Chia-Feng Lu

Co-activation of primary motor cortex ipsilateral to muscles contracting in a unilateral motor task.

OBJECTIVE This study aims to investigate the role of the primary motor cortex ipsilateral to the movement (ipsilateral M1) in unilateral motor execution. METHODS Fifteen right-handed healthy subjects underwent functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) experiments. Motor tasks were performed with the right-side limb. Subjects followed visual cues to execute movements in the scanner and independent component analysis (ICA) was applied to analyse the data. Interhemispheric inhibition (IHI), short-interval intracortical inhibition (SICI) and recruitment curves (RCs) of motor-evoked potentials (MEPs) in right M1 were measured by TMS and responses were recorded from the left flexor carpi radialis (FCR) and left anterior deltoid (AD). RESULTS Group ICA showed activations of bilateral M1s highly related to motor tasks. Additionally, TMS results showed significant increases of MEP RCs on the left FCR and left AD during right wrist flexion and right shoulder flexion. Prominent decreases of IHI and SICI were also observed under the same conditions. CONCLUSIONS During unilateral muscle contraction, co-activation of the ipsilateral M1 involves additional processes modulated by intra- and interhemispheric interactions and its size of activations is specifically enhanced on the homotopic representation. SIGNIFICANCE The ipsilateral M1 plays a central role in unilateral motor executions.

Maintaining Gait Performance by Cortical Activation during Dual-Task Interference: A Functional Near-Infrared Spectroscopy Study.

In daily life, mobility requires walking while performing a cognitive or upper-extremity motor task. Although previous studies have evaluated the effects of dual tasks on gait performance, few studies have evaluated cortical activation and its association with gait disturbance during dual tasks. In this study, we simultaneously assessed gait performance and cerebral oxygenation in the bilateral prefrontal cortices (PFC), premotor cortices (PMC), and supplemental motor areas (SMA), using functional near-infrared spectroscopy, in 17 young adults performing dual tasks. Each participant was evaluated while performing normal-pace walking (NW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT). Our results indicated that the left PFC exhibited the strongest and most sustained activation during WCT, and that NW and WMT were associated with minor increases in oxygenation levels during their initial phases. We observed increased activation in channels in the SMA and PMC during WCT and WMT. Gait data indicated that WCT and WMT both caused reductions in walking speed, but these reductions resulted from differing alterations in gait properties. WCT was associated with significant changes in cadence, stride time, and stride length, whereas WMT was associated with reductions in stride length only. During dual-task activities, increased activation of the PMC and SMA correlated with declines in gait performance, indicating a control mechanism for maintaining gait performance during dual tasks. Thus, the regulatory effects of cortical activation on gait behavior enable a second task to be performed while walking.

Disrupted cerebellar connectivity reduces whole-brain network efficiency in multiple system atrophy

Multiple system atrophy of the cerebellar type is a sporadic neurodegenerative disorder of the central nervous system. We hypothesized that the white matter degeneration of the cerebellum and pons in this disease may cause a breakdown of cerebellar structural networks and further reduce the network efficiency of cerebellar‐connected cerebral regions. Diffusion tensor tractography was used to construct the structural networks of 19 cerebellar‐type multiple system atrophy patients, who were compared with 19 age‐ and sex‐matched controls. Graph theory was used to assess the small‐world properties and topological organization of structure networks in both the control and patient groups. Our results showed that the cerebellar‐type multiple system atrophy patients exhibited altered small‐world architecture with significantly increased characteristic shortest path lengths and decreased clustering coefficients. We also found that white matter degeneration in the cerebellum was characterized by reductions in network strength (number and integrity of fiber connections) of the cerebellar regions, which further induced extensively decreased network efficiency for numerous cerebral regions. Finally, we found that the reductions in nodal efficiency of the cerebellar lobules and bilateral sensorimotor, prefrontal, and basal ganglia regions negatively correlated with the severity of ataxia for the cerebellar‐type multiple system atrophy patients. This study demonstrates for the first time that the brains of cerebellar‐type multiple system atrophy patients exhibit disrupted topological organization of white matter structural networks. Thus, this study provides structural evidence of the relationship between abnormalities of white matter integrity and network efficiency that occurs in cerebellar‐type multiple system atrophy.

