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Biomedical subjects

Y Gahery

Publications and source records attributed to Y Gahery.

At least 19 recordsLinked to original sources
PubMed1997

Gait initiation and impairments of ground reaction forces as illustrated in old age by 'La marche à petits pas'.

Ground reaction forces during gait initiation and kinematics of the first step were recorded in 11 elderly patients with idiopathic 'marche à petits pas' and 18 age-matched normal adults. Smaller values of vertical forces, and impaired amplitudes and directions of anteroposterior forces might explain start difficulties of the patients. Higher vertical displacement of the foot, and laborious establishment of the rhythm in the patients could also be related to the perturbations observed in the reaction forces. These perturbations are likely to reflect impairments of muscular synergies of the lower limbs and the lack of limb co-ordination.

Aged↗
PubMed1993

Effect of optic nerve stimulation on neurons in pericruciate cortex of cats.

The distribution of optic chiasm input to different types of neurons in pericruciate cortex of cats agreed with previous work using light flashes. Neuron response times served to differentiate the input pathways to pericruciate cortex, and the types of neurons they influence. Input from the optic chiasm arrived in three distinct surges: the first via the superior colliculus, the second via an unidentified pathway, and the third via the visual cortex. A fourth, diffuse surge arrived in the postcruciate cortex via some unidentified pathway. Stimulation of the contralateral side of the optic chiasm had a weaker effect than stimulation of the ipsilateral side; it evoked activity at a higher threshold, with fewer spikes per response, and at a longer latency. The difference in response latency between the two sides was largest on neurons responding to the first surge, decreasing in later surges, and being least on those neurons responding to the last surge. About 2.3% of the postcruciate and 15% of the precruciate neurons responded only to optic chiasm stimulation; they were isolated in the granular layers, and their responses could not be influenced by prior cutaneous input. It is suggested that much of the visual input to pericruciate cortex serves to modulate on-going cortical output and, thereby, the behavior of the animal.

Animals↗
PubMed1993

Somatotopical effects of local microinjection of GABAergic agents in Deiters nucleus on the posturokinetic responses to cortical stimulation.

The postural adjustments that accompany the limb flexion following stimulation of the motor cortex in the cat are in part at least mediated by the lateral vestibular nucleus (LVN). In fact, inactivation of vestibulospinal (VS) neurons by unilateral injection of GABA agonists into the LVN decreased the early component of the responses in all of the postural limbs without modifying the threshold, latency, or amplitude of the cortically induced flexion movement. Just the opposite result was obtained after injection into the same structure of GABA antagonists. Experiments were performed to find out whether these VS influences were somatotopically organized. Microinjection of 0.25 microL of the GABA-A agonist muscimol or the GABA-B agonist baclofen (at 1.5 to 4 micrograms/microL saline) into the rostroventral part of the LVN (rvLVN) of one side produced hypotonia in the ipsilateral and hypertonia in the contralateral forelimb. The same injection also reduced the early component of the postural responses to cortical stimulation in both forelimbs, but not in the hindlimbs. On the other hand, unilateral injection of the same agents into the dorsocaudal part of the LVN (dcLVN) produced similar effects, but they were limited to the hindlimbs. The results obtained, which lasted for about 2 to 3 h, were not only site-specific but were also dose-dependent. Injection into the rvLVN or dcLVN of 0.25 microL of the GABA-A antagonist bicuculline or the GABA-B antagonist phaclofen (at 8 or 5 micrograms/microL saline) produced localized changes in posture as well as in the post-urokinetic responses to cortical stimulation. These were opposite in sign to those elicited by the corresponding agonists. In conclusion, it appears that: 1) the motor cortex utilizes descending volleys passing through the LVN in order to elicit the early postural adjustments during a cortically induced limb movement; 2) the resulting VS influences are somatotopically organized; 3) the amplitude of these postural responses can be affected by inhibitory influences probably exerted by Purkinje cells of the cerebellar vermis on the related VS neurons through both GABA-A and GABA-B receptors.

Animals↗
PubMed1992

GABA receptors in Deiters nucleus modulate posturokinetic responses to cortical stimulation in the cat.

