Biomedical subjects

Guang H Yue

Publications and source records attributed to Guang H Yue.

At least 19 recordsLinked to original sources

PubMed2006

Effects of surface EMG rectification on power and coherence analyses: an EEG and MEG study.

Coherence between electromyography (EMG) and electroencephalography (EEG) or magnetoencephalography (MEG) is frequently examined to gain insights on neuromuscular binding. Commonly, EMG signals are rectified before coherence is computed. However, the appropriateness of EMG rectification in computing EMG-EEG/MEG coherence has never been validated. Since rectification is a non-linear operation and alters the EMG power spectrum, such a validation is important to ensure the accuracy of coherence calculation. In this study we experimentally investigated the effects of EMG rectification on EMG power spectra and its coherence with EEG/MEG signals. Subjects performed sustained isometric index finger abduction at approximately 5-10% maximal voluntary force (in both EEG-EMG and MEG-EMG experiments) and index finger tapping at approximately 2-4Hz (in EEG-EMG experiment only). Bipolar surface EMG data from the first dorsal interosseus (FDI) and EEG/MEG signals from the contralateral primary sensorimotor area (C3) were recorded simultaneously. Power spectra and coherence with the EEG/MEG were calculated before and after EMG rectification. The results show that rectification shifts EMG power to lower frequencies, possibly enhancing peaks of motor unit firing. Coherences with the EEG/MEG signals were not significantly changed by EMG rectification, indicating EMG rectification is overall an appropriate procedure in power and coherence analyses.

Adult↗

PubMed2006

Quantifying degeneration of white matter in normal aging using fractal dimension.

Although degeneration of brain white matter (WM) in aging is a well-recognized problem, its quantification has mainly relied on volumetric measurements, which lack detail in describing the degenerative adaptation. In this study, WM structural complexity was evaluated in healthy old and young adults by analyzing the three-dimensional fractal dimension (FD) of WM segmented from magnetic resonance images of brain. FDs detected in the old were significantly smaller than in the young subjects. Specifically, WM interior structure complexity degenerated in the left hemisphere in old men but in the right hemisphere in old women. Men showed more complex WM patterns than women. An asymmetrical (right-greater-than-left-hemisphere) complexity pattern was observed in the interior and general structures of WM, yet the surface complexity was symmetrical across WM structures of the two hemispheres. WM volumes were also measured, but no significant decline was found with aging. These results suggest that the deterioration of WM complexity is not uniformly distributed between the genders and across brain hemispheres.

Adolescent↗

PubMed2006

Management of fatigue in cancer patients.

Cancer-related fatigue (CRF) is either a symptom or a syndrome depending on criteria for diagnosis. CRF is present in 20% to 30% of long-term cancer survivors and 80% to 90% during treatment and at the end of life. Assessment requires determining the presence, severity, and interference with daily activities. Different descriptors for fatigue (eg, tiredness, lack of vigor) measure different patient experiences. Associated factors such as depression, pain, insomnia, dyspnea, anemia, and deconditioning worsen CRF and should be treated if present. Associated factors that contribute to the severity of fatigue differ depending on the stage of cancer. Pharmacologic interventions include recombinant erythropoietin, psychostimulants, corticosteroid, anti-inflammatory drugs other than steroids, and L-carnitine. Advances in the management of CRF will require an understanding of the underlying mechanism before target-specific therapies can be developed.

Animals↗

PubMed2006

Prolonged cognitive planning time, elevated cognitive effort, and relationship to coordination and motor control following stroke.

Understanding cortical function can provide accurately targeted interventions after stroke. Initially, stroke survivors had prolonged cognitive planning time and elevated cognitive effort, highly correlated with motor control impairments. Exploratory results suggest that neurorehabilitation, accurately targeted to dyscoordination, weakness, and dysfunctional task component execution, can improve cognitive processes controlling motor function.

Adaptation, Physiological↗

PubMed2005

Classification of large array surface myoelectric potentials from subjects with and without low back pain.

