Biomedical subjects

Kewei Chen

Publications and source records attributed to Kewei Chen.

23 records · Page 2Linked to original sources

PubMed2002

Tasting a liquid meal after a prolonged fast is associated with preferential activation of the left hemisphere.

We used positron emission tomographic scanning of the brain and measures of regional cerebral blood flow to investigate the response of 44 right-handed people to the oral administration of 2 ml of a liquid formula meal after a 36 h fast (and shortly before the administration of a satiating amount of the same meal). Several areas of the left hemisphere were significantly more activated than the contralateral, including the frontal operculum, ventral insula, and piriform cortex. In contrast with reports of right-hemisphere dominance in chemosensory perception in non-hungry individuals, our study reveals a preferential activation of the left hemisphere when people who are very hungry are briefly exposed to the chemical and physical properties of a liquid meal. This raises the possibility that the physiological context in which perception takes place (i.e. extreme vs moderate vs no hunger) may importantly affect the brain representation of chemosensory stimuli.

Adult↗

PubMed2002

Sex differences in the human brain's response to hunger and satiation.

BACKGROUND: Sex differences in eating behavior are well documented, but it is not known whether these differences have neuroanatomical correlates. Recent neuroimaging studies have provided functional maps of the human cerebral areas activated in response to hunger and satiation. OBJECTIVE: The objective of this study was to assess whether the brain's response to a meal is sex-specific. DESIGN: Using positron emission tomography, we measured regional cerebral blood flow, a marker of neuronal activity, to investigate the functional neuroanatomy of hunger (36-h fast) and satiation (in response to a liquid meal) in 22 women and 22 men. RESULTS: We observed extensive similarities, as well as some differences, between the sexes. In response to hunger, the men tended to have greater activation in the frontotemporal and paralimbic areas than did the women (P < 0.005). In response to satiation, the women tended to have greater activation in the occipital and parietal sensory association areas and in the dorsolateral prefrontal cortex than did the men (P < 0.005); in contrast, the men tended to have greater activation in the ventromedial prefrontal cortex than did the women (P < 0.005). CONCLUSIONS: Despite extensive similarities in the brain responses to hunger and satiation between the men and women, our study showed sex-specific brain responses to a meal that indicate possible differences between men and women in the cognitive and emotional processing of hunger and satiation. This study provides a foundation for investigating the brain regions and cognitive processes that distinguish normal and abnormal eating behavior in men and women.

Adult↗

PubMed2002

Longitudinal PET Evaluation of Cerebral Metabolic Decline in Dementia: A Potential Outcome Measure in Alzheimer's Disease Treatment Studies.

OBJECTIVE: It is well established that regional cerebral metabolic rates for glucose assessed by [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) in patients with Alzheimer's disease in the mental resting state (eyes and ears covered) provide a sensitive, in vivo metabolic index of Alzheimer's disease dementia. Few studies, however, have evaluated longitudinal declines in regional cerebral glucose metabolism in patients with dementia caused by Alzheimer's disease. In addition, the available studies have not used recently developed brain mapping algorithms to characterize the progression of Alzheimer's disease throughout the brain, and none considered the statistical power of regional cerebral glucose metabolism in testing the ability of treatments to attenuate the progression of dementia. METHOD: The authors used FDG PET and a brain mapping algorithm to investigate cross-sectional reductions in regional cerebral glucose metabolism, longitudinal decline in regional cerebral glucose metabolism after a 1-year follow-up, and the power of this method to evaluate treatments for Alzheimer's disease in patients with mild to moderate dementia. PET scans were initially acquired in 14 patients with Alzheimer's disease and 34 healthy comparison subjects of similar age and sex. Repeat scans were obtained in the patients 1 year later. Power analyses for voxels showing maximal decline over the 1-year period in regional cerebral glucose metabolism (mg/100 g per minute) were computed to estimate the sample sizes needed to detect a significant treatment response in a 1-year, double-blind, placebo-controlled treatment study. RESULTS: The patients with Alzheimer's disease had significantly lower glucose metabolism than healthy comparison subjects in parietal, temporal, occipital, frontal, and posterior cingulate cortices. One year later, the patients with Alzheimer's disease had significant declines in glucose metabolism in parietal, temporal, frontal, and posterior cingulate cortices. Using maximal glucose metabolism reductions in the left frontal cortex, we estimated that as few as 36 patients per group would be needed to detect a 33% treatment response with one-tailed significance of p</=0.005 and 80% power in a 1-year, double-blind, placebo-controlled treatment study. CONCLUSIONS: These findings indicate that brain metabolism as assessed by FDG PET during mental rest is a sensitive marker of disease progression in Alzheimer's disease over a 1-year period. These findings also support the feasibility of using FDG PET as an outcome measure to test the ability of treatments to attenuate the progression of Alzheimer's disease.

Aged↗

PubMed2002

Neuroimaging and obesity: mapping the brain responses to hunger and satiation in humans using positron emission tomography.

The hypothalamus has a major role in the control of food intake. However, neurotracing studies have shown that the hypothalamus receives input from several other regions of the brain that are likely to modulate its activity. Of particular interest to the understanding of human eating behavior is the possible involvement of the cortex. Using positron emission tomography (PET), we generated functional brain maps of the neuroanatomical correlates of hunger (after a 36-h fast) and satiation (after oral administration of a liquid formula meal) in lean and obese subjects. Results in lean individuals indicate that the neuroanatomical correlates of hunger form a complex network of brain regions including the hypothalamus, thalamus, and several limbic/paralimbic areas such as the insula, hippocampal/parahippocampal formation, and the orbitofrontal cortex. Satiation was associated with preferentially increased neuronal activity in the prefrontal cortex. Our studies also indicate that the brain responses to hunger/satiation in the hypothalamus, limbic/paralimbic areas (commonly associated with the regulation of emotion), and prefrontal cortex (thought to be involved in the inhibition of inappropriate response tendencies) might be different in obese and lean individuals. In conclusion, neuroimaging of the human brain is proving to be an important tool for understanding the complexity of brain involvement in the regulation of eating behavior. PET studies might help to unravel the neuropathophysiology underlying human obesity.

Adolescent↗

PubMed2002

[Natural increase of parasitoids population of diamondback moth Plutella xylostella under ecological control condition].

The parasitoids of diamondback moth Plutella xylostella was unfolded year after year since a series of ecological measurement was taken in Shenzhen Longgang Demonstrate Ecological Farm. The parasitical eggs of diamondback moth by Trichogrammatoidea bactraz and Trichogramma ostrinae were firstly found in the field in September 1999. Another two parasitoids, Trichogramma confusum and Trichogramma bilingensis also had a certain parasitism in nature. Now, the four Trichogramma species had already established their natural population, and their average parasitism was 15% around the year, and reached 25-30% at the harvesting period in Autumn, among them, Trichogramma confusum was predominant in quantity, which showed that ecological control played an important role in augmenting and protecting the population of Trichogramma in nature.

Animals↗