Biomedical subjects

Ai-Hua Chen

Publications and source records attributed to Ai-Hua Chen.

7 recordsLinked to original sources

PubMed2006

A robust method for spike sorting with automatic overlap decomposition.

Spike sorting is the mandatory first step in analyzing multiunit recording signals for studying information processing mechanisms within the nervous system. Extracellular recordings usually contain overlapped spikes produced by a number of neurons adjacent to the electrode, together with unknown background noise, which in turn induce some difficulties in neural signal identification. In this paper, we propose a robust method to deal with these problems, which employs an automatic overlap decomposition technique based on the relaxation algorithm that requires simple fast Fourier transforms. The performance of the presented system was tested at various signal-to-noise ratio levels based on synthetic data that were generated from real recordings.

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PubMed2005

Color information encoded by the spatiotemporal patterns of light response in ganglion cells of chick retina.

In the present study, the light responses of ganglion cells to chromatic stimulus were recorded from isolated retina of neonatal chick. It was found that for some non-color-opponent ganglion cells, the spatiotemporal patterns of the cells' light responses were related to the chromatic information that they received. When stimulus with some chromatic component was applied, some ganglion cells would generate distinguishable temporal patterns of light responses although these cells can be classified as non-color-opponent according to their light responses. The results suggest that in chick retina, the color information might be encoded not only by the color opponent ganglion cells, but also the spatiotemporal patterns of some ganglion cells that are traditionally classified as non-color-opponent subtype.

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PubMed2005

Information transmission rate changes of retinal ganglion cells during contrast adaptation.

During adaptation to high-contrast stimulation, retinal ganglion cell's responsiveness change is characterized by decreased firing rate and declined sensitivity. In order to examine the modification of information transmission properties of the ganglion cell during this adaptation process, neural activities were recorded extracellularly from the chicken retina using a multi-electrode recording system, and the information transmission rate of the retinal ganglion cells was estimated. The results show that the response entropy and noise entropy of the ganglion cells both decreased during the adaptation process, which resulted in a modest decline of information transmission rate of ganglion cells after several seconds' adaptation. However, due to the decrease of the neuron's firing rate during the adaptation, it is revealed that the information carried by each spike was increased as compared to pre-adaptation, suggesting that retinal ganglion cells' information processing strategies during contrast adaptation may reflect economical principle by promoting each spike more informative. These results also suggest that contrast adaptation and sensitivity rescaling of the visual neurons provide an efficient manner in information transmission and save the system's metabolic cost in the meantime.

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PubMed2005

Protective and anti-fatigue effects of aspirin against heatstroke in rats.

The purpose of this study is to determine whether aspirin can reduce interleukin-1beta(IL-1beta) concentration and exert protective effects against heatstroke. The heatstroke rat model was established through exposing rat to a high ambient temperature (HAT, Ta 41 degrees C, relative humidity 65%) in a simulative HAT chamber to induce heatstroke. Three parts were performed in the present experiment: (1) To determine the effects of pretreatment with aspirin against heatstroke;(2) To prove the effects of specifically reducing inducible nitric oxide synthase (iNOS) against rat heatstroke by iNOS selective prohibitor aminoguanidine (AG);(3) To determine the effects of aspirin against heatstroke and fatigue. In part 1 and 2, Sprague-Dawley rats were randomly assigned to control and aspirin groups or AG groups respectively. Mean arterial blood pressure (MAP), colonic temperature (T(co)), electrocardiograph (ECG) were monitored during heat exposure (HE) and blood samples were taken 0 and 60 min after HE for IL-1betaassay or nitric oxide (NO) assay. In part 3, additional control and aspirin groups of conscious rats were put in a barrel with 41 degrees C water and kept swimming until drowning over 10 s, and then intervals were recorded as survival time. The results from part 1 showed that from 0 to 50 min after HE, MAPs of control group and aspirin group were not significantly different. About 50-60 min after HE, MAPs of both groups were decreased abruptly and MAPs of control group were decreased significantly in comparison with those of aspirin group. T(co) of both groups was increased until to 42 degrees C, without significant difference. Time of heatstroke onset was not significantly different, while survival time was significantly longer in aspirin group than that in control group. Plasma IL-1betaconcentrations in both groups were significantly increased after HE, and the concentration was significantly higher in the control group than that in aspirin group 60 min after HE. In part 3, the survival time was significantly longer in aspirin group than that in control group. In part 2, MAPs of both groups from 0 to 50 min after HE were not significantly different, whereas 55-60 min after HE, MAPs of control group were decreased significantly in comparison with those of AG group;T(co) of both groups was increased after HE until to 42 degrees C, but without significant difference. The time of the heatstroke onset and survival time of AG group were significantly longer than that of control group;the plasma NO concentrations of two groups were significantly higher 60 min after HE than those 0 min after HE, and the plasma NO concentration of control group was significantly higher than that of AG group 60 min after HE. In conclusion, IL-1betamay contribute to heatstroke through inducing iNOS, which attenuates the tone of peripheral blood vessel, and pretreatment with aspirin can provide preventive effects against heatstroke and reinforce the heat and fatigue endurance, which may be associated with inhibition of systemic IL-1betalevels and local iNOS levels.

