Functional Connectivity in the Motor Network Largely Matures Before Motor Function

The brain changes in many ways in the first year. It is not known which of these changes are most critical for the development of cognitive functions. According to the Interactive Specialization Theory, developments in behaviour result from changes in brain connectivity. We tested this using functional connectivity magnetic resonance imaging (fcMRI) of the motor system. fcMRI was acquired at three and nine months – two time-points between which motor behaviour develops enormously. Infants were additionally compared with adults. Subjects were scanned with a 3T MRI scanner, yielding BOLD signal time-courses that were correlated with one another. Our results do not support the Interactive Specialization Theory, as connectivity did not change with motor development and instead was adult-like in the youngest infants. fcMRI has enabled deeper exploration of network connectivity patterns and continues to emerge as a leading method in infant neuroscience

Priming cardiovascular exercise improves complex motor skill learning by affecting the trajectory of learning-related brain plasticity

In recent years, mounting evidence from animal models and studies in humans has accumulated for the role of cardiovascular exercise (CE) in improving motor performance and learning. Both CE and motor learning may induce highly dynamic structural and functional brain changes, but how both processes interact to boost learning is presently unclear. Here, we hypothesized that subjects receiving CE would show a different pattern of learning-related brain plasticity compared to non-CE controls, which in turn associates with improved motor learning. To address this issue, we paired CE and motor learning sequentially in a randomized controlled trial with healthy human participants. Specifically, we compared the effects of a 2-week CE intervention against a non-CE control group on subsequent learning of a challenging dynamic balancing task (DBT) over 6 consecutive weeks. Structural and functional MRI measurements were conducted at regular 2-week time intervals to investigate dynamic brain changes during the experiment. The trajectory of learning-related changes in white matter microstructure beneath parieto-occipital and primary sensorimotor areas of the right hemisphere differed between the CE vs. non-CE groups, and these changes correlated with improved learning of the CE group. While group differences in sensorimotor white matter were already present immediately after CE and persisted during DBT learning, parieto-occipital effects gradually emerged during motor learning. Finally, we found that spontaneous neural activity at rest in gray matter spatially adjacent to white matter findings was also altered, therefore indicating a meaningful link between structural and functional plasticity. Collectively, these findings may lead to a better understanding of the neural mechanisms mediating the CE-learning link within the brain

Neurobehavioral Strategies of Skill Acquisition in Left and Right Hand Dominant Individuals

The brain consists of vast networks of connected pathways communicating through synchronized electrochemical activity propagated along fiber tracts. The current understanding is that the brain has a modular organization where regions of specialized processes are dynamically coupled through long-range projections of dense axonal networks connecting spatially distinct regions enabling signal transfer necessary for all complex thought and behavior, including regulation of movement. The central objective of the dissertation was to understand how sensorimotor information is integrated, allowing for adaptable motor behavior and skill acquisition in the left-and right-hand dominant populations. To this end participants, of both left- and right-hand dominance, repeatedly completed a visually guided, force matching task while neurobiological and neurobehavioral outcome measurements were continuously recorded via EEG and EMG. Functional connectivity and graph theoretical measurements were derived from EEG. Cortico-cortical coherence patterns were used to infer neurostrategic discrepancies employed in the execution of a motor task for each population. EEG activity was also correlated with neuromuscular activity from EMG to calculate cortico-muscular connectivity. Neurological patterns and corresponding behavioral changes were used to express how hand dominance influenced the developing motor plan, thereby increasing understanding of the sensorimotor integration process. The cumulative findings indicated fundamental differences in how left- and right-hand dominant populations interact with the world. The right-hand dominant group was found to rely on visual information to inform motor behavior where the left-hand dominant group used visual information to update motor behavior. The left-hand group was found to have a more versatile motor plan, adaptable to both dominant, nondominant, and bimanual tasks. Compared to the right-hand group it might be said that they were more successful in encoding the task, however behaviorally they performed the same. The implications of the findings are relevant to both clinical and performance applications providing insight as to potential alternative methods of information integration. The inclusion of the left-hand dominant population in the growing conceptualization of the brain will generate a more complete, stable, and accurate understanding of our complex biology

Lifespan Differences in Cortico-Striatal Resting State Connectivity

Distinctive cortico-striatal circuits that serve motor and cognitive functions have been recently mapped based on resting state connectivity. It has been reported that age differences in cortico-striatal connectivity relate to cognitive declines in aging. Moreover, children in their early teens (i.e., youth) already show mature motor network patterns while their cognitive networks are still developing. In the current study, we examined age differences in the frontal-striatal ?cognitive? and ?motor? circuits in children and adolescence, young adults (YAs), and older adults (OAs). We predicted that the strength of the ?cognitive? frontal-striatal circuits would follow an inverted ?U? pattern across age; children and OAs would have weaker connectivity than YAs. However, we predicted that the ?motor? circuits would show less variation in connectivity strength across the lifespan. We found that most areas in both the ?cognitive? and ?motor? circuits showed higher connectivity in YAs than children and OAs, suggesting general inverted ?U?-shaped changes across the lifespan for both the cognitive and motor frontal-striatal networks.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140317/1/brain.2013.0155.pd

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

DYNAMICS OF FUNCTIONAL CONNECTIVITY WITHIN CORTICAL MOTOR NETWORK DURING MOTOR LEARNING IN STROKE - CORRELATIONS WITH "TRUE" MOTOR RECOVERY

