Modularity of auditory spatial representations

Abstract : Auditory spatial functions are of crucial importance in everyday life. Determining the origin of sound sources in space plays a key role in a variety of tasks including orientation of attention, disentangling of complex acoustic patterns reaching our ears in noisy environments. Following brain damage, auditory spatial processing can be disrupted, resulting in severe handicaps. Complaints of patients with sound localization deficits include the inability to locate their crying child or being over-loaded by sounds in crowded public places. Yet, the brain bears a large capacity for reorganization following damage and/or learning. This phenomenon is referred as plasticity and is believed to underlie post-lesional functional recovery as well as learning-induced improvement. The aim of this thesis was to investigate the organization and plasticity of different aspects of auditory spatial functions. Overall, we report the outcomes of three studies: In the study entitled "Learning-induced plasticity in auditory spatial representations" (Spierer et al., 2007b), we focused on the neurophysiological and behavioral changes induced by auditory spatial training in healthy subjects. We found that relatively brief auditory spatial discrimination training improves performance and modifies the cortical representation of the trained sound locations, suggesting that cortical auditory representations of space are dynamic and subject to rapid reorganization. In the same study, we tested the generalization and persistence of training effects over time, as these are two determining factors in the development of neurorehabilitative intervention. In "The path to success in auditory spatial discrimination" (Spierer et al., 2007c), we investigated the neurophysiological correlates of successful spatial discrimination and contribute to the modeling of the anatomo-functional organization of auditory spatial processing in healthy subjects. We showed that discrimination accuracy depends on superior temporal plane (STP) activity in response to the first sound of a pair of stimuli. Our data support a model wherein refinement of spatial representations occurs within the STP and that interactions with parietal structures allow for transformations into coordinate frames that are required for higher-order computations including absolute localization of sound sources. In "Extinction of auditory stimuli in hemineglect: space versus ear" (Spierer et al., 2007a), we investigated auditory attentional deficits in brain-damaged patients. This work provides insight into the auditory neglect syndrome and its relation with neglect symptoms within the visual modality. Apart from contributing to a basic understanding of the cortical mechanisms underlying auditory spatial functions, the outcomes of the studies also contribute to develop neurorehabilitation strategies, which are currently being tested in clinical populations.

Controlled study of 50-Hz repetitive transcranial magnetic stimulation for the treatment of Parkinson disease.

OBJECTIVE: To investigate the safety and efficacy of 50-Hz repetitive transcranial magnetic stimulation (rTMS) in the treatment of motor symptoms in Parkinson disease (PD). BACKGROUND: Progression of PD is characterized by the emergence of motor deficits that gradually respond less to dopaminergic therapy. rTMS has shown promising results in improving gait, a major cause of disability, and may provide a therapeutic alternative. Prior controlled studies suggest that an increase in stimulation frequency might enhance therapeutic efficacy. METHODS: In this randomized, double blind, sham-controlled study, the authors investigated the safety and efficacy of 50-Hz rTMS of the motor cortices in 8 sessions over 2 weeks. Assessment of safety and clinical efficacy over a 1-month period included timed tests of gait and bradykinesia, Unified Parkinson's Disease Rating Scale (UPDRS), and additional clinical, neurophysiological, and neuropsychological parameters. In addition, the safety of 50-Hz rTMS was tested with electromyography-electroencephalogram (EMG-EEG) monitoring during and after stimulation. RESULTS: The authors investigated 26 patients with mild to moderate PD: 13 received 50-Hz rTMS and 13 sham stimulation. The 50-Hz rTMS did not improve gait, bradykinesia, and global and motor UPDRS, but there appeared a short-lived "on"-state improvement in activities of daily living (UPDRS II). The 50-Hz rTMS lengthened the cortical silent period, but other neurophysiological and neuropsychological measures remained unchanged. EMG/EEG recorded no pathological increase of cortical excitability or epileptic activity. There were no adverse effects. CONCLUSION: It appears that 50-Hz rTMS of the motor cortices is safe, but it fails to improve motor performance and functional status in PD. Prolonged stimulation or other techniques with rTMS might be more efficacious but need to be established in future research.

