Ab initio molecular-dynamics simulation of liquid As(x)Te(1-x) alloys

Ab initio molecular-dynamics simulations have been used to investigate the structure and dynamics properties of the liquid alloy As(x)Te(1-x) at 800 K and at the five compositions x = 0.2, 0.3, 0.4, 0.5 and 0.6. We present results for the static structure factors, diffusion coefficients and frequency spectra, in addition to the electronic density of states. Both the results for the structural and dynamic properties are in relatively good agreement with the experimental data available. The results also indicate that the increase in the number of As atoms reduces the metallic character of the sample in close connection with a corresponding disruption of the Te chain structure.

Accurate and robust extraction of brain regions using a deformable model based on radial basis functions

Brain extraction from head magnetic resonance (MR) images is a classification problem of segmenting image volumes into brain and non-brain regions. It is a difficult task due to the convoluted brain surface and the inapparent brain/non-brain boundaries in images. This paper presents an automated, robust, and accurate brain extraction method which utilizes a new implicit deformable model to well represent brain contours and to segment brain regions from MR images. This model is described by a set of Wendland's radial basis functions (RBFs) and has the advantages of compact support property and low computational complexity. Driven by the internal force for imposing the smoothness constraint and the external force for considering the intensity contrast across boundaries, the deformable model of a brain contour can efficiently evolve from its initial state toward its target by iteratively updating the RBF locations. In the proposed method, brain contours are separately determined on 2D coronal and sagittal slices. The results from these two views are generally complementary and are thus integrated to obtain a complete 3D brain volume. The proposed method was compared to four existing methods, Brain Surface Extractor, Brain Extraction Tool, Hybrid Watershed Algorithm, and Model-based Level Set, by using two sets of MR images as well as manual segmentation results obtained from the Internet Brain Segmentation Repository. Our experimental results demonstrated that the proposed approach outperformed these four methods when jointly considering extraction accuracy and robustness.

Female menstrual phases modulate human prefrontal asymmetry: a magnetoencephalographic study

We previously reported that the trait/baseline prefrontal cortex (PFC) activity expresses a dynamic plasticity during female menstrual cycle. The shift of asymmetric lateralization of PFC baseline activity pinpoints a possible emotional regulation of negative affection. The current emotional Go/NoGo study aimed to investigate the state PFC responses of different menstrual phases during fear facial stimulation in fourteen healthy women. Our data disclosed that the menstrual cycle was coupled with a shift of asymmetric lateralization of frontal activation across different menstrual phases. Evoked magnetic field activity in the time window 200-300 ms (M1) and 300-450 ms (M2) after stimulus onset demonstrated significant interactions between hemispheric side and menstrual phase. The right hemispheric dominance in periovulatory phase (OV) changed to left hemispheric dominance in menstrual (MC) phase. Significant association between the anxiety score and the left PFC activation was particularly observed in MC phase. Our study revealed a plastic resilience of functional organization of human brain and a dynamic automaticity of inter-hemispheric synergism for possible adaptive regulation under the aversive confrontation in accordance with hormonal fluctuation during the menstrual cycle.

The resting frontal alpha asymmetry across the menstrual cycle: a magnetoencephalographic study

Gonadotropic hormones play an important role in the regulation of emotion. Previous studies have demonstrated that estrogen can modulate appetitive (approach/positive) and aversive (avoidance/negative) affective behaviors during the menstrual cycle. Frontal alpha asymmetry (a measure of relative difference of the alpha power between the two anterior hemispheres) has been associated with the trait and state reactivity of different affective styles. We studied the pattern change of frontal alpha asymmetry across the menstrual cycle. 16 healthy women participated in this resting magneto-encephalographic (MEG) study during the peri-ovulatory (OV) and menstrual (MC) phases. Our results showed significant interaction of resting MEG alpha activity between hemispheric side and menstrual phases. Difference in spontaneous frontal alpha asymmetry pattern across the menstrual cycle was also noted. Relatively higher right frontal activity was found during the OV phase; relatively higher left frontal activity was noted during the MC phase. The alteration of frontal alpha asymmetry might serve a sub-clinical correlate for hormonal modulation effect on dynamic brain organization for the predisposition and conceptualization of different affective styles across the menstrual cycle.