Journal Article↗

PubMed2005

Luminance adaptation increased the contrast sensitivity of retinal ganglion cells.

In the present study, the activity changes of chicken retinal ganglion cells in response to light stimuli with defined contrast were investigated, in the presence of various levels of sustained background illumination. Following a step increase of light illumination, the firing rate of most retinal ganglion cells increased abruptly, and then decreased to a steady-state level with a much lower firing rate during the sustained application of light. However, when a test flash was applied, which superimposed the prolonged background illumination, an increased firing rate was observed. Moreover, the neuron firing rate was increased to a greater extent when the intensity of the background illumination was higher. This may suggest that the neuron sensitivity can be modified by the background illumination level, although the neuron firing rate was reduced during sustained illumination.

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PubMed2004

Firing rates and dynamic correlated activities of ganglion cells both contribute to retinal information processing.

In the present study, the electrical activities of paired retinal ganglion cells, under full field light stimuli with a variety of chromatic configurations, were recorded from a small functioning piece of retina using multi-electrode array (MEA). Neurons that had increased firings at light-ON and -OFF transients and did not show color-opponent properties were investigated. Single neuronal analysis showed that firing rate of each individual neuron was dependent on the intensity of illumination. Multi-unit analyses revealed that adjacent neurons often fired in synchrony in response to light stimulation. However, in some cases, the strength of correlation between the paired neurons was higher when the retina was exposed to red or green light, and the correlation was attenuated when yellow or white light was given. This seems to suggest that the ensemble activity of non-color-opponent ganglion cells might partly participate in color-information processing, with the red- and green-pathway inputs influencing each other. Such arrangement reflects principle of parsimony: the firing rates of single neuron represent the luminance intensity, and the correlated activities may tell the brain about the color information.

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PubMed2002

[Association between aldosterone synthase gene polymorphism and hypertrophic cardiomyopathy].

OBJECTIVE: To investigate the relationship between aldosterone synthase (CYP11B2) gene polymorphism and hypertrophic cardiomyopathy (HCM). METHODS: Fifteen HCM patients and 18 healthy subjects were enrolled in this study. Peripheral blood samples were collected from these subjects to exact genome DNA. PCR and Hae III restriction endonuclease digestion were employed to study -344C/T polymorphism of CYP11B2 gene. RESULTS: CYP11B2 gene showed a significant difference in CT genotype distribution in HCM groups as compared with that in the control groups (P<0.05). CONCLUSION: CT genotype of CYP11B2 gene may be one of factors responsible for the pathogenesis of HCM in a proportion of patients.

Cardiomyopathy, Hypertrophic↗