Movement DisordersVolume 33, Issue 10 p. 1664-1665 Letters: New Observations Visual cueing using laser shoes reduces freezing of gait in Parkinson's patients at home Claudia Barthel MSc, Claudia Barthel MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorMilou van Helvert MSc, Milou van Helvert MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorRenée Haan MSc, Renée Haan MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorArno M. Janssen PhD, Arno M. Janssen PhD Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorArnaud Delval MD, PhD, Arnaud Delval MD, PhD Lille university medical center, Department of clinical neurophysiology, Lille, FranceSearch for more papers by this authorNienke M. de Vries PhD, Nienke M. de Vries PhD Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorVivian Weerdesteyn PhD, Vivian Weerdesteyn PhD Department of Rehabilitation, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands Sint Maartenskliniek Research, Development & Education, Nijmegen, The NetherlandsSearch for more papers by this authorBettina Debû PhD, Bettina Debû PhD Grenoble Alpes University, Grenoble, France Grenoble Institute of Neurosciences, Institut National de la Santé et de la Recherche Médicale, U1216 Grenoble, FranceSearch for more papers by this authorRichard van Wezel PhD, Richard van Wezel PhD Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, The NetherlandsSearch for more papers by this authorBastiaan R. Bloem MD, PhD, Bastiaan R. Bloem MD, PhD Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorMurielle U. Ferraye PhD, Corresponding Author Murielle U. Ferraye PhD m.u.ferraye@utwente.nl Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The NetherlandsCorresponding author: Dr. Murielle Ferraye, Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands; m.u.ferraye@utwente.nlSearch for more papers by this author Claudia Barthel MSc, Claudia Barthel MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorMilou van Helvert MSc, Milou van Helvert MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorRenée Haan MSc, Renée Haan MSc Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorArno M. Janssen PhD, Arno M. Janssen PhD Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorArnaud Delval MD, PhD, Arnaud Delval MD, PhD Lille university medical center, Department of clinical neurophysiology, Lille, FranceSearch for more papers by this authorNienke M. de Vries PhD, Nienke M. de Vries PhD Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorVivian Weerdesteyn PhD, Vivian Weerdesteyn PhD Department of Rehabilitation, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands Sint Maartenskliniek Research, Development & Education, Nijmegen, The NetherlandsSearch for more papers by this authorBettina Debû PhD, Bettina Debû PhD Grenoble Alpes University, Grenoble, France Grenoble Institute of Neurosciences, Institut National de la Santé et de la Recherche Médicale, U1216 Grenoble, FranceSearch for more papers by this authorRichard van Wezel PhD, Richard van Wezel PhD Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, The NetherlandsSearch for more papers by this authorBastiaan R. Bloem MD, PhD, Bastiaan R. Bloem MD, PhD Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The NetherlandsSearch for more papers by this authorMurielle U. Ferraye PhD, Corresponding Author Murielle U. Ferraye PhD m.u.ferraye@utwente.nl Department of Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The NetherlandsCorresponding author: Dr. Murielle Ferraye, Biomedical Signal and Systems Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands; m.u.ferraye@utwente.nlSearch for more papers by this author First published: 29 September 2018 https://doi.org/10.1002/mds.27455Citations: 4 Funding agencies: This research was funded by the Hersenstichting for Murielle U. Ferraye (project F2015(1)-21) and by a European Community's Seventh Framework Programme FP7/2012 under Grant 316639 to Claudia Barthel. The institution Radboud University Medical Center (Radboudumc) does not have any conflict of interest related to the self-developed laser shoes as they appear in the present article. A London-based company developed a more customer-friendly version of the laser shoes, and Radboudumc is currently discussing the possibility of receiving a financial interest in this commercial version of the laser shoes, where part of the interests will be redistributed to M.U. Ferraye. Relevant conflicts of interests/financial disclosures: : Nothing to report. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume33, Issue10October 2018Pages 1664-1665 RelatedInformation