Detection of synchronization between chaotic signals: An adaptive similarity-based approach

We present an adaptive similarity-based approach to detect generalized synchronization (GS) with n:m phase synchronization (PS), where n and m are integers and one of them is 1. This approach is based on the similarity index (SI) and Gaussian mixture model with the minimum description length criterion. The clustering method, which is shown to be superior to the closeness and connectivity of a continuous function, is employed in this study to detect the existence of GS with n:m PS. We conducted a computer simulation and a finger-lifting experiment to illustrate the effectiveness of the proposed method. In the simulation of a Rössler-Lorenz system, our method outperformed the conventional SI, and GS with 2:1 PS within the coupled system was found. In the experiment of self-paced finger-lifting movement, cortico-muscular GS with 1:2 and 1:3 PS was found between the surface electromyogram signals on the first dorsal interossei muscle and the magnetoencephalographic data in the motor area. The GS with n:m PS ( n or m=1 ) has been simultaneously resolved from both simulation and experiment. The proposed approach thereby provides a promising means for advancing research into both nonlinear dynamics and brain science.

Healthy-side dominance of middle- and long-latency neuromagnetic fields in idiopathic sudden sensorineural hearing loss

Any lesion along the neural axis may induce a subsequent functional reorganization at the level above. The present study used magnetoencephalography to investigate auditory-evoked magnetic fields [a component of the middle-latency auditory evoked fields peaking at approximately 50 ms (P50m) and a component of the long-latency auditory evoked fields peaking at approximately 100 ms (N100m)] on stimulation of both healthy and affected ears in patients with acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL) of moderate degree in order to elucidate the functional plasticity of the auditory system. Sixteen right-handed, previously untreated adult patients with acute unilateral left (n = 8) or right (n = 8) ISSNHL of moderate degree were studied. Sixteen right-handed healthy volunteers with normal hearing served as control. Auditory neuromagnetic responses, measured by a whole-head 306-channel neuromagnetometer, were detected by monaural tone stimulation applied to affected and healthy ears, respectively, in different sessions. Intragroup and intergroup interhemispheric differences of peak dipole strengths and latencies of P50m and N100m, respectively, to monaural tones were evaluated. Healthy-side amplitude dominance of both P50m and N100m was found in ISSNHL, i.e. contralateral dominance was preserved on affected-ear stimulation but ipsilateral dominance was seen on healthy-ear stimulation. The phenomena could be attributed to the combined contralateral attenuation and ipsilateral enhancement of P50m and N100m activity in response to healthy-ear stimulation. Our findings confirmed that functional modulation can occur within the first few tens of milliseconds of evoked response at the auditory cortex in ISSNHL. The mechanisms of healthy-side dominance might be ascribed to a functional retune of auditory pathways, i.e. conjoined contralateral inhibition and ipsilateral excitation of the auditory pathway in response to healthy-ear stimulation. The effect could be registered in cortical responses.

Dimensional complexity of neuromagnetic activity reduced during finger movement of greater difficulty

OBJECTIVE

We investigated the variation in dimensionality (D2) of neuromagnetic activity over the primary sensorimotor cortex (SM1) in healthy adults performing motor tasks of different difficulty.

METHODS

Magnetoencephalography (MEG) was used to record neuromagnetic activity during self-paced, brisk unimanual finger extension at a rate of 1 and 2 Hz using the index finger of the dominant and non-dominant hands in 16 healthy subjects. Motor task difficulty was rated by the relative difference in time measurement between 1 and 2 Hz finger movements of both hands. The relative difference in dimensionality of SM1 activity was calculated by subtracting the D2 value in 2 Hz movement from that in 1 Hz one within subjects.

RESULTS

Simple regression analyses show a significantly negative relationship between the relative dimensional complexity and the relative motor task difficulty in the contralateral SM1 for the left- (p<0.05), but not the right- (p=0.447) hand movement.

