; and (b) the newly assessed long length of the parallel fiber. The parallel fiber, by virtue of its connection through Purkinje cells to the deep nuclei, appears optimally designed to combine the actions at several joints and to link the modes of adjacent nuclei into more complex coordinated acts. We review the old question of whether the cerebellum is responsible for the coordination of body parts as opposed to the tuning of downstream executive centers, and conclude that it is both, through mechanisms that have been described in the cerebellar cortex. We argue that such a mechanism would require an adaptive capacity, and support the evidence and interpretation that it has one. We point out that many parts of the motor system may be involved in different types of motor learning for different purposes, and that the presence of the many does not exclude an existence of the one in the cerebellar cortex. The adaptive role of the cerebellar cortex would appear to be specialized for combining simpler elements of movement into more complex synergies, and also in enabling simple, stereotyped reflex apparatus to respond differently, specifically, and appropriately under different task conditions. Speed of learning and magnitude of memory for both novel synergies and task-specific performance modifications are other attributes of the cerebellar cortex.

Adaptation, Physiological↗
PubMed1991

Basal ganglia motor control. I. Nonexclusive relation of pallidal discharge to five movement modes.

1. To evaluate the various hypotheses that the basal ganglia preferentially control one mode of movement to the exclusion of others, we recorded the discharge of single neurons in the globus pallidus (GP) in rhesus monkeys during their performance of five trained wrist-movement tasks. The tasks were designed to dissociate several modes and parameters of movement to see whether pallidal neurons would discharge in relation to one and not the others. All tasks were performed by flexing and extending the wrist with opposing or assisting torque loads (0.2 Nm). The five tasks included 1) VisStep, a visually cued step tracking task; 2) VisRamp, a visually guided hold-ramp-hold tracking task; 3) VisSine, a visually guided rapid sinusoidal tracking task; 4) SelfRamp, a self-paced hold-ramp-hold task with delayed alternation, trained velocity, and no visual feedback of wrist position; and 5) SelfSine, a self-paced rapid sinusoidal movement without visual feedback of wrist position. Wrist position and velocity were monitored during all recordings; and wrist, arm, shoulder, and back electromyographs (EMGs) were monitored periodically. Unit discharge was recorded extracellularly from both segments of the GP. The results were similar in the present analysis and are considered together. As a control, units were also recorded in the dentate nucleus of the lateral cerebellum, and the EMGs of many muscles were recorded in limbs, neck and trunk. 2. For 100 GP neurons [41 in the internal segment (GPi) and 59 in the external segment (GPe)], the activity of which changed with task performance, the discharge patterns varied greatly across tasks. The discharge of 96/97 neurons (99%) changed during VisStep, 66/91 neurons (73%) changed during VisRamp, 41/81 neurons (51%) changed during VisSine, 7/34 neurons (21%) changed during SelfRamp, and 25/80 neurons (31%) changed during SelfSine. Of 74 neurons that were fully tested in four or more tasks, 16 (21%) were related only to one task; only 17 cells (23%) were related to all tasks; and, for the remaining 41 (55%) neurons, the relation of the discharge of a given neuron to one task did not predict its relation to other tasks. These task-dependent differences in the discharge of pallidal neurons were not correlated with differences in wrist position, velocity, load, or muscle activity (see also the following paper--Mink and Thach, 1991a). 3. From these data, we conclude that no one task engaged all pallidal neurons to the exclusion of other tasks.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Basal ganglia motor control. II. Late pallidal timing relative to movement onset and inconsistent pallidal coding of movement parameters.