Reorganization of functional connectivity during the motor task using EEG time–frequency cross mutual information analysis

OBJECTIVE This study investigates the functional organization of cortical networks during self-determinant arm movement using the time sequences of the alpha (8-12 Hz) and beta (16-25 Hz) bands. METHODS The time-frequency cross mutual information (TFCMI) method was used to estimate the EEG functional connectivity in the alpha and beta bands for seven healthy subjects during four functional states: the resting, preparing, movement-onset, and movement-offset states. RESULTS In the preparing state, the maintenance of the central-executive network (CEN, prefrontal-parietal connection) suppressed the motor network in the alpha band to plan the next movement, whereas the CEN was deactivated in the beta band to retain visual attention (the frontal-occipital connection). A significant decrease of the CEN in the alpha band occurred after a visual cue in the movement-onset state, followed by a significant increase in motor-network connectivity in the beta band until the movement-offset state. CONCLUSIONS The temporal-spectral modulation mechanism allows the brain to manifest multiple functions subject to energy budget. SIGNIFICANCE The TFCMI method was employed to estimate EEG functional connectivity and effectively demonstrate the reorganization process between four functional states.

Three-dimensional reconstruction of cranial defect using active contour model and image registration.

In neurosurgery, cranial incisions during craniotomy can be recovered by cranioplasty—a surgical operation using cranial implants to repair skull defects. However, surgeons often encounter difficulties when grafting prefabricated cranial plates into defective areas, since a perfect match to the cranial incision is difficult to achieve. Previous studies using mirroring technique, surface interpolation, or deformed template had limitations in skull reconstruction to match the patient’s original appearance. For this study, we utilized low-resolution and high-resolution computed tomography images from the patient to repair skull defects, whilst preserving the original shape. Since the accuracy of skull reconstruction was associated with the partial volume effects in the low-resolution images and the percentage of the skull defect in the high-resolution images, the low-resolution images with intact skull were resampled and thresholded followed by active contour model to suppress partial volume artifacts. The resulting low-resolution images were registered with the high-resolution ones, which exhibited different percentages of cranial defect, to extract the incised cranial part. Finally, mesh smoothing refined the three-dimensional model of the cranial defect. Simulation results indicate that the reconstruction was 93.94% accurate for a 20% skull material removal, and 97.76% accurate for 40% skull material removal. Experimental results demonstrate that the proposed algorithm effectively creates a customized implant, which can readily be used in cranioplasty.

Altered Resting-State Functional Connectivity of Striatal-Thalamic Circuit in Bipolar Disorder

Bipolar disorder is characterized by internally affective fluctuations. The abnormality of inherently mental state can be assessed using resting-state fMRI data without producing task-induced biases. In this study, we hypothesized that the resting-state connectivity related to the frontal, striatal, and thalamic regions, which were associated with mood regulations and cognitive functions, can be altered for bipolar disorder. We used the Pearsons correlation coefficients to estimate functional connectivity followed by the hierarchical modular analysis to categorize the resting-state functional regions of interest (ROIs). The selected functional connectivities associated with the striatal-thalamic circuit and default mode network (DMN) were compared between bipolar patients and healthy controls. Significantly decreased connectivity in the striatal-thalamic circuit and between the striatal regions and the middle and posterior cingulate cortex was observed in the bipolar patients. We also observed that the bipolar patients exhibited significantly increased connectivity between the thalamic regions and the parahippocampus. No significant changes of connectivity related to the frontal regions in the DMN were observed. The changed resting-state connectivity related to the striatal-thalamic circuit might be an inherent basis for the altered emotional and cognitive processing in the bipolar patients.

