Biomedical subjects

E Ribot-Ciscar

Publications and source records attributed to E Ribot-Ciscar.

13 recordsLinked to original sources

PubMed2004

Spontaneous bursting neuronal discharges recorded from peripheral nerve in human: injury discharges or not?

This paper deals with a spontaneous, bursting neuronal activity which can not be altered by any stimulation in the periphery or voluntary actions or by cognitive tasks. An initial description of such units led to the conclusion that this activity was generated ectopically at the site of a previous or present impalement of a nerve fibre. The aim of the current study was to record a larger number of these units by using microneurography, in order to characterise their firing properties and particularly, see if any subtypes of units could be identified. In conclusion, this paper suggests that some of these discharges could be related to an injury of the nerve fibre, however most of them could not. Some hypothesis regarding the nature of these bursting activities are suggested.

Action Potentials↗

PubMed2000

Increased muscle spindle sensitivity to movement during reinforcement manoeuvres in relaxed human subjects.

1. The effects of reinforcement manoeuvres, such as mental computation and the Jendrassik manoeuvre, on muscle spindle sensitivity to passively imposed sinusoidal stretching (1.5 deg, 2 Hz) in relaxed subjects were analysed. 2. The unitary activity of 26 muscle spindle afferents (23 Ia, 3 II) originating from ankle muscles was recorded using the microneurographic method. Particular care was paid to the subjects' state of physical and mental relaxation. 3. The results showed that the activity of 54 % of the Ia afferents was modified during mental computation. The modifications took the form of either an increase in the number of spikes (mean, 26 % among 11 Ia fibres) or a shortening in the latency of the response to sinusoidal stretching (mean, 13 ms among 3 Ia fibres), or both. They were sometimes accompanied by an enhanced variability in the instantaneous discharge frequency. The three secondary endings tested exhibited no change in their sensitivity to stretch during mental computation. 4. The increased sensitivity to passive movements sometimes began as soon as the instructions were given to the subjects and sometimes increased during mental computation. In addition, the increased sensitivity either stopped after the subjects gave the right answer or continued for several minutes. 5. During the performance of a Jendrassik manoeuvre, the Ia units underwent changes similar to those described above for mental computation. 6. It was concluded that muscle spindle sensitivity to movement can be modified in relaxed human subjects. The results reinforce the idea that the fusimotor system plays a role in arousal and expectancy, and contribute to narrowing the gap between human and behaving animal data.

Action Potentials↗

PubMed2000

Proprioceptive population coding of two-dimensional limb movements in humans: I. Muscle spindle feedback during spatially oriented movements.

The proprioceptive coding of multidirectional ankle joint movements was investigated, focusing in particular on the question as to how accurately the direction of a movement is encoded when all the proprioceptive information from all the muscles involved in the actual movement is taken into account. During ankle movements imposed on human subjects, the activity of 30 muscle spindle afferents originating in the extensor digitorum longus, tibialis anterior, extensor hallucis longus and peroneus lateralis muscles was recorded from the lateral peroneal nerve using the microneurographic technique. In the first part of the study, it was proposed to investigate whether muscle spindle afferents have a preferred direction, as previously found to occur in the case of cortical cells, and to analyze the neural coding of the movement trajectories using a "population vector model." This model is based on the idea that neuronal coding can be analyzed in terms of a series of vectors, each based on specific movement parameters. In the present case, each vector gives the mean contribution of a population of muscle spindle afferents within one directionally tuned muscle. A given population vector points in the "preferred sensory direction" of the muscle to which it corresponds, and its length is the mean frequency of all the afferents within that muscle. Our working hypothesis was that the sum of these weighted vectors points in the same direction as the ongoing movement. The results show that each muscle spindle afferent, and likewise each muscle, has a specific preferred sensory direction, as well as a preferred sensory sector within which it is capable of sending sensory information to the central nervous system. Interestingly, the results also demonstrate that the preferred directions are the same as the directions of vibration-induced illusions. In addition, the results show that the neuronal population vector model describes the multipopulation proprioceptive coding of spatially oriented 2D limb movements, even at the peripheral sensory level, based on the sum vectors calculated from all the muscles involved in the movement. In an accompanying paper, the coding of more complex 2D movements such as those involved in drawing rectilinear and curvilinear geometrical shapes was investigated.

Adult↗

PubMed2000

Proprioceptive population coding of two-dimensional limb movements in humans: II. Muscle-spindle feedback during "drawing-like" movements.