CONCLUSIONS

The present data suggest that a motor task of greater difficulty may engender a reduction of simultaneously active quasi-independent neuronal generators in the contralateral SM1 underpinned by stronger neuronal connectivity of a relatively low dimensionality.

SIGNIFICANCE

The decrease in dimensional complexity of MEG activity associated with a motor task of greater difficulty gives new insights to motor control strategy.

Maximum contrast beamformer for electromagnetic mapping of brain activity

Beamforming technique can be applied to map the neuronal activities from magnetoencephalographic/electroencephalographic (MEG/EEG) recordings. One of the major difficulties of the scalar-type MEG/EEG beamformer is the determination of accurate dipole orientation, which is essential to an effective spatial filter. This paper presents a new beamforming technique which exploits a maximum contrast criterion to maximize the ratio of the neuronal activity estimated in a specified active state to the activity estimated in a control state. This criterion leads to a closed-form solution of the dipole orientation. Experiments with simulation, phantom, and finger-lifting data clearly demonstrate the effectiveness, efficiency, and accuracy of the proposed method.

Effects of cognitive demands on postmovement motor cortical deactivation

Postmovement beta-rebounds induced by different intermovement intervals were investigated using magnetoencephalography in 14 healthy participants to test the hypothesis that postmovement motor cortical deactivation over the primary motor cortex depends on movement-related cognitive demands. Shorter latency and lower amplitude in postmovement beta-rebounds over the contralateral primary motor cortex were noted in the short-movement interval movement (repetitive finger lifting). Greater latency span of postmovement beta-rebounds jittering using single-trial analysis in the long-movement interval movement (discrete finger lifting) was observed. The study elucidates that the temporal interval between two adjacent movements reflecting different degrees of cognitive demands can affect postmovement motor cortical deactivation in terms of postmovement beta-rebounds latency and amplitude, and latency span of postmovement beta-rebounds jittering. Postmovement motor cortical deactivation can reflect cognitive demands in addition to motor and somatosensory processing.

Effects of hypobaric hypoxia on adenine nucleotide pools, adenine nucleotide transporter activity and protein expression in rat liver

AIM: To explore the effect of hypobaric hypoxia on mitochondrial energy metabolism in rat liver.

METHODS: Adult male Wistar rats were exposed to a hypobaric chamber simulating 5000 m high altitude for 23 h every day for 0 (H0), 1 (H1), 5 (H5), 15 (H15) and 30 d (H30) respectively. Rats were sacrificed by decapitation and liver was removed. Liver mitochondria were isolated by differential centrifugation program. The size of adenine nucleotide pool (ATP, ADP, and AMP) in tissue and mitochondria was separated and measured by high performance liquid chromatography (HPLC). The adenine nucleotide transporter (ANT) activity was determined by isotopic technique. The ANT total protein level was determined by Western blot.

RESULTS: Compared with H0 group, intra-mitochondrial ATP content decreased in all hypoxia groups. However, the H5 group reached the lowest point (70.6%) (P < 0.01) when compared to the control group. Intra-mitochondrial ADP and AMP level showed similar change in all hypoxia groups and were significantly lower than that in H0 group. In addition, extra-mitochondrial ATP and ADP content decreased significantly in all hypoxia groups. Furthermore, extra-mitochondrial AMP in groups H5, H15 and H30 was significantly lower than that in H0 group, whereas H1 group had no marked change compared to the control situation. The activity of ANT in hypoxia groups decreased significantly, which was the lowest in H5 group (55.7%) (P < 0.01) when compared to H0 group. ANT activity in H30 group was higher than in H15 group, but still lower than that in H0 group. ANT protein level in H5, H15, H30 groups, compared with H0 group decreased significantly, which in H5 group was the lowest, being 27.1% of that in H0 group (P < 0.01). ANT protein level in H30 group was higher than in H15 group, but still lower than in H0 group.