1. We have tested the hypothesis that the basal ganglia initiate some one or several modes of movement by recording the change in discharge frequency of pallidal neurons during visually triggered step and visually paced ramp moves in relation to the visual stimulus onset, the change in the electromyograph (EMG), and the movement onset of trained rhesus monkeys. 2. The modal times of change for globus pallidus pars interna (GPi) were significantly later than those for forearm agonist muscle EMG. By contrast, the modal time of change for the cerebellar dentate nucleus preceded that for wrist agonist EMG. 3. The direction of change in discharge frequency of the GPi cells was for 71% an increase and for 29% a decrease. 4. Because of the relatively late change of activity of GPi neurons, we propose that GPi neurons cannot initiate these movements, as others have also suggested. The commands for the initiation of these movements may instead be generated by structures that include the lateral cerebellum and the anterior cerebral cortex. 5. We have also tested the hypothesis that the pallidum of the basal ganglia or the dentate of the lateral cerebellum may control the direction and other parameters of the trajectory by recording from both structures to see whether cell discharge correlated with the parameter and whether the correlation was consistent across tasks. Two rhesus monkeys were trained to perform hold-ramp-hold and hold-step-hold visually guided movements in opposite directions by flexing and extending the wrist with and against uniform oppositely directed torque loads (0.2 Nm). Wrist position, velocity, force, and EMG were recorded simultaneously. Movement amplitudes and directional intent were computed and inferred, respectively. 6. Task related neurons were classified as follows: 1) directional, if the discharge rate was reciprocal for opposite movements or if it increased or decreased during movement in one direction only; 2) bidirectional, if the discharge rate increased or decreased during movement in both directions; and 3) "other," if it was directional under one load and bidirectional under the other. During step tracking, 34 GPi, 47 globus pallidus pars externa (GPe), and 44 cerebellar dentate nuclear neurons were related to the task. Of the GPi cells, 14 (41%) were directional, 6 (18%) bidirectional, and 14 (41%) other. Of the GPe neurons, 13 (28%) were directional, 19 (40%) bidirectional, and 15 (32%) other. Of the dentate cerebellar nuclear cells, 5 (11%) were bidirectional, 31 (70%) bidirectional, and 8 (18%) other.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Basal ganglia motor control. III. Pallidal ablation: normal reaction time, muscle cocontraction, and slow movement.

1. Inactivation of the portions of globus pallidus pars interna (GPi) containing the greatest concentration of wrist-related neurons was achieved in two rhesus monkeys with microinjections of muscimol (temporary) and kainic acid (permanent). 2. After muscimol injection, there was onset within 30 s of 1) tonic and phasic coactivation of wrist flexors and extensors; 2) slightly greater activation of the flexors, giving a flexor bias in postural holds and the endpoint of movements; and 3) slowness of all movements with a prolonged movement time. Nevertheless, 4) movements made by lessening prior loaded muscle activity (to move in the direction of the load) were slower than movement made by increasing muscle activity (to move against the direction of the load). Despite marked slowing of all movements, there was 5) a normal reaction time for movement onset. Finally, there was 6) a reduced amplitude of most movements. Open room behavior included 7) spiraling contralateral to the lesion while walking. Effects were reproducible (12 injections), were apparent for 7-8 h and were usually completely gone by the next day's testing. 3. After kainic acid injection, there was a period of mixed effects, followed by a period of permanent defects (observed for up to 24 days) that duplicated the temporary effects of muscimol. 4. By contrast, muscimol inactivation of the cerebellar dentate nucleus resulted in 1) a prolonged reaction time and 2) an increased variability of movement trajectory, but 3) without change in movement time or peak velocity. Open room behavior included overshoot in reaching for fruit with the forelimb ipsilateral to the injection. 5. From the facts that normal pallidal neurons fire constantly, that pallidal neurons inhibit their target neurons, and that the muscimol effect was immediate, we conclude that the release of the target neurons from the tonic inhibition allowed them to fire in patterns that promoted a maintained state of cocontraction of agonist and antagonist muscles. From the fact that movement time was prolonged, we conclude that the maintained state of neural activity that caused the muscle cocontraction interfered with the commands for voluntary movement, which were generated by other mechanisms. From the fact that reaction time for movement onset was normal, we conclude that the pallidal neurons may play little or no role in the voluntary initiation of these movements, which are instead generated by other structures that include the anterior cerebral cortex and the lateral cerebellum.

Animals↗
PubMed1987

Preferential relation of pallidal neurons to ballistic movements.

The activity of single globus pallidus neurons was recorded in monkeys trained to perform 5 different wrist movement tasks that were designed to dissociate several modes of movement. Most neurons had activity changes related to visually guided movements and not to self-paced movements. The greatest activity changes were seen during prompt, ballistic, step-tracking movements and several neurons were related only to ballistic movements.

Animals↗
PubMed1987

Cerebellar inputs to motor cortex.

The macaque cerebellar nuclei all project topically onto a common thalamic field that is somatotopically organized in its projection to motor cortex. The complete overlap (except at the cellular level) of dentate and interpositus (and possibly fastigius and vestibular nuclei) projection onto the somatotopic thalamic field implies a complete body representation within each cerebellar nucleus, rather than a preferential representation of trunk in fastigius, proximal limb in interpositus and digits in dentate, as is sometimes supposed. Dentate receives from association cortex and generates the earliest signals, which assist motor cortex in initiating goal-directed movements. Interpositus receives the spinocerebellar projection and provides a fast input to motor cortex from the periphery, perhaps used in transcortical 'reflex' responses and in the control of oscillation. Fastigius and vestibular nuclei provide an opportunity for labyrinthine control of motor cortex activities-even for the digits. What is unique about cerebellar input to motor cortex? Recent work has emphasized two aspects: switching of a cerebellar signal on or off through Purkinje cell inhibition, and adjusting the magnitude of the signal to optimize motor performance.

