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Sabine Meunier

Publications and source records attributed to Sabine Meunier.

9 recordsLinked to original sources
PubMed2007

Impaired modulation of motor cortex excitability by homonymous and heteronymous muscle afferents in focal hand dystonia.

A decrease of heteronymous median nerve-evoked inhibition of corticospinal projections to forearm extensor muscles was reported in a group of 10 dystonic patients by Bertolasi and colleagues in 2003. Here we tested the excitability of corticomotoneuronal connections to both wrist extensor (ECR) and flexor (FCR) muscles after conditioning stimulation of median and also radial nerve at rest in a group of 25 patients with focal hand dystonia compared to 20 healthy subjects. We also investigated the effect of the wrist dystonic posture, either in flexion or in extension, on the afferent modulation of ECR and FCR motor evolved potentials (MEPs). The heteronymous (median-induced) but also homonymous (radial-induced) inhibitions (interstimuli intervals 13-21 ms) of ECR MEP size observed in healthy subjects were decreased in patients. In addition, homonymous (median-induced) facilitation of FCR MEP size was also decreased in patients while heteronymous inhibition (radial-induced) was not. Neither the involvement of the target muscle in the dystonic posture nor the origin of the afferent volley (from a dystonic muscle) influenced the degree of impairment of afferent modulation of the MEP. These findings support the view that a global abnormal somatosensory coupling in focal hand dystonia may contribute to an inadequate motor command to wrist muscles.

Adolescent↗
PubMed2006

Spinal use-dependent plasticity of synaptic transmission in humans after a single cycling session.

The spinal cord is able to express use-dependent plasticity, as demonstrated in spinalized cats following treadmill training. In humans, spinal use-dependent plasticity is inferred from modifications in the size of H reflex, which are often more prominent after skilled motor training. Plasticity can develop at synaptic connections between afferent fibres and/or descending tracts and motoneurones or interneurones interposed in the spinal pathways. Here we explore whether skilled training induces a change in synaptic efficacy at the synapse between Ia afferents and soleus (Sol) motoneurones. Synaptic efficacy can be modulated presynaptically through changes of the probability of transmitter release (homosynaptic depression, HD). The frequency-related depression of the Sol H reflex, thought to reflect HD, was tested at rest, before and after one single skilled (14 subjects) or non-skilled (9 subjects) cycling training session. Performance improved in both groups but to a larger extent with skilled training, while HD increased immediately after and the day following skilled training in the absence of changes with non-skilled training. These results support the view that spinal cord function is able to encode a local motor memory.

Adult↗
PubMed2006

Time-frequency analysis reveals decreased high-frequency oscillations in writer's cramp.

High-frequency oscillations (HFO) have been suggested to reflect the activity of thalamocortical and/or intracortical neurons bursting at high frequencies. These circuits seem to be involved in pathophysiological mechanisms of focal dystonia. In healthy subjects, we characterized the spectrotemporal properties of HFO patterns evoked by dominant-hand median-nerve stimulation, using magnetoencephalography coupled with time-frequency analysis. Then, we investigated HFO in patients with writer's cramp and found that HFO patterns are strongly decreased in power and disorganized in time. This supports the assumption that abnormal HFOs reflect pathophysiological mechanisms occurring in focal dystonia, possibly resulting from a dysfunction of somatosensory processing.

Adult↗
PubMed2006

Lack of inhibitory interaction between somatosensory afferent inputs and intracortical inhibitory interneurons in focal hand dystonia.

We looked for an impaired interaction in the primary motor cortex between intracortical inhibitory circuits and circuits fed by somatosensory inputs in patients with writer's cramp. Short-interval intracortical inhibition (sICI) to wrist extensor carpi radialis muscle (ECR) was conditioned by stimulation of antagonist muscle afferents and sICI to first dorsal interosseus (FDI) muscle by homotopic cutaneous afferents stimulation. sICI was assessed at rest and during a tonic contraction of the target muscle. Eighteen patients with writer's cramp (10 having a wrist dystonic posture in flexion during writing and 8 in extension) were compared to 14 control subjects. Peripheral inputs decreased sICI in control subjects. This decrease was lost in patients in both FDI and ECR, regardless of the wrist dystonic posture. By contrast, contraction-induced depression of sICI appeared dependant on the dystonic status of the muscle: depression of sICI to ECR was abolished in patients with wrist dystonic posture in flexion, but not in patients with dystonic posture in extension, sICI even giving way to motor-evoked potential facilitation. Loss of interaction between interneurons mediating sICI and peripheral inputs probably belongs to the initial abnormalities underlying dystonia. Lack of peripherally induced sICI modulation may oppose wrist and/or hand muscles synergies.

