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Y Lamarre

Publications and source records attributed to Y Lamarre.

At least 55 records · Page 3Linked to original sources
PubMed1986

Activity of dentate neurons during arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey.

Single-unit recordings were obtained from 404 neurons in the dentate and interposed nuclei in two monkeys trained to perform simple movements of the elbow in response to three different sensory cues: a light, a tone, and a small, brief perturbation of the trained forearm. Both flexion and extension movements were investigated. Those dentate neurons that showed a clear modulation before the onset of movement (149 of 318 cells recorded) were classified as stimulus related or movement related on the basis of an analysis of the timing of the initial change in discharge. Seventy-one percent of these dentate neurons (106/149) were classified as stimulus related, and 21% (31/149) were classified as movement related. Within the stimulus-related group 87% responded selectively to only one or two of the sensory cues (selective stimulus-related neurons), most often the teleceptive cues, whereas the remaining 13% responded nonselectively to all three cues (nonselective stimulus-related neurons). Interposed neurons, in contrast, showed principally movement-related discharge, and this represented the initial change in discharge in 89% of the neurons. Eleven percent of the interposed cells showed a selective response to the somesthetic cue. The discharge of 28 out of 91 dentate neurons tested with both flexion and extension movements varied with the direction of movement. Few dentate neurons (9%) were found to display any direction sensitivity when considering the discharge preceding the onset of movement, and none of these showed a reciprocal pattern. The discharge of a greater proportion of neurons (24%) was direction sensitive during movement and was occasionally reciprocal. In the same monkeys, however, 78% of the neurons in the neighboring interposed nucleus were direction sensitive, and one-quarter of these displayed reciprocal patterns of discharge. Thus, the discharge of dentate neurons, occurring well in advance of a conditioned movement, cannot specify direction in this simple reaction-time (RT) task. The sensory responses of selective stimulus-related dentate cells ended near the onset of movement but were time locked to the stimulus and not to the movement. When a neuron was responsive to two of the cues the response did not vary with the modality of the stimulus apart from changes in the latency. The initial sensory response was usually followed by later "secondary" changes in discharge that were temporally related to the movement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Electromyographic studies of congenital mirror movements.

We studied two patients with congenital mirror movements. In one, the movements were associated with impaired sensation and a cervicodorsal meningocele. In the other, no abnormality of the nervous system was found. In an EMG study, the normal temporal characteristics, response latency, duration, and amount of EMG on the normal and mirror sides suggest that similar motor commands are responsible for both voluntary and mirror movements.

Adolescent↗
PubMed1985

Initial agonist burst duration changes with movement amplitude in a deafferented patient.

Changes in the duration of the initial agonist burst were studied in a deafferented human. The patient had been functionally deafferented for five years, having no touch, vibration, pressure or kinesthetic sensation nor any tendon reflexes in the four limbs. Pain and temperature sensation were intact and motor fibres were unaffected. The subject made visually guided step-tracking movements using flexion/extension movements about the elbow. Initial agonist burst duration increased with movement amplitude. Burst duration was approximately 65 ms in small movements (6-12 deg) increasing to 136 ms in intermediate (36 deg) and 200 ms in large (54 and 60 deg) movements. Similar changes in initial burst duration with movement amplitude were seen when the subject made non-visually guided movements. It is concluded that the duration of the initial agonist burst is centrally determined.

Adult↗
PubMed1984

Discharge properties of area 5 neurones during arm movements triggered by sensory stimuli in the monkey.