An algorithm was developed and tested for differentiating between the spatial distribution of large arrays of surface electromyographic (LASE) data from subjects with and without low back pain (LBP). The surface EMG data from 62 channels were collected from the low back of 161 healthy and 44 acute (less than 6-weeks) LBP subjects in three minimum stress postural positions including standing, 20 degrees of trunk flexion (at hip joint) and standing with arms extended forward holding a 1.36kg (3lb) weight in each hand. These data were statistically analyzed and the spatial distribution of the root mean square (RMS) values was used in a multivariate quadratic discriminant model to reclassify the healthy and acute LBP subjects. The most predictive results were obtained from the 'flexion' group of experiments and correctly reclassified 95.5% (42/44) of the acute LBP subjects and 99.4% (160/161) of the healthy subjects. The success rate of this reclassification based on surface distribution of myoelectric potentials was found to be better than the reported patient classifications based on a smaller set of electrode pairs using fewer subjects [Peach JP, McGill SM, Classification of low back pain with use of spectral electromyogram parameters. Spine 23(10):1998;1117-23; Roy SH, De Luca CJ, Emley M, Oddsson LI, Buijs RJ, Levins JA, Newcombe DS, Jabre JF. Classification of back muscle impairment based on the surface electromyographic signal. J Rehabil Res Dev 34(4):1997;405-14 [review]]. The results indicated the potential of the model for clinical patient classification.

Action Potentials↗

PubMed2005

Reductions in interhemispheric motor cortex functional connectivity after muscle fatigue.

Muscle fatigue has been known to differentially affect the activation level of the primary motor cortices (MIs) of the brain's two hemispheres. Whether this fatigue-related decoupling influence on the motor cortical signals extends beyond the motor action to the after-fatigue-task resting state is unknown. This question can be addressed by analyzing functional connectivity (FC) of low-frequency oscillations of resting-state functional MRI (fMRI) signals of the MIs. Low-frequency oscillations (<0.08 Hz) have been detected in many fMRI studies and appear to be synchronized between functionally related areas. These patterns of FC have been shown to differ between normal and various pathological states. The purpose of this study was to examine muscle fatigue-induced resting-state interhemispheric motor cortex FC changes in healthy subjects. We hypothesized that muscle fatigue would create a temporary "disrupted state" in the brain, and would decrease resting state interhemispheric motor cortical FC. Ten healthy subjects performed repetitive unilateral handgrip contractions that induced significant muscle fatigue, with resting state fMRI data collected before and after the task. After excluding two subjects due to gross head motion, interhemispheric motor cortex FC was assessed by cross-correlating the MI fMRI signal time courses. We found that the number of significant interhemispheric correlations in the MI fMRI signals decreased significantly after the performance of the fatigue task. These results suggest that resting state interhemispheric motor cortex FC may be used as an index of recovery from fatigue.

Adult↗

PubMed2005

Fatigue induces greater brain signal reduction during sustained than preparation phase of maximal voluntary contraction.

Animal studies have shown that there are cell populations only discharging phasically before a motor task and others only active tonically during holding phase of the task. How muscle fatigue influences these two types of cell populations, however, is unknown. Because the phasic neurons are only active briefly before the task but the tonic ones are active continuously throughout the task, we hypothesized that fatigue would have a less effect on cortical signals during the preparation phase (representing phasic discharge) than that during the sustained phase (representing tonic discharge). Eight participants performed 200 handgrip maximal voluntary contractions (MVCs) with simultaneous recordings of scalp electroencephalographic (EEG), handgrip force, and finger flexor surface electromyographic (EMG) signals. Power spectrograms of the EEG during the preparation and sustained phases were analyzed in each of the five 40-trial blocks, with data from the first block representing a condition of moderate fatigue and the last, severe fatigue. Movement-related cortical potential (MRCP) was derived by trigger-averaging 40 EEG epochs in each block. The power of all EEG frequencies did not alter significantly during the preparation phase but decreased significantly during the sustained phase of the contraction. The MRCP negative potential (NP) related to motor task preparation only showed minimal changes. These results suggest that MVC-induced fatigue has differential effects on cortical signals during motor task preparation compared to its execution and maintenance. The signals of the two phases may represent activities of the two cortical cell populations previously found by animal studies.

Adult↗

PubMed2005

A three-dimensional fractal analysis method for quantifying white matter structure in human brain.

