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Biomedical subjects

Kewei Chen

Publications and source records attributed to Kewei Chen.

At least 19 recordsLinked to original sources
PubMed2006

Relationships between plasma leptin concentrations and human brain structure: a voxel-based morphometric study.

We have previously demonstrated that obese people have reduced grey matter (GM) in several brain areas, including regions implicated in the regulation of taste (i.e., inferior frontal operculum and postcentral gyrus), reward (i.e., putamen), and behavioural processing (i.e., middle frontal gyrus), compared with their lean counterparts. It is well established that the brain may serve as a direct target for adiposity signals, one of the most important being leptin. We investigated the relationships between fasting plasma leptin concentrations and brain tissue composition in a group of 32 young adult Caucasians (12M/20F, age 32+/-1 years, body fat 29+/-1%, mean+/-S.E.) with normal glucose tolerance by using voxel-based morphometry of magnetic resonance imaging scans. Fasting plasma leptin concentrations were positively correlated with GM volumes of the left cerebellum and left inferior temporal gyrus and negatively associated with GM volumes of the left inferior frontal operculum, left postcentral gyrus, and right putamen (P<0.001, uncorrected for multiple comparisons) after adjustment for sex, percent body fat, age, fasting plasma insulin concentrations (i.e., the major determinants of plasma leptin), and global GM volume (thus allowing for an assessment of regional effects only). This study showed an independent, negative correlation between fasting plasma leptin concentrations, which are increased in obesity, and the volumes of GM in brain areas where obese people have reduced GM compared to their lean counterparts. These relationships may explain some of the abnormalities in brain morphology recently found to be associated with excess body fatness.

Adolescent↗
PubMed2006

Regional network of magnetic resonance imaging gray matter volume in healthy aging.

Healthy aging has been associated with brain volume reductions preferentially affecting the frontal cortex, but also involving other regions. We used a network model of regional covariance, the Scaled Subprofile Model, with magnetic resonance imaging voxel-based morphometry to identify the regional distribution of gray matter associated with aging in 26 healthy adults, 22-77 years old. Scaled Subprofile Model analysis identified a pattern that was highly correlated with age (R2=0.66, P<or=0.0001). Older age was associated with less gray matter in the bilateral frontal, temporal,thalamic, and right cerebellar regions. Gender differences suggested more advanced brain aging in the men. In this healthy adult sample, aging was associated with a regional pattern of gray matter atrophy most prominently involving the frontal and temporal cortices. Scaled Subprofile Model network analysis may aid in the detection and tracking of brain aging and in the evaluation of putative antiaging therapies.

Adult↗
PubMed2006

Arithmetic processing in the brain shaped by cultures.

The universal use of Arabic numbers in mathematics raises a question whether these digits are processed the same way in people speaking various languages, such as Chinese and English, which reflect differences in Eastern and Western cultures. Using functional MRI, we demonstrated a differential cortical representation of numbers between native Chinese and English speakers. Contrasting to native English speakers, who largely employ a language process that relies on the left perisylvian cortices for mental calculation such as a simple addition task, native Chinese speakers, instead, engage a visuo-premotor association network for the same task. Whereas in both groups the inferior parietal cortex was activated by a task for numerical quantity comparison, functional MRI connectivity analyses revealed a functional distinction between Chinese and English groups among the brain networks involved in the task. Our results further indicate that the different biological encoding of numbers may be shaped by visual reading experience during language acquisition and other cultural factors such as mathematics learning strategies and education systems, which cannot be explained completely by the differences in languages per se.

Adult↗
PubMed2006

Network analysis of single-subject fMRI during a finger opposition task.

The analysis of functional magnetic resonance imaging (fMRI) data has typically relied on univariate methods to identify areas of brain activity related to cognitive and behavioral task performance. We investigated the ability of multivariate network analysis using a modified form of principal component analysis, the Scaled Subprofile Model (SSM), applied to single-subject fMRI data to identify patterns of interactions among brain regions over time during an anatomically well-characterized simple motor task. We hypothesized that each subject would exhibit correlated patterns of brain activation in several regions known to participate in the regulation of movement including the contralateral motor cortex and the ipsilateral cerebellum. EPI BOLD images were acquired in six healthy participants as they performed a visually and auditorally paced finger opposition task. SSM analysis was applied to the fMR time series on a single-subject basis. Linear combinations of the major principal components that predicted the expected hemodynamic response to the order of experimental conditions were identified for each participant. These combinations of SSM patterns were highly associated with the expected hemodynamic response, an indicator of local neuronal activity, in each participant (0.84 </= R(2) </= 0.97, all P's < 0.0001). As predicted, the combined pattern in each subject was characterized most prominently by relatively increased activations in contralateral sensorimotor cortex and ipsilateral cerebellum. Additionally, all subjects showed areas of relatively decreased activation in the ipsilateral sensorimotor cortex and contralateral cerebellum. The application of network analysis methods, such as SSM, to single-subject fMRI data can identify patterns of task-specific, functionally interacting brain areas in individual subjects. This approach may help identify individual differences in the task-related functional connectivity, track changes in task-related patterns of activity within or between fMRI sessions, and provide a method to identify individual differences in response to treatment.