Unitary discharge was recorded from 157 cells in area 5 of 2 monkeys trained to perform rapid movements of the contralateral arm. Ninety-six cells were task-related. The earliest movement-related modulation in discharge for the large majority of cells (92%) followed the onset of electromyographic (EMG) activity. The discharge pattern of almost all units for which discharge was recorded during movements in opposite directions varied with direction, most often in a nonreciprocal manner. Discharge was correlated with peak velocity in 23% of the excited cells (n = 52). Almost the entire population of cells correlated with velocity were located in the upper part of the anterior bank of the intraparietal sulcus, suggesting that there may be at least two different functional subregions within the arm representation of area 5. Forty percent of the movement-related units had a short latency response to a small, brief perturbation of the elbow which served as one of the movement cues. These sensory responses were labile, not being present in every trial for a large number of cells. Thirty-six percent of the perturbation-sensitive cells were classified as reaction time (RT)-dependent on the basis of a correlation between RT and either the magnitude or the frequency of occurrence of the response. The response was clearly dependent on the subsequent motor response being absent when movement was extinguished. This dependence of the sensory response on the subsequent movement is a property which might represent a neural substrate for somatic sensory attention. The results also support the idea that the RT-dependent cells may be involved in the initiation of the shortest RT movements in response to the somaesthetic cue.

Acoustic Stimulation↗
PubMed1983

Fast ballistic arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey. I. Activity of precentral cortical neurons.

Single-unit recordings from motor cortex (area 4) were obtained in two monkeys trained to perform simple flexion and extension movements of the arm in response to somesthetic, visual, and auditory signals. All neurons tested showed movement-related responses that were identical for equivalent movements irrespective of the modality of the triggering stimulus. Progressively longer reaction times were always associated with progressively longer latencies of unit responses. When visual and auditory stimuli were presented simultaneously, the intensity and the duration of both motor and unitary responses remained unchanged as if only one stimulus (auditory) had been given. When the auditory stimulus was appropriately delayed with respect to the visual one, shortening of motor reaction time was observed with a corresponding shortening of the latency of unit responses. In addition to movement-related responses, some neurons showed sensory-related responses mainly to the somesthetic stimulus (37%) and more rarely to the auditory (11%) and visual stimuli (3%). These "sensory" responses preceded and were independent of the movement-related responses; they showed no obvious correlation with the reaction time. Whenever tested, the somatosensory responses persisted after extinction of the motor responses. These findings suggest that, in our experimental conditions, area 4 neurons of the monkey are not involved in the early processing of sensory information required for the initiation of simple, triggered movements. Rather, they appear to generate signals that are mainly related to the characteristics of the motor responses.

Acoustic Stimulation↗
PubMed1983

Fast ballistic arm movements triggered by visual, auditory, and somesthetic stimuli in the monkey. II. Effects of unilateral dentate lesion on discharge of precentral cortical neurons and reaction time.

Single-unit recordings from motor cortex (area 4) were obtained before and after dentate lesion in two monkeys executing fast elbow flexions and extensions in response to randomly presented visual, auditory, and somesthetic stimuli. There were no starting or ending reference points or preparatory signals. Monkeys were trained to perform movements larger than 15 degrees within 500 ms of the stimulus presentation. After electrolytic lesion of the dentate nucleus ipsilateral to the trained arm, changes in reaction time (RT) were observed. Mean daily RTs of movements triggered by light and sound were lengthened by 50-70 ms. RTs of movements triggered by somesthetic stimuli were not changed in one monkey, whereas a small increase of only 20 ms was observed in the other animal. Spontaneous firing of precentral neurons was about the same before and after dentate lesion. However, movement-related responses of cortical neurons were affected by the lesion. Whenever there was an increase in RT according to the triggering stimuli, a corresponding increase in the response time of neurons (RS) appeared. Both RS and RT increased by the same amount when movements were triggered by visual and auditory stimuli, whereas they remained about the same when somesthetic stimuli were used to trigger movements. In contrast, the time interval between the appearance of the change of neuronal firing and onset of arm displacement (RM) was not modified after the lesion. Gating of sensory conditioning inputs and modification of RT by the presentation of more than one stimulus were not abolished by dentate lesion. As a whole, the effects of dentate lesion on motor cortical neurons are consistent with the hypothesis that the neocerebellum controls the initiation of simple ballistic limb movements by controlling the discharge of motor cortex neurons. The effects could be attributed to the withdrawal of a facilitatory influence of dentate neurons on the motor cortical cells, particularly for movements triggered by teleceptive inputs.

