Muriel Panouillères | University of Oxford (original) (raw)

Papers by Muriel Panouillères

The Journal of Physiology, Jun 23, 2015

Transcranial direct current stimulation (TDCS) over the primary motor cortex (M1) or the lateral ... more Transcranial direct current stimulation (TDCS) over the primary motor cortex (M1) or the lateral cerebellum can improve motor adaptation in young and older adults, but as yet no direct comparisons of TDCS effects exist between the two age groups and the two stimulation sites. r TDCS over M1 enhanced the motor adaptation in both age groups by ß30% relative to their respective non-stimulated groups and improved the performance of older adults to the extent that it compared with that of young adults without stimulation. r The study suggests that the plastic mechanisms activated by TDCS that underpin improvements in motor behaviour in young adults remain available in older adults. r The results indicate that TDCS may be a useful tool to help combat the normal decline in motor performance seen in normal healthy ageing.

The Journal of Neuroscience, Apr 8, 2015

The posterior vermis of the cerebellum is considered to be critically involved in saccadic adapta... more The posterior vermis of the cerebellum is considered to be critically involved in saccadic adaptation. However, recent evidence suggests that the adaptive decrease (backward adaptation) and the adaptive increase (forward adaptation) of saccade amplitude rely on partially separate neural substrates. We investigated whether the posterior cerebellum could be differentially involved in backward and forward adaptation by using transcranial direct current stimulation (TDCS). To do so, participants' saccades were adapted backward or forward while they received anodal, cathodal, or sham TDCS. In two extra groups, subjects underwent a nonadaptation session while receiving anodal or cathodal TDCS to control for the direct effects of TDCS on saccadic execution. Surprisingly, cathodal stimulation tended to increase the extent of both forward and backward adaptations, while anodal TDCS strongly impaired forward adaptation and, to a smaller extent, backward adaptation. Forward adaptation was accompanied by a greater increase in velocity with cathodal stimulation, and reduced duration of change for anodal stimulation. In contrast, the expected velocity decrease in backward adaptation was noticeably weaker with anodal stimulation. Stimulation applied during nonadaptation sessions did not affect saccadic gain, velocity, or duration, demonstrating that the reported effects are not due to direct effects of the stimulation on the generation of eye movements. Our results demonstrate that cerebellar excitability is critical for saccadic adaptation. Based on our results and the growing evidence from studies of vestibulo-ocular reflex and saccadic adaptation, we conclude that the plasticity at the level of the oculomotor vermis is more fundamentally important for forward adaptation than for backward adaptation.

Revue Neurologique, Apr 1, 2021

Introduction Si la maladie de Parkinson idiopathique (MPI) est le syndrome parkinsonien (SP) dege... more Introduction Si la maladie de Parkinson idiopathique (MPI) est le syndrome parkinsonien (SP) degeneratif le plus frequent, le diagnostic differentiel avec les autres SP peut etre difficile, retardant une prise en charge adaptee. Objectifs L’objectif de cette etude etait d’identifier les neuromarqueurs oculomoteurs sensibles pour le diagnostic differentiel des SP grâce a l’oculometrie couplee a une approche de machine learning. Patients et methodes L’etude a inclus 43 patients avec MPI (n = 10), atrophie multisystematisee (AMS) (n = 5) ou paralysie supranucleaire progressive (PSP) (n = 28) a un stade non avance de la maladie. L’examen oculomoteur consistait en des tâches de pro-saccades et d’anti-saccades. Les parametres saccadiques spatio-temporels ont ete extraits, ainsi que les taux d’erreurs et de correction aux anti-saccades. Les analyses ont ete realisees en deux etapes : tests non-parametriques puis approche de machine learning (analyse discriminante lineaire [ADL]). Resultats Des differences significatives entre les patients PSP et non-PSP ont ete observees sur plusieurs parametres (vitesse des pro-saccades, ondes-carrees, erreurs aux anti-saccades et leur taux de corrections). Les combinaisons de ces parametres obtenues par l’ADL expliquent 85 % de la variance entre les 3 groupes de patients. Discussion Les resultats observes corroborent ceux de la litterature tout en affinant la selection des parametres specifiques pour le diagnostic differentiel des SP. L’ADL offre un premier algorithme de classification des patients, dont la valeur predictive pourra etre precisee par l’apport de futures donnees. Conclusion Cette etude ouvre la voie a un test standardise oculometrique rapide, robuste et fiable pour le diagnostic differentiel de patients atteints de SP, completant ainsi les donnees cliniques.