Acoustic Stimulation↗
PubMed2006

Brain abnormalities in human obesity: a voxel-based morphometric study.

Obesity is accompanied by damage to several tissues. Overweight is a risk factor for Alzheimer's disease and other neurodegenerative disorders. Whether structural abnormalities associated with excess body fat may also occur in the brain is unknown. We sought to determine to what extent excess body fat is associated with regional alterations in brain structure using voxel-based morphometry (VBM), a whole-brain unbiased technique based upon high-definition 3D magnetic resonance imaging (MRI) scans normalized into a common standard space and allowing for an objective assessment of neuroanatomical differences throughout the brain. We studied 24 obese (11 male, 13 female; age: 32 +/- 8 years; body mass index [BMI]: 39.4 +/- 4.7 kg/m2) and 36 lean (25 male, 11 female; mean age: 33 +/- 9 years; BMI: 22.7 +/- 2.2 kg/m2) non-diabetic Caucasians. In comparison with the group of lean subjects, the group of obese individuals had significantly lower gray matter density in the post-central gyrus, frontal operculum, putamen, and middle frontal gyrus (P < 0.01 after adjustment for sex, age, handedness, global tissue density, and multiple comparisons). BMI was negatively associated with GM density of the left post-central gyrus in obese but not lean subjects. This study identified structural brain differences in human obesity in several brain areas previously involved in the regulation of taste, reward, and behavioral control. These alterations may either precede obesity, representing a neural marker of increased propensity to gaining weight, or occur as a consequence of obesity, indicating that also the brain is affected by increased adiposity.

Adult↗
PubMed2006

Less activation of the left dorsolateral prefrontal cortex in response to a meal: a feature of obesity.

BACKGROUND: In an exploratory positron emission tomography study of postprandial regional cerebral blood flow, which is a marker of neuronal activity, obese men differed from lean men in several brain regions, including the prefrontal cortex. The subjects received a meal proportional to their body size; therefore, the meal volume was different for each person. OBJECTIVE: We investigated whether differences in the brain responses of obese and lean men to a meal represent satiety or feelings of gastric distension. DESIGN: We studied 9 lean (x +/- SD body fat: 15 +/- 5%; age: 33 +/- 10 y) and 9 obese (body fat: 31 +/- 4%; age: 32 +/- 10 y) men given a fixed amount (400 mL) of a liquid meal. We compared their results with those in 11 lean (body fat: 16 +/- 5%; age: 35 +/- 8 y) and 11 obese (body fat: 33 +/- 5%; age: 28 +/- 5 y) previously studied men given a meal proportional to their body size. We performed analyses by using a two-level, random-effects approach in the STATISTICAL PARAMETRIC MAPPING software package and a significance level of P < or = 0.001, uncorrected for multiple comparisons. RESULTS: Compared with lean men, obese men had consistently less postprandial activation in the left dorsolateral prefrontal cortex, irrespective of meal size. CONCLUSION: Because the dorsolateral prefrontal cortex has been implicated in the inhibition of inappropriate behavior, satiety, and meal termination, differential responses of neuronal activity to food intake in this area may contribute to a propensity for obesity or to the difficulty in losing weight experienced by obese men.

Adult↗
PubMed2006

A preliminary fluorodeoxyglucose positron emission tomography study in healthy adults reporting dream-enactment behavior.

