A comparison among different techniques for human ERG signals processing and classification

Feature detection in biomedical signals is crucial for deepening our knowledge about the involved physiological processes. To achieve this aim, many analytic approaches can be applied but only few are able to deal with signals whose time dependent features provide useful clinical information. Among the biomedical signals, the electroretinogram (ERG), that records the retinal response to a light flash, can improve our comprehension of the complex photoreceptoral activities.The present study is focused on the analysis of the early response of the photoreceptoral human system, known as a-wave ERG-component. This wave reflects the functional integrity of the photoreceptors, rods and cones, whose activation dynamics are not yet completely understood. Moreover, since in incipient photoreceptoral pathologies eventual anomalies in a-wave are not always detectable with a “naked eye” analysis of the traces, the possibility to discriminate pathologic from healthy traces, by means of appropriate analytical techniques, could help in clinical diagnosis.In the present paper, we discuss and compare the efficiency of various techniques of signal processing, such as Fourier analysis (FA), Principal Component Analysis (PCA), Wavelet Analysis (WA) in recognising pathological traces from the healthy ones. The investigated retinal pathologies are Achromatopsia, a cone disease and Congenital Stationary Night Blindness, affecting the photoreceptoral signal transmission. Our findings prove that both PCA and FA of conventional ERGs, don't add clinical information useful for the diagnosis of ocular pathologies, whereas the use of a more sophisticated analysis, based on the wavelet transform, provides a powerful tool for routine clinical examinations of patients.     

A tool for analyzing information from data storage tags: the continuous wavelet transform (CWT)

Electronic Data Storage Tags (DSTs) have the potential of providing long term, high-resolution observation data of individual fish in the ecosystem. However, traditional time series analysis methods are limited in extracting the required information from DSTs. The continuous wavelet transform (CWT) is a tool for decomposing a time series into instantaneous frequency versus time characteristics. This allows data signals, which are restricted to specific frequencies (localized frequencies), or frequency components, which are restricted to specific time intervals (time localized) to be extracted and displayed in a highly intuitive way. The aim of this short communication is to present the CWT as a tool for extracting information from DST data. In the first case, synthetically generated data is used to demonstrate how the methodology captures different time–frequency dependent patterns in the time series data. The relevance of the methodology to real field data is demonstrated by an analysis of DST depth data from tagged Barents Sea coastal cod. This work has also enjoyed partial funding from the EU-FP5-Q5RS200200813 CODYSSEY project.     

Fine structure of the low-frequency spectra of heart rate and blood pressure

Background  

The aim of this study was to explore the principal frequency components of the heart rate and blood pressure variability in the low frequency (LF) and very low frequency (VLF) band. The spectral composition of the R–R interval (RRI) and systolic arterial blood pressure (SAP) in the frequency range below 0.15 Hz were carefully analyzed using three different spectral methods: Fast Fourier transform (FFT), Wigner-Ville distribution (WVD), and autoregression (AR). All spectral methods were used to create time–frequency plots to uncover the principal spectral components that are least dependent on time. The accurate frequencies of these components were calculated from the pole decomposition of the AR spectral density after determining the optimal model order – the most crucial factor when using this method – with the help of FFT and WVD methods.     

