Neuronal identification of signal periodicity by balanced inhibition

Many animals, including men, use periodicity information, e.g., amplitude modulations of acoustic stimuli, as a vital cue to auditory object formation. The underlying neuronal mechanisms, however, still remain a matter of debate. Here, we mathematically analyze a model for periodicity identification that relies on the interplay of excitation and delayed inhibition. Our analytical results show how the maximal response of such a system varies systematically with the time constants of excitation and inhibition. The model reliably identifies signal periodicity in the range from about ten to several hundred Hertz. Importantly, the model relies on biologically plausible parameters only. It works best for excitatory and inhibitory neuronal couplings of equal strength, the so-called ‘balanced inhibition’. We show how balanced inhibition can serve to identify low-frequency signal periodicity and how variation of a single parameter, the inhibitory time constant, can tune the system to different frequencies.     

Frequency and periodicity are represented in orthogonal maps in the human auditory cortex: evidence from magnetoencephalography

Timbre and pitch are two independent perceptual qualities of sounds closely related to the spectral envelope and to the fundamental frequency of periodic temporal envelope fluctuations, respectively. To a first approximation, the spectral and temporal tuning properties of neurons in the auditory midbrain of various animals are independent, with layouts of these tuning properties in approximately orthogonal tonotopic and periodotopic maps. For the first time we demonstrate by means of magnetoencephalography a periodotopic organization of the human auditory cortex and analyse its spatial relationship to the tonotopic organization by using a range of stimuli with different temporal envelope fluctuations and spectra and a magnetometer providing high spatial resolution. We demonstrate an orthogonal arrangement of tonotopic and periodotopic gradients. Our results are in line with the organization of such maps in animals and closely match the perceptual orthogonality of timbre and pitch in humans. Accepted: 25 July 1997     

On the origin of three base periodicity in genomes

Genomes of almost all organisms have been found to exhibit several periodicities, the most prominent one is the three base periodicity. It is more pronounced in the gene coding regions and has been exploited to identify the segments of a genome that code for a protein. The reason for this three base periodicity in the gene-coding region has been attributed to inhomogeneous nucleotide compositions in the three codon positions. However, this reason cannot explain the three base periodicity present at the level of the whole genome where the codon concept is not applicable. Even though the distribution of each nucleotide is uniform at the positions 0(mod 3), 1(mod 3) and 2(mod 3) when the whole genome data is considered, our analysis reveals that the three base periodicity is arising because of higher correlations among the nucleotides separated by three bases.     

Cellular Expression and Proteolytic Processing of Presenilin Proteins Is Developmentally Regulated During Neuronal Differentiation

Abstract: We have determined the expression of the Alzheimer's disease-associated proteins presenilin-1 and presenilin-2 in primary cultures of rat hippocampal neurons. Neurons highly express presenilin-1 and presenilin-2, whereas both proteins were not detected in astrocytes. Further, we have analyzed the subcellular localization and expression in rat hippocampal neurons during development. Although presenilin proteins were localized predominantly to the endoplasmic reticulum in nonneuronal cells transfected with presenilin cDNAs, in neurons, presenilin proteins were also found in compartments not staining with antibodies to grp78(BiP). Presenilin-1 and presenilin-2 were predominantly detected in vesicular structures within the somatodendritic compartment with much less expression in axons. Polarized distribution of presenilin-1 and presenilin-2 differs slightly, with more presenilin-2 expressed in axons compared with presenilin-1. Presenilin expression was found to be developmentally regulated. Presenilin expression strongly increased during neuronal differentiation until full morphological polarization and then declined. No full-length presenilin-1 or presenilin-2 could be detected within cell lysates. At early developmental stages the expected ～34-kDa N-terminal proteolytic fragment of presenilin-1 and the ～38-kDa fragment of presenilin-2 were detected. Later during differentiation we predominantly detected a ～38-kDa fragment for presenilin-1 and a ～42-kDa fragment for presenilin-2. By epitope mapping, we show that these slower migrating peptides represent N-terminal proteolytic fragments, cleaved C-terminal to the conventional site of processing. It is noteworthy that both presenilin-1 and presenilin-2 undergo alternative proteolytic cleavage at the same stage of neuronal differentiation. Regulation of presenilin expression and proteolytic processing might have implications for the pathological as well as the biological function of presenilins during aging in the human brain.     