To assess, in a cross-sectional study, the feasibility and immediate efficacy of laser shoes, a new ambulatory visual cueing device with practical applicability for use in daily life, on freezing of gait (FOG) and gait measures in Parkinson disease (PD).We tested 21 patients with PD and FOG, both "off" and "on" medication. In a controlled gait laboratory, we measured the number of FOG episodes and the percent time frozen occurring during a standardized walking protocol that included FOG provoking circumstances. Participants performed 10 trials with and 10 trials without cueing. FOG was assessed using offline video analysis by an independent rater. Gait measures were recorded in between FOG episodes with the use of accelerometry.Cueing using laser shoes was associated with a significant reduction in the number of FOG episodes, both "off" (45.9%) and "on" (37.7%) medication. Moreover, laser shoes significantly reduced the percent time frozen by 56.5% (95% confidence interval [CI] 32.5-85.8; p = 0.004) when "off" medication. The reduction while "on" medication was slightly smaller (51.4%, 95% CI -41.8 to 91.5; p = 0.075). These effects were paralleled by patients' positive subjective experience on laser shoes' efficacy. There were no clinically meaningful changes in the gait measures.These findings demonstrate the immediate efficacy of laser shoes in a controlled gait laboratory, and offer a promising intervention with potential to deliver in-home cueing for patients with FOG.This study provides Class III evidence that for patients with PD, laser shoes significantly reduce FOG severity (both number and duration of FOG episodes).

I thank van Gerpen et al. for their comment on our laser shoes article,1 and for sharing the lasting cueing experience of their patient using laser light on a rolling walker.2 In the accompanying article in Neurology Today , Prof. Horak raised doubts with respect to the lasting effects of cueing in general, and of laser shoes in particular.3 Habituation remains a recurring concern when it comes to continuous cueing.4 This is why observations—like this—are most welcome, especially because on-demand cueing remains challenging, and true clinical utility depends on further development of automated methods able to detect freezing prior to its occurrence or within short enough latencies to allow the patients to react in time to prevent freezing.5 Both freezing and falls are, indeed, very sudden and unpredictable events. This is why it is of extreme importance that external cueing devices not only help the patients overcome freezing but also prevent its occurrence. Our study capitalized on the laser shoes' unique way of alternately delivering cueing to each foot at a crucial moment of the gait cycle,1 to enhance cue saliency and further reduce possible habituation effects, although this remains to be tested.

Background: Freezing of gait (FOG) is a mysterious, complex and debilitating phenomenon in Parkinson’s disease. Adequate assessment is a pre-requisite for managing FOG, as well as for assigning participants in FOG research. The episodic nature of FOG, as well as its multiple clinical expressions make its assessment challenging. Objective: To highlight the available assessment tools and to provide practical, experience-based recommendations for reliable assessment of FOG. Methods: We reviewed FOG assessment from history taking, questionnaires, lab and home-based measurements and examined how these methods account for presence and severity of FOG, their limits and advantages. The practicalities for their use in clinical and research practice are highlighted. Results: According to the available assessment tools severity of FOG is marked by one or a combination of multiple clinical expressions including frequency, duration, triggering circumstances, response to levodopa, association with falls and fear of falling, or need for assistance to avoid falls. Conclusions: To date, a unique methodological tool that encompasses the entire complexity of FOG is lacking. Combining methods should give a better picture of FOG severity, in accordance with the precise clinical or research context. Further development of any future assessment tool requires understanding and thorough analysis of the specific clinical expressions of FOG.