The early component of the postural responses which accompany the limb flexion during unilateral stimulation of the motor cortex in the cat is not of reflex origin, but results from a central command. These postural adjustments are characterized by a decreased force under the limb diagonally opposite to the moving one and an increased force under the other two. Since the lateral vestibular nucleus (LVN) exerts an excitatory influence on ipsilateral limb extensor motoneurons, experiments were performed in cats to establish whether the cortical-induced postural changes were mediated through the LVN. This structure is tonically inhibited by GABAergic synapses originating from Purkinje cells of the cerebellar vermis, so that local microinjection into the LVN of GABA agonists or antagonists should either decrease or increase the spontaneous discharge of their neurons. Unilateral microinjection of 0.25 microliters of the GABA-A agonist muscimol or the GABA-B agonist baclofen (at 2-4 micrograms/microliters saline) into the LVN produced a short-lasting episode of ipsilateral postural hypotonia and contralateral hypertonia, during which the cats were unable to stand on the measurement platform. When, shortly after, some recovery of the postural activity appeared, no changes in threshold, latency or amplitude of the cortical-induced flexion movement were observed; however, the early component of the postural responses decreased in the other three limbs. Moreover, the slope of the response curve of the moving limb remained unmodified, while that of the early component of the postural responses, which involved the remaining limbs, decreased following stimulation of the motor cortex at different stimulus intensities. These effects started a few min after the injection and lasted for about 2-3 h. The effects described above were dose-dependent. Moreover, histological controls indicated that the structure responsible for these postural changes corresponded to the middle part of the LVN. The specificity of the results was shown by the fact that unilateral microinjection of 0.25 microliters of the GABA-A antagonist bicuculline or the GABA-B antagonist phaclofen (at 5-8 micrograms/microliter saline) into the LVN produced a postural asymmetry opposite in sign to that elicited in the same experiments by the corresponding agonists. These injections did not modify the amplitude of the cortical-induced limb flexion, but rather enhanced the amplitude of the early component of the postural responses in the other three limbs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Injection of a cholinergic agonist in the dorsolateral pontine tegmentum of cats affects the posturokinetic responses to cortical stimulation.

Microinjection into the dorsolateral pontine tegmentum of the muscarinic agonist bethanechol, leading to activation of cholinoceptive pontine reticular formation (pRF) neurons and the related medullary inhibitory reticulospinal system, did not modify the threshold, latency and amplitude of the forelimb flexion elicited by unilateral stimulation of the corresponding motor cortex. However, the remaining limbs which displayed a diagonal pattern of postural adjustments showed a dissociation of their postural responses in 2 components: the early component of central origin greatly decreased in amplitude, while the late component attributed to reflex mechanism triggered by the unbalance brought about by the flexion movement increased. Further evidence indicated that the pRF system intervenes in the gain regulation of the early postural responses during the cortically induced limb movement.

Animals↗
PubMed1990

Cholinoceptive pontine reticular structures modify the postural adjustments during the limb movements induced by cortical stimulation.

1. Activation of the pontine reticular formation (pRF) and the related medullary inhibitory reticulospinal (RS) system decreases the postural activity. This effect can be achieved either by local injection into the dorsal pontine tegmentum of cholinergic agonists which excite cholinoceptive pRF neurons, or by injection of noradrenergic agents which block the inhibitory influence exerted by the locus coeruleus (LC) neurons on the pRF. The main aim on the present study was to analyze the effects of tonic activation of these pRF neurons on the postural adjustments accompanying limb movements induced by motor cortex stimulation. In particular, electrodes were implanted chronically in the motor cortex of cats and stainless steel guide tubes of small size, later used for drug injection, were set bilaterally into sites just above the responsive regions. 2. Limb flexion elicited by stimulation of the motor cortex was accompanied by a diagonal pattern of postural adjustment, characterized by a decreased force exerted by the limb diagonally opposite to the moving one and an increased force exerted by the other two. 3. Microinjection into the pRF of both sides of 0.25 microliter of the muscarinic agonist bethanechol at the concentration of 8 or 16 micrograms/microliters in buffered artificial cerebrospinal fluid produced a short-lasting episode of postural atonia followed by a period of reduced postural activity, during which the cats were still able to stand on the measurement platform. Under this condition no changes in threshold, latency and amplitude of the flexion response were observed in the performing limb; however, the postural responses were considerably affected. In particular, when the performing limb was a forelimb, the other anterior limb showed a dissociation of the postural response in two distinct components. The first anticipatory component, which had a short latency (12-15 msec) and was considered to be centrally triggered, decreased in amplitude after injection of bethanechol and sometimes disappeared; on the other hand the second component, which had a long latency (50-60 msec) and was thus considered to be of reflex origin, increased in amplitude, due to the instability resulting from the depression of the early postural response. Similar results also affected to a lesser extent the hindlimbs. Moreover, body oscillations were observed and monitored from the force platforms following the late component of the postural responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Bethanechol↗
PubMed1988

Ambulatory computer system for recording and controlling locomotion.