Encoding of a spectrally-complex communication sound in the bullfrog's auditory nerve

1. A population study of eighth nerve responses in the bullfrog, Rana catesbeiana, was undertaken to analyze how the eighth nerve codes the complex spectral and temporal structure of the species-specific advertisement call over a biologically-realistic range of intensities. Synthetic advertisement calls were generated by Fourier synthesis and presented to individual eighth nerve fibers of anesthetized bullfrogs. Fiber responses were analyzed by calculating rate responses based on post-stimulus-time (PST) histograms and temporal responses based on Fourier transforms of period histograms. 2. At stimulus intensities of 70 and 80 dB SPL, normalized rate responses provide a fairly good representation of the complex spectral structure of the stimulus, particularly in the low- and mid-frequency range. At higher intensities, rate responses saturate, and very little of the spectral structure of the complex stimulus can be seen in the profile of rate responses of the population. 3. Both AP and BP fibers phase-lock strongly to the fundamental (100 Hz) of the complex stimulus. These effects are relatively resistant to changes in stimulus intensity. Only a small number of fibers synchronize to the low-frequency spectral energy in the stimulus. The underlying spectral complexity of the stimulus is not accurately reflected in the timing of fiber firing, presumably because firing is 'captured' by the fundamental frequency. 4. Plots of average localized synchronized rate (ALSR), which combine both spectral and temporal information, show a similar, low-pass shape at all stimulus intensities. ALSR plots do not generally provide an accurate representation of the structure of the advertisement call. 5. The data suggest that anuran peripheral auditory fibers may be particularly sensitive to the amplitude envelope of sounds.     

Automatic identification of rainfall in acoustic recordings

The rainfall regime is one of the main abiotic components that can cause modifications in the breeding activity of animal species. It has a direct effect on the environmental conditions, and acts as a modifier of the landscape and soundscape. Variations in water quality and acidity, flooding, erosion, and sound distortion are usually related with the presence of rain. Thereby, ecological studies in populations and communities would benefit from improvements in the estimation of rainfall patterns throughout space and time.In this paper, a method for automatic detection of rainfall in forests by using acoustic recordings is proposed. This approach is based on the estimation of the mean value and signal to noise ratio of the power spectral density in the frequency band in which the sound of the raindrops falling over the vegetation layers of the forest is more prominent (i.e. 600–1200 Hz). The results of this method were compared with human auditory identification and data provided by a pluviometer. We achieved a correlation of 95.23% between the data provided by the pluviometer and the predictions of a regression model. Furthermore, we attained a general accuracy between 92.90% and 99.98% when identifying different intensity levels of rainfall on recordings.Nowadays, passive monitoring recorders have been extensively used to study of acoustic-based breeding processes of several animal species. Our method uses the signals acquired by these recorders in order to identify and quantify rainfall events in short and long time spans. The proposed approach will automatically provide information about the rainfall patterns experienced by target species based on audio recordings.     

Surface EMG signal processing during isometric contractions

This paper provides an overview of techniques suitable for the estimation, interpretation and understanding of time variations that affect the surface electromyographic (EMG) signal during sustained voluntary or electrically elicited contractions. These variations concern amplitude variables, spectral variables and muscle fiber conduction velocity, are interdependent and are referred to as the ‘fatigue plot'. The fatigue plot provides information suitable for the classification of muscle behavior. In addition, the information obtainable by means of linear electrode arrays is discussed, and applications of mathematical models for the interpretation of array signals are presented. The model approach provides additional ways for the classification of muscle behavior.     