We present a 79-year-old man with a 12-year history of Parkinson's disease. Severe freezing of gait and falls largely dominated the clinical presentation. Even high doses of levodopa medication alleviated his condition only partially. External cueing, for example in the form of serial, spatially separated stripes on the floor (visual cues) or rhythmic beeps (auditory cues), has been advocated as a "powerful" treatment tool and the possible "clue" to the management of freezing of gait [ [1] Nieuwboer A. Feys P. de Weerdt W. Dom R. Is using a clue the clue to the treatment of freezing in Parkinson's disease?. Physiother. Res. Int. 1997; 2: 125-132 Crossref PubMed Scopus (37) Google Scholar ]. Cueing has been recommended as effective intervention for both mild and troublesome cases of freezing [ [2] Nonnekes J. Snijders A.H. Nutt J.G. Deuschl G. Giladi N. Bloem B.R. Freezing of gait: a practical approach to management. Lancet Neurol. 2015; 14: 768-778 Abstract Full Text Full Text PDF PubMed Scopus (224) Google Scholar ]. Positive effects of cueing have mainly been demonstrated under carefully controlled experimental conditions in the laboratory setting, and visual cueing appears to be the preferred cueing mode for freezing [ [3] Lee S.J. Yoo J.Y. Ryu J.S. Park H.K. Chung S.J. The effects of visual and auditory cues on freezing of gait in patients with Parkinson disease. Am. J. Phys. Med. Rehabil. 2012; 91: 2-11 Crossref PubMed Scopus (74) Google Scholar ]. Thus far, it has proved difficult to translate these laboratory observations on cueing into the patients' own real-life environment, and in particular to deliver cueing continuously as an ambulatory intervention that can assist patients, regardless of where they are. To achieve this, it would be ideal to have a mobile cueing device with practical applicability for use in daily life. Here, we introduce the self-developed laser-shoe, a new laser-based cueing device for freezing of gait. The projection of a laser beam onto the floor from a stick or a rolling walker yielded contradictory results before [ 4 Bunting-Perry L. Spindler M. Robinson K.M. Noorigian J. Cianci H.J. Duda J.E. Laser light visual cueing for freezing of gait in Parkinson disease: a pilot study with male participants. J. Rehabil. Res. Dev. 2013; 50: 223-230 Crossref PubMed Scopus (25) Google Scholar , 5 Buated W. Sriyudthsak M. Sribunruangrit N. Bhidayasiri R. A low-cost intervention for improving gait in Parknson's disease patients: a cane providing visual cues. Eur. Geriatr. Med. 2012; 3: 126-130 Abstract Full Text Full Text PDF Scopus (10) Google Scholar ]. This is perhaps not surprising because stationary lines on the floor were only effective when placed regularly at a distance from the foot. This crucial requirement can hardly be achieved by manually-controlled devices, placing additional demands upon the patients' already diminished attentional resources. These considerations motivated us to develop the "laser-shoe". Specifically, this laser-shoe consists of a normal shoe equipped with a transverse line-generating laser mounted on the nose of the shoe (Fig. 1). Its originality comes from the strategic location of a switch -under the sole of the contralateral shoe-that controls the laser. The loading of the body weight onto the switch upon heel contact during the gait cycle turns on the laser. The laser line now appears orthogonally in front of the patient's contralateral foot that is about to enter the swing phase, and thus acts as the visual cue. This cycle repeats itself when the other heel strike (of the opposite foot) occurs. As such, the visual cues are being delivered intermittently and, importantly, are tuned exactly to the step frequency of the patient. Moreover, unlike the traditional stationary visual cues (e.g. stripes pasted into the floor), the visual laser cues are always present, wherever the patient is walking. The laser-shoe is designed specifically to respect a critical feature for cueing efficiency: reducing the attentional demands of gait and facilitating attentional allocation for gait by reducing the need to internally plan and update the scaling and timing of the stepping movements [ [6] Rochester L. Nieuwboer A. Baker K. Hetherington V. Willems A- M. Chavret F. et al. The attentional cost of external rhythmical cues and their impact on gait in Parkinson's disease: effect of cue modality and task complexity. J. Neural Transm. 2007; 114: 1243-1248 Crossref PubMed Scopus (113) Google Scholar ]. Alternatively, visual cueing could compensate for a sensory-perceptual deficit in relation to faulty proprioceptive feedback, providing visual verification of proper stepping and enhanced optic flow. In this view, visual cueing efficiency would pertain to sensory-perceptual rather than cognitive mechanisms. A recent paper attempted to disentangle the two alternatives [ [7] Beck E.N. Ehgoetz Martens K.A. Almeida Q.J. Freezing of gait in Parkinson's disease: an overload problem?. PLoS One. 2015; 10: e0144986 Crossref Scopus (43) Google Scholar ]. Whatever the mechanism at play, our patient was greatly helped by the laser-shoes while under chronic dopaminergic medication, as illustrated in the accompanying videos. While wearing the laser-shoes (but with the laser beam switched off), the patient's gait was interrupted by multiple freezing episodes and instability requiring physical assistance, especially when negotiating obstacles (Video 1, Video still A). The visual cues provided by the laser lines remarkably normalized his gait pattern, strongly reducing his freezing (Video 2, Video still B). Improvement extended to his home situation where he was given the possibility to experience the laser-shoes for a week. These videos show a striking effect of the laser-shoes and underscore how, when successfully using a cueing strategy, a single step can separate freezing from freedom. We propose the laser-shoes as an elegant and user-friendly form of visual cueing. Further clinical studies in larger numbers of patients must now study whether this promising new approach has potential to effectively reduce freezing when used as an ambulatory cueing device in daily life settings.