Sleep and information processing in individuals who have sustained a traumatic brain injury

Individuals who have sustained a traumatic brain injury (TBI) often complain of t roubl e sleeping and daytime fatigue but little is known about the neurophysiological underpinnings of the s e sleep difficulties. The fragile sleep of thos e with a TBI was predicted to be characterized by impairments in gating, hyperarousal and a breakdown in sleep homeostatic mechanisms. To test these hypotheses, 20 individuals with a TBI (18- 64 years old, 10 men) and 20 age-matched controls (18-61 years old, 9 men) took part in a comprehensive investigation of their sleep. While TBI participants were not recruited based on sleep complaint, the fmal sample was comprised of individuals with a variety of sleep complaints, across a range of injury severities. Rigorous screening procedures were used to reduce potential confounds (e.g., medication). Sleep and waking data were recorded with a 20-channel montage on three consecutive nights. Results showed dysregulation in sleep/wake mechanisms. The sleep of individuals with a TBI was less efficient than that of controls, as measured by sleep architecture variables. There was a clear breakdown in both spontaneous and evoked K-complexes in those with a TBI. Greater injury severities were associated with reductions in spindle density, though sleep spindles in slow wave sleep were longer for individuals with TBI than controls. Quantitative EEG revealed an impairment in sleep homeostatic mechanisms during sleep in the TBI group. As well, results showed the presence of hyper arousal based on quantitative EEG during sleep. In wakefulness, quantitative EEG showed a clear dissociation in arousal level between TBls with complaints of insomnia and TBls with daytime fatigue. In addition, ERPs indicated that the experience of hyper arousal in persons with a TBI was supported by neural evidence, particularly in wakefulness and Stage 2 sleep, and especially for those with insomnia symptoms. ERPs during sleep suggested that individuals with a TBI experienced impairments in information processing and sensory gating. Whereas neuropsychological testing and subjective data confirmed predicted deficits in the waking function of those with a TBI, particularly for those with more severe injuries, there were few group differences on laboratory computer-based tasks. Finally, the use of correlation analyses confirmed distinct sleep-wake relationships for each group. In sum, the mechanisms contributing to sleep disruption in TBI are particular to this condition, and unique neurobiological mechanisms predict the experience of insomnia versus daytime fatigue following a TBI. An understanding of how sleep becomes disrupted after a TBI is important to directing future research and neurorehabilitation.

Rest-activity cycle disturbances in the acute phase of moderate to severe traumatic brain injury

Background. Sleep-wake disturbances are among the most persistent sequelae after traumatic brain injury (TBI) and probably arise during the hospital stay following TBI. These disturbances are characterized by difficulties sleeping at night and staying awake during the day. Objective. The aim of the present study was to document rest-activity cycle consolidation in acute moderate/severe TBI using actigraphy and to assess its association with injury severity and outcome. Methods. In all, 16 hospitalized patients (27.1 ± 11.3 years) with moderate/severe TBI wore actigraphs for 10 days, starting in the intensive care unit (ICU) when continuous sedation was discontinued and patients had reached medical stability. Activity counts were summed for daytime (7:00-21:59 hours) and nighttime periods (22:00-6:59 hours). The ratio of daytime period activity to total 24-hour activity was used to quantify rest-activity cycle consolidation. An analysis of variance was carried out to characterize the evolution of the daytime activity ratio over the recording period. Results. Rest-activity cycle was consolidated only 46.6% of all days; however, a significant linear trend of improvement was observed over time. Greater TBI severity and longer ICU and hospital lengths of stay were associated with poorer rest-activity cycle consolidation and evolution. Patients with more rapid return to consolidated rest-activity cycle were more likely to have cleared posttraumatic amnesia and have lower disability at hospital discharge. Conclusions. Patients with acute moderate/ severe TBI had an altered rest-activity cycle, probably reflecting severe fragmentation of sleep and wake episodes, which globally improved over time. A faster return to rest-activity cycle consolidation may predict enhanced brain recovery.