Arm motor recovery after stroke is usually incomplete; six months after onset about two-thirds of patients suffer from arm motor impairment that significantly impacts the individual's activities of daily living. Thus, novel concepts beyond current strategies for arm motor rehabilitation after stroke are needed. An essential approach for this is to better understand whether motor learning-related neural changes in stroke are similar with those in healthy controls and how these neural changes relate to recovery of the pre-morbid movement pattern or "true" recovery. Abnormal task-related activation in primary and non-primary motor cortices has been a consistent finding in functional MRI studies of stroke. Disturbed functional network architecture, e.g., the influence that one motor area exerts over another, also impacts stroke recovery. The outcome measures chosen to evaluate recovery are also important for the interpretation of these brain changes. Thus, the long-range goal of this work was to longitudinally investigate the changes in cortical motor function at two levels, regional (micro-circuitry, regional activation) and network (macro-circuitry, functional connectivity), following an arm-focused motor training in chronic stroke survivors and how these brain changes relate to recovery of the pre-morbid movement pattern or "true" recovery. In the Chapter I, we reviewed the literature concerning the pathophysiology of stroke, neural substrates of motor control, and motor learning principles and neural substrates in healthy and pathological (stroke) brain. In the Chapter II, we examined the relationships between task-related motor activation and clinical and kinematic metrics of arm motor impairment in survivors of subcortical stroke. We found evidence that primary motor activation was significantly correlated to kinematic metrics of arm motor impairment, but not with clinical metrics. In the Chapter III, we longitudinally investigated the regional changes in motor-related activation (functional MRI) in primary and non-primary motor areas following an arm-focused motor training in stroke survivors and age-sex matched healthy controls. We demonstrated that similar changes in the motor areas contralateral to the trained arm were found with training in both stroke and healthy participants. We also demonstrated a significant increase in motor performance in both groups as well as a normalization of the correlations between bilateral motor activation and movement kinematics in participants with stroke. In the Chapter IV, we also investigated the changes in functional connectivity between primary and non-primary motor areas following an arm-focused motor training and how these changes correlate with "true" motor recovery. We demonstrated significant enhanced functional connectivity in motor areas contralateral to the trained hand (or ipsilesional), although no "normalization" of the inter-hemispheric inhibition following training in our survivors. We also showed a "normalization" of the relationships between cortical motor functional connectivity and movement kinematics. In the Chapter V, we concluded that the present dissertation work support the hypotheses that motor system is plastic at different levels, regional and network, even in the chronic stage of stroke and some of these changes are similar with those reported in healthy controls. Further, these changes provide a substrate for "true" recovery. These findings promote the use of neuroimaging and kinematic metrics to improve our understanding of the neural substrates underlying reorganization in remaining intact brain structures after stroke. Such an approach may further enable monitoring recovery or compensation based on this reorganization and evaluating new treatment regimes that assist motor recovery

Physical and Mental Coordination in the Elderly: A Causal Role for the Cerebellum?

The mechanisms underlying the progressive changes in tissues and organs that characterise normal ageing remain unclear. The cerebellum is known to play a major role in motor function, but recent research suggests it plays an equivalent role in cognition. Working with the hypothesis that cortico-cerebellar loops ensure smooth and coordinated activity in both domains, this thesis investigates the possible role of the cerebellum in normal ageing and in interventions to improve function, seeking to contribute to both theoretical and applied approaches to ageing. Study one investigated relationships between motor and cognitive function using raw data from a national normative sample of adults aged 16 to 75, employing a test battery assessing motor and cognitive skills. Differences between age groups were demonstrated in some tests of complex processing speed, working memory and executive function, with suggestive evidence that senescence in tests is reflected in tests sensitive to cerebellar function. Study two refined the battery, while including further measures of motor and memory performance to investigate linkages between cognitive and cerebellar function. Using a sample of 256 older adults, results were variable but provided evidence that pegboard performance could act as a predictor of some cognitive functions. Study three investigated a proactive intervention for healthy older adults designed to improve cerebellar function, and therefore balance and executive function. This involved an 8-10 week self-administered, internet-based coordinative exercise intervention using a ‘cerebellar challenge’ suite of graded activities. Performance on a basket of tests was assessed before and after, and also compared with performance changes in a no-intervention control group. Significantly greater benefits for the intervention group than the controls were found for balance physical coordination and controlled information processing. Overall, these studies support current research indicating cerebellar contribution to both cognitive and motor problems arising in old age, and present evidence that non-verbal memory and controlled speeded information problems may be alleviated through targeted activities affecting cerebellar function improving postural stability and physical coordination

Fractals in the Nervous System: conceptual Implications for Theoretical Neuroscience

This essay is presented with two principal objectives in mind: first, to document the prevalence of fractals at all levels of the nervous system, giving credence to the notion of their functional relevance; and second, to draw attention to the as yet still unresolved issues of the detailed relationships among power law scaling, self-similarity, and self-organized criticality. As regards criticality, I will document that it has become a pivotal reference point in Neurodynamics. Furthermore, I will emphasize the not yet fully appreciated significance of allometric control processes. For dynamic fractals, I will assemble reasons for attributing to them the capacity to adapt task execution to contextual changes across a range of scales. The final Section consists of general reflections on the implications of the reviewed data, and identifies what appear to be issues of fundamental importance for future research in the rapidly evolving topic of this review