STUDY OBJECTIVES: To test the hypothesis that healthy adults reporting dream-enactment behavior (DEB+) have reduced cerebral metabolic rate for glucose (CMRgl) in regions preferentially affected in patients with dementia with Lewy bodies (DLB). DESIGN: Automated brain-mapping algorithms were used to compare regional fluorodeoxyglucose (FDG) positron emission tomography (PET) measurements from previously evaluated DEB cases and controls. SETTING: Tertiary-care academic medical centers. PARTICIPANTS: Seventeen cognitively normal patients with DEB+ and 17 control subjects (DEB-) who were individually matched for age (59 +/- 11 years), education level (16 +/- 4 years), sex (67% women), body mass index (26 +/- 4.8 kg/m2), first-degree relative with dementia (85%), and proportion of apolipoprotein E (APOE) e4 carriers (13 e4 carriers, 4 noncarriers). INTERVENTIONS: FDG-PET. MEASUREMENTS AND RESULTS: DEB was associated with significantly lower CMRgl in several brain regions known to be preferentially affected in both DLB and Alzheimer disease (parietal, temporal, and posterior cingulate cortexes) and in several other regions, including the anterior cingulate cortex (p < .001, uncorrected for multiple comparisons). The DEB-associated CMRgl reductions were significantly greater in the APOE e4 noncarriers than in the carriers. CONCLUSIONS: These preliminary findings suggest that cognitively normal persons with DEB have reduced CMRgl in brain regions known to be metabolically affected by DLB, supporting further study of DEB as a possible risk factor for the development of DLB.

Adult↗
PubMed2006

[Effects of high temperature on laboratory Trichogramma ostriniae population].

In this paper, the life tables of laboratory Trichogramma ostriniae population reared on Corcyra cephalonica eggs at 26 degrees C, 29 degrees C, 32 degrees C and 35 degrees C were constructed, and the effects of high temperature on the development and reproduction of this population were analyzed. The results showed that high temperature (32 degrees C to approximately 35 degreees C) greatly affected the development of T. ostriniae. The egg-larva survival rate was 94.2% at 26 degrees C and 88.6% at 29 degrees C, and decreased to 80.1% at 32 degrees C and 53.2% at 35 degrees C. The pupa survival rate also descended with the raise of temperature. The egg load and the body- and egg sizes of newly emerged female wasps were negatively responded to temperature. 12 h-old adult female had an egg load of 37.9, which was decreased with the raise of temperature, and about 29.6, 21.6 and 13.7 mature eggs were found at 29 degrees C, 32 degrees C and 35 degrees C, respectively. All females could complete their normal copulation and oviposition at 26 degrees C and 29 degrees C, but about 6.7% and 60% females could not reproduce at 32 degrees C and 35 degrees C, respectively.

Animals↗
PubMed2006

[Control effect of natural enemies on Plutella xylostella under ecological restoration condition].

A field study on the life table of diamondback moth (DBM) Plutella xylostella showed that the population increase index of DBM in chemical control plot was 52.52, while that of four continuous generations of DBM in ecological restoration plot was 16. 9, 7.16, 3.71 and 4.02, respectively, indicating that the control effect of natural enemies on target pest was greatly improved. The main factor affecting the first and forth generations of DBM was the parasitism of Cotesia plutella, while those affecting the second and third generations of DBM were the predator of the 4'h instar larva and the parasitism of Trichogramma, with the corresponding exclusive index of population control (EIPC) being 1.39, 1.54, 1.56 and 1.74, respectively. There was an obvious time lag effect of natural enemies on their target pest, and thus, to protect and multiply the population of natural enemies in the field should be the key point of fully exerting the potential of natural enemies in their pest control.

Animals↗
PubMed2005

Correlations between apolipoprotein E epsilon4 gene dose and brain-imaging measurements of regional hypometabolism.

Patients with Alzheimer's disease (AD) have abnormally low positron emission tomography (PET) measurements of the cerebral metabolic rate for glucose (CMRgl) in regions of the precuneus and the posterior cingulate, parietotemporal, and frontal cortex. Apolipoprotein E (APOE) epsilon4 gene dose (i.e., the number of epsilon4 alleles in a person's APOE genotype) is associated with a higher risk of AD and a younger age at dementia onset. We previously found that cognitively normal late-middle-aged APOE epsilon4 carriers have abnormally low CMRgl in the same brain regions as patients with probable Alzheimer's dementia. In a PET study of 160 cognitively normal subjects 47-68 years of age, including 36 epsilon4 homozygotes, 46 heterozygotes, and 78 epsilon4 noncarriers who were individually matched for their gender, age, and educational level, we now find that epsilon4 gene dose is correlated with lower CMRgl in each of these brain regions. This study raises the possibility of using PET as a quantitative presymptomatic endophenotype to help evaluate the individual and aggregate effects of putative genetic and nongenetic modifiers of AD risk.

Age of Onset↗
PubMed2005

Cerebral asymmetry in children when reading Chinese characters.