Actitudes hacia la discapacidad : la influencia de variables individuales y contextuales

Este trabajo constituye una revisión de la influencia de las variables individuales y contextuales sobre las actitudes hacia la discapacidad. Para alcanzar este objetivo, se describió el concepto de discapacidad desde una perspectiva social, en donde se concibió la discapacidad como un aspecto relacional en vez de una característica individual. Por otra parte se describieron las actitudes hacia la discapacidad, los tipos y sus consecuencias, teniendo en cuenta las percepciones, creencias, emociones, información sobre discapacidad y variables sociodemográficas las cuales tienen un papel significativo en la formación y mantenimiento de las actitudes hacia la discapacidad. Adicionalmente se presentaron algunas de las estrategias de intervención que tiene como propósito mejorar las actitudes, aspecto que puede ayudar o contribuir a la aceptación de las personas con discapacidad. Finalmente, el presente trabajo muestra la necesidad de continuar el estudio de las actitudes hacia la discapacidad, y el mejorar las intervenciones basadas en los hallazgos presentados.

Estimulacion magnetica trascraneal en el desempeno motor en enfermedades del sistema nervioso central: Revision Sistematica

Introducción: El uso de la estimulación cerebral no invasiva en procesos de rehabilitación es de gran interés, por cuanto con mediación tecnológica se generan nuevas posibilidades de recuperación motora, a partir de la activación de la corteza cerebral. El objetivo del estudio es establecer la evidencia del uso terapéutico de la EMT, relacionado con el desempeño motor de pacientes con enfermedades del sistema nervioso central. Metodología: Se realizó una revisión sistemática de la literatura. Se incluyeron 10 estudios en el análisis cualitativo que incluyó la evaluación de calidad con la escala de Jadad y del riesgo de sesgo con la herramienta Cochrane. Fueron excluidos 1613 estudios. Se aplicó el protocolo del estudio para la extracción, revisión y validez de los estudios incluidos. Resultados: La evidencia disponible muestra resultados positivos del uso terapéutico de la EMT en el desempeño motor en aspectos como la aceleración, la fuerza de pinza y de agarre, la estabilidad y la fuerza muscular, así como una mejor velocidad de la marcha y una disminución en la frecuencia y severidad de los espasmos. Discusión: La EMT puede constituir una estrategia terapéutica para mejorar el desempeño motor en pacientes con ECV, Lesión Medular y enfermedad de Parkinson, que requiere más investigación por la heterogeneidad de los diseños y medidas de descenlace utilizados, así como por la alta variabilidad interindividual que hace complejo estandarizar los protocolos de su uso terapéutico.

Ejercicio y resultados clínicos en pacientes con enfermedad de Parkinson: una revisión sistemática y metaanálisis