Animals↗
PubMed1985

Functional mapping of the human cerebellum with positron emission tomography.

Alterations of local neuronal activity induced within the human cerebellum by tactile stimulation and voluntary movement were mapped with positron emission tomographic measurements of brain blood flow. Finger movements produced bilateral, parasagittal blood-flow increases in anterior, superior hemispheric cortex of the cerebellum. Responses to tactile finger stimulation were coextensive with responses to voluntary finger movements but were less intense. Saccadic eye movements produced midline blood-flow increases in the posterior vermis of the cerebellum. Positron emission tomography now permits investigation of functional-anatomical relations within the human cerebellum.

Brain Mapping↗
PubMed1985

Trained slow tracking. I. Muscular production of wrist movement.

Electromyographic (EMG) activity was recorded from those forearm muscles that act across the wrist as highly trained monkeys tracked slow hold-ramp-hold target trajectories with angular wrist position. During performance of this task, the forearm flexors and extensors had a common "basic pattern" of EMG activity. Flexor digitorum sublimis (FDS) and extensor digitorum communis (EDC), though commonly classified as prime movers of the fingers, were the most active flexor and extensor muscles during these movements at the wrist. The basic pattern of EMG activity was analyzed by varying independently 1) the movement direction, 2) the initial and final held wrist positions, 3) the ramp-movement velocity, and 4) the direction and magnitude of maintained external torque load. Most of the modulation of the basic pattern was related to wrist position: EMG amplitude was greatest at the extreme of muscle shortening. There was a slight difference in EMG activity between flexion and extension ramps that was related purely to the direction of movements, independent of wrist position, velocity, and external load; EMG amplitude was greater when a muscle was shortening and less when it was lengthening. During ramp movement, there was little or no observed EMG activity related to velocity (8-28 degrees/s). The magnitude of EMG activity varied in proportion to the external torque load, but this load-related component was additive, and the basic pattern of activity (related to direction and position) did not change with load. From these results we infer that a muscle's EMG activity was determined by 1) passive elastic properties of the wrist and the active length-tension characteristics of the muscle itself (position), 2) asymmetries in the muscle's contractile force depending on whether it was lengthening or shortening (direction), and 3) magnitude of the external torque load (force). By contrast, since no EMG activity was related to velocity in these slow movements, passive viscous properties and velocity-related cross-bridge kinetics were apparently so slight as to make undetectable the small additional EMG activity and contractile force presumably required to overcome them. A model of the muscle forces acting at the wrist incorporates these experimental observations.

Animals↗
PubMed1985

Trained slow tracking. II. Bidirectional discharge patterns of cerebellar nuclear, motor cortex, and spindle afferent neurons.

Single-unit discharge was recorded in the dentate and interposed cerebellar nuclei, motor cortex, and C7 and C8 dorsal root ganglia during trained, slow hold-ramp-hold tracking, rapid alternating movement, torque-pulse perturbation, and action tremor of the monkey's wrist. Fifty-seven dentate and 45 interposed neurons were found in two monkeys that discharged in relation to slow tracking movement. Nearly all neurons had a distinct bidirectional pattern of discharge consisting of an abrupt increase (or decrease) in firing frequency at or before the onset of movement that was variably maintained throughout the ramp and was independent of movement direction. None of the neurons showed a clear relationship to direction, position, velocity, or load during the performance of this task. Nevertheless, many of these neurons discharged in relation to rapid alternation and (for interpositus) torque pulses in patterns that were directionally reciprocal. Some interpositus neurons showed a modulation related to tremor superimposed on the bidirectional discharge related to slow ramps. Twenty-nine neurons in motor cortex of one monkey discharged during slow hold-ramp-hold tracking in two patterns. Class I neurons (14 of 29) showed gradually changing, directionally reciprocal modulations of firing frequency for movements in opposite directions. These neurons were often related to torque load and/or to wrist position but not to velocity. The discharge pattern was similar to the pattern of activity of forearm muscles. Class II neurons (15 of 29) showed an abrupt change in firing frequency that was bidirectional. They were often related to torque load and/or to velocity but not to position. Motor cortex neurons discharged in relation to rapid alternating movements, torque pulses, and tremor in similar patterns that did not distinguish the two classes. Five units in dorsal root ganglia were identified as muscle spindle afferents. During ramps, their pattern of discharge was bidirectional and resembled the bidirectional discharge patterns of neurons in motor cortex (class II) and cerebellum. For some cells the bidirectional pattern varied slightly in relation to the direction and velocity of movement and the amount of torque load, but it was not related to the large changes in wrist position (muscle length). Modulation in relation to tremor was superimposed on the bidirectional pattern related to ramps. The comparison of spindle afferent discharge with the concurrent electromyogram (EMG) of the parent muscle suggested that spindles were driven by gamma-fusimotor activity dissociated from that of homonymous alpha-skeletomotor neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Activity of muscle spindles, motor cortex and cerebellar nuclei during action tremor.

