Biomedical subjects

H Devanne

Publications and source records attributed to H Devanne.

8 recordsLinked to original sources

PubMed2006

The effect of repetitive transcranial magnetic stimulation on dystonia: a clinical and pathophysiological approach.

Dystonia is characterized by sustained muscle contraction, which frequently causes repetitive, twisting movements or abnormal posture. The precise pathophysiological mechanisms of dystonia are still unknown. Several studies did demonstrate that, although motor cortex hyperexcitability appears to be responsible for abnormal co-contraction and overflow to adjacent muscles, plasticity mechanisms and integrative sensorimotor processing are also likely to be involved in this condition. Current dystonia treatments are based on oral medication, injection of botulinum toxin and, in a low proportion of cases, bi-pallidal deep brain stimulation. However, treatment outcome is generally disappointing. A few researchers have reported the application of repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex or the premotor cortex, with the goal of decreasing motor cortex hyperexcitability. This article reviews all studies using this technique in dystonia and discusses rTMS therapeutic impact and its possible mechanisms of action in this indication. Currently, the premotor cortex seems to be the best target for rTMS in dystonia. Rather than merely reducing the hyperexcitability of the primary motor cortex, this technique's clinical benefit seems to result from modifications in plasticity and restoration of sensorimotor integration. The corollary technique for chronic rTMS is electrical cortical stimulation. Even though this new therapeutic tool may have therapeutic promise, more studies are required to confirm it. In particular, we need to broaden our knowledge of rTMS impact on the various forms of dystonia and to optimize target localization.

Dystonia↗

PubMed2005

Motor cortex plasticity induced by extensive training revealed by transcranial magnetic stimulation in human.

This study examines the effect of high-level skilled behaviour on motor cortex representations of upper extremity muscles of ten sportswomen. We used transcranial magnetic stimulation to map proximal medial deltoid and distal extensor carpi radialis muscle representations on both hemispheres during low-level voluntary contraction. We compared cortical representation areas between two groups of subjects and between hemispheres within subjects. The first group comprised five elite volleyball attackers and the second group five runners. Four stimuli were delivered on multiple scalp sites (1.5 cm apart) to induce motor-evoked potentials recorded by surface EMG. Maps were described in terms of excitable scalp positions and of motor-evoked potentials. We observed differences in map areas between the two groups. Volleyball players had larger cortical representations of the proximal medial deltoid muscle than runners. Furthermore, the volleyball players had larger map areas for dominant muscles compared with non-dominant muscles. There was no difference, however, in map area for either muscle between the dominant and non-dominant arm in the runner group. Our results show that heavy training in a specific skill induces an expansion of proximal muscle representation in the contralateral primary motor cortex. This enlarged map area for proximal muscle is accompanied by an increase in the overlapping of proximal and distal muscle representations. This could reflect the fact that motor learning of co-ordinated movement involves a common control of both muscles. This reorganization supports the hypothesis of a cortical plasticity driven by activity.

Adult↗

PubMed1998

Role of proprioceptive information in the temporal coordination between joints.

Ten subjects made rapid, simultaneous movements of jaw (elevation or lowering) and right foot (ankle flexion or extension) in two experimental situations: (1) in response to an external signal (reaction-time situation), and (2) in a self-paced situation. We calculated the mean time intervals between the onsets of electromyographic (EMG) activity of agonist muscles (tibialis anterior or gastrocnemius lateralis compared with masseter or digastricus pars anterior) and those between the onsets of movement acceleration at each joint. Despite the fact that subjects reported simultaneous jaw-foot movements, there was always a short time interval between the two movements as between the agonist EMG activities. When the subjects were asked to perform a jaw elevation movement simultaneously with an ankle movement (flexion or extension), the sign of the time interval was dependent on the situation of movement initiation. In the reaction-time situation, the jaw motor activity preceded that of the ankle, whereas the reverse temporal order was observed in the self-paced situation. This is consistent with a previous hypothesis suggesting that the simultaneity of two motor actions is centrally established through two separate central processes: reactive or predictive. When subjects tried to perform simultaneous jaw lowering and foot flexion or extension movements, the strict temporal order observed when considering jaw elevation and ankle movements disappeared. The jaw motor activity generally preceded that of ankle in the reactive situation, but, depending on the subjects, it preceded or followed the ankle motor activity during self-paced movements. It is likely that the specific spindle supply of jaw muscles accounts for these results. Indeed, the jaw depressor muscles, in contrast to the elevators, lack muscle spindles. Our results suggest that the kinesthetic inputs used by the upper central nervous system to synchronize two rapid voluntary movements are mainly those from spindles located in the muscles that accelerate the movement, suggesting a strong alpha-gamma linkage.