PLOS ONE, Feb 23, 2016

Procedural learning is a form of memory where people implicitly acquire a skill through repeated ... more Procedural learning is a form of memory where people implicitly acquire a skill through repeated practice. People with Parkinson's disease (PD) have been found to acquire motor adaptation, a form of motor procedural learning, similarly to healthy older adults but they have deficits in long-term retention. A similar pattern of normal learning on initial exposure with a deficit in retention seen on subsequent days has also been seen in mirror-reading, a form of non-motor procedural learning. It is a well-studied fact that disrupting sleep will impair the consolidation of procedural memories. Given the prevalence of sleep disturbances in PD, the lack of retention on following days seen in these studies could simply be a side effect of this well-known symptom of PD. Because of this, we wondered whether people with PD would present with deficits in the short-term retention of a non-motor procedural learning task, when the test of retention was done the same day as the initial exposure. The aim of the present study was then to investigate acquisition and retention in the immediate short term of cognitive procedural learning using the mirror-reading task in people with PD. This task involved two conditions: one where triads of mirror-inverted words were always new that allowed assessing the learning of mirror-reading skill and another one where some of the triads were presented repeatedly during the experiment that allowed assessing the word-specific learning. People with PD both ON and OFF their normal medication were compared to healthy older adults and young adults. Participants were re-tested 50 minutes break after initial exposure to probe for short-term retention. The results of this study show that all groups of participants acquired and retained the two skills (mirror-reading and wordspecific) similarly. These results suggest that neither healthy ageing nor the degeneration within the basal ganglia that occurs in PD does affect the mechanisms that underpin the acquisition of these new non-motor procedural learning skills and their short-term memories.

Frontiers in Human Neuroscience, Mar 9, 2016

Journal of Neurophysiology, Mar 1, 2009

The accuracy of saccadic eye movements is maintained over the long term by adaptation mechanisms ... more The accuracy of saccadic eye movements is maintained over the long term by adaptation mechanisms which decrease or increase saccade amplitude. It is still unknown whether these opposite adaptive changes rely on common mechanisms. Here, a double-step target paradigm was used to adaptively decrease (backward second target step) or increase (forward step) the amplitude of reactive saccades in one direction only. To test which sensory-motor transformation stages are subjected to these adaptive changes, we measured their transfer to anti-saccades in which sensory and motor vectors are spatially dissociated. In the backward adaptation condition, all subjects showed a significant amplitude decrease for adapted pro-saccades and a significant transfer of adaptation to anti-saccades performed in the adapted direction but not to oppositely-directed anti-saccades elicited by a target jump in the adapted direction. In the forward adaptation condition, only 14 out of 19 subjects showed a significant amplitude increase for pro-saccades, and no significant adaptation transfer to anti-saccades was detected in either the adapted or non-adapted direction. These findings suggest that, whereas the level(s) of forward adaptation cannot be resolved, the mechanisms involved in backward adaptation of reactive saccades take place at a sensory-motor level downstream from the vector inversion process of anti-saccades and differ markedly from those involved in forward adaptation.

bioRxiv (Cold Spring Harbor Laboratory), Jul 26, 2017

Comprehending speech can be particularly challenging in a noisy environment and in the absence of... more Comprehending speech can be particularly challenging in a noisy environment and in the absence of semantic context. It has been proposed that the articulatory motor system would be recruited especially in difficult listening conditions. However, it remains unknown how signal-to-noise ratio (SNR) and semantic context affect the recruitment of the articulatory motor system when listening to continuous speech. The aim of the present study was to address the hypothesis that involvement of the articulatory motor cortex increases when the intelligibility and clarity of the spoken sentences decreases, because of noise and the lack of semantic context. We applied Transcranial Magnetic Stimulation (TMS) to the lip and hand representations in the primary motor cortex and measured motor evoked potentials from the lip and hand muscles, respectively, to evaluate motor excitability when young adults listened to sentences. In Experiment 1, we found that the excitability of the lip motor cortex was facilitated during listening to both semantically anomalous and coherent sentences in noise, but neither SNR nor semantic context modulated the facilitation. In Experiment 2, we replicated these findings and found no difference in the excitability of the lip motor cortex between sentences in noise and clear sentences without noise. Thus, our results show that the articulatory motor cortex is involved in speech processing even in optimal and ecologically valid listening conditions and that its involvement is not modulated by the intelligibility and clarity of speech.

Journal of Eye Movement Research, Feb 24, 2012

Journal of Vision, Apr 8, 2010

... task-specificity bases are still poorly understood. We addressed these issues here by studyin... more ... task-specificity bases are still poorly understood. We addressed these issues here by studying adaptation of saccadic eye movements, a well-established model of sensorimotor plasticity. The cerebellum plays a major role in ...