It was proposed to study the proprioceptive sensory coding of movement trajectories during the performance of two-dimensional "drawing-like" movements imposed on the tip of the foot. For this purpose, the activity of the muscle-spindle afferents from the Extensor digitorum longus, Tibialis anterior, Extensor hallucis longus, and Peroneus lateralis muscles was recorded from the lateral peroneal nerve using the microneurographic technique. The drawing movements, describing geometrical shapes such as squares, triangles, ellipses, and circles, were imposed at a constant velocity in both the clockwise and counterclockwise directions. A total number of 44 muscle-spindle afferents were tested, 36 of which were identified as primary and eight as secondary afferents. Whatever the shape of the imposed foot movement, the primary endings from one muscle never discharged throughout the whole trajectory (on average, they discharged for only 49.2% of the length of the trajectory), whereas all the secondary endings discharged for most part of the drawing trajectories (average: 84.8%). The relationship between afferent discharge rate and direction could be described with a cosine-shaped tuning function. The peak of this function corresponded to the preferred sensory direction of the receptor-bearing muscles. The whole path of a given geometrical drawing movement was found to be coded in turn by each of the primary afferents originating from each of the muscles successively stretched. The contribution of each population of muscle afferents from each ankle muscle was represented by a "population vector", whose orientation was the preferred direction of the muscle under consideration and whose length was the mean instantaneous frequency of the afferent population. The "sum vector" corresponding to the sum of all these weighted "population vectors" was found to point in the instantaneous direction of the drawing trajectory, i.e., the tangent to the trajectory. These findings suggest that trajectory information is already encoded at the peripheral level on the basis of the integrated inputs provided by sets of receptors belonging to all the muscles acting on a given joint.

Adult↗

PubMed2000

Changes in tactile spatial discrimination and cutaneous coding properties by skin hydration in the elderly.

Neurosensory tactile functions were investigated in human subjects by two different and complementary experimental approaches. First, a conventional psychophysical method (two-point gap discrimination) was used to determine the tactile discrimination threshold by analyzing the subjects' ability to detect a gap of variable width between two contact points when a series of stimuli was applied to the skin. Using this method we confirmed the marked degradation of tactile spatial acuity with age and showed that skin discriminative function was partially restored after hydration of the skin with a moisturizer. The second approach consisted of a microneurographic recording of tactile afferent fibers in response to two types of mechanical stimuli applied reproducibly to the corresponding receptive fields. With this method, we found that the afferent messages were depressed following hydration of the skin surface. Thus, partial restoration of tactile spatial acuity after hydration appears to be due to both a softening of the stratum corneum permitting better localization of the stimulus and a weaker transfer of the stimulus toward the sensory receptors.

Adult↗

PubMed1998

Muscle spindle activity following muscle tendon vibration in man.

Muscle spindle primary endings originating from the Tibialis anterior, Extensor Digitorum Longus and Lateral Peroneal muscles were recorded by the microneurographic technique. Their resting activity and stretch sensitivity after muscle tendon vibration (80 Hz, 30 s) were compared with those in the previbratory period. Most of the units (73%) exhibited a decreased spontaneous firing rate whereas a few others either conserved (13.5%) or increased (13.5%) their resting discharge after vibration. A complete recovery necessitated 40 s. The static stretch sensitivity of the units was decreased during the 3 s following vibration exposure and returned to the control level (about 14 s). The results are discussed in the light of previous psychophysiological studies reporting an altered position sense and a development of involuntary muscle contractions in postvibratory periods.

Adult↗

PubMed1998

Ago-antagonist muscle spindle inputs contribute together to joint movement coding in man.

The proprioceptive feedback associated with the performance of even quite simple movements is always generated by the whole set of muscles subjected to mechanical deformation (lengthening, shortening, contraction, etc.) during that particular movement. The question was addressed here as to how muscle spindle feedbacks arising from agonist and antagonist muscles may contribute to the coding of movement parameters such as the direction and velocity. For this purpose, the activity of single muscle spindle afferents located in the lateral peroneal nerve was analysed using the microneurographic technique, in human subjects performing repetitive voluntary movements, i.e., plantar/dorsal flexions of the ankle, at three different velocities (3, 4.5 and 6 degrees/s). The data obtained suggest that in humans, the direction of a slow movement may be specified on the basis of the spindle discharge rate, which is greater in the stretched than in the shortened muscle, and that the velocity of this movement might be correlated with the difference between the spindle activity occurring in the agonist and antagonist muscles. These neurophysiological data are in agreement with the results of previous psychophysical studies showing for example that a sensation of illusory movement can be elicited only when there exists an imbalance between the agonist versus antagonist vibration-induced Ia inputs. In addition, the greater the difference between the vibration frequencies applied to the two antagonist muscles, the higher the perceived movement velocity was found to be. All in all, joint movement perception seems to result from the co-processing by the central nervous system of the multiple spindle feedbacks originating from the whole set of muscles involved in the performance of a movement.

Adult↗

PubMed1996

Human motor unit activity during post-vibratory and imitative voluntary muscle contractions.

Applying mechanical vibration for short periods to a muscle tendon induces long-lasting involuntary contractions which develop soon after the vibration offset in the previously vibrated muscle. In the present study, the question was raised as to whether these post-vibratory motor responses are mediated by the activity of supraspinal neural population or whether they may involve in addition some peripheral facilitatory influences operating at the motoneuronal level. To investigate this question, we analysed the unitary activity of 48 motor units belonging to the wrist extensor radialis muscles of the human hand, after attempting to classify them as slow or fast, during both post-vibratory and voluntary contractions having almost the same amplitudes and time-courses. The motor units were found to be activated in much the same way with both types of contraction. Similarities were observed as regards: the nature of the motor units activated, the order of recruitment of the motor unit population, the motor units' force recruitment thresholds, the mean interspike interval and the standard deviation. These analogies suggest that post-vibratory contraction may mainly involve a supraspinal tonic drive, but the possibility that these involuntary contractions may have a spinal origin cannot be completely ruled out.