Acceleration↗

PubMed1998

Intracortical connections between motor cortical zones controlling antagonistic muscles in the cat: a combined anatomical and physiological study.

Experiments were done on nine cats anaesthetized with pentobarbitone to determine whether motor cortical zones controlling antagonistic muscles are synaptically interconnected. Motor cortical zones controlling wrist flexors, or extensors, were identified by microstimulation and intramuscular electromyographic recordings (microstimulation: 11 pulses at 333 pulses/s, current 10-40 microA). The position of each zone of interest was marked by a small ink spot on the surface of the cortex and on a scaled drawing of the cortical surface (cruciate region). Following the identification of wrist flexor and extensor zones the anterograde tracer biocytin was injected into one, or two, wrist extensor zones at three depths (400, 800 and 1500 microm) from the cortical surface. A small injection of horseradish peroxidase (HRP)--producing a dark brown spot of approximately 300-500 microm--was made in layer II-III of one or more wrist flexor zones. Similar HRP injections were made in the deep layers of wrist extensor zones that were not labelled by biocytin. The HRP injections served to mark the position of potential targets of biocytin-labelled fibres. In some experiments the biocytin was injected into a wrist flexor zone and HRP was deposited in one or more wrist extensor zones. Biocytin-labelled fibres (blue) were found throughout the expanse of the forelimb representation zone, as has been previously reported. More specifically, in all animals biocytin-labelled fibres were found in identified cortical zones controlling the same muscle(s) as well as in zones controlling an antagonist(s). Club-like swellings, indicative of synaptic boutons, were observed on these fibres. The density of labelled fibres was greater in the upper cortical layers (II-III), but a large number of terminals were also present in the lower cortical layers (V-VI). We conclude that there exist intracortical circuits linking motor cortical zones controlling antagonistic muscles. Elucidating the nature and function of these circuits is likely to be important for understanding the mode of operation of the motor cortex.

Animals↗

PubMed1997

Input-output properties and gain changes in the human corticospinal pathway.

Experiments were done to determine the form of the input-output relation (i.e. stimulus intensity vs response amplitude) of the corticospinal pathway of the first dorsal interosseous and the tibialis anterior, respectively. Our purpose was to determine from these quantitative relations which input-output parameters would be useful measures in studies dealing with motor cortical task dependence. The motor cortex was excited by focal transcranial magnetic stimuli and the evoked motor response were recorded with surface electromyographic electrodes. In some experiments the discharge probability of single motor units in response to magnetic stimuli of increasing intensity was determined from intramuscular recordings. For both muscles the form of the input-output relation was sigmoidal. The steepness of the relation increased, up to 4-7 times the value at rest, with increasing tonic background activity. The threshold decreased, but only slightly, with increasing tonic background activity. The minimum value of the threshold was reached at activation levels of about 10-20% of the maximum tonic effort, whereas the steepness of the relation reached its maximum at higher activation levels, typically about 30-40% of the maximum tonic effort. These observations imply that these two input-output parameters of the corticospinal pathway - one reflecting the bias level (threshold) and the other the gain (slope) - are determined by different neural mechanisms. The plateau level of the sigmoidal input-output relation was not influenced by the background activation level, except that in some subjects (4/9) it could not be reached when no background motor activity was present. This was probably due, for the most part, to limitation of the maximum stimulator output. Additionally, this finding may reflect a change in the intrinsic excitability of the motor cortex in going from rest to activity, or that convergent inputs from different descending and afferent systems are required for maximal activation of motoneuron pools. Thus, the threshold, steepness and plateau level characterize the input-output parameters of the human corticospinal pathway for a given level of motor activity. In contrast to the nonlinear input-output relation of the corticospinal pathway as whole, which includes the motoneuron pool and any spinal interneuronal relays, the discharge probability of all single motor units was a linearly increasing function of the stimulus strength (r> or =0.9, P<0.01). Thus, the sigmoidal input-output relation of the corticospinal pathway, as a whole, is not due to the input-output properties of single motoneurons. The possible neural mechanisms which underlie the shape and parameters of the input-output relation as well as the methodological implications of the results are considered.

Adult↗

PubMed1997

Differential control of reciprocal inhibition during walking versus postural and voluntary motor tasks in humans.