Journal of Vision, Jul 25, 2013

Journal of Neurophysiology, Jun 15, 2014

Plastic changes of saccades (i.e., following saccadic adaptation) do not transfer between opposit... more Plastic changes of saccades (i.e., following saccadic adaptation) do not transfer between oppositely directed saccades, except when multiple directions are trained simultaneously, suggesting a saccadic planning in retinotopic coordinates. Interestingly, a recent study in human healthy subjects revealed that after an adaptive increase of rightwardscanning saccades, both leftward and rightward double-step, memoryguided saccades, triggered toward the adapted endpoint, were modified, revealing that target location was coded in spatial coordinates (Zimmermann et al. 2011). However, as the computer screen provided a visual frame, one alternative hypothesis could be a coding in allocentric coordinates. Here, we questioned whether adaptive modifications of saccadic planning occur in multiple coordinate systems. We reproduced the paradigm of Zimmermann et al. (2011) using target light-emitting diodes in the dark, with and without a visual frame, and tested different saccades before and after adaptation. With double-step, memory-guided saccades, we reproduced the transfer of adaptation to leftward saccades with the visual frame but not without, suggesting that the coordinate system used for saccade planning, when the frame is visible, is allocentric rather than spatiotopic. With single-step, memory-guided saccades, adaptation transferred to leftward saccades, both with and without the visual frame, revealing a target localization in a coordinate system that is neither retinotopic nor allocentric. Finally, with single-step, visually guided saccades, the classical, unidirectional pattern of amplitude change was reproduced, revealing retinotopic coordinate coding. These experiments indicate that the same procedure of adaptation modifies saccadic planning in multiple coordinate systems in parallel-each of them revealed by the use of different saccade tasks in postadaptation.

Scientific Reports, May 24, 2017

Early detection of the behavioural deficits of neurodegenerative diseases may help to describe th... more Early detection of the behavioural deficits of neurodegenerative diseases may help to describe the pathogenesis of such diseases and establish important biomarkers of disease progression. The aim of this study was to identify how sensorimotor adaptation of the upper limb, a cerebellar-dependent process restoring movement accuracy after introduction of a perturbation, is affected at the preclinical and clinical stages of spinocerebellar ataxia type 6 (SCA6), an inherited neurodegenerative disease. We demonstrate that initial adaptation to the perturbation was significantly impaired in the eighteen individuals with clinical motor symptoms but mostly preserved in the five pre-clinical individuals. Moreover, the amount of error reduction correlated with the clinical symptoms, with the most symptomatic patients adapting the least. Finally both pre-clinical and clinical individuals showed significantly reduced de-adaptation performance after the perturbation was removed in comparison to the control participants. Thus, in this large study of motor features in SCA6, we provide novel evidence for the existence of subclinical motor dysfunction at a pre-clinical stage of SCA6. Our findings show that testing sensorimotor de-adaptation could provide a potential predictor of future motor deficits in SCA6. Spinocerebellar ataxia type 6 (SCA6) is a common form of autosomal dominant cerebellar ataxia presenting in adults 1 , corresponding to up to 31% of autosomal dominant ataxias in some countries 2. It is caused by a pathological expansion of the polyglutamine-encoding CAG repeat in the CACNA1A gene on chromosome 19 3 and it is 100% penetrant. The mutation primarily leads to the degeneration of Purkinje cells in the cerebellar cortex 4,5 , affecting first midline structures such as the vermis 6. SCA6 is characterized by a late age of onset and a slow progression of symptoms including limb and gait ataxia, dysarthria and nystagmus 4. In a recent review 7 , it was suggested that a certain threshold of degeneration is required before patients with spinocerebellar ataxias begin to experience symptoms. This view has been strengthened in a mouse-model study of SCA6, in which Purkinje cells loss occurs at 4 months without motor symptoms. In this model, motor dysfunctions only become apparent when the mice reach the age of 8 months 8. The time lag between neuronal degeneration and symptom onset suggests that the initial cerebellar dysfunction is either functionally irrelevant or compensated for. An important alternative, however, is that functional motor changes on a subclinical level precede the onset of overt clinical motor manifestations. The cerebellum is a key structure in sensorimotor adaptation, a critical process which progressively restores optimal motor performance when consistent errors are repeatedly encountered 9. Indeed, brain imaging has shown the involvement of the cerebellum in various sensorimotor adaptation conditions 10-13. Moreover, transiently modifying cerebellar function using non-invasive brain stimulation also affects sensorimotor adaptation 14-21. Finally, numerous studies have demonstrated that individuals with cerebellar damage (lesion or degeneration) show impaired adaptation of limb and saccadic eye movements 22-36. Given the key role of the cerebellum in sensorimotor adaptation, this process is an excellent candidate both to screen for pre-clinical deficits in SCA6 and to track disease progression in the clinical patients. The present study has two aims: (1) to establish