Fractal dimension (FD) is increasingly used to quantify complexity of brain structures. Previous research that analyzed FD of human brain mainly focused on two-dimensional measurements. In this study, we developed a three-dimensional (3D) box-counting method to measure FD of human brain white matter (WM) interior structure, WM surface and WM general structure simultaneously. This method, which firstly incorporates a shape descriptor (3D skeleton) representing interior structure and combines the three features, provides a more comprehensive characterization of WM structure. WM FD of different brain segments was computed to test robustness of the method. FDs of fractal phantoms were computed to test the accuracy of the method. The consistency of the computed and theoretical FD values suggests that our method is accurate in measuring FDs of fractals. Statistical analysis was performed to examine sensitivity of the method in detecting WM structure differences in a number of young and old subjects. FD values of the WM skeleton and surface were significantly greater in young than old individuals, indicating more complex WM structures in young people. These results suggest that our method is accurate in quantifying three-dimensional brain WM structures and sensitive in detecting age-related degeneration of the structures.

Age Factors↗

PubMed2005

EMG and MMG of agonist and antagonist muscles as a function of age and joint angle.

The aim of this study was to determine the effect of elbow joint position on electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in young and old women. Surface EMG and MMG were recorded from the triceps and biceps brachii, and brachioradialis muscles during isometric elbow extensions in young and old women. The measurements were carried out at an optimal joint angle (A(o)), as well as at smaller (A(s) = A(o) - 30 degrees ) and larger (A(l) = A(o) + 30 degrees ) angles. The normalized to force EMG amplitude (RMS-EMG/F) was smaller in old women compared to young in all muscles. The RMS-EMG/F of the triceps brachii muscle was not affected by muscle length while that of the biceps brachii and brachioradialis muscles increased at shortest muscle length in both groups. The normalized to force MMG amplitude (RMS-MMG/F) was smaller in old than in young in the triceps brachii muscle only. There was an increase in RMS-MMG/F with triceps brachii and biceps brachii muscle shortening in both groups, and in the brachioradialis muscle -- in young only. Compared to young, older women exhibited a bigger force fluctuation during maximum voluntary contraction, but these did not contribute significantly to the RMS-MMG. Skinfold thickness accounted for the RMS-EMG/F and RMS-MMG/F differences seen between old and young women in the biceps brachii muscle only. It is concluded that, the EMG and MMG response to muscles length change in agonist and antagonist muscles is generally similar in old and young women but the optimal angle shifts toward a bigger value in older women.

Adult↗

PubMed2005

Fatigue induced by intermittent maximal voluntary contractions is associated with significant losses in muscle output but limited reductions in functional MRI-measured brain activation level.

The main purpose of this study was to characterize brain activation patterns during a fatigue task involving repetitive maximal voluntary contractions (MVC) of finger flexor muscles. Fourteen young, healthy human participants performed approximately 100 handgrip MVCs (each 2-s contraction was followed by a 1-s rest) while their brain was imaged by functional MRI (fMRI). The handgrip force and electromyograms (EMG) of the finger flexors declined progressively to about 40% of the initial values at the end of the fatigue task, suggesting that significant muscle fatigue had occurred. In contrast, the level of the fMRI signal in the primary (sensorimotor), secondary (supplementary motor), and association (prefrontal and cingulate) motor-function cortices did not change significantly throughout the fatigue task (although the signal of the primary sensorimotor cortex showed a clear trend of decline). The fMRI data from the task of intermittent handgrip MVCs differed dramatically from those obtained in a 2-min sustained handgrip MVC published in a recent report, in which the overall fMRI-measured brain activation level was substantially lower and followed an increase-then-decrease pattern compared to the linear decreases in force and EMG. These results support the notion that the motor cortical centers control the tasks of repetitive and continuous muscle contractions differently and that there is a decoupling in the signal changes of the brain and muscles during muscle fatigue processes induced by maximal voluntary contractions.

Electromyography↗

PubMed2005

Selective atrophy of left hemisphere and frontal lobe of the brain in old men.

In this study, volumes of the whole brain, hemispheres, and frontal lobes of young and elderly adults were quantified by an automated method. Effects of age, sex, and side on absolute and relative volumes of the brain structures were evaluated. Compared with the young group, elderly participants showed a 15% volume loss in the whole brain and hemispheres, and a 22% volume loss in the frontal lobes. The relative volume of the left hemisphere in the elderly group decreased more than that of the right hemisphere. Elderly men showed significantly greater left hemisphere and left frontal lobe volume losses than did elderly women, indicating that the larger left hemisphere relative volume reduction is largely contributed to by selective atrophy of the left frontal lobe volume in elderly men. These results may reflect age- and sex-related functional deterioration in the left brain.

Adult↗

PubMed2004

Distinct brain activation patterns for human maximal voluntary eccentric and concentric muscle actions.