CONCLUSION: Hypobaric hypoxia decreases the mitochondrial ATP content in rat liver, while mitochondrial ATP level recovers during long-term hypoxia exposure. The lower level of extra-mitochondrial ATP may be related to the decrease of ANT activity during hypoxia exposure.

[Characteristics of adenine nucleotide translocator in mitochondria of rat cerebral cortex during hypobaric hypoxia exposure]

The purpose of the present study was to explore the effects of hypoxic exposure on mitochondrial adenine nucleotide translocator (ANT) activity and its characteristics. Male Wistar rats were exposed to hypoxia in a hypobaric chamber simulating high altitude at 5 000 m for 1, 5, 15 and 30 d. Control rats were fed outside the hypobaric chamber. Rats were sacrificed by decapitation and mitochondria from the cerebral cortex were isolated by differential centrifugation at each time point. The ANT activity was detected by the atractyloside (ATR)-inhibitor stop technique. Mitochondria was initiated by addition of (3)H-ADP and terminated after 12 s by quick addition of ATR. The radioactivity was measured in a liquid scintillation counter. Nonspecific binding of (3)H-ADP to mitochondria was estimated by incubation of mitochondrial samples with ATR prior to the addition of (3)H-ADP. This blank was substracted from the measured radioactivities. The activity of ANT was expressed as nanomoles (3)H-ADP per minute per milligram protein. The ANT density was determined by titrating the rate of state 3 respiration with increasing concentrations of carboxyatractyloside (CAT). Mitochondria were pre-incubated with CAT in a respiratory medium before ADP addition to initiate state 3 respiration. Plots of O2 consumption versus CAT appeared biphasic with an increasing inhibitory segment followed by a steady respiration, indicating that state 3 respiration was completely inhibited. The density of ANT was determined by the amount of CAT required to completely inhibit state 3 respiration, assuming a 1:1 binding stoichiometry, which was expressed as ANT density per milligram mitochondria protein. (ATP+ADP) in mitochondria was measured by high performance liquid chromatography (HPLC). The results showed that there was an obvious decrease in the ANT activity during hypoxic exposure. The lowest ANT activity was seen in 5 d group. Partial recovery of ANT activity was observed in 15 and 30 d groups, but ANT activity was still lower than that in the control group (P<0.01). Compared with that in normoxic control group, no change of ANT density in mitochondria was observed in hypoxia group (P>0.05). The turnover number of ANT in control, 1, 5, 15, 30 d groups were 16.67, 1.90, 0.40, 1.81, 4.73 pmol ADP/(min.pmol ANT), respectively. However, (ATP+ADP) in mitochondria in 1, 5, 15, 30 d groups were 63.37%, 48.44%, 52.73%, 60.16% of control group respectively. Therefore, the turnover number of energy production and expenditure were reduced. These observations suggest that the change of ANT activity may be one of the mechanisms of cellular oxidative phosphorylation dysfunction during hypoxic exposure.

Developing a camera-phone-based drug barcode reader and support system

The Food and Drug Administration (FDA) published a rule that require certain human drug and biological product labels to have a linear bar code, to help reduce the number of medication errors. This paper descripts a software support system for care givers and patients to identify the barcode use a camera phone. It is an economical and effective way if we can create software to help people to identify the barcode and show the information they need just on their phone.

Recognition of Motor Imagery Electroencephalography Using Independent Component Analysis and Machine Classifiers

Motor imagery electroencephalography (EEG), which embodies cortical potentials during mental simulation of left or right finger lifting tasks, can be used to provide neural input signals to activate a brain computer interface (BCI). The effectiveness of such an EEG-based BCI system relies on two indispensable components: distinguishable patterns of brain signals and accurate classifiers. This work aims to extract two reliable neural features, termed contralateral and ipsilateral rebound maps, by removing artifacts from motor imagery EEG based on independent component analysis (ICA), and to employ four classifiers to investigate the efficacy of rebound maps. Results demonstrate that, with the use of ICA, recognition rates for four classifiers (fisher linear discriminant (FLD), back-propagation neural network (BP-NN), radial-basis function neural network (RBF-NN), and support vector machine (SVM)) improved significantly, from 54%, 54%, 57% and 55% to 70.5%, 75.5%, 76.5% and 77.3%, respectively. In addition, the areas under the receiver operating characteristics (ROC) curve, which assess the quality of classification over a wide range of misclassification costs, also improved from .65, .60, .62, and .64 to .74, .76, .80 and .81, respectively.