Description of an original miniature computer system capable of recording biomechanical parameters during locomotion, providing auditory signals which can be used in biofeedback locomotor learning, and triggering functional electrical stimulation of nerves and muscles at preselected moments in the locomotor cycle. The system, which is worn on the patient's back, is connected to appropriate gauges with which it is possible to measure knee angle and to record the time of heel contact with the ground. The relevant data are stored in the system memory and can be transferred to a microcassette and later displayed as a function of time on a video screen or printed on paper. The same data can be used on-line to provide a patient with a sound signal as a basis for biofeedback training. This kind of training has been successfully used to correct knee hyperextension during locomotion in hemiplegic patients. The system can also be used to trigger a stimulator and thus constitutes a valuable tool for investigations and treatments involving functional electrical stimulation. Many other applications may be developed, both in basic research and in various fields where motor training is required.

Biofeedback, Psychology↗
PubMed1988

Postural adjustments to head movements in the cat.

Head movements induced by motor cortex stimulation in the cat are accompanied by variations in the vertical force exerted by each limb. These postural responses were found to show stereotyped patterns: with head dorsiflexions an increase was observed in the force exerted by the anterior limbs and a decrease at the posterior limb level. From comparison between the latencies of the force variations, the beginning of head acceleration, and EMG activity in the limb extensor muscles, it was concluded that triggering of these postural responses is not reflex, but depends on the same command as the movement itself. This early response might be a means of avoiding the downward movement of the trunk which would otherwise result from the reaction force corresponding to the upward head movement.

Animals↗
PubMed1987

Associated movements, postural adjustments and synergies: some comments about the history and significance of three motor concepts.

Associated movements, postural adjustments and synergies are three motor concepts directly related to each other, although their historical developments have followed relatively independent paths. We show in this study how some notions, often very old, are evolving and become more precise as the number of observations and experimental results increases. We show also how the relationships between these notions and the terms associated with them may vary depending on the historical period and on the authors. The various kinds of muscular activity related to a movement, which are the object of this review, present several aspects, each of them being often described by different terms, which are analyzed. On the other hand we study the various meanings of some terms or expressions, which may correspond to very different aspects of the motor system. The three concepts analyzed have in common a definition from final manifestations (essentially muscular and mechanical) of motor activity. This characteristic is probably due to the lack of enough experimental data to use more refined criteria for definition, like those based upon nervous structures implicated, mechanisms involved or functional significance. The situation may change in the near future, as this field of investigation is now entering a phase of rapid development.

Animals↗
PubMed1981

Description and applications of a programmable stimulation system for electrophysiology, used as a computer peripheral.

An original programmable stimulation and data acquisition system of general interest for electrophysiology is presented. It can be used as a peripheral of any 12 (or more) bits mini- or microcomputer. With the software described it is possible to determine stimulation parameters automatically as a function of results obtained during the experiment or from the keyboard. Verification of parameters is carried out by permanent registration on the terminal screen, in numerical and analog form, and by facultative printout from the teleprinter. Two applications in electrophysiology are presented: the measurement of thresholds and the establishment of response curves.

Analog-Digital Conversion↗
PubMed1981

[Postural support for local movements in cats and dogs].

A comparative analysis of adjustment of posture for performance of different kinds of local movements (movements elicited by electrical stimulation of the motor cortex; proprioceptive reaction of placing the paw on a support, conditioned lifts of the paw) was made in cats and dogs. The present experimental data were obtained in two laboratories independent of each other. For their quantitative analysis a number of criteria was elaborated which allow to obtain characteristics of the posture at concrete moments and differential characteristics based on the measurement of vertical forces of the limbs support. It was shown that the general characteristics of posture adjustment (the so called diagonal pattern) are identical in cats and dogs and in different kinds of movements; the degree of diagonality, however, depends considerably on the kind of movement. During conditioned movements the diagonality coefficient is higher in dogs than in cats.

Animals↗