Eccentric muscle contractions generate greater force at a lower level of activation and subject muscles to more severe damage than do concentric actions. A recent investigation has revealed that electroencephalogram (EEG)-derived movement-related cortical potential (MRCP) is greater and occurs earlier for controlling human eccentric than concentric submaximal muscle contractions. However, whether the central nervous system (CNS) control signals for high-intensity or maximal-effort eccentric movements differ from those for concentric actions is unknown. The purpose of this study was to determine whether the MRCP signals differ between the two types of maximal-effort contractions. Eight volunteers performed 40 maximal voluntary eccentric and 40 maximal voluntary concentric elbow flexor contractions on a Kin-Com isokinetic dynamometer. Scalp EEG signals (62 channels) were measured along with force, joint angle, and electromyographic (EMG) signals of the performing muscles. MRCP-based two-dimensional brain maps were created to illustrate spatial and temporal distributions of the MRCP signals. Although the level of elbow flexor muscle activity was lower during eccentric than concentric movements, MRCP-indicated cortical activation was greater both in amplitude and area dimension for the eccentric task. Detailed comparisons of individual electrode signals suggested that eccentric movements needed a significantly longer time for early preparation and a significantly greater magnitude of cortical activity for later movement execution. The extra preparation time and higher amplitude of activation may reflect CNS activities that account for the higher risk of injury, higher degree of movement difficulty, and unique motor unit activation pattern associated with maximal-level eccentric muscle actions.

Adult↗

PubMed2004

Reproducibility of fMRI at 1.5 T in a strictly controlled motor task.

Reproducibility of functional MRI (fMRI) data has been controversial. This issue was examined in this study by evaluating a strictly controlled voluntary force-matching handgrip task. Handgrip force, electromyogram (EMG), and fMRI data of brain activity were simultaneously recorded during the task performance. The task was repeated three times in each of the two experimental sessions. While force remained unchanged and EMG showed little variation across trials and sessions, the results revealed that fMRI-measured brain signals varied significantly among individual trials. However, the averaged fMRI signals over the three trials did not show significant difference between the two sessions. Our data suggest that fMRI is better at defining brain activation qualitatively than quantitatively, i.e., the locations of the activation areas could be reproduced quite reliably while their sizes fluctuated substantially.

Adult↗

PubMed2004

Altered central nervous system signal during motor performance in chronic fatigue syndrome.

OBJECTIVE: The purpose of this study was to determine whether brain activity of chronic fatigue syndrome (CFS) patients during voluntary motor actions differs from that of healthy individuals. METHODS: Eight CFS patients and 8 age- and gender-matched healthy volunteers performed isometric handgrip contractions at 50% maximal voluntary contraction level. They first performed 50 contractions with a 10 s rest between adjacent trials--'Non-Fatigue' (NFT) task. Subsequently, the same number of contractions was performed with only a 5 s rest between trials--'Fatigue' (FT) task. Fifty-eight channels of surface EEG were recorded simultaneously from the scalp. Spectrum analysis was performed to estimate power of EEG frequency in different tasks. Motor activity-related cortical potential (MRCP) was derived by triggered averaging of EEG signals associated with the muscle contractions. RESULTS: Major findings include: (i) Motor performance of the CFS patients was poorer than the controls. (ii) Relative power of EEG theta frequency band (4-8 Hz) during performing the NFT and FT tasks was significantly greater in the CFS than control group (P < 0.05). (iii) The amplitude of MRCP negative potential (NP) for the combined NFT and FT tasks was higher in the CFS than control group (P < 0.05) (iv) Within the CFS group, the NP was greater for the FT than NFT task (P<0.01), whereas no such difference between the two tasks was found in the control group. CONCLUSIONS: These results clearly show that CFS involves altered central nervous system signals in controlling voluntary muscle activities, especially when the activities induce fatigue. SIGNIFICANCE: Physical activity-induced EEG signal changes may serve as physiological markers for more objective diagnosis of CFS.

Adult↗

PubMed2004

Automated human frontal lobe identification in MR images based on fuzzy-logic encoded expert anatomic knowledge.