Implementation of an elaborated neuromorphic model of a biological photoreceptor

We describe here an elaborated neuromorphic model based on the photoreceptors of flies and realised in both software simulation and hardware using discrete circuit components. The design of the model is based on optimisations and further elaborations to the mathematical model initially developed by van Hateren and Snippe that has been shown to accurately simulate biological responses in simulations under both steady-state and limited dynamic conditions. The model includes an adaptive time constant, nonlinear adaptive gain control, logarithmic saturation and a nonlinear adaptive frequency response mechanism. It consists of a linear phototransduction stage, a dynamic filter stage, two divisive feedback loops and a static nonlinearity. In order to test the biological accuracy of the model, impulses and step responses were used to test and evaluate the steady-state characteristics of both the biological (fly) and artificial (new neuromorphic model) photoreceptors. These tests showed that the model has faithfully captured most of the essential characteristics of the insect photoreceptor cells. The model showed a decreasing response to impulsive stimuli when the background intensity was increased, indicating that the circuit adapted to background luminance in order to improve the overall operating range and better encode the contrast of the stimulus rather than luminance. The model also showed the same change in its frequency response characteristics as the biological photoreceptors over a luminance range of 70,000 cd/m², with the corner frequency of the circuit ranging from 10 to 90 Hz depending on the current state of adaptation. Complex naturalistic experiments have also further proven the robustness of the model to perform in real-world scenario. The model showed great correlation to the biological photoreceptors with an r ² value exceeding 0.83. Our model could act as an excellent platform for future experiments that could be carried out in scenarios where in vivo intracellular recording from biological photoreceptors would be impractical or impossible, or as a front-end for an artificial imaging system.     

Photoreceptors of Bryozoan Larvae (Cheilostomata, Cellularioidea)

The ultrastructure of potential photoreceptors in larvae of Tricellaria occidentalis and four species of Bugula is described and compared with previously reported photoreceptors in larvae of Bugula neritina and Scrupocellaria bertholetti. A single sensory cell forms the functional unit of each photoreceptor. This cell is distinguished by a concentration of pigment vesicles in its apical part, a direct connection with the nervous system, and a large number of cilia that form the photoreceptoral organelle. These cilia have axonemes morphologically identical to those of motile cilia. The membranes of sensory cilia are unbeaded and qualitatively less osmophilic than those of the motile cilia of adjacent accessory and coronal cells. Three photoreceptor types are designated based on topological complexity: Type I, in which the sensory cell is flush with adjacent coronal cells and the photoreceptoral organelle is unprotected; Type II, in which the apical surface of the sensory cell is invaginated, forming a lumen containing the photoreceptoral organelle; and Type III, in which the sensory cell is at the base of an epidermal invagination and the photoreceptoral organelle is protected in a lumen formed by the sensory cell and accessory cells. There is a greater range of morphological variation among photoreceptors in larvae of Bugula spp. than between those of two species of the related genera Scrupocellaria and Tricellaria.     

Melatonin modulates the neural activity in the photosensory pineal organ of the trout: Evidence for endocrine-neuronal interactions

Summary Hormonal and neural signals transmitted from the pineal organ to the brain in cold-blooded vertebrates presumably convert information about the ambient illumination into signals which may be used to mediate photoperiodic and circadian responses. The possible intrapineal function of melatonin was investigated by recording intra- and extracellularly from photoreceptors and second-order neurons in the isolated superfused pineal organ of the trout (Salmo gairdneri). Melatonin added through the perfusion bath to the explanted pineal organ caused a dose-related and reversible inhibition of ganglion cells of the luminance type whereas the hormone did not significantly affect the membrane potential of photoreceptors and their light-evoked response. The observed effects seem to be independent from photoperiod and adaptation conditions. These results suggest that melatonin provides a feedforward signal to intrapineal neurons regulating the neural output of the organ.Laboratory of Fish Biology, School of Agriculture, Nagoya University, Chikusa, Nagoya 464 Japan     

Regeneration pattern analysis of Quercus liaotungensis in a temperate forest using two-dimensional wavelet analysis

This paper introduces the two-dimensional (2D) wavelet analysis as a general interrogative technique for the detection of spatial structure in lattice data. The 2D wavelet analysis detects components of hierarchical structure and displays the locational information of the components. Patches and gaps of different spatial scales in graphical presentation of wavelet coefficients can be linked to the local ecological processes that determine patterns at stand or landscape scales. Derived from the 2D wavelet transform function, the calculation of wavelet variance can reduce the four-dimensional data of wavelet coefficients to a two-dimensional wavelet variance function and quantify the contribution of the given scale to the overall pattern. We illustrate the use of the 2D wavelet analysis by analyzing two simulated patterns and identifying the regeneration pattern of the Quercus liaotungensis in a warm temperate forest in north China. Our results indicate that the recruitment of Q. liaotungensis occurs in an overlapping area between the patch of adult and canopy gap at scales of 45 m×45 m–70 m×70 m and 20 m×20 m–30 m×30 m. The regeneration pattern of Q. liaotungensis can be mainly ascribed to a trade-off between two ecological processes: recruitment around parent trees and the physiological light requirements of seedlings and saplings. Our results provide a general portrayal of the regeneration pattern for the dispersal-limited and shade-intolerant Quercus species. We find that the two-dimensional wavelet analysis efficiently characterizes the scale-specific pattern of Q. liaotungensis at different life-history stages.     