Phospholipase D Activity of Rat Brain Neuronal Nuclei

Abstract: Phospholipase D activity of rat brain neuronal nuclei, measured with exogenous phosphatidylcholine as substrate, was characterized. The measured activity of neuronal nuclei was at least 36-fold greater than the activity in glia nuclei. The pH optimum was 6.5, and unsaturated but not saturated fatty acids stimulated the enzyme. The optimal concentration of sodium oleate for stimulation of the enzyme activity was 1.2 m M in the presence of 0.75 m M phosphatidylcholine. This phospholipase D activity was cation independent. In the absence of NaF, used as a phosphatidic acid phosphatase inhibitor, the principal product was diglyceride; whereas in the presence of NaF, the principal product was phosphatidic acid. The phospholipase D, in addition to having hydrolytic activity, was able to catalyze a transphosphatidylation reaction. Maximum phosphatidylethanol formation was seen with 0.2–0.3 M ethanol. GTPγS, ATPγS, BeF₂, AIF₃, phosphatidic acid, and phosphatidylethanol inhibited the neuronal nuclei phospholipase D activity. The addition of the cytosolic fraction of brain, liver, kidney, spleen, and heart to the incubation mixtures resulted in inhibition of the phospholipase D activity. Phospholipase D activity was detectable in nuclei prepared from rat kidney, spleen, heart, and liver.     

Exogenous Choline Enhances the Synthesis of Acetylcholine Only Under Conditions of Increased Cholinergic Neuronal Activity

Abstract: The effect of choline (60 mg/kg, i.p.) on fluphenazine- and pentylenetetrazol-induced alterations in the concentration of acetylcholine (ACh) and/or the rate of sodium-dependent high-affinity choline uptake (HACU) in rat striatum and hippocampus was studied. Systemic administration of the dopamine receptor blocking agent fluphenazine hydrochloride (0.5 mg/kg, i.p.) decreased the concentration of ACh in the striatum; this effect was prevented by the prior administration of choline. The central nervous system stimulant pentylenetetrazol (30 mg/kg, i.p.) reduced the concentration of ACh in both striatum and hippocampus and increased the velocity of HACU in the hippocampus. Pretreatment with choline totally prevented the depletion of ACh induced by pentylenetetrazol in the striatum. In the hippocampus, prior administration of choline prevented the pentylenetetrazol-induced increase in the rate of HACU and attenuated the effect of pentylenetetrazol on the levels of ACh. Results indicate that the acute administration of choline antagonizes pharmacologically induced alterations in cholinergic activity as assessed by the rate of HACU and the steady-state concentration of ACh. Furthermore, data support the hypothesis that the administration of choline increases the ability of central cholinergic neurons to synthesize ACh under conditions of increased neuronal activity.     

温度对神经元网络活动的影响

利用多通道微电极阵列上培养的海马神经元网络,通过分析28～41℃范围内不同温度时网络自发放电频率．幅度和相邻峰电位时间间隔(interspike interval,ISI)的变化,探讨了温度对网络活动的影响。发现温度升高过程中放电频率、幅度呈不同程度增大的趋势,峰电位数目的变化程度随其间隔的增大呈减小趋势。结果表明体外培养的胎鼠海马神经元的网络活动具有温度敏感性。     

Multiplexing and demultiplexing logic functions for computing signal processing tasks in synthetic biology

Building biological devices to perform computational and signal processing tasks is one of the main research issues in synthetic biology. Herein, two modular biological systems that could mimic multiplexing and demultiplexing logic functions are proposed and discussed. These devices, called multiplexer (mux) and demultiplexer (demux), respectively, have a remarkable importance in electronic, telecommunication, and signal processing systems and, similarly, they could play a crucial role if implemented in a living organism, such as Escherichia coli. BioBrick standard parts were used to design mux and demux and to construct two genetic circuits that could carry out the desired tasks. A modular approach, mimicking basic logic gates (AND, OR, and NOT) with protein/autoinducer or protein/DNA interactions and interconnecting them to create the final circuits, was adopted. A mathematical model of the designed gene networks was been defined and simulations performed to validate the expected behavior of the systems. In addition, circuit subparts were tested in vivo and the results used to determine some of the parameters of the mathematical model. According to both the experimental and simulated results, guidelines for future finalization of mux and demux are provided.     