Identification of human brain structures in MR images comprises an area of increasing interest, which also presents numerous methodological challenges. Here we describe a new knowledge-based automated method designed to identify several major brain sulci and then to define the frontal lobes by using the identified sulci as landmarks. To identify brain sulci, sulcal images were generated by morphologic operations and then separated into different components based on connectivity analysis. Subsequently, the individual anatomic features were evaluated by using fuzzy membership functions. The crisp decisions, i.e., the identification of sulci, were made by taking the maximum of the summation of all the membership functions. The identification was designed in a hierarchical order. The longitudinal fissure was extracted first. The left and right central sulci were then identified based on the left and right hemispheres. Next, the lateral sulci were identified based on the central sulci and hemispheres. Finally, the left and right frontal lobes were defined from the two hemispheres. The method was evaluated by visual inspection, comparison with manual segmentation, and comparison with manually volumetric results in references. The average Jaccard similarities of left and right frontal lobes between the automated and manual segmentation were 0.89 and 0.91, respectively. The average Kappa indices of left and right frontal lobes between the automated and manual segmentation were 0.94 and 0.95, respectively. These results show relatively high accuracy of using this novel method for human frontal lobe identification and segmentation.

Algorithms↗

PubMed2004

From mental power to muscle power--gaining strength by using the mind.

The purposes of this project were to determine mental training-induced strength gains (without performing physical exercises) in the little finger abductor as well as in the elbow flexor muscles, which are frequently used during daily living, and to quantify cortical signals that mediate maximal voluntary contractions (MVCs) of the two muscle groups. Thirty young, healthy volunteers participated in the study. The first group (N = 8) was trained to perform "mental contractions" of little finger abduction (ABD); the second group (N = 8) performed mental contractions of elbow (ELB) flexion; and the third group (N = 8) was not trained but participated in all measurements and served as a control group. Finally, six volunteers performed training of physical maximal finger abductions. Training lasted for 12 weeks (15 min per day, 5 days per week). At the end of training, we found that the ABD group had increased their finger abduction strength by 35% (P < 0.005) and the ELB group augmented their elbow flexion strength by 13.5% (P < 0.001). The physical training group increased the finger abduction strength by 53% (P < 0.01). The control group showed no significant changes in strength for either finger abduction or elbow flexion tasks. The improvement in muscle strength for trained groups was accompanied by significant increases in electroencephalogram-derived cortical potential, a measure previously shown to be directly related to control of voluntary muscle contractions. We conclude that the mental training employed by this study enhances the cortical output signal, which drives the muscles to a higher activation level and increases strength.

Adult↗

PubMed2003

Human brain activation during sustained and intermittent submaximal fatigue muscle contractions: an FMRI study.

During prolonged submaximal muscle contractions, electromyographic (EMG) signals typically increase as a result of increasing motor unit activities to compensate for fatigue-induced force loss in the muscle. It is thought that cortical signals driving the muscle to higher activation levels also increases, but this has never been experimentally demonstrated. The purpose of this study was to quantify brain activation during submaximal fatigue muscle contractions using functional magnetic resonance imaging (fMRI). Twelve volunteers performed a sustained handgrip contraction for 225 s and 320 intermittent handgrip contractions ( approximately 960 s) at 30% maximal level while their brain was imaged. For the sustained contraction, EMG signals of the finger flexor muscles increased linearly while the target force was maintained. The fMRI-measured cortical activities in the contralateral sensorimotor cortex increased sharply during the first 150 s, then plateaued during the last 75 s. For the intermittent contractions, the EMG signals increased during the first 660 s and then began to decline, while the handgrip force also showed a sign of decrease despite maximal effort to maintain the force. The fMRI signal of the contralateral sensorimotor area showed a linear rise for most part of the task and plateaued at the end. For both the tasks, the fMRI signals in the ipsilateral sensorimotor cortex, prefrontal cortex, cingulate gyrus, supplementary motor area, and cerebellum exhibited steady increases. These results showed that the brain increased its output to reinforce the muscle for the continuation of the performance and possibly to process additional sensory information.

Adult↗

PubMed2003

Fractal dimension in human cerebellum measured by magnetic resonance imaging.

Fractal dimension has been used to quantify the structures of a wide range of objects in biology and medicine. We measured fractal dimension of human cerebellum (CB) in magnetic resonance images of 24 healthy young subjects (12 men and 12 women). CB images were resampled to a series of image sets with different 3D resolutions. At each resolution, the skeleton of the CB white matter was obtained and the number of pixels belonging to the skeleton was determined. Fractal dimension of the CB skeleton was calculated using the box-counting method. The results indicated that the CB skeleton is a highly fractal structure, with a fractal dimension of 2.57 +/- 0.01. No significant difference in the CB fractal dimension was observed between men and women.

Adolescent↗