Neural mechanisms for color perception in the primary visual cortex

New neurophysiological results show the existence of multiple transformations of color signals in the primary visual cortex (V1) in macaque monkey. These different color mechanisms may contribute separately to the perception of color boundaries and colored regions. Many cells in V1 respond to color and to black-white (luminance) patterns. These neurons are spatially selective and could provide signals about boundaries between differently colored regions. Other V1 neurons that prefer color over luminance respond without much spatial selectivity to colored stimuli, and could be the neural basis for the response to local color modulation within a region. How these different types of color cells combine inputs from cone photoreceptors is what gives them their different spatial selectivities for color.     

Feature extraction and recognition of epileptiform activity in EEG by combining PCA with ApEn

This paper proposes a new method for feature extraction and recognition of epileptiform activity in EEG signals. The method improves feature extraction speed of epileptiform activity without reducing recognition rate. Firstly, Principal component analysis (PCA) is applied to the original EEG for dimension reduction and to the decorrelation of epileptic EEG and normal EEG. Then discrete wavelet transform (DWT) combined with approximate entropy (ApEn) is performed on epileptic EEG and normal EEG, respectively. At last, Neyman–Pearson criteria are applied to classify epileptic EEG and normal ones. The main procedure is that the principle component of EEG after PCA is decomposed into several sub-band signals using DWT, and ApEn algorithm is applied to the sub-band signals at different wavelet scales. Distinct difference is found between the ApEn values of epileptic and normal EEG. The method allows recognition of epileptiform activities and discriminates them from the normal EEG. The algorithm performs well at epileptiform activity recognition in the clinic EEG data and offers a flexible tool that is intended to be generalized to the simultaneous recognition of many waveforms in EEG.     

Evidence for different nonlinear summation schemes for lines and gratings at threshold

Within a wide class of multichannel models of the visual system it is suggested that spatial distributions of luminance are processed by the independent activation of grating detectors, or spatial frequency channels. Probability summation is often described in terms of Quick's nonlinear pooling model [Quick RF (1974) Kybernetik 16:65–67]. Using this model, we find evidence for the existence of different kinds of nonlinear summation at threshold; for compound gratings with well-separated spatial frequency components, the threshold functions indicate nonlinear summation which is not compatible with probability summation, while for line patterns well separated in the spatial domain the probability summation rule proves compatible with the data. Received: 24 June 1998 / Accepted in revised form: 16 March 1999     

Topographic analysis of dimension estimates of EEG and filtered rhythms in epileptic patients with complex partial seizures

Nonlinear dynamic properties were analyzed on the EEG and filtered rhythms recorded from healthy subjects and epileptic patients with complex partial seizures. Estimates of correlation dimensions of control EEG, interictal EEG and ictal EEG were calculated. The values were demonstrated on topograms. The delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz) and gamma (30–40 Hz) components were obtained and considered as signals from the cortex. Corresponding surrogate data was produced. Firstly, the influence of sampling parameters on the calculation was tested. The dimension estimates of the signals from the frontal, temporal, parietal and occipital regions were computed and compared with the results of surrogate data. In the control subjects, the estimates between the EEG and surrogate data did not differ (P > 0.05). The interictal EEG from the frontal region and occipital region, as well as its theta component from the frontal region, and temporal region, showed obviously low dimensions (P < 0.01). The ictal EEG exhibited significantly low-dimension estimates across the scalp. All filtered rhythms from the temporal region yielded lower results than those of the surrogate data (P < 0.01). The dimension estimates of the EEG and filtered components markedly changed when the neurological state varied. For each neurological state, the dimension estimates were not uniform among the EEG and frequency components. The signal with a different frequency range and in a different neurological state showed a different dimension estimate. Furthermore, the theta and alpha components demonstrated the same estimates not only within each neurological state, but also among the different states. These results indicate that the theta and alpha components may be caused by similar dynamic processes. We conclude that the brain function underlying the ictal EEG has a simple mechanism. Several heterogeneous dynamic systems play important roles in the generation of EEG. Received: 10 December 1999 / Accepted in revised form: 8 May 2000     