Phenotypic integration and the evolution of signal repertoires: A case study of treefrog acoustic communication

Animal signals are inherently complex phenotypes with many interacting parts combining to elicit responses from receivers. The pattern of interrelationships between signal components reflects the extent to which each component is expressed, and responds to selection, either in concert with or independently of others. Furthermore, many species have complex repertoires consisting of multiple signal types used in different contexts, and common morphological and physiological constraints may result in interrelationships extending across the multiple signals in species’ repertoires. The evolutionary significance of interrelationships between signal traits can be explored within the framework of phenotypic integration, which offers a suite of quantitative techniques to characterize complex phenotypes. In particular, these techniques allow for the assessment of modularity and integration, which describe, respectively, the extent to which sets of traits covary either independently or jointly. Although signal and repertoire complexity are thought to be major drivers of diversification and social evolution, few studies have explicitly measured the phenotypic integration of signals to investigate the evolution of diverse communication systems. We applied methods from phenotypic integration studies to quantify integration in the two primary vocalization types (advertisement and aggressive calls) in the treefrogs Hyla versicolor, Hyla cinerea, and Dendropsophus ebraccatus. We recorded male calls and calculated standardized phenotypic variance–covariance ( P ) matrices for characteristics within and across call types. We found significant integration across call types, but the strength of integration varied by species and corresponded with the acoustic similarity of the call types within each species. H. versicolor had the most modular advertisement and aggressive calls and the least acoustically similar call types. Additionally, P was robust to changing social competition levels in H. versicolor. Our findings suggest new directions in animal communication research in which the complex relationships among the traits of multiple signals are a key consideration for understanding signal evolution.     

小波变换与生物医学信号处理

作为数字信号处理领域的一个重要分支,生物医学信号处理理论与技术的研究一直受到国内外科技工作者的高度重视。小波变换是近年来发展起来的一种新的信号分析工具。本文结合生物医学信号与小波变换的特点,探讨了小波变换在生物医学信号处理领域的应用前景。     

Disposition of Gangliosides and Sialosylglycoproteins in Neuronal Membranes

Abstract Labeled gangliosides and glycoproteins were obtained by incubation of homogenized neuronal perikarya from rat brain with CMP-[³H] N -acetyl neuraminic acid. The highest degree of labelling was observed in a subcellular fraction that also showed the highest specific activities for several ganglioside glycosyltransferases. The [³H] sialosylglycoconjugates of this fraction remained associated with the membranes after treatment with 1 m -KCl, 125 m m -EDTA, repeated freezing and thawing, or controlled sonication, but were solubilized by sodium deoxycholate (DOC) at a concentration high enough to solubilize the choline phospholipids. About 75% of the neuraminidase-labile sialosyl residues of these labeled endogenous gangliosides and glycoproteins were protected from the action of added neuraminidase or pronase or both enzymes added together. The protection was not abolished by pretreatment of the membranes with high ionic strength or with EDTA but was abolished by sonication or low concentration of DOC. Between 50 and 80% of the neuraminidase-labile sialosyl residues of the gangliosides of the neuronal perikaryon membrane fraction labeled in vivo by an intracerebral injection of N -[³H]acetylmannos-amine were, at 3 h after the injection, also protected from the action of added neuraminidase. The protection was abolished by the addition of DOC. In contrast with the behavior of the labeled glycoconjugates of this neuronal perikaryon fraction, the gangliosides and sialosylglycoproteins from intact synaptosomes were accessible to neuraminidase. It is suggested that most gangliosides and sialosylglycoproteins are sialosylated as intrinsic components of the neuronal perikaryon membrane fraction and that at some stage of the process of transport through the axon and incorporation into the synaptic plasma membrane they change their accessibility to added enzymes.     

Multiple acoustic features underlie vocal signal recognition in tamarins: antiphonal calling experiments

We examine which acoustic features are relevant for recognition of the cotton-top tamarin (Saguinus oedipus) combination long-call. This vocalization, emitted by both males and females, functions in maintaining group cohesion, territory defense and mate attraction. Using the tamarins natural antiphonal vocal response to hearing a combination long-call as the primary measure of recognition, we presented subjects with synthetic exemplars of combination long-calls in which we manipulated across one of three acoustic dimensions: frequency, time and amplitude. Results indicated that although acoustic features in the frequency and time domains are important for combination long-call recognition, the changes in amplitude within and between syllables are not. Furthermore, while the fundamental frequency appears to be the used to encode information about the frequency contour, the temporal information is derived from the harmonics. Overall, these results suggest that tamarins use a specific suite of acoustic features for combination long-call recognition.Abbreviations CLC combination long-call - F0 fundamental frequency - JND just noticeable difference - JMD just meaningful difference - IPI inter-pulse interval     