Background: Freezing of gait (FOG) is a common and debilitating phenomenon in Parkinson's disease (PD). Wearable accelerometers might help to assess FOG in the research setting. Here, we evaluate whether accelerometry can detect FOG while executing rapid full turns and while walking with rapid short steps (the two most common provoking circumstances for FOG).Methods: We included 23 PD patients, who all had objective FOG. Participants performed several walking tasks, including walking rapidly with short steps and rapid full turns in both directions with a triaxial linear waist-mounted accelerometer. Two independent experts identified FOG episodes using offline video-analysis (gold standard). A validated algorithm [ratio between pathological freezing (3-8 Hz)- and normal locomotor frequencies (0.5-3 Hz)] was applied on the accelerometer data to detect FOG episodes.Results: Clinically, FOG was most often observed during full rapid turns (81% of all episodes), followed by walking with short rapid steps (12% of all episodes). During full rapid turns, accelerometry yielded a sensitivity of 78% and specificity of 59%. A sensitivity of 64% and specificity of 69% was observed during walking rapidly with small steps. Combining all tasks rendered a sensitivity of 75% and specificity of 76%.Conclusion: Our results suggest that FOG can be detected from a single lumbar accelerometer during several walking tasks, including full rapid turns and walking with short steps rapidly, with reasonable sensitivity and specificity. This approach holds promise for possible implementation as complementary objective outcome in a research setting, but more work remains needed to improve the sensitivity and specificity. (C) 2015 Elsevier Ltd. All rights reserved.

Le freezing est un symptôme handicapant de la maladie de Parkinson. L’amélioration initiale procurée par le traitement dopaminergique faiblit aux stades plus avancés et d’autres stratégies doivent être développées pour améliorer la marche. L’utilisation d’indices extérieurs est efficace chez certains patients, mais aucun dispositif d’indiçage utilisable à domicile n’a réussi à reproduire à long terme les observations souvent spectaculaires faites en laboratoire. Nous avons développé « Cue-shoe », une chaussure disposant d’un module laser sur l’avant-pied contrôlé par un interrupteur situé sous la semelle. Lors du contact du pied au sol, le poids du corps sur l’interrupteur active le laser. Une ligne lumineuse orthogonale au pied controlatéral entrant en phase d’oscillation apparaît alors au sol. Cinq patients équipés d’accéléromètres triaxiaux ont été évalués au laboratoire en conditions de marche normale et de manœuvres visant à déclencher du freezing, avec et sans indices. L’analyse des données d’accélérométrie a permis de mesurer le pourcentage de freezing. Les paramètres de marche, le score au nouveau questionnaire de freezing (NFOGQ) et un score frontal ont également été mesurés. Sous traitement médicamenteux, on observe une amélioration significative de la cadence en présence d’indices (114,0 pas/min avec indices ; 120,2 pas/min sans). Chez trois des cinq patients, les plus sévères mais dont le fonctionnement exécutif était préservé, le freezing a été amélioré de 21,7 à 55,2 % en présence de l’indice. Ces résultats préliminaires sont prometteurs et suggèrent que ce nouveau dispositif d’indiçage visuel pourrait améliorer considérablement le freezing chez certains patients.