Repeated electrode penetration of the dentate and interpositus nuclei in a rhesus monkey transformed an 11-13 Hz physiologic tremor into a much larger action tremor at 5-7 Hz. This tremor was associated with muscle spindle spike train modulation and reflexly evoked tremor modulation of interpositus and motor cortex neurons as well as electromyogram (EMG). No tremor modulation was observed in spike trains recorded from dentate. The timing relationships of the spindle, EMG, and interpositus tremor discharges suggest that the interpositus plays a direct role in tremor suppression. Dentate, by contrast, may function indirectly by setting optimal transcortical long loop reflex dynamics concerned with intended voluntary movement.

Animals↗
PubMed1983

Cytoarchitectonic delineation of the ventral lateral thalamic region in the monkey.

The cytoarchitecture of the ventral lateral region of the primate thalamus has been appraised in the frontal, parasagittal and horizontal planes. A morphologically distinct region, possessing a sparse and diffuse distribution of large and small neurons is identified. The region includes several nuclei previously separately named by Olszewski. These are nuclei VPLo, VLc, X, VLps, and some cellular extensions into the VLo nucleus. The whole zone is continuous, and it is shown that no clear separation exists between any of the previously identified subnuclei. Connectional grounds are given for suggesting that this region should be considered as a common cerebellar relay nucleus to motor cortex. Morphological criteria for distinguishing the cell-sparse nucleus from adjacent nuclei are given. These cytological criteria provide a basis for the experimental analysis of cortical and subcortical connectivity of the ventral lateral thalamic region. Close attention was paid to the border between the VPLo nucleus and the VPLc nucleus. VPLc is separated from VPLo by a clear border, and no transitional zone can be detected in the parasagittal or horizontal planes. Previous ambiguities in the delineation of the VPLo-VPLc border probably stem from analysis in the frontal plane, in which the border is not clear.

Animals↗
PubMed1983

Distribution of cerebellar terminations and their relation to other afferent terminations in the ventral lateral thalamic region of the monkey.

The efferent projections of the deep cerebellar nuclei were studied and their fiber trajectories and thalamic termination zones described. The thalamic termination zones for the dentate, interposed and fastigial nuclei are identical and coincide with the cytoarchitectonically unique cell-sparse region of the ventral lateral complex. This region includes nuclei VPLo, VLc, VLps, X and extensions of these between the cell clusters of nucleus VLo. The inputs from dentate and interpositus are contralateral, dense, and their termination patterns extend continuously throughout all nuclear components of the cell-sparse zone. Interdigitation of these two inputs within the cell-sparse region is directly demonstrated. The fastigial input is more restricted but bilateral. Each of the deep cerebellar nuclei also projects to the central lateral nucleus of the intralaminar complex. The strong interconnection of the cell-sparse zone with cortical area 4 is confirmed. The patterns of retrogradely labeled thalamocortical cells and of anterogradely labeled corticothalamic terminations following cortical injections of horseradish peroxidase and of tritiated amino acids, extend continuously through the VPLo-VLc region and its extensions, but do not invade the posteriorly situated VPLc nucleus. Thalamic inputs from the dorsal column nuclei terminate independently within the morphologically distinct VPLc nucleus adjacent to the cell-sparse cerebellar terminal zone. The dorsal column-lemniscal terminations do not overlap the cerebellar terminations. The clear segregation of the two sets of terminations is demonstrated directly using an anterograde double labeling method. Spinothalamic terminations end in VPLc but extend into the cerebellar terminal zone. Another ascending input, from the vestibular nuclei, is also shown to terminate within the cell-sparse zone. Comparison with other studies implies that cerebellar, pallidal and substantia nigral inputs do not converge in the monkey thalamus and that the nuclei in which they terminate project to different cortical areas. The relation of these and of sensory influences ascending to motor cortex from the periphery are discussed.

Animals↗