This study examined cerebral asymmetry, especially in the hierarchical visual system, when reading Chinese characters. Twelve right-handed Chinese children (mean age = 11.6 years) were scanned while performing semantic and phonological tasks. Strong leftward asymmetry was found in the left inferior frontal cortex (BA44/45/47), the parietal lobule (BA40), and the cingulate cortex (BA24/32). In the visual system, we found significant left-hemispheric dominance in the fusiform cortex (BA19/37), but no asymmetry was found in the primary visual cortex (BA17/18). The differential results for the primary visual cortex versus high-order visual cortex (i.e., the fusiform cortex) are discussed in terms of the contribution of the logographic nature of Chinese characters to the asymmetry pattern in the hierarchical visual system.

Brain Mapping↗
PubMed2005

Sensory experience of food and obesity: a positron emission tomography study of the brain regions affected by tasting a liquid meal after a prolonged fast.

The sensory experience of food is a primary reinforcer of eating and overeating plays a major role in the development of human obesity. However, whether the sensory experience of a forthcoming meal and the associated physiological phenomena (cephalic phase response, expectation of reward), which prepare the organism for the ingestion of food play a role in the regulation of energy intake and contribute to the development of obesity remains largely unresolved. We used positron emission tomography (PET) and 15O-water to measure changes in regional cerebral blood flow (rCBF) and to assess the brain's response to the oral administration of 2 ml of a liquid meal (Ensure Plus, 1.5 kcal/ml) after a 36-h fast and shortly before consuming the same meal. Twenty-one obese (BMI > 35 kg/m2, 10M/11F, age 28 +/- 6 years, body fat 40 +/- 6%) and 20 lean individuals (BMI < 25 kg/m2, 10M/10F, age 33 +/- 9 years, body fat 21 +/- 7%) were studied. Compared to lean individuals, obese individuals had higher fasting plasma glucose (83.3 +/- 6.2 vs. 75.5 +/- 9.6 mg/dl; P = 0.0003) and insulin concentrations (6.1 +/- 3.5 vs. 2.5 +/- 1.7 microU/ml; P < 0.0001) and were characterized by a higher score of dietary disinhibition (i.e., the susceptibility of eating behavior to emotional factors and sensory cues, 5.7 +/- 3.6 vs. 3.5 +/- 2.7; P = 0.01) assessed by the Three Factor Eating Questionnaire. In response to the sensory experience of food, differences in rCBF were observed in several regions of the brain, including greater increases in the middle-dorsal insula and midbrain, and greater decreases in the posterior cingulate, temporal, and orbitofrontal cortices in obese compared to lean individuals (P < 0.05, after small volume correction). In a multiple regression model, percentage of body fat (P = 0.04), glycemia (P = 0.01), and disinhibition (P = 0.07) were independent correlates of the neural response to the sensory experience of the meal in the middle-dorsal insular cortex (R2 = 0.45). We conclude that obesity is associated with an abnormal brain response to the sensory aspects of a liquid meal after a prolonged fast especially in areas of the primary gustatory cortex. This is only partially explained by the elevated glycemia and high level of disinhibition which characterize individuals with increased adiposity. These results provide a new perspective on the understanding of the neuroanatomical correlates of abnormal eating behavior and their relationship with obesity in humans.

Adipose Tissue↗
PubMed2004

An automated algorithm for the computation of brain volume change from sequential MRIs using an iterative principal component analysis and its evaluation for the assessment of whole-brain atrophy rates in patients with probable Alzheimer's disease.

This article introduces an automated method for the computation of changes in brain volume from sequential magnetic resonance images (MRIs) using an iterative principal component analysis (IPCA) and demonstrates its ability to characterize whole-brain atrophy rates in patients with Alzheimer's disease (AD). The IPCA considers the voxel intensity pairs from coregistered MRIs and identifies those pairs a sufficiently large distance away from the iteratively determined PCA major axis. Analyses of simulated and real MRI data support the underlying assumption of a linear relationship in paired voxel intensities, identify an outlier distance threshold that optimizes the trade-off between sensitivity and specificity in the detection of small volume changes while accounting for global intensity changes, and demonstrate an ability to detect changes as small as 0.04% of brain volume without confounding effects of between-scan shifts in voxel intensity. In eight patients with probable AD and eight age-matched normal control subjects, the IPCA was comparable to the established but partly manual digital subtraction (DS) method in characterizing annual rates of whole-brain atrophy: resulting rates were correlated (Spearman rank correlation = 0.94, P < 0.0005) and comparable in distinguishing probable AD from normal aging (IPCA-detected atrophy rates: 2.17 +/- 0.52% per year in the patients vs. 0.41 +/- 0.22% per year in the controls [Wilcoxon-Mann-Whitney test P = 7.8 x 10(-4)]; DS-detected atrophy rates: 3.51 +/- 1.31% per year in the patients vs. 0.48 +/- 0.29% per year in the controls [P = 7.8 x 10(-4)]). The IPCA could be used in tracking the progression of AD, evaluating the disease-modifying effects of putative treatments, and investigating the course of other normal and pathological changes in brain morphology.