Spatial, seasonal and species variations of harmful algal blooms in the South Yellow Sea and East China Sea

The occurrences of harmful algal blooms (HABs), in terms of frequency and area in the Chinese coastal waters, have been increasing since 1980s and caused considerable economic losses. In the present study, we have analyzed spatial and seasonal characteristics of HAB events in the southern Yellow Sea and East China Sea along Chinese coast from 1933 to 2004. With a total 435 HAB records, the most frequent HAB occurrence area (FHA) is off the Yangtze River mouth and another two FHA areas are located south of the Yangtze River estuary along about isobaths of 30–60 m coastal water in the East China Sea. The time of HAB occurrence shifted during our study period: from autumn (August–October) before 1980s to July–August in 1980s, during May–July in 1990s, and May–June for the period of 2000–2004. Causative species were found to be different: Noctiluca scintillans and Skeletonema costatum were dominant causative species prior to 2000; and Prorocentrum donghaiense Lu was dominant from 2000 to 2004 and also caused large blooms in May. Trichodesmium sp. caused many HABs in autumn (August–October) prior to 1980s with only one HAB between 1980 and 2004. The changes of the dominant HAB species may have affected the timings of HAB occurrence, as well as the increasing HAB-affected areas in recent years.     

Electroencephalograms of patients with initial signs of depression: Independent component analysis

Independent component analysis (ICA) of 19-channel background EEG was performed in 111 patients with the early signs of depressive disorders and in 526 healthy subjects. The power spectra of the independent components were compared in the depressive patients and in healthy subjects at the eyes closed and eyes opened states. Statistically significant differences between the groups were detected in three frequency bands: θ (4–7.5 Hz), α (7.5–14 Hz), and β (14–20 Hz). Increased θ and α activities in parietal and occipital derivations of depressive patients may have been caused by a reduced cortical activity in the projection of these derivation. Diffuse enhancement of the β activity may be correlated with anxiety symptoms that are pronounced in the clinical picture of depressive disorders at early stages of the disease. ICA used to compare quantitative EEG parameters in different groups of patients and in healthy persons makes it possible to localize the differences more accurately than the traditional analysis of EEG spectra.     

Temperature and the temporal resolving power of fly photoreceptors

A hot head gives an insect a clearer view of a moving world because warming reduces motion blur by accelerating photoreceptor responses. Over a natural temperature range, 19–34 °C, the speed of response of blowfly (Calliphora vicina) photoreceptors more than doubles, to produce the fastest functional responses recorded from an ocular photoreceptor. This acceleration increases temporal resolving power, as indicated by the corner frequency of the response power spectrum. When light adapted, the corner frequency increases from 53 Hz to 119 Hz with a Q ₁₀ of 1.9, and when dark adapted from 8 Hz to 32 Hz with a Q ₁₀ of 3.0. Temperature sensitivity originates in the phototransduction cascade, and is associated with signal amplification. The temperature sensitivity of photoreceptors must be taken into account when studying the mechanisms, function and ecology of vision, and gives a distinct advantage to insects that thermoregulate. Accepted: 2 February 2000     

Contribution of human melanopsin retinal ganglion cells to steady-state pupil responses