Cerebral Cortex, Oct 5, 2012

Sensorimotor adaptation ensures movement accuracy despite continuously changing environment and b... more Sensorimotor adaptation ensures movement accuracy despite continuously changing environment and body. Adaptation of saccadic eye movements is a classical model of sensorimotor adaptation. Beside the well-established role of the brainstem-cerebellum in the adaptation of reactive saccades (RSs), the cerebral cortex has been suggested to be involved in the adaptation of voluntary saccades (VSs). Here, we provide direct evidence for a causal involvement of the parietal cortex in saccadic adaptation. First, the posterior intraparietal sulcus (pIPS) was identified in each subject using functional magnetic resonance imaging (fMRI). Then, a saccadic adaptation paradigm was used to progressively reduce the amplitude of RSs and VSs, while single-pulse transcranial magnetic stimulation (spTMS) was applied over the right pIPS. The perturbations of pIPS resulted in impairment for the adaptation of VSs, selectively when spTMS was applied 60 ms after saccade onset. In contrast, the adaptation of RSs was facilitated by spTMS applied 90 ms after saccade initiation. The differential effect of spTMS relative to saccade types suggests a direct interference with pIPS activity for the VS adaptation and a remote interference with brainstem-cerebellum activity for the RS adaptation. These results support the hypothesis that the adaptation of VSs and RSs involves different neuronal substrates.

Scientific Reports, Apr 30, 2018

The original version of this Article contained a typographical error in the spelling of the autho... more The original version of this Article contained a typographical error in the spelling of the author Sonia Benitez-Rivero, which was incorrectly given as Sonia Benitez-Riveiro. In addition, an incorrect version of the drawing of the joystick in Figure 1 was inadvertently used.

bioRxiv (Cold Spring Harbor Laboratory), Jul 28, 2017

Older adults often experience difficulties in understanding speech, partly because of age-related... more Older adults often experience difficulties in understanding speech, partly because of age-related hearing loss. In young adults, activity of the left articulatory motor cortex is enhanced and it interacts with the auditory cortex via the left-hemispheric dorsal stream during speech processing. Little is known about the effect of ageing and age-related hearing loss on this auditory-motor interaction and speech processing in the articulatory motor cortex. It has been proposed that upregulation of the motor system during speech processing could compensate for hearing loss and auditory processing deficits in older adults. Alternatively, age-related auditory deficits could reduce and distort the input from the auditory cortex to the articulatory motor cortex, suppressing recruitment of the motor system during listening to speech. The aim of the present study was to investigate the effects of ageing and age-related hearing loss on the excitability of the tongue motor cortex during listening to spoken sentences using transcranial magnetic stimulation and electromyography. Our results show that the excitability of the tongue motor cortex was facilitated during listening to speech in young and older adults with normal hearing. This facilitation was significantly reduced in older adults with hearing loss. These findings suggest a decline of auditorymotor processing of speech in adults with age-related hearing loss.

Cerebellum & ataxias, Jan 4, 2021

Background: Transcranial Direct Current Stimulation (tDCS) over the prefrontal cortex has been sh... more Background: Transcranial Direct Current Stimulation (tDCS) over the prefrontal cortex has been shown to modulate subjective, neuronal and neuroendocrine responses, particularly in the context of stress processing. However, it is currently unknown whether tDCS stimulation over other brain regions, such as the cerebellum, can similarly affect the stress response. Despite increasing evidence linking the cerebellum to stress-related processing, no studies have investigated the hormonal and behavioural effects of cerebellar tDCS. Methods: This study tested the hypothesis of a cerebellar tDCS effect on mood, behaviour and cortisol. To do this we employed a single-blind, sham-controlled design to measure performance on a cerebellar-dependent saccadic adaptation task, together with changes in cortisol output and mood, during online anodal and cathodal stimulation. Forty-five participants were included in the analysis. Stimulation groups were matched on demographic variables, potential confounding factors known to affect cortisol levels, mood and a number of personality characteristics. Results: Results showed that tDCS polarity did not affect cortisol levels or subjective mood, but did affect behaviour. Participants receiving anodal stimulation showed an 8.4% increase in saccadic adaptation, which was significantly larger compared to the cathodal group (1.6%). Conclusion: The stimulation effect on saccadic adaptation contributes to the current body of literature examining the mechanisms of cerebellar stimulation on associated function. We conclude that further studies are needed to understand whether and how cerebellar tDCS may module stress reactivity under challenge conditions.