信号处理技术在生物分子序列分析中的应用

信号处理技术在生物分子序列分析中的应用主要包括周期分析、基因预测、相似和重复序列分析、蛋白质分子结构预测等。涉及的技术方法有：Fourier变换、小波变换、相关分析、分形技术、非线性信号处理技术等。本文将全面回顾这些应用。     

Convergence of temporal and spectral information into acoustic images of complex sonar targets perceived by the echolocating bat,Eptesicus fuscus

1. FM echolocating bats (Eptesicus fuscus) were trained to discriminate between a two-component complex target and a one-component simple target simulated by electronically-returned echoes in a series of experiments that explore the composition of the image of the two-component target. In Experiment I, echoes for each target were presented sequentially, and the bats had to compare a stored image of one target with that of the other. The bats made errors when the range of the simple target corresponded to the range of either glint in the complex target, indicating that some trace of the parts of one image interfered with perception of the other image. In Experiment II, echoes were presented simultaneously as well as sequentially, permitting direct masking of echoes from one target to the other. Changes in echo amplitude produced shifts in apparent range whose pattern depended upon the mode of echo presentation. 2. Eptesicus perceives images of complex sonar targets that explicitly represent the location and spacing of discrete glints located at different ranges. The bat perceives the target's structure in terms of its range profile along a psychological range axis using a combination of echo delay and echo spectral representations that together resemble a spectrogram of the FM echoes. The image itself is expressed entirely along a range scale that is defined with reference to echo delay. Spectral information contributes to the image by providing estimates of the range separation of glints, but it is transformed into these estimates. 3. Perceived absolute range is encoded by the timing of neural discharges and is vulnerable to shifts caused by neural amplitude-latency trading, which was estimated at 13 to 18 microseconds per dB from N1 and N4 auditory evoked potentials in Eptesicus. Spectral cues representing the separation of glints within the target are transformed into estimates of delay separations before being incorporated into the image. However, because they are encoded by neural frequency tuning rather than the time-of-occurrence of neural discharges, the perceived range separation of glints in images is not vulnerable to amplitude-latency shifts. 4. The bat perceives an image that is displayed in the domain of time or range. The image receives no evident spectral contribution beyond what is transformed into delay estimates. Although the initial auditory representation of FM echoes is spectrogram-like, the time, frequency, and amplitude dimensions of the spectrogram appear to be compressed into an image that has only time and amplitude dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dissection of a model for neuronal parabolic bursting

We have obtained new insight into the mechanisms for bursting in a class of theoretical models. We study Plant's model [24] for Aplysia R-15 to illustrate our view of these so-called parabolic bursters, which are characterized by low spike frequency at the beginning and end of a burst. By identifying and analyzing the fast and slow processes we show how they interact mutually to generate spike activity and the slow wave which underlies the burst pattern. Our treatment is essentially the first step of a singular perturbation approach presented from a geometrical viewpoint and carried out numerically with AUTO [12]. We determine the solution sets (steady state and oscillatory) of the fast subsystem with the slow variables treated as parameters. These solutions form the slow manifold over which the slow dynamics then define a burst trajectory. During the silent phase of a burst, the solution trajectory lies approximately on the steady state branch of the slow manifold and during the active phase of spiking, the trajectory sweeps through the oscillation branch. The parabolic nature of bursting arises from the (degenerate) homoclinic transition between the oscillatory branch and the steady state branch. We show that, for some parameter values, the trajectory remains strictly on the steady state branch (to produce a resting steady state or a pure slow wave without spike activity) or strictly in the oscillatory branch (continuous spike activity without silent phases). Plant's model has two slow variables: a calcium conductance and the intracellular free calcium concentration, which activates a potassium conductance. We also show how bursting arises from an alternative mechanism in which calcium inactivates the calcium current and the potassium conductance is insensitive to calcium. These and other biophysical interpