Biomedical subjects

Pei-Ji Liang

Publications and source records attributed to Pei-Ji Liang.

12 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

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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PubMed2005

Ca2+-permeable and Ca2+-impermeable AMPA receptors coexist on horizontal cells.

Fura-2 fluorescent calcium imaging was used for analyzing the subtype of AMPA receptors in freshly dissociated horizontal cells of carp retina. Exogenous application of AMPA induced an increase of intracellular concentration of free Ca2+ ([Ca2+]i) in horizontal cells, while the [Ca2+]i increase was partly inhibited by nifedipine. The residual [Ca2+]i increase was completely eliminated by joro spider toxin-3, a blocker of Ca2+-permeable AMPA receptors. On the other hand, the application of pentobarbital, which blocked Ca2+-impermeable AMPA receptors, could also partly inhibit the increase of [Ca2+]i, implying that the application of AMPA induced the activation of both Ca2+-permeable and Ca2+-impermeable AMPA receptors and the consequent activation of voltage-gated Ca2+ channels. Taken together, these results suggested that Ca2+-permeable and Ca2+-impermeable AMPA receptors were coexpressed on horizontal cells.

Adjuvants, Anesthesia↗

PubMed2004

Role of Ca2+ store in AMPA-triggered Ca2+ dynamics in retinal horizontal cells.

Fura-2 fluorescent calcium imaging was applied to measure [Ca(2+)](i) in freshly dissociated horizontal cells of carp retina, and a model containing endoplasmic reticulum (ER) membrane processes and plasma membrane processes was constructed for quantitative analyses of the AMPA-triggered calcium dynamics. A transient increase followed by a sustained steady level of [Ca(2+)](i) was observed when 100 microM AMPA was applied, while the initial transient increase of [Ca(2+)](i) was suppressed by exogenously applied ryanodine. The model analyses results suggest that the AMPA-triggered calcium dynamics involves a number of cytoplasmic and endoplasmic processes that interact with each other. It also suggests that calcium store is an important part contributing to the transient calcium signal.

Animals↗

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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PubMed2004

Spike sorting based on automatic template reconstruction with a partial solution to the overlapping problem.

A new method for spike sorting is proposed which partly solves the overlapping problem. Principal component analysis and subtractive clustering techniques are used to estimate the number of neurons contributing to multi-unit recording. Spike templates (i.e. waveforms) are reconstructed according to the clustering results. A template-matching procedure is then performed. Firstly all temporally displaced templates are compared with the spike event to find the best-fitting template that yields the minimum residue variance. If the residue passes the chi(2)-test, the matching procedure stops and the spike event is classified as the best-fitting template. Otherwise the spike event may be an overlapping waveform. The procedure is then repeated with all possible combinations of two templates, three templates, etc. Once one combination is found, which yields the minimum residue variance among the combinations of the same number of component templates and makes the residue pass the chi(2)-test, the matching procedure stops. It is unnecessary to check the remaining combinations of more templates. Consequently, the computational effort is reduced and the over-fitting problem can be partly avoided. A simulated spike train was used to assess the performance of the proposed method, which was also applied to a real recording of chicken retina ganglion cells.

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PubMed2004

Possible mechanism of flicking-induced short-term plasticity in retinal cone-LHC synapse: a computational study.

In retinal cone-HC synapse, it has been found that repetitive stimulation could induce postsynaptic short-term responsiveness enhancement. However, the detailed mechanism underlying this short-term plasticity in the retinal graded neurons remains unclear. In this study, based on an ion-channel model described using Hodgkin--Huxley equations, the possible mechanism of repetitive-stimulation-induced short-term plasticity in the synapse between retinal cones and horizontal cells was investigated. The computational simulation results, together with evidence from experimental observations, suggest that the short-term modification of signal transmission between the retinal graded neurons is likely to be attributed to the regulatory effects that calcium-dependent process exerts on the single-channel properties of the postsynaptic AMPA receptors.

Animals↗

PubMed2003

Effects of diazepam on closed- and open-loop optokinetic nystagmus (OKN) in humans.

The effects of diazepam on optokinetic nystagmus (OKN) eye movements were studied under closed-loop and open-loop conditions in healthy humans. The open-loop condition was achieved by adding the eye-movement velocity signal of OKN to the computer-generated signal controlling the moving stimulus grating. Each of four subjects received a single oral dose of 5 mg diazepam or a placebo on two separate days in a double-blind randomized fashion. OKN eye movements were measured 90 min after administration of the treatments. As compared to placebo, diazepam significantly reduced the gain of open-loop OKN, but did not modify the gain of closed-loop OKN. The results indicate that the OKN gain under the open-loop condition is a more sensitive detector of the parameter changes of the OKN system than under the closed-loop condition. Thus, open-loop OKN gain can provide an objective, quantitative measure of benzodiazepine agonist effects.

Adult↗

PubMed2003

Dopamine effect on the stimulus pattern related changes in response characteristics of R/G horizontal cells in carp retina.

Repetitive red flashes increased the R/G horizontal cells' red response amplitude and induced a hyperpolarization of the cells' dark membrane potential. These phenomena were eliminated in 6-OHDA pretreated retinas and restored by exogenous dopamine, which suggests the involvement of dopamine receptor activity changes instead of dopamine release changes. Furthermore, the phenomena persisted on D(1) receptor antagonist (SKF-83566) application, whereas they diminished on D(2) receptor antagonist (eticlopride) application, indicating that the mechanism is related to a D(2) receptor, possibly located on photoreceptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed2003

Metabotropic glutamate receptor-mediated hetero-synaptic interaction of red- and green-cone inputs to LHC of carp retina.

The role of presynaptic metabotropic glutamate receptor (mGluR) on the interaction of red- and green-cone signals was investigated in luminosity-type horizontal cell (LHC) of isolated carp retina. It was found that a dim red background could enhance LHC's light response to green stimulus, and a dim green background was also able to increase the cell's response to red flash. Such mutual color enhancement was eliminated by application of groups II and III mGluR antagonist (S)-methyl-4-carboxyphenyl-glycine (MCPG). Furthermore, inhibition of glutamate uptake by using D-aspartate (D-Asp) or DL-threo-beta-hydroxy-aspartic acid (THA) completely blocked the mutual enhancement of color signals in LHC. However, the GABAergic feedback pathway in the outer retina was unnecessarily involved.

Animals↗