Spatiotemporal brain dynamics in response to muscle stimulation

The objective of the present study was to assess the spatiotemporal scenario of brain activity associated with sensory stimulation of the abductor pollicis brevis muscle. Spatiotemporal dipole models, using realistic individual boundary element head models, were built from somatosensory evoked potentials (SEPs; 64 Ch. EEG) to nonpainful and painful intramuscular electrostimulation (IMES) as well as to cutaneous electrostimulation delivered to the distal phalanx of the thumb. Nonpainful and painful muscle stimuli resulted in activation of the same brain regions. In temporal order, these were: the contralateral primary sensorimotor cortex, contralateral dorso-lateral premotor area (PM), bilateral operculo-insular cortices, caudal cingulate motor area (CMA), and posterior cingulate cortex/precuneus. Brain processing induced by muscle sensory input showed a characteristic pattern in contrast to cutaneous sensory input, namely: (1) no early SEP components to IMES; (2) an initial IMES component likely generated by proprioceptive input is not present for digit stimulation; (3) one source was located in the PM only for IMES. This source was unmasked by the lower stimulus intensity; (4) a source for IMES was located in the contralateral caudal CMA rather than being located in the cingulate gyrus. Cerebral sensory processing of input from the muscle involved several sensory and motor areas and likely occurs in two parallel streams subserving higher order somatosensory processing as well as sensory-motor integration. The two streams might on one hand involve sensory discrimination via SI and SII and on the other hand integration of sensory feedback for further motor processing via MI, lateral PM area, and caudal CMA.

Orthographic and phonological processing of Chinese characters: an fMRI study

The present study used functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying the orthographic and phonological processing of Chinese characters. Four tasks were devised, including one homophone judgment and three physical judgments of characters, pseudo-characters, and Korean-like nonsense figures. While the left occipitotemporal region, left dorsal processing stream, and right middle frontal gyrus constitute a network for orthographic processing, the left premotor gyrus, left middle/inferior frontal gyrus, supplementary motor area (SMA), and the left temporoparietal region work in concert for phonological processing. The ventral part of the left inferior frontal cortex responds specifically to the character stimuli, suggesting a general lexical processing role for this region for linguistic material. The stronger activation of the dorsal visual stream by Chinese homophone judgment pinpoints a tight coupling between phonological representation of Chinese characters and corresponding orthographic percepts. The concomitant engagement of sets of regions for different levels of Chinese orthographic and phonological processing is consistent with the notion of distributed parallel processing.

ICA-based spatiotemporal approach for single-trial analysis of postmovement MEG beta synchronization⋆

The extraction of event-related oscillatory neuromagnetic activities from single-trial measurement is challenging due to the non-phase-locked nature and variability from trial to trial. The present study presents a method based on independent component analysis (ICA) and the use of a template-based correlation approach to extract Rolandic beta rhythm from magnetoencephalographic (MEG) measurements of right finger lifting. A single trial recording was decomposed into a set of coupled temporal independent components and corresponding spatial maps using ICA and the reactive beta frequency band for each trial identified using a two-spectrum comparison between the postmovement interval and a reference period. Task-related components survived dual criteria of high correlation with both the temporal and the spatial templates with an acceptance rate of about 80%. Phase and amplitude information for noise-free MEG beta activities were preserved not only for optimal calculation of beta rebound (event-related synchronization) but also for profound penetration into subtle dynamics across trials. Given the high signal-to-noise ratio (SNR) of this method, various methods of source estimation were used on reconstructed single-trial data and the source loci coherently anchored in the vicinity of the primary motor area. This method promises the possibility of a window into the intricate brain dynamics of motor control mechanisms and the cortical pathophysiology of movement disorder on a trial-by-trial basis.