The association between exercise-induced muscle damage and cortical activity in the alpha and beta frequency range

Includes abstract.Includes bibliographical references (p. 139-178).This thesis examines the regulation of muscle function following exercise-induced muscle damage (EIMD), in an attempt to determine whether regulation occurs primarily in the muscle (neuromuscular) or further upstream. Upstream regulation has been hypothesized to occur in the lower brain structures, but one may assume that the efferent output to the muscle should be guided by the motor and pre-motor cortex alongside other associated cortical areas

Neurophysiological Adaptations to Resistance Training and Repetitive Grasping

Perhaps the most prominent feature of the central nervous system is its ability to respond to experience and its environment. Understanding the processes and mechanisms that govern adaptive behavior provides insights into its plastic nature. Capitalizing on this plasticity is of critical importance in response to injury and recovery: 35, 106), and the importance of its promotion is increasingly recognized by rehabilitation scientists. Neurophysiological techniques permitting study of cortical function in vivo may play a significant role in validating exercise interventions and disease management approaches: 14). It may be possible that with these advances we may better understand the relationship between brain function and therapeutic approaches. For this purpose, we present data on both cumulative and acute effects of motor training to better understand adaptive processes. Neural adaptations accompany resistance training, but current evidence regarding the nature of these adaptations is best characterized as indirect, particularly with respect to adaptation within central or supraspinal centers: 56). To this end, we recorded movement-related cortical potentials: MRCP), i.e. electroencephalography: EEG)-derived event-related potentials, in healthy adults prior to and following a program of lower body resistance training. The cumulative effects of nine progressive training sessions resulted in attenuation of relative MRCP amplitudes. We interpreted these findings in terms of neural efficiency such that for the same pre-training load, central effort is diminished post-training. These data demonstrate the impact of cumulative motor training sessions in fostering a reduction in the level of cortical motor activation. Such a program may be of a particular utility for individuals with limited motor reserves such as those with Parkinson disease: PD). Although cumulative effects may foster a more efficient cortical network, the acute demands of a training session have received less attention. It is reasonable to assume that the reverse might be expected: i.e. augmented amplitude) during a motor training session, much like the muscular system is taxed during resistance training exercise. At the level of the cortex, neural activity was studied by recording the MRCP during 150 repetitive handgrip contractions at a high intensity. The goal of this work was to examine whether central adaptive processes used to maintain task performance vary as a function of age or PD. We found that for healthy young adults, augmented activation of motor cortical centers is responsible for maintaining performance. However, this was not observed for older adults with and without PD, where minimal changes in cortical activity were observed over the duration of the protocol. Our findings suggest that older adults and those with PD may rely on alternative mechanisms: i.e. mobilization of additional cortical and subcortical structures) to maintain task performance as compared to increasing activity locally as seen with younger adults. Taken together, our work further supports the adaptable nature of the central nervous system. We note in passing the utility of the MRCP paradigm for observing such effects

NON INVASIVE INVESTIGATION OF SENSORIMOTOR CONTROL FOR FUTURE DEVELOPMENT OF BRAIN-MACHINE-INTERFACE (BMI)

My thesis focuses on describing novel functional connectivity properties of the sensorimotor system that are of potential interest in the field of brain-machine interface. In particular, I have investigated how the connectivity changes as a consequence of either pathologic conditions or spontaneous fluctuations of the brain's internal state. An ad-hoc electronic device has been developed to implement the appropriate experimental settings. First, the functional communication among sensorimotor primary nodes was investigated in multiple sclerosis patients afflicted by persistent fatigue. I selected this condition, for which there is no effective pharmacological treatment, since existing literature links this type of fatigue to the motor control system. In this study, electroencephalographic (EEG) and electromyographic (EMG) traces were acquired together with the pressure exerted on a bulb during an isometric hand grip. The results showed a higher frequency connection between central and peripheral nervous systems (CMC) and an overcorrection of the exerted movement in fatigued multiple sclerosis patients. In fact, even though any fatigue-dependent brain and muscular oscillatory activity alterations were absent, their connectivity worked at higher frequencies as fatigue increased, explaining 67% of the fatigue scale (MFIS) variance (p=.002). In other terms, the functional communication within the central-peripheral nervous systems, namely involving primary sensorimotor areas, was sensitive to tiny alterations in neural connectivity leading to fatigue, well before the appearance of impairments in single nodes of the network. The second study was about connectivity intended as propagation of information and studied in dependence on spontaneous fluctuations of the sensorimotor system triggered by an external stimulus. Knowledge of the propagation mechanisms and of their changes is essential to extract significant information from single trials. The EEG traces were acquired during transcranial magnetic stimulation (TMS) to yield to a deeper knowledge about the response to an external stimulation while the cortico-spinal system passes through different states. The results showed that spontaneous increases of the excitation of the node originating the transmission within the hand control network gave rise to dynamic recruitment patterns with opposite behaviors, weaker in homotopic and parietal circuits, stronger in frontal ones. As probed by TMS, this behavior indicates that the effective connectivity within bilateral circuits orchestrating hand control are dynamically modulated in time even in resting state. The third investigation assessed the plastic changes in the sensorimotor system after stroke induced by 3 months of robotic rehabilitation in chronic phase. A functional source extraction procedure was applied on the acquired EEG data, enabling the investigation of the functional connectivity between homologous areas in the resting state. The most significant result was that the clinical ameliorations were associated to a ‘normalization’ of the functional connectivity between homologous areas. In fact, the brain connectivity did not necessarily increase or decrease, but it settled within a ‘physiological’ range of connectivity. These studies strengthen our knowledge about the behavioral role of the functional connectivity among neuronal networks’ nodes, which will be essential in future developments of enhanced rehabilitative interventions, including brain-machine interfaces. The presented research also moves the definition of new indices of clinical state evaluation relevant for compensating interventions, a step forward