Acoustic Stimulation↗
PubMed1983

Human jaw reflexes.

Although the jaw reflexes are analogous in many ways to the corresponding limb reflexes, important differences do exist. The myotatic reflex appears to contribute more stiffness to the jaw-closing muscles than to limb muscles. The jaw tends to swing up and down during locomotion, and, to maintain a stable position in relationship to the skull, it is necessary that the muscles be made stiff by tonic contraction and/or through a powerful servoreflex. The short conduction pathway and rapid contraction of jaw muscles allow reflex effects to act with little phase lag and to provide efficient compensation. If limb muscle reflexes were equally powerful, their effects could be of more nuisance than help in overcoming expected loads because they occur so late. Perhaps the lack of Renshaw cell inhibition of trigeminal MNs and the potentiation of the jaw jerk reflex by chin vibration are features designed to maintain the strength of the myotatic reflex during locomotion. The jaw-opening reflex (including exteroceptive suppression of jaw-closer muscle activity) is bilaterally symmetrical rather than bilaterally reciprocal, as are the analogous spinal flexor withdrawal reflexes. Bilateral braking is necessary to stop closure, because the mandible crosses the midline, whereas withdrawal of a limb often needs to be compensated for by extension of the other to maintain balance. It has recently been shown in animals that limb and jaw reflex responses are highly context dependent: the size and direction of limb reflexes depend on the phase of locomotion (Forssberg et al., 1977), and the gain of the jaw-opening reflex is increased during the closing phase of mastication (Lund et al., 1981).

Electromyography↗
PubMed1981

Patterns of muscular and motor cortical activity during a simple arm movement in the monkey.

This article describes the behavior of motor cortex neurons recorded in macaque monkeys (Macaca mulatta) which had been trained to make extension and flexion movements about the elbow in response to auditory, visual, or somesthetic cues. The pattern of activity of 65% of those movement-related neurons which were recorded during both flexion and extension was reciprocally related to the direction of movement. However, the movements of extension and flexion were made by co-contraction of the biceps and triceps in a pattern that did not match that of the motor cortex neurons. The majority of motor cortex neurons had firing frequencies that were related to movement parameters but by their nature could not be directly involved in the control of alpha motoneurons in both directions of movement. We suggest that they could, instead, control the fusimotor system. It is more likely that alpha motoneurons are controlled by the 35% of motor cortex neurons that, like the muscles, do not show reciprocal patterns of activity for movements in opposite directions.

Afferent Pathways↗
PubMed1979

Activity of postcentral cortical neurons of the monkey during conditioned movements of a deafferented limb.

Unit recordings were performed in the sensorimotor cortex of awake monkeys during performance of learned movements of the contralateral arm. The movements were triggered by a sound stimulus. The neuronal discharge in association with movement was observed before and after deafferentation (C2--T5) of the operant limb. Whereas neurons recorded in the motor cortex (area 4) and in the parietal association cortex (area 5) still modified their activity in relation to movement performed by the deafferented arm, the neurons recorded in the primary sensory cortex (areas3, 1 and 2) showed no activity change in relation to movement after deafferentation. This finding strongly suggests that modification of discharge of postcentral neurons seen during ballistic arm movement is mainly the result of input from the moving limb (peripheral feedback) and not the result of input from other structures of the central nervous system (internal feedback).

Afferent Pathways↗
PubMed1978

Activity of pre-entral neurones in conscious monkeys: effects of deafferentation and cerebellar ablation.

