Energy, Dynamics, and Disorder of Human Brain on Voluntary Movement: Neuromagnetic Studies of Movement Emergence, Phase Space Transition, and Parkinson's Disease
| Autor: | Yu-Zu Wu, 吳育儒 |
|---|---|
| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 This thesis presents a research on the energy, dynamics, and disorder of human brain responsible for finger movements at different inter-movement intervals (IMIs) using whole-head 306-channel magnetoencephalography (MEG). The aim of this study was to advance the knowledge of movement-related brain dynamics in both normal subjects and the patients with Parkinson’s disease (PD). Studies were designed to target the subtle energy changes of MEG signals in postmovement motor cortical deactivation, the temporarily cortical transition between ordered and disordered states, and the dynamic evolution of cortical dimensional complexity using both linear and nonlinear approaches. Throughout the study, analyses of beta energy, beta entropy (disorder), and correlation dimension (D2; phase space transition) of MEG signals over the rolandic areas were used as an index of dynamic changes in the local neuronal activity. Beta energy rebound indexed as postmovement peak beta rebound (PMBR) was used to study the subtle change of postmovement motor cortical deactivation at different IMIs (reflecting different cognitive demands). Longer latency and higher amplitude in PMBR are observed for the longer-IMI movement. Cognitive demands other than motor and somatosensory processing play an important role during movement emergency. Spatiotemporal dynamics of MEG signals responsible for voluntary finger movement at different IMIs were studied using equivalent current dipoles (ECD) modeling. Three movement-related magnetic field components, motor field, movement-evoked field I (MEFI), and movement-evoked field II, are clearly observed. Only the amplitude of MEFI, however, shows significant difference between the different IMIs. The ECD approach does not seem to provide enough insights into the subtle changes of human brain in the voluntary movements with different IMIs. Transient cortical dynamics related to voluntary movement emergence are described using both beta entropy (disorder) and D2 (complexity). In the resting state, high disorder and high complexity make the neuronal coupling more possible and instant. High disorder and low complexity contribute to the neuronal integration and parallel information processes as movement emergence. Low disorder and high complexity indicate that most of the coupled neuronal ensembles are segregated after movement emergence, and only little information is processed. Cortical dimensional complexity has been demonstrated to correlate with the motor task difficulty, i.e. movement variability. An increase of movement variability reflects either a reduced ability of human brain to control several degrees of freedom or an active freezing of the degrees of freedom that is a strategy for the motor task with greater effort in the early stage of motor learning. Motor task of greater difficulty with a reduction of simultaneously active neuronal generators may be underpinned by stronger neuronal connectivity of a relatively low D2. The disorder of human brain with PD is described by dimensional complexity (D2). Parkinsonism resting tremor (involuntary movement) can result in either low D2 in a resting condition or high D2 in the voluntary repetitive movement. High D2 implies that more simultaneously active neuronal ensembles were emerged with weak coupling for parallel processing of two different tasks. Parkinsonian resting tremor is essentially detrimental to the cortical information processing by increasing the work load of neuronal networks. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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