Effects of dance therapy on balance, gait and neuro-psychological performances in patients with Parkinson's disease and postural instability

Postural Instability (PI) is a core feature of Parkinson’s Disease (PD) and a major cause of falls and disabilities. Impairment of executive functions has been called as an aggravating factor on motor performances. Dance therapy has been shown effective for improving gait and has been suggested as an alternative rehabilitative method. To evaluate gait performance, spatial-temporal (S-T) gait parameters and cognitive performances in a cohort of patients with PD and PI modifications in balance after a cycle of dance therapy

Toward a greater understanding of the brain processes underlying handgrip and handgrip fatigue

Handgrip is a ubiquitous human movement that determines how we interact with our environment. It is involved in almost every aspect of daily life (e.g. opening a door, handling cutlery, using tools) and like all human movement, its application is limited by muscle fatigue. However, the supraspinal mechanisms of handgrip and handgrip fatigue are not fully understood despite the importance of this fundamental movement, numerous publications, and its presence as a longstanding research topic. This thesis investigates the brain mechanisms of handgrip and handgrip fatigue using fMRI. It begins with a review of the literature in Chapter one, which evaluates the theories and evidence for central control of handgrip and muscle fatigue as well as describing the rationale to perform the experiments in this thesis. The methodology and analyses are also reviewed to provide rationale for their use and to facilitate the interpretation of subsequent experimental results. In order to understand the supraspinal mechanisms of handgrip and handgrip fatigue it is logical to first understand the most fundamental grip type (power vs. precision) and pattern (static vs. dynamic) by which handgrip can be performed

Malondialdehyde Suppresses Cerebral Function by Breaking Homeostasis between Excitation and Inhibition in Turtle Trachemys scripta

The levels of malondialdehyde (MDA) are high in the brain during carbonyl stress, such as following daily activities and sleep deprivation. To examine our hypothesis that MDA is one of the major substances in the brain leading to fatigue, the influences of MDA on brain functions and neuronal encodings in red-eared turtle (Trachemys scripta) were studied. The intrathecal injections of MDA brought about sleep-like EEG and fatigue-like behaviors in a dose-dependent manner. These changes were found associated with the deterioration of encoding action potentials in cortical neurons. In addition, MDA increased the ratio of γ-aminobutyric acid to glutamate in turtle's brain, as well as the sensitivity of GABAergic neurons to inputs compared to excitatory neurons. Therefore, MDA, as a metabolic product in the brain, may weaken cerebral function during carbonyl stress through breaking the homeostasis between excitatory and inhibitory neurons