After limb deafferentation, there was no gross alteration in the initiation and performance of a sound-triggered ballistic movement. The pattern of neuronal discharge in the arm area of the motor cortex was not significantly modified. In the absence of cerebellum, the reaction time of motor cortex cells was about 150 msec longer than the reaction time observed in normal and deafferented animals. This was associated with an equal retardation in the onset of ENG changes in the limb muscles. This observation is compatible with the idea that the motor cortex is normally situated downstream to the cerebellum in the initiation of some movements. However, the motor cortex is necessary for the initiation and execution of simple sound-triggered movements since its removal results in a permanent inability to perform the task. Finally, in the absence of peripheral feedback, the pattern of motor output to the agonistic and antagonistic muscles was initiated normally and thus appeared to be preprogrammed centrally. The importance of the motor cortex as a "reflex center" in the control of slower movements is obviously not challenged by these observations since the motor task that we have used depends very little or not at all on sensory feedback (Stark, 1968). What these results indicate, however, is that the execution of some voluntary fast ballistic movements can be entirely preprogrammed independently of peripheral and cerebellar influences, and that the program, which is mainly concerned with generating velocity signals, appears to require the integrity of the motor cortex for its execution.

Afferent Pathways↗
PubMed1978

Involvement of the cerebellum in the initiation of fast ballistic movement in the monkey.

Monkeys were trained to perform a fast ballistic flexion or extension of the elbow in response to a sound cue. The reaction time was about 250 msec in the normal monkey and remained so after deafferentation of the operant arm. In a cerebellectomized animal, the reaction time was consistently longer, being, on the average, 400 msec. This was associated with an equal retardation in the onset of neural changes in the motor cortex. These results are interpreted as evidence for the involvement of the cerebellum in the initiation of some fast ballistic movements.

Animals↗
PubMed1977

Electrophysiological and anatomical estimation of the number of motor units in the monkey extensor digitorum brevis muscle.

The electrophysiological technique used to estimate the number of motor units in man (McComas et al., 1971b) was tested in six monkeys. The number of motor units was estimated electrophysiologically in the extensor digitorum brevis (EDB) after deafferentation by excision of the lumbo-sacral dorsal root ganglia. In five animals, the mean number of motor units obtained by the technique was in good agreement with the number of alpha motor fibres counted in the nerve to EDB. However, the results obtained in one animal with partial denervation of the EDB indicate that the technique might be unreliable, at least at certain stages, after a peripheral nerve lesion.

Animals↗
PubMed1975

Central mechanisms of tremor in some feline and primate models.

For several years our interest has been in a postural Parkinson-like tremor at 4-6/sec. which can be produced in the monkey by lesions of the central nervous system. We have also studied the effects of harmaline, a drug which evokes or intensifies the Parkinson-like tremor in lesioned animals and which also induces a fine, generalized tremor at 7-12/sec. in normal animals. The results obtained so far indicate that these two types of tremor are generated by two independent central mechanisms which do not require the integrity of peripheral feedback loops. The experimental Parkinson-like tremor is generated by a thalamo-cortical mechanism while the olivo-cerebellar system is responsible for the faster "physiological" tremor. Similar tremor mechanisms may be involved in some movement disorders in man.

Animals↗
PubMed1975

Load compensation in human masseter muscles.

The reaction of masseter and digastric muscles to changes in the load applied during a movement was studied in human volunteers. 2. Rapid stretch of the jaw-closing muscles evoked a monosynaptic jaw-jerk reflex response in the masseteric electromyogram (e.m.g.) after a delay of 6-8 msec. 3. The averaged integrated e.m.g. activity of the masseter was increased 5-10 msec after the rapid application of a load during voluntary closure of the jaw. It was not necessary to stretch the muscle to obtain this apparently monosynaptic response. 4. A compensatory increase in the velocity of movement followed 6-10 msec after the e.m.g. peak. 5. Unloading the masseter muscle during contraction was followed by a fall in e.m.g. activity, beginning after a latency of 6-5--1 msec, with later phases of depression beginning 27--36 and 60--70 msec after unloading. 6. The spindle-poor digastric muscles were not monosynaptically activated during loading, but responded with a latency of 24--34 msec. 7. It is concluded that monosynaptic e.m.g. changes are a prominent feature of the load compensation system in human jaw-closing muscles but not in jaw-opening muscles.

Adolescent↗