The recent discovery of melanopsin-containing retinal ganglion cells (mRGCs) has led to a fundamental reassessment of non-image forming processing, such as circadian photoentrainment and the pupillary light reflex. In the conventional view of retinal physiology, rods and cones were assumed to be the only photoreceptors in the eye and were, therefore, considered responsible for non-image processing. However, signals from mRGCs contribute to this non-image forming processing along with cone-mediated luminance signals; although both signals contribute, it is unclear how these signals are summed. We designed and built a novel multi-primary stimulation system to stimulate mRGCs independently of other photoreceptors using a silent-substitution technique within a bright steady background. The system allows direct measurements of pupillary functions for mRGCs and cones. We observed a significant change in steady-state pupil diameter when we varied the excitation of mRGC alone, with no change in luminance and colour. Furthermore, the change in pupil diameter induced by mRGCs was larger than that induced by a variation in luminance alone: that is, for a bright steady background, the mRGC signals contribute to the pupillary pathway by a factor of three times more than the L- and M-cone signals.     

Spawning and biparental egg-care in a temperate filefish,Paramonacanthus japonicus (Monacanthidae)

Synopsis Reproductive habits of a temperate filefish, Paramonacanthus japonicus, were studied on a rocky reef at Tsuyazaki, Fukuoka, Japan, from 1989 through 1990. Males had territories of 30–70m² and defended them from conspecific males and potential egg predators such as another filefish, Stephanolepis cirrhifer. Egg masses were found on the sandy bottom in male territories. Individual discrimination of males and females occurring in three male territories revealed that males and females stayed in stable pairs during one month of observation in 1989. In these stable pairs, males fed only within their territories, but females occasionally foraged outside. The occurrence of egg masses within male territories and biparental egg care showed that fish were reproducing as monogamous pairs. Contrary to this, males tagged in 1990 changed their territories after the disappearance of females, and males and females mated polygamously. Spawning was observed only four times during the study period, between 1633 and 1754h. Prior to spawning, the female prepared a spawning bed on the sandy bottom. The male nuzzled the female and the pair spawned, touching their gonopores on the spawning bed. Spawning was very quick and took only 1–3 seconds. The adhesive eggs were spherical with a diameter of 0.56 mm. They were mixed with sand particles and formed a doughnut-shaped mass of about 4 cm in diameter. One egg mass contained 3300–3800 embryos of similar developmental stage, which hatched 2–3 days later. P. japonicus appears to be monogamous but may also practice polygamy when pair-bonds are unstable.     

Isolation and characterization of a thermostable cellulase-producing <Emphasis Type="Italic">Fusarium chlamydosporum</Emphasis>

A thermostable cellulase-producing fungus, HML 0278, was identified as Fusarium chlamydosporum by morphological characteristics and ITS rDNA sequence analysis. HML 0278 produced extracellular cellulases in solid-state fermentation using sugar cane bassage as the carbon source. Native-PAGE analysis demonstrated that this fungus strain was capable of producing the three major components of cellulases and xylanase, with a yield of 281.8 IU/g for CMCase, 182.4 IU/g for cellobiohydrolase, 135.2 IU/g for β-glucosidase, 95.2 IU/g for filter paper activity, and 4,720 IU/g for xylanase. More importantly, the CMCase and β-glucosidase produced by HML 0278 showed stable enzymatic activities within pH 4–9 and pH 4–10, and at temperatures below 70 and 60°C, respectively.     

Antitumor activity of bent metallocenes: electronic structure analysis using DFT computations