Action Potentials↗

PubMed1996

Alteration of human cutaneous afferent discharges as the result of long-lasting vibration.

The unitary activities of slowly (15 SAI) and fast-adapting type I (12 FAI) skin mechanoreceptive afferent units innervating the anterior part of the human leg and foot were recorded by using the microneurographic method. The recordings were performed both at rest and on application of cutaneous stimuli of various intensities before and after exposure of the corresponding receptive fields to vibration (0.5 mm peak to peak, 100 pulses/s, 10 min). The results show that 11% of the units tested, which were previously silent, developed a bursting pattern of postvibratory activity, which lasted 12 min on average. This induced resting activity may account for the tingling sensations usually perceived after exposure to vibration. Furthermore, application of vibration to the cutaneous receptive fields impaired the response properties of the corresponding cutaneous fibers much more markedly in the case of the SAI than in the FAI units. More specifically, less than one-half of the FAI fibers tested showed a postvibratory depressed sensitivity to skin stroking applied at various velocities that persisted for only a few minutes, whereas the responses of all the SAI units to suprathreshold maintained skin indentations applied with increasing amplitudes decreased significantly for 20 min. These fairly durable changes in the transductive properties of the mechanoreceptive afferent units probably lead to an impairment of perceptual and sensorimotor processes and consequently may at least partly account for the alterations in sensorimotor performance that have been reported to occur in humans after exposure to vibration.

Adult↗

PubMed1993

[Transcutaneous mechanical vibrations: analgesic effect and antinociceptive mechanisms].

Although vibration has been used empirically for a long time in medicine, it was only about ten years ago that it began to be investigated scientifically. In the first part of this paper, we review the main data showing that vibratory stimulations can relieve both acute and chronic pain. In the second part, we consider the mechanisms responsible for the observed analgesic effects and discuss the nature of the sensory receptors involved and the effects of their activation on the triggering of central pain control systems.

Analgesia↗

PubMed1991

Post-contraction changes in human muscle spindle resting discharge and stretch sensitivity.

The activities of human muscle spindle primary endings were recorded in the lateral peroneal nerve using the microneurographic method. The aim of the study was to test whether voluntary isometric contraction causes any after-effects, first in the resting discharge of muscle spindle primary endings and secondly in their responses to a slow ramp stretch. To investigate the latter point, the initial angular position of the ankle was passively adjusted until the unit fell silent, in order to introduce a delay in the responses to muscle stretch. The results were as follows: (1) most of the units did not exhibit the "post-contraction sensory discharge" reported to occur in numerous animal experiments; this means that the muscle spindle resting discharge was essentially the same before and after isometric voluntary contraction. (2) Isometric voluntary contraction led to changes in muscle spindle stretch sensitivity which resulted in a reduction in the stretch threshold and a decrease in the muscle spindle dynamic sensitivity. These data suggest that the after-effects observed may have been triggered by static fusimotor neurones. The results are discussed with reference to the theory according to which the processing by the CNS of muscular proprioceptive messages deals mainly with signals arising from muscles stretched during movement, and it is concluded that the coactivation of alpha and gamma motoneurones during the contraction facilitates the coding of the parameters of forthcoming stretching movements, by the muscle spindles.

Adult↗

PubMed1990

[Tendon vibrations as a tool for clinical investigation of the myotatic loop].

The degree of alteration of the myotatic loop was evaluated in 6 patients with polyradiculoneuropathy by studying deep reflexes and vibratory motor responses. The results showed that the reflex motor responses induced by vibration reappeared 2 to 4 weeks before the deep reflexes. Vibrations, therefore, could be a useful tool for the clinical follow-up of polyradiculoneuropathy.

Adult↗

PubMed1989

Vibration sensitivity of slowly and rapidly adapting cutaneous mechanoreceptors in the human foot and leg.

The activities of 30 rapidly adapting cutaneous receptors (FA) and 23 slowly adapting cutaneous receptors (SA) were recorded from the lateral peroneal nerve using the microneurographic method. Their sensitivity to mechanical vibrations with constant amplitude applied at various frequencies to the center of the receptive field was studied. These two populations of cutaneous receptors were found to be very sensitive to this stimulus: they could be driven in a one to one manner up to between 100 and 200 Hz. The difference lay in the response observed when the vibration frequency was increased to above this critical value: the FA receptors sharply stopped firing, whereas the SA receptors became progressively unlinked from the stimulus. The effects of vibration on the physiological messages were also studied. The results showed that the messages coding the properties of tactile stimuli were either completely or partly masked by the receptor response to vibration. These vibration-induced modifications of cutaneous sensory messages might be at least partly responsible for the sensorimotor alterations observed when subjects are exposed to vibration.

Electrophysiology↗