Adolescent↗
PubMed2004

Motor execution and imagination networks in post-stroke dystonia.

Reorganization of motor execution and imagination networks was studied in six patients with unilateral dystonia secondary to a subcortical stroke and compared with seven control subjects using fMRI. Patients performed imagined and real auditory-cued hand movements. Movements of the dystonic hand resulted in overactivity in bilateral motor, premotor, and prefrontal cortex, insula, precuneus, and cerebellum, in parietal areas and the striatum contralateral to the lesion. Movements of the unaffected hand resulted in overactivity in bilateral preSMA, prefrontal, and parietal areas, insula and cerebellum, the ipsilateral premotor cortex and the contralateral striatum to the lesion. Mental representation of movements with each hand resulted in overactivity in bilateral parietal, premotor and prefrontal areas. These results suggest that execution and mental representation of movement are altered in these patients.

Adult↗
PubMed2003

Changes in propriospinally mediated excitation of upper limb motoneurons in stroke patients.

It has been argued that, in humans, a part of the descending command to upper limb motoneurons is transmitted through cervical propriospinal pre-motoneurons. We explored whether excitation of these putative propriospinal neurons projecting onto extensor carpi radialis (ECR) motoneurons was modified in patients recovering from stroke. Suppression of the voluntary on-going ECR EMG activity by stimulation of cutaneous afferents in the superficial radial nerve was used to estimate the component of the descending command passing through the propriospinal relay. The degree of suppression was assessed on both sides of 30 stroke patients (divided into two groups, whether recovery of wrist extension was poor or good by the time of the investigation) and of 34 age-matched controls. Single cutaneous volleys elicited a suppression which was symmetrical and of the same degree in patients and controls. In contrast, the amount of on-going EMG suppression produced by a train, which was symmetrical in normal subjects, was asymmetrical in most stroke patients: it indeed was significantly greater on the affected side of stroke patients with poor recovery of wrist extension than (i) in their non-affected side; (ii) in controls; and (iii) in the affected side of patients with good recovery. Cutaneous suppression of the H reflex, the motor evoked potential (MEP) and the on-going EMG was compared in three patients with poor recovery by the time of the first test; there was a small suppression of the H reflex on the affected side, but the asymmetry was much less than that of the on-going EMG and the MEP. In patients explored twice during the course of recovery, the asymmetry in the suppression of the on-going EMG tended to disappear, while recovery of wrist extension improved. This suggests that, when patients have not yet recovered, a relatively greater component of the descending command is mediated through the propriospinal relay. The findings are consistent with transiently increased efficacy of descending (possibly reticulospinal) projections onto propriospinal neurons, due to hyperexcitability of these neurons or unmasking and/or reorganization of the projections to them.

Adult↗
PubMed2003

Dystonia: lessons from brain mapping.

Functional neuroimaging with positron emission tomography, single photon emission computer tomography, magnetic resonance imaging, and magnetoencephalography have provided powerful tools to elucidate anatomo-functional impairment underlying movement disorders such as dystonic movements. They have revealed that presymptomatic cerebral abnormalities may be a common feature in dystonia whatever the clinical status. Techniques using specific markers have recently focused on the type of receptors that may be dysactivated and on the kind of neurotransmitter that may be dysregulated in dystonia.

Brain↗
PubMed2002

Central nervous system lesions and segmental activity.

Study of activity in segmental pathways can help in understanding the pathophysiology of clinical disorders due to basal ganglia damage. Disynaptic Ia reciprocal inhibition (DI) acts by actively inhibiting antagonistic motoneurones and reducing the inhibition of agonist ones. During movement, activity of interneurones mediating DI is significantly modulated by descending inputs. In Parkinsonian patients, this descending modulation almost completely vanished. Lack of modulation was not dependent on L-DOPA as it occurred in treated patients and was not modified when patients were off medication. A potent heteronymous group II excitation of quadriceps MNs has been recently demonstrated in normal subjects after stimulation of the common peroneal nerve. This group II excitation was significantly enhanced in the rigid lower limb of Parkinsonian patients. We propose that enhanced group II excitation could contribute to rigidity in PD and result from a change in a tonic noradrenergic descending inhibitory control from locus coeruleus.

Efferent Pathways↗