Fractional Anisotropy in Corpus Callosum Is Associated with Facilitation of Motor Representation during Ipsilateral Hand Movements

Background Coactivation of primary motor cortex ipsilateral to a unilateral movement (M1ipsilateral) has been observed, and the magnitude of activation is influenced by the contracting muscles. It has been suggested that the microstructural integrity of the callosal motor fibers (CMFs) connecting M1 regions may reflect the observed response. However, the association between the structural connectivity of CMFs and functional changes in M1ipsilateral remains unclear. The purpose of this study was to investigate the relationship between functional changes within M1ipsilateral during unilateral arm or leg movements and the microstructure of the CMFs connecting both homotopic representations (arm or leg). Methods Transcranial magnetic stimulation was used to assess changes in motor evoked potentials (MEP) in an arm muscle during unilateral movements compared to rest in fifteen healthy adults. Functional magnetic resonance imaging was then used to identify regions of M1 associated with either arm or leg movements. Diffusion-weighted imaging data was acquired to generate CMFs for arm and leg areas using the areas of activation from the functional imaging as seed masks. Individual values of regional fractional anisotropy (FA) of arm and leg CMFs was then calculated by examining the overlap between CMFs and a standard atlas of corpus callosum. Results The change in the MEP was significantly larger in the arm movement compared to the leg movement. Additionally, regression analysis revealed that FA in the arm CMFs was positively correlated with the change in MEP during arm movement, whereas a negative correlation was observed during the leg movement. However, there was no significant relationship between FA in the leg CMF and the change in MEP during the movements. Conclusions These findings suggest that individual differences in interhemispheric structural connectivity may be used to explain a homologous muscle-dominant effect within M1ipsilateral hand representation during unilateral movement with topographical specificity.

Classification of bipolar disorder using basal-ganglia-related functional connectivity in the resting state

The emotional and cognitive symptoms of bipolar disorder (BD) are suggested to involve in a distributed neural network. The resting-state functional magnetic resonance imaging (fMRI) offers an important tool to investigate the alterations in brain network level of BD. The aim of this study was to discriminate BD patients from healthy controls using whole-brain resting-state functional connectivity patterns. The majority of most discriminating functional connectivities were between the basal ganglia and three core neurocognitive networks, including the default mode, executive control and salience networks. Using these resting-state functional connectivities between the basal ganglia and three core neurocognitive networks as the features, the clustering accuracy achieved 90%.

Sculpting the Intrinsic Modular Organization of Spontaneous Brain Activity by Art.

Artistic training is a complex learning that requires the meticulous orchestration of sophisticated polysensory, motor, cognitive, and emotional elements of mental capacity to harvest an aesthetic creation. In this study, we investigated the architecture of the resting-state functional connectivity networks from professional painters, dancers and pianists. Using a graph-based network analysis, we focused on the art-related changes of modular organization and functional hubs in the resting-state functional connectivity network. We report that the brain architecture of artists consists of a hierarchical modular organization where art-unique and artistic form-specific brain states collectively mirror the mind states of virtuosos. We show that even in the resting state, this type of extraordinary and long-lasting training can macroscopically imprint a neural network system of spontaneous activity in which the related brain regions become functionally and topologically modularized in both domain-general and domain-specific manners. The attuned modularity reflects a resilient plasticity nurtured by long-term experience.

Medullo-ponto-cerebellar white matter degeneration altered brain network organization and cortical morphology in multiple system atrophy.

The cerebellum involves diverse functions from motor coordination to higher cognitive functions. Impairment of the cerebellum can cause ataxia and cerebellar cognitive affective syndrome. Multiple system atrophy of the cerebellar type (MSA-C) is a neurodegenerative disorder with atrophy of medullo-ponto-cerebellar (MPC) white matter (WM). To understand the role of the cerebellum from the perspective of the local structure to the global function in the presence of MPC WM degeneration, we acquired T1-weighted and diffusion tensor images for 17 patients with MSA-C and 19 normal controls. We concurrently used the measures of local morphology, including MPC WM volume and inner surface area, and properties of global network organization based on graph theory for the MSA-C and control groups. The results showed that MPC WM degeneration caused the destruction of cerebello-ponto-cerebral loops, resulting in reduced communication efficiency between regions in the whole-brain network. In addition, the sulcal area of the inner cortical surface in the cerebellum decreased linearly with the MPC WM volume, and the inferoposterior lobe exhibited a steeper atrophy rate than that of vermis regions. We concluded that the integrity of MPC WM is critical in sustaining the local morphology and the global functions of the whole-brain fiber network.