Neural plasticity of the motor system: Functional specialization vs. integration

Handedness, the well-defined preference whereby one hand is used in favour of the other is a common feature of everyday assignments. About 90% of the human population is right-handed which associates with a left hemisphere motor dominance, as each side of the brain controls movement of the opposite side of the body. In contrast to the strong movement-related capabilities of the left hemisphere, the right hemisphere is superior for spatially-related functions. This capacity is crucial when we for instance need to direct our attention to a particular location in space. Based on these distinctive functions, interactions between both sides of the brain are considered important to ensure unified motor behaviour. For example when drawing a complex geometric figure, the movement and spatial demands need to be accurately integrated to accomplish the task successfully. Despite our ability to produce skilled and adaptive motor actions, there are still many questions unanswered concerning the brain's processing capabilities to achieve this type of behaviour. Accordingly the present research proposal includes several studies that describe the neural circuits for the control of skilled movements. First it is aimed at assessing the neural organization that underlies hand skilfulness. This involves evaluating the learning-related changes when acquiring a new motor task from an unskilled to a skilled performance. It is argued that practice has an important impact on neural processing that is modified as skill proficiency increases. Furthermore the effect of attention upon the processing demands will be established. It is hypothesized that attention influences the neural circuitry associated with the task demands. Second it is aimed at investigating the distinctiveness of handedness in skilled actions, including the degree as well as the direction of handedness. In view of the degree of handedness the aim is to compare the neural networks that control the performance of the preferred vs. non-preferred arm, under normal and sensorimotor conflict conditions (i.e., in case of a mismatch between an intended and expected outcome, such as when incongruent visual information is provided during movement performance). It is argued that distinct neural processing underlies the performance of both arms, which will become most evident under incongruent sensorimotor situations. In view of the direction of handedness the aim is to contrast the neural circuits that regulate motor performance in various handedness groups (i.e., right- and left-handers). It is hypothesized that right- and left-handers will show different neural processing profiles. All studies in this research proposal include electroencephalography (EEG) techniques, which employs sensors (electrodes) placed on the scalp to pick up electrical activity generated by the brain. Subsequently advanced analysis of the EEG signals will assess the involvement of various brain regions and how they in-teract with one other in view of motor performance. It is believed that the outcomes of this work will advance our knowledge concerning the brain's circuits that underlie motor behaviour. Furthermore this assessment is also important to improve rehabilitation programs that could initiate new interventional techniques for enhancing functional benefits after brain damage.

A superiority of the left hemisphere for movement organization is generally acknowledged. However functions directed by the right hemisphere such as spatial processing demands are also indispensable for a successful motor act. Hence it is argued that neural control of motor behaviour is achieved by means of interactive communication that involves both hemispheres and that is dynamically driven by task- and performer-related factors. The research proposal includes several studies that aim at exposing the neural dynamics that relate to the representation and regulation of skilled movement. First it is intended to assess the neural connectivity patterns that underlie manual skilfulness. This involves evaluating the learning-driven changes when acquiring a complex motor task from an unskilled to a skilled performance. Furthermore the influence of motor and spatial attention is evaluated, based on observations that a hemispheric dissociation of these attentional systems exists. Second it is aimed to determine the degree and direction of handedness by contrasting the neural circuits that guide motor performance of the preferred vs. non-preferred arm in right- and left-handers. All the studies in this research proposal take advantage of EEG technology. We specifically focus on the measurement of coherence, which provides a valuable analytical tool to investigate functional connectivity patterns across frequency bands. In addition cross-frequency analysis is applied to determine coupling between frequency bands. It is anticipated that the outcomes will enhance present insights into the neural organization of skilled actions and the processes that are instantiated in the brain-behaviour relation. Furthermore this knowledge is important to promote rehabilitation programs that take advantage of interhemispheric resources to reacquire, guide and reinforce movement capabilities. Overall these insights are decisive for theories of motor control in health and disease.