INTERACTION OF CEREBRAL, CARDIAC AND MUSCULAR CHANGES INDUCED BY ACUTE ENDURANCE EXERCISE

Resting and premotor brain activity seems to be decisive for numerous motor behaviors. The literature has shown that acute endurance exercise may modulate the brain activity and reduce the motor performances. The aim of this thesis is to investigate the links between the modulations in resting and premotor electroencephalographic activity, and the knee-extensor neuromuscular function and the autonomic cardiovascular activity changes after an endurance exercise performed on an ergocycle. In parallel, this work aims to bring to the field of exercise sciences a new analysis method of the functional state of the resting brain, namely, the microstate analysis. In the first article, we reported a reduction in premotor potential amplitude and maximal voluntary contraction force after exercise. The decrease in premotor brain activity shows links with the neuromuscular function and suggests that mechanisms implicated in a voluntary contraction may reside at the premotor level, even before movement arises. In the second article, we reported a main effect of exercise on microstate C stability, which was characterized by an increase in its duration, time coverage and explained variance, and a greater percentage of transition towards this microstate. This study suggests that the modulations of microstate C may reflect a dominance of the salience resting-state network, likely under the influence of muscle afferents and endogenous stimuli, which could affect the voluntary motor command. In the third article, we showed that the increase in microstate C mean duration and the modulations in heart rate variability persist during the 1 hour after exercise. The modifications in microstate C temporal properties may reflect the adjustment of the autonomic cardiovascular activity and/or an increase in exercise-related cardiovascular arousal. By investigating the resting and premotor brain activity, the present thesis provides a better understanding of the motor response modulations after endurance exercise and opens up novel opportunities for exploring the interactions between the global functional state of the brain and the exercise-related physiological responses. -- L’activité cérébrale de repos et pré-motrice semble être déterminante pour de nombreux comportements moteurs. La littérature a montré qu’un exercice physique d’endurance aigu pouvait moduler l’activité cérébrale et réduire les performances motrices. Le but de cette thèse est d’investiguer les liens entre les modulations de l’activité électroencéphalographique de repos et pré-motrice, et les modifications de la fonction neuromusculaire des muscles extenseurs du genou et de l’activité cardiaque autonome à la suite d’un exercice d’endurance réalisé sur ergocycle. En parallèle, ce travail vise à apporter au champ des sciences de l’exercice une nouvelle méthode d’analyse de l’état fonctionnel global du cerveau au repos, à savoir l’analyse de micro-état. Dans le premier article, nous avons observé une réduction de l’amplitude du potentiel pré- moteur et de la force maximale volontaire après l’exercice. La réduction de l’activité cérébrale pré-motrice présente des liens avec les modulations de la fonction neuromusculaire, suggérant que des mécanismes impliqués dans une contraction volontaire pourraient résider au niveau pré-moteur, avant même que le mouvement soit produit. Dans le deuxième article, nous avons observé un effet principal de l’exercice sur la stabilité du micro-état C, caractérisé par une augmentation de sa durée, du temps couvert et de sa variance expliquée, ainsi qu’un pourcentage de transition vers ce micro-état plus important. Cette étude suggère que les modulations du micro-état C pourraient refléter une dominance du réseau de repos saillant, probablement sous l’influence d’afférences musculaires et de stimuli endogènes, qui exercerait une influence sur la commande motrice volontaire. Dans le troisième article, nous avons montré que l’augmentation de la durée moyenne du micro- état C persiste 1 heure après l’arrêt de l’exercice, tout comme les modulations de la variabilité de la fréquence cardiaque. Les modifications des propriétés temporelles du micro-état C pourraient refléter l’ajustement de l’activité cardiaque autonome et/ou une augmentation de l’éveil cardiovasculaire lié à l’exercice. En étudiant l’activité cérébrale de repos et pré-motrice, cette thèse fournit une meilleure compréhension des modulations de la réponse motrice à la suite d’un exercice physique d’endurance et ouvre de nouvelles opportunités pour explorer les interactions entre l’état fonctionnel global du cerveau au repos et les réponses physiologiques liées à l’exercice

Eye-Hand Coordination Varies According to Changes in Cognitive-Motor Load and Eye Movements Used

In this dissertation three studies were used to help improve the understanding of eye- hand coordination control of visuomotor reaching tasks with varying cognitive loads. Specifically, we considered potential performance differences based on eye-movements, postural influences, as well as fitness level of the young adult participants. A brief introduction in chapter 1 is followed by a detailed literature review in chapter 2. Results from the three studies presented in chapter’s 3-5 further advance our knowledge of the integrated control used for goal-directed visually-guided reaches. In the first study (chapter 3), the additional cost associated with the use of smooth pursuit slowed hand movement speed when the eyes and hand moved in distinct directions, yet improved accuracy over the use of saccadic eye movements and eye fixation. We concluded that eye-movement choice can influence various types of visually-guided reaching with different cognitive demands and that researchers should provide clear eye-movement instructions for participants and/or monitor the eyes when assessing similar upper limb control to account for possible differences. In the second study (chapter 4), results revealed slower speed and poor accuracy of hand movements along with less body sway for visually-guided reaching when the eyes and hand moved in opposite directions during eye-hand decoupling compared to when the eyes and hand moved in the same direction (eye-hand coupling). In contrast, standing up did not significantly influence reaching performance compared to sitting. We concluded that increases in cognitive demands for eye-hand coordination created a greater need for postural control to help improve the goal- directed control of reaching. In the third study (chapter 5), we found no evidence of eye-hand coordination differences between highly fit or sedentary participants, yet cerebral activation in the centro-parietal location differed between tasks involving eye-hand coupling/decoupling. We concluded that reaching performance declines accompanied increased sensorimotor demands during eye-hand decoupling that may link to prior/current athletic experience and not fitness level. Overall, alterations in visually-guided goal-directed reaching movements involving eye-hand coupling and decoupling depend on changes in eye-movements utilized and not on low threat postural changes or fitness levels of the young adults performing the task