Aged↗
PubMed2004

[Interspecific competition between Trichogramma confusum and T. pretiosum on Corcyra cephaloica factitious eggs].

By means of single and mixed inoculation, this paper studied the interspecific competition between T. confusum and T. pretiosum on the factitious eggs of Corcyra cephaloica under different parasitoid densities, host densities and inoculated spaces. The results showed that for both singly and mixed inoculated groups, the parasitism increased with parasitoid density but decreased with host density, whereas the percentage of female progeny dropped with parasitoid density but enhanced with host density. No significant effect was observed on adult emergence for all parasitoid and host density treatments. In mixed inoculated group, the proportion of T. pretiosum in the progeny decreased with parasitoid density but increased with host density, and was more than 50% in all treatments, indicating that T. pretiosum had a stronger competitive ability than T. confusum. In the spaces ranging from 4 cm3 to 102 cm3, the parasitism decreased gradually in both singly and mixed inoculated groups. The percentage of female progeny and adult emergence had no significant difference among different inoculated spaces. In mixed inoculated group, the proportion of T. pretiosum in the progeny was more than 50% in all treatments except space 102 cm3, but decreased with space, which suggested that T. confusum could improve their competitive ability through increasing their search areas and looking for more hosts.

Animals↗
PubMed2003

Functional brain abnormalities in young adults at genetic risk for late-onset Alzheimer's dementia.

Fluorodeoxyglucose positron emission tomography (PET) studies have found that patients with Alzheimer's dementia (AD) have abnormally low rates of cerebral glucose metabolism in posterior cingulate, parietal, temporal, and prefrontal cortex. We previously found that cognitively normal, late-middle-aged carriers of the apolipoprotein E epsilon4 allele, a common susceptibility gene for late-onset Alzheimer's dementia, have abnormally low rates of glucose metabolism in the same brain regions as patients with probable AD. We now consider whether epsilon4 carriers have these regional brain abnormalities as relatively young adults. Apolipoprotein E genotypes were established in normal volunteers 20-39 years of age. Clinical ratings, neuropsychological tests, magnetic resonance imaging, and PET were performed in 12 epsilon4 heterozygotes, all with the epsilon3/epsilon4 genotype, and 15 noncarriers of the epsilon4 allele, 12 of whom were individually matched for sex, age, and educational level. An automated algorithm was used to generate an aggregate surface-projection map that compared regional PET measurements in the two groups. The young adult epsilon4 carriers and noncarriers did not differ significantly in their sex, age, educational level, clinical ratings, or neuropsychological test scores. Like previously studied patients with probable AD and late-middle-aged epsilon4 carriers, the young epsilon4 carriers had abnormally low rates of glucose metabolism bilaterally in the posterior cingulate, parietal, temporal, and prefrontal cortex. Carriers of a common Alzheimer's susceptibility gene have functional brain abnormalities in young adulthood, several decades before the possible onset of dementia.

Adult↗
PubMed2003

Clustering huge data sets for parametric PET imaging.

A new preprocessing clustering technique for quantification of kinetic PET data is presented. A two-stage clustering process, which combines a precluster and a classic hierarchical cluster analysis, provides data which are clustered according to a distance measure between time activity curves (TACs). The resulting clustered mean TACs can be used directly for estimation of kinetic parameters at the cluster level, or to span a vector space that is used for subsequent estimation of voxel level kinetics. The introduction of preclustering significantly reduces the overall time for clustering of multiframe kinetic data. The efficiency and superiority of the preclustering scheme combined with thresholding is validated by comparison of the results for clustering both with and without preclustering for FDG-PET brain data of 13 healthy subjects.

Algorithms↗
PubMed2003

Improving tissue segmentation of human brain MRI through preprocessing by the Gegenbauer reconstruction method.

The Gegenbauer image reconstruction method, previously shown to improve the quality of magnetic resonance images, is utilized in this study as a segmentation preprocessing step. It is demonstrated that, for all simulated and real magnetic resonance images used in this study, the Gegenbauer reconstruction method improves the accuracy of segmentation. Although it is more desirable to use the k-space data for the Gegenbauer reconstruction method, only information acquired from MR images is necessary for the reconstruction, making the procedure completely self-contained and viable for all human brain segmentation algorithms.

Algorithms↗