The antitumor activities of bent metallocenes [Cp–M–Cp]²⁺ (M = Ti, V, Nb, Mo) and complexes of them with guanine, adenine, thymine and cytosine nucleotides have been probed using electronic structure calculations. DFT/BP86 calculations have revealed that the bent metallocene–nucleotide interaction strongly depends on the stability of the hydrolyzed form of the bent metallocene dichloride [Cp₂M]²⁺ species, and in turn the stability of the [Cp₂M]²⁺ species strongly depends on the electronic structure of [Cp₂M]²⁺. Detailed electronic structure and Walsh energy analyses have been carried out for the hydrolyzed forms of four [Cp–M–Cp]²⁺ (M = Ti, V, Nb, Mo) species to find out why the bent structure is unusually stable. Energy changes that occur during the bending process in frontier molecular orbitals as well as the p(π)–d(π) overlap have been invoked to account for the anticipated antitumor activities of these species. The bonding situation and the interactions in bent metallocene–nucleotide adducts were elucidated by fragment analysis. Of the four nucleotides complexed with the four bent metallocenes, adenine and guanine show better binding abilities than the other two nucleotides. Metallocenes of second-row transition metals exhibit better binding with pyrimidine-base nucleotides. In particular, the Lewis acidic bent metallocenes interact strongly with nucleotides. The antitumor activity is directly related to the binding strength of the bent metallocene with nucleotide adducts, and the computed interaction energy values correlate very well with the experimentally observed antitumor activities.     

Investigating the effects of opioid drugs on electrocortical activity using wavelet transform

 Fetal electrocortical activity (ECoG) is characterized by two distinct patterns: HVSA (high voltage, slow activity) and LVFA (low voltage, fast activity). Using the wavelet transform (WT), we recently reported that the frequency characteristics of these two ECoG patterns undergo significant maturational changes prior to birth (Akay et al. 1994a). We now report that fetal ECoG can also be significantly affected by pharmacological agents. In this paper, we compared the effects of two opioid drugs (morphine and [D-Pen², D-Pen⁵]enkephalin, DPDPE) on fetal ECoG, using the chronically instrumented fetal lamb model. Morphine was infused intravenously (i.v.) at 2.5 mg/h, while DPDPE was infused into the lateral cerebroventricle (i.c.v.) at 30 μg/h. The ECoG was analyzed using WT. We performed multiresolution decomposition for four sets of parameters D _{2 j} where −1<j<−4. The four series WTs represent the detail signal bandwidths: (1) 16–32 Hz, (2) 8–16 Hz, (3) 4–8 Hz, (4) 2–4 Hz. The data were subjected to statistical analysis using the Kolmogorov–Smirnov (KS) test. Both morphine and DPDPE resulted in a significant increase in power in the first wavelet band, while power was reduced in the second, third and fourth wavelet bands. In addition, both drugs resulted in a disruption of the normal cyclic pattern between the two ECoG patterns. There was a difference in the time course of action between morphine and DPDPE. This is the first occasion in which continuous ECoG has been subjected to rigorous statistical analysis. The results suggest that the WT-KS method is most suitable for quantitating changes in the ECoG induced by pharmacological agents. Received: 21 January 1994/Accepted in revised form: 15 September 1994     

Time/frequency events of surface mechanomyographic signals resolved by nonlinearly scaled wavelets

The purpose of this investigation is to introduce a wavelet analysis designed for analyzing short events reflecting bursts of muscle activity in non-stationary mechanomyographic (MMG) signals. A filter bank of eleven nonlinearly scaled wavelets that maintain the optimal combination of time and frequency resolution across the frequency range of MMG signals (5–100 Hz) was used for the analysis. A comparison with the short-time Fourier transform, Wigner-Ville transform and continuous wavelet transform using a test signal with known time–frequency characteristics showed that the MMG wavelet analysis resolved the intensity, timing, and frequencies of events in a more distinct way without overemphasizing high or low frequencies or generating interference terms. The analysis was used to process MMG signals from the vastus lateralis, rectus femoris, and vastus medialis muscles obtained during maximal concentric and eccentric isokinetic movements. Muscular events were observed that were precisely located in time and frequency in a muscle-specific way, thereby showing periods of synergistic contractions of the quadriceps muscles. The MMG wavelet spectra showed different spectral bands for concentric and eccentric isokinetic movements. In addition, the high and low frequency bands seemed to be activated independently during the isokinetic movement. What generates these bands is not yet known, however, the MMG wavelet analysis was able to resolve them, and is therefore applicable to non-stationary MMG signals.