Antecedentes. La enfermedad de Parkinson (EP) es la segunda enfermedad neurodegenerativa más común en el mundo, la cual afecta el componente físico, psicológico y social de los individuos que la padecen. Numerosos estudios han abordado los beneficios de diferentes programas de ejercicio, llegando a ser una estrategia no-farmacológica efectiva para aminorar el deterioro funcional de los pacientes con EP. Objetivo. Determinar los efectos de las diferentes modalidades de ejercicio físico en los principales desenlaces clínicos en pacientes con EP. Métodos. Se consultaron las bases de datos MEDLINE, EMBASE, Scopus, CENTRAL y PEDro desde febrero de 1990 hasta febrero de 2014 para identificar Ensayos Clínicos Aleatorizados (ECA) publicados. Además, se examinaron las listas de referencias de otras revisiones y de estudios identificados. La extracción de datos se realizó por dos autores independientes. Se empleó un modelo de efectos aleatorios en presencia de heterogeneidad estadística (I2>50%). El sesgo de publicación fue evaluado mediante el gráfico de embudo. Resultados: Un total de 18 estudios fueron incluidos. Se encontraron diferencias estadísticamente significativas en las intervenciones con ejercicio y las siguientes medidas de resultado, severidad de los síntomas motores (MDS-UPDRS) DME 1.44, IC 95% [-2.09 a -0.78] (p<0.001) I2= 87,9% y el equilibrio DME 0,52 IC 95% [0,30 a 0,74] (p<0.001) I2= 85,6%. En el análisis de subgrupos en la modalidad de ejercicio aeróbico, en MDS-UPDRS DME -1,28, IC 95% [-1,98 a -0,59] (p<0.001), 3 calidad de vida DME -1,91 IC 95% [-2,76 a -1,07] (p<0.001), equilibrio DME 0,54 IC 95% [0,31 a 0,77] (p<0.001), 10-m WT DME 0,15 IC 95% [0,06 a 0,25] (p<0.001) y Vo2 máximo DME -1,09 IC 95% [-1,31 a -0,88] (p=0.001), 6MWT DME 40,46 IC 95% [11,28 a 69,65] (p=0.007). Conclusiones: El ejercicio aeróbico produjo mejoras significativas en MDS UPDRS, equilibrio, calidad de vida, 10-m WT y y Vo2 máximo; mientras que el ejercicio combinado mejoró la fuerza.

Analysis of the Fugl-Meyer outcome measures assessing the effectiveness of robot-mediated stroke therapy

Robot-mediated therapies offer a new approach to neurorehabilitation. This paper analyses the Fugl-Meyer data from the Gentle/S project and finds that the two intervention phases (sling suspension and robot mediated therapy) have approximately equal value to the further recovery of chronic stroke subjects (on average 27 months post stroke). Both sling suspension and robot mediated interventions show a recovery over baseline and further work is needed to establish the common factors in treatment, and to establish intervention protocols for each that will give individual subjects a maximum level of recovery.

Reach and grasp therapy: effects of the Gentle/G System assessing sub-acute stroke whole-arm rehabilitation

This paper reports preliminary results of a reach and grasp study of robot mediated neurorehabilitation. These results are presented on a case-by-case basis and give a good indication of a positive effect of robot mediated therapy. The study investigated both reach and grasp assistance and although it is not possible to attribute the response to the benefits of providing assistance of both modalities the study is a good indicator that this strategy should be pursued. The paper also reports on the benefits of motivational queues such as exercise scores and on subject attitudes to the robot mediated therapy.

Multivariate analysis of the Fugl-Meyer outcome measures assessing the effectiveness of GENTLE/S robot-mediated stroke therapy

Background: Robot-mediated therapies offer entirely new approaches to neurorehabilitation. In this paper we present the results obtained from trialling the GENTLE/S neurorehabilitation system assessed using the upper limb section of the Fugl-Meyer ( FM) outcome measure. Methods: We demonstrate the design of our clinical trial and its results analysed using a novel statistical approach based on a multivariate analytical model. This paper provides the rational for using multivariate models in robot-mediated clinical trials and draws conclusions from the clinical data gathered during the GENTLE/S study. Results: The FM outcome measures recorded during the baseline ( 8 sessions), robot-mediated therapy ( 9 sessions) and sling-suspension ( 9 sessions) was analysed using a multiple regression model. The results indicate positive but modest recovery trends favouring both interventions used in GENTLE/S clinical trial. The modest recovery shown occurred at a time late after stroke when changes are not clinically anticipated. Conclusion: This study has applied a new method for analysing clinical data obtained from rehabilitation robotics studies. While the data obtained during the clinical trial is of multivariate nature, having multipoint and progressive nature, the multiple regression model used showed great potential for drawing conclusions from this study. An important conclusion to draw from this paper is that this study has shown that the intervention and control phase both caused changes over a period of 9 sessions in comparison to the baseline. This might indicate that use of new challenging and motivational therapies can influence the outcome of therapies at a point when clinical changes are not expected. Further work is required to investigate the effects arising from early intervention, longer exposure and intensity of the therapies. Finally, more function-oriented robot-mediated therapies or sling-suspension therapies are needed to clarify the effects resulting from each intervention for stroke recovery.