1 Aix-Marseille Université/CNRS, Laboratoire Parole et Langage (LPL), UMR 7309, 13100, Aix-en-Provence, France 2 Université Grenoble-Alpes, 38000, Grenoble, France 3 INSERM U836 – Grenoble Institut des Neurosciences, 38000, Grenoble, France 4 Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands 5 Centre Hospitalier Universitaire de Grenoble, 38000, Grenoble, France 6 Université Lyon I/CNRS, Centre de Neurosciences Cognitives, UMR 5229, Lyon, France 7 Hôpitaux Universitaires, Genève, Switzerland

OBJECTIVE:To compare the influence of low-frequency (10-25 Hz) versus higher (60-80 Hz) frequency stimulation of the pedunculopontine nucleus area (PPNa) on akinaesia, freezing of gait and daytime sleepiness.METHOD:We included nine patients with Parkinson's disease (PD) and severe gait disorders. In this double-blind randomised cross-over study, patients were assessed after 24 h of PPNa stimulation. Assessments included the motor part of the Unified Parkinson's Disease Rating Scale, the Epworth Sleepiness Scale and a behavioural gait assessment.RESULTS:Compared with 60-80 Hz, 10-25 Hz PPNa stimulation led to decreased akinaesia, gait difficulties and daytime sleepiness in 7/9 patients. In one patient, these symptoms were aggravated under 10-25 Hz stimulation compared with 60-80 Hz.CONCLUSION:These results are in keeping with the benefits of chronic PPNa stimulation for gait and postural difficulties in patients with PD, and with regard to the influence of patients' clinical characteristics, differential neuronal loss in the PPNa and electrode location. We conclude that in patients with PPNa stimulation, low frequency provides a better outcome than high-frequency stimulation.

Improvement of gait disorders following pedunculopontine nucleus area stimulation in patients with Parkinson's disease has previously been reported and led us to propose this surgical treatment to patients who progressively developed severe gait disorders and freezing despite optimal dopaminergic drug treatment and subthalamic nucleus stimulation. The outcome of our prospective study on the first six patients was somewhat mitigated, as freezing of gait and falls related to freezing were improved by low frequency electrical stimulation of the pedunculopontine nucleus area in some, but not all, patients. Here, we report the speech data prospectively collected in these patients with Parkinson's disease. Indeed, because subthalamic nucleus surgery may lead to speech impairment and a worsening of dysarthria in some patients with Parkinson's disease, we felt it was important to precisely examine any possible modulations of speech for a novel target for deep brain stimulation. Our results suggested a trend towards speech degradation related to the pedunculopontine nucleus area surgery (off stimulation) for aero-phonatory control (maximum phonation time), phono-articulatory coordination (oral diadochokinesis) and speech intelligibility. Possibly, the observed speech degradation may also be linked to the clinical characteristics of the group of patients. The influence of pedunculopontine nucleus area stimulation per se was more complex, depending on the nature of the task: it had a deleterious effect on maximum phonation time and oral diadochokinesis, and mixed effects on speech intelligibility. Whereas levodopa intake and subthalamic nucleus stimulation alone had no and positive effects on speech dimensions, respectively, a negative interaction between the two treatments was observed both before and after pedunculopontine nucleus area surgery. This combination effect did not seem to be modulated by pedunculopontine nucleus area stimulation. Although limited in our group of patients, speech impairment following pedunculopontine nucleus area stimulation is a possible outcome that should be considered before undertaking such surgery. Deleterious effects could be dependent on electrode insertion in this brainstem structure, more than on current spread to nearby structures involved in speech control. The effect of deep brain stimulation on speech in patients with Parkinson's disease remains a challenging and exploratory research area.

On considère généralement que les troubles de la marche et de l’équilibre de la maladie de Parkinson dépendent du même processus physiopathologique, à savoir l’extension du processus pathologique à des structures mésencéphaliques et du tronc cérébral non dopaminergiques. Néanmoins, les substrats spécifiques de ces deux symptômes restent relativement mystérieux. Cette étude en imagerie cérébrale se propose de les comparer. Neuf patients parkinsoniens présentant un freezing et/ou des troubles de l’équilibre, et dix-sept sujets sains contrôles ont effectué une tâche d’équilibre dynamique et une tâche de marche, ainsi que deux tâches d’imagerie, motrice (IM) et visuelle (IV). Le protocole manipulait la difficulté de la tâche motrice (et non visuelle), permettant ainsi de vérifier la bonne réalisation des tâches d’imagerie (Bakker et al., 2008 ; Ferraye et al., 2014). L’activité cérébrale des sujets a été enregistrée (scanner IRM-3Tesla) pendant les tâches d’imagerie. Tous les patients ont réussi à réaliser la tâche d’équilibre dynamique. L’interaction entre difficulté de la tâche et type d’imagerie est significative pour les deux groupes de sujet dans le cas de la marche, et pour le groupe contrôle seulement dans le cas de la tâche d’équilibre. Chez les patients, l’absence d’interaction entre difficulté de la tâche d’équilibre et type d’imagerie souligne la complexité de la tâche d’équilibre dynamique sans remettre en cause l’engagement des patients dans les tâches d’imagerie. Les analyses cérébrales sont en cours et bénéficieront d’une augmentation de la taille de l’échantillon du groupe de patients.