Experiments were done to determine whether the strength of reciprocal inhibition from ankle flexors to extensors can be controlled independently of the level of ongoing motor activity in a task-dependent manner. In this paper we use the term reciprocal inhibition in the functional sense--inhibition of the antagonist(s) during activity of the agonist(s)--without reference to specific neural pathways that may be involved. The strength of reciprocal inhibition of the soleus alpha-motoneurons was determined by measuring the amplitude of the H reflex during voluntary, postural, and locomotor tasks requiring activity of the ankle flexor tibialis anterior (TA). Differences in the strength of reciprocal inhibition between tasks were determined from plots of the soleus H reflex amplitude versus the mean value of the TA electromyogram (EMG). Additionally, in tasks involving movement, the correlation between the H reflex amplitude and the joint kinematics was calculated. In most subjects (15 of 22) the soleus H reflex decreased approximately linearly with increasing tonic voluntary contractions of the TA. The H reflex also decreased approximately linearly with the TA EMG activity when subjects where asked to lean backward. There were no statistical differences between the regression lines obtained in these tasks. In some subjects (7 of 22), however, the H reflex amplitude was independent of the level of TA EMG activity, except for a sudden drop at high levels of TA activity (approximately 60-80% of maximum voluntary contraction). The type of relation between the soleus H reflex and the TA EMG activity in these tasks was not correlated with the maximum H reflex to maximum M wave (Hmax/Mmax) ratio measured during quiet standing. In marked contrast, during the swing phase of walking--over the same range of TA EMG activity as during the tonic voluntary contraction task--the H reflex was reduced to zero in most subjects (24 of 31). In seven subjects the H reflex during the swing phase was reduced to some 5% of the value during quiet standing. The same result was found when subjects were asked to produce a stepping movement with one leg (OLS) in response to an auditory "go" signal. Additionally, in the OLS task it was possible to examine the behavior of the H reflex during the reaction time and thus to evaluate the relative contribution of central commands versus movement-related afferent activity to the inhibition of the soleus H reflex. In 11 of 12 subjects the H reflex attained its minimum value before either the onset of EMG activity or movement of any of the leg joints. It is significant that the H reflex was most powerfully inhibited during the swing phase of walking and the closely related OLS task. The H reflex was also measured during isolated ankle dorsiflexion movements. The subjects were asked to track a target displayed on a computer screen with dorsiflexion movements of the ankle. The trajectory of the target was the same as that of the ankle during the swing phase of walking. The soleus H reflexes were intermediate in size between the values obtained in the tonic contraction task and the walking or OLS tasks. A negative, but weak, correlation (r2 < 0.68) between the soleus H reflex and the TA EMG was found in 3 of 10 subjects. Furthermore, there was no correlation between the H reflex amplitude and the ankle angular displacement or angular velocity. In this task, as in the OLS task, the H reflex began to decrease during the reaction time before the onset of TA EMG activity. We conclude that the strength of reciprocal inhibition of the soleus alpha-motoneuron pool can thus be controlled independently of the level of motor activity in the ankle flexors. The strength of the inhibition of the antagonist(s) depends on the task, and for each task the strength of the inhibition is not necessarily proportional to the level of motor activity in the agonist(s). (ABSTRACT TRUNCATED)

Adult↗

PubMed1995

Biomechanical analysis of simple jaw movements in Friedreich's ataxia.

The jaw movement kinematics in relation to the EMG activity of two antagonistic jaw muscles (the masseter and the digastricus pars anterior) were examined in healthy subjects and patients with Friedreich's disease. Dysarthria and ataxia are the main characteristics of this disease. Jaw movement was monitored with a magnetometer system, and bipolar surface electrodes were used to record EMG activity. Unidirectional opening, unidirectional closing and opening-closing movements of the mandible were performed in a simple reaction time situation. The data were compared with those for normal control subjects. The kinematic and electromyographic characteristics were: (a) prolonged total movement duration resulting from increased acceleration and deceleration durations; (b) decreased maximum velocity, and a secondary peak in the velocity profile; (c) tonic EMG activity in muscles supposedly at rest; (d) prolonged EMG bursts. Premotor reaction time was also increased. These characteristics are similar to those, previously described, of limb movements in subjects with cerebellar dysfunctions and suggest that the alterations of jaw movement in Friedreich's ataxia could be due to a deficit in cerebellar control.

Adult↗

PubMed1992

Electromyographic recording of the jaw reflex in Friedreich ataxia.

Jaw jerk was studied in 10 subjects with Friedreich ataxia, and 10 normal subjects for comparison. Electromyographic recording from the right masseter muscle showed a reflex response in all cases, in contrast to the absence of tendon reflexes in the four limbs for the ataxics. The mean latency of the jaw jerk was normal. These observations indicate that the jaw reflex arc is preserved, and that no damage to the trigeminal neuromuscular pathway exists for all the patients observed.

Adult↗