Decreased variability of dynamic phase synchronization in brain networks during hand movement.

Dynamic functional connectivity analysis, a rapidly growing method, has been demonstrated to provide new spatiotemporal information about how brain motor network would reorganize from rest to motor tasks. Phase synchronization analysis, which has been widely applied in EEG-based FC analysis, is a promising alternative method in dynamic FC analysis. In this study, fMRI data were recorded from 28 healthy volunteers when they are resting and performing hand closing and opening (HCO) task. Dynamic FC was estimated by phase synchronization analysis. In addition, functional connectivity variability (FCV) was compared between rest and HCO to investigate the modulation induced by motor task on dynamics of motor-related FC and network. Results showed that the FCVs in network-of-interest, including default-mode network and motor network, decreased during HCO comparing with rest. Our results demonstrated that the unconstrained mental activities, which resulted in high FCV during rest, would focus on motor execution during HCO and thus led to decreased FCV during HCO.

Asymmetry of hemispheric interdependences in the early hours following unilateral stroke: An electrophysiological study in rats.

Disturbance of interhemispheric interactions after stroke has been widely reported. However, the dynamic change in the hyperacute stage of stroke remains to be elucidated. In this study, interhemispheric interactions and brain asymmetry in the early hours after infarction were investigated in animals from the aspect of nonlinear interdependences using bilateral EEG recordings. Both the right-to-left and the left-to-right hemispheric interdependences were impaired after unilateral stroke, with a significant decrease in the first two hours and a low level in the following twenty-two hours. The ipsilesional to contralesional interdependence was found more vulnerable to unilateral stroke, and the symmetry between the right-to-left and the left-to-right hemispheric interdependences was damaged. The brain symmetry index after four hours was significantly correlated with the infarct volume at twenty-four hours, suggesting its prognostic role as early as four hours post-stroke.

Resting-state EEG network change in alpha and beta bands after upper limb amputation.

To investigate the reorganization of functional brain network following amputation, twenty-two right-hand amputees and twenty-four age- and education-matched controls participated in a resting-state EEG study. EEG networks in alpha and beta bands were constructed using phase synchronization. Both global and local network parameters were compared between amputees and healthy controls. In the aspect of global connectivity, amputees showed increased clustering coefficient (C), decreased characteristic path length (L) and increased small worldness (S) in alpha band, and an increase of L in beta band. Meanwhile, in comparison with the controls, the right-hand amputees have lower nodal degree (k) in the sensorimotor cortex but higher k in the parietal area in the right hemisphere in alpha band. These alterations of network following amputation implied a decreased inhibition from the intact sensorimotor area and increased connections in the right parietal area, which supported the unmasking theory. Such connectivity changes might also relate to the phantom limb phenomenon.

Phase synchronization analysis of EEG signals: an evaluation based on surrogate tests.

Phase synchronization (PS) analysis has been demonstrated to be a useful method to infer functional connectivity with multichannel neural signals, e.g., electroencephalography (EEG). Methodological problems on quantifying functional connectivity with PS analysis have been investigated extensively, but some of them have not been fully solved yet. For example, how long a segment of EEG signal should be used in estimating PS index? Which methods are more suitable to infer the significant level of estimated PS index? To address these questions, this paper performs an intensive computation study on PS analysis based on surrogate tests with 1) artificial surrogate data generated by shuffling the rank order, the phase spectra, or the instantaneous frequency of original EEG signals, and 2) intersubject EEG pairs under the assumption that the EEG signals of different subjects are independent. Results show that 1) the phase-shuffled surrogate method is workable for significance test of estimated PS index and yields results similar to those by intersubject EEG surrogate test; 2) generally, a duration of EEG waves covering about 3 16 cycles is suitable for PS analysis; and 3) the PS index based on mean phase coherence is more suitable for PS analysis of EEG signals recorded at relatively low sampling rate.

Auditory guidance systems for the visually impaired people / 生物医学工程学杂志

Visually impaired people face many inconveniences because of the loss of vision. Therefore, scientists are trying to design various guidance systems for improving the lives of the blind. Based on sensory substitution, auditory guidance has become an interesting topic in the field of biomedical engineering. In this paper, we made a state-of-technique review of the auditory guidance system. Although there have been many technical challenges, the auditory guidance system would be a useful alternative for the visually impaired people.

Entropy analysis of the EEG alpha activity in depression patients / 生物医学工程学杂志

The alpha rhythm in electroencephalograph has been associated with the mental state of the brain. The aim of the present study was to analyze the complexity of the alpha activity in depression patients by Renyi entropy (RE) under two conditions, i.e., resting with eyes closed followed by a simple mental arithmetic. The EEGs were recorded in 20 depression patients and 20 age-matched control subjects. Results showed that the alpha activity of depression patients is more complex during resting and is more regular during the mental arithmetic than that of the controls. RE analysis can well characterize the alpha activity in depression patients and could be a valuable tool to study cognitive process and also a potential effective approach for the diagnosis of depression.

Review of visual prosthesis (I)--retinal prosthesis / 生物医学工程学杂志

Research on how to totally or partially restore the vision has attracted more attention in the fields of neural engineering and tissue engineering. Neural interface and visual prosthesis offer alternative ways for partially repairing the visual impairment. The most widely used visual prosthetics are based on retinal stimulation. This article is a state-of-art review of the principles, technical details and the limitations of retinal prosthesis.

Review of visual prosthesis (II)--cortical visual prosthesis, optic nerve prosthesis and vision substitution devices / 生物医学工程学杂志

Cortical visual prosthesis, optic nerve visual prosthesis and vision substitution devices are alternative ways for repairing the visual impairment in case of optic nerve injury, retina lose or blindness without fully developed central visual system. This article is a state-of-art review of the principles, technical details and the limitations of different types of prostheses beyond the retinal prosthesis.

Review of researches on retinal model / 生物医学工程学杂志

Retinal model is an essential part in the retinal prosthesis. Based on the retinal physiology and the experimental data, the model is able to simulate the information processing in the retina, and can be used to investigate the relation between the input image and the neuron firing. We can categorize the models into circuit realization and algorithm realization. This article is a state-of-art review of different types of retinal models.