This study examines the cerebral structures involved in dynamic balance using a motor imagery (MI) protocol. We recorded cerebral activity with functional magnetic resonance imaging while subjects imagined swaying on a balance board along the sagittal plane to point a laser at target pairs of different sizes (small, large). We used a matched visual imagery (VI) control task and recorded imagery durations during scanning. MI and VI durations were differentially influenced by the sway accuracy requirement, indicating that MI of balance is sensitive to the increased motor control necessary to point at a smaller target. Compared to VI, MI of dynamic balance recruited additional cortical and subcortical portions of the motor system, including frontal cortex, basal ganglia, cerebellum and mesencephalic locomotor region, the latter showing increased effective connectivity with the supplementary motor area. The regions involved in MI of dynamic balance were spatially distinct but contiguous to those involved in MI of gait (Bakker et al., 2008; Snijders et al., 2011; Crémers et al., 2012), in a pattern consistent with existing somatotopic maps of the trunk (for balance) and legs (for gait). These findings validate a novel, quantitative approach for studying the neural control of balance in humans. This approach extends previous reports on MI of static stance (Jahn et al., 2004, 2008), and opens the way for studying gait and balance impairments in patients with neurodegenerative disorders.

The pedunculopontine area (PPNa) including the pedunculopontine and cuneiform nuclei, belongs to the mesencephalic locomotor region. Little is known about the oscillatory mechanisms underlying the function of this region in postural and gait control. We examined the modulations of the oscillatory activity of the PPNa and cortex during stepping, a surrogate of gait, and stance in seven Parkinson's disease patients who received bilateral PPNa implantation for disabling freezing of gait (FOG). In the days following the surgery, we recorded behavioural data together with the local field potentials of the PPNa during sitting, standing and stepping-in-place, under two dopaminergic medication conditions (OFF and ON levodopa). Our results showed that OFF levodopa, all subjects had FOG during step-in-place trials, while ON levodopa, stepping was effective (mean duration of FOG decreasing from 61.7±36.1% to 7.3±10.1% of trial duration). ON levodopa, there was an increase in PPNa alpha (5-12 Hz) oscillatory activity and a decrease in beta (13-35 Hz) and gamma (65-90 Hz) bands activity. PPNa activity was not modulated during quiet standing and sitting. Our results confirm the role of the PPNa in the regulation of gait and suggest that, in Parkinson disease, gait difficulties could be related to an imbalance between low and higher frequencies.

We examined executive functioning in patients with Parkinson's disease exhibiting, or not, levodopa-resistant freezing of gait (L-FOG). 38 advanced-stage patients with L-FOG were identified in a consecutive series of 400 patients. They were matched with 38 patients without L-FOG. All patients underwent prospective evaluations of cognitive and motor functioning before subthalamic nucleus surgery, and 1 year after. A composite frontal score, a measure of executive functioning, was compared between the two groups. We also examined correlations between the frontal score and the score on the FOG item of the Unified Parkinson Disease Rating Scale II. Results show that after surgery, patients with L-FOG, as a group, were more impaired in executive functioning than control patients. However, individual data analysis showed preserved executive functions in 11 patients with L-FOG. In addition, there was no correlation between L-FOG severity and the degree of executive impairment. Therefore, frontal dysfunction may be one mechanism underlying L-FOG in a number of patients with Parkinson's disease. However, since some patients develop L-FOG despite the preservation of executive functions, lesions or dysfunction of other neuronal structures are likely to be involved.