Neural activation and functional connectivity during motor imagery of bimanual everyday actions

Bimanual actions impose intermanual coordination demands not present during unimanual actions. We investigated the functional neuroanatomical correlates of these coordination demands in motor imagery (MI) of everyday actions using functional magnetic resonance imaging (fMRI). For this, 17 participants imagined unimanual actions with the left and right hand as well as bimanual actions while undergoing fMRI. A univariate fMRI analysis showed no reliable cortical activations specific to bimanual MI, indicating that intermanual coordination demands in MI are not associated with increased neural processing. A functional connectivity analysis based on psychophysiological interactions (PPI), however, revealed marked increases in connectivity between parietal and premotor areas within and between hemispheres. We conclude that in MI of everyday actions intermanual coordination demands are primarily met by changes in connectivity between areas and only moderately, if at all, by changes in the amount of neural activity. These results are the first characterization of the neuroanatomical correlates of bimanual coordination demands in MI. Our findings support the assumed equivalence of overt and imagined actions and highlight the differences between uni- and bimanual actions. The findings extent our understanding of the motor system and may aid the development of clinical neurorehabilitation approaches based on mental practice.

Analysis of EEG signal to detect motor command generation towards stroke rehabilitation

Our aim is to reconstruct the brain-body loop of stroke patients via an EEG-driven robotic system. After the detection of motor command generation, the robotic arm should assist patient’s movement at the correct moment and in a natural way. In this study we performed EEG measurements from healthy subjects performing discrete spontaneous motion. An EEG analysis based on the temporal correlation of the brain activity was employed to determine the onset of single motion motor command generation.

Corticospinal tract integrity and lesion volume play different roles in chronic hemiparesis and its improvement through motor practice

Background. Initial evidence suggests that the integrity of the ipsilesional corticospinal tract (CST) after stroke is strongly related to motor function in the chronic state but not the treatment gain induced by motor rehabilitation. Objective. We examined the association of motor status and treatment benefit by testing patients with a wide range of severity of hemiparesis of the left and right upper extremity. Method. Diffusion tensor imaging was performed in 22 patients beyond 12 months after onset of stroke with severe to moderate hemiparesis. Motor function was tested before and after 2 weeks of modified constraint-induced movement therapy. Results. CST integrity, but not lesion volume, correlated with the motor ability measures of the Wolf Motor Function Test and the Motor Activity Log. No differences were found between left and right hemiparesis. Motor performance improved significantly with the treatment regime, and did so equally for patients with left and right arm paresis. However, treatment benefit was not associated with either CST integrity or lesion volume. Conclusion. CST integrity correlated best in this small trial with chronic long-term status but not treatment-induced improvements. The CST may play a different role in the mechanisms mediating long-term outcome compared to those underlying practice-induced gains after a chronic plateau in motor function.

Evaluation of reach and grasp robot-assisted therapy suggests similar functional recovery patterns on proximal and distal arm segments in sub-acute hemiplegia

This paper provides some additional evidence in support of the hypothesis that robot therapies are clinically beneficial in neurorehabilitation. Although only 4 subjects were included in the study, the design of the intervention and the measures were done so as to minimise bias. The results are presented as single case studies, and can only be interpreted as such due to the study size. The intensity of intervention was 16 hours and the therapy philosophy (based on Carr and Shepherd) was that coordinated movements are preferable to joint based therapies, and that coordinating distal movements (in this case grasps) helps not only to recover function in these areas, but has greater value since the results are immediately transferable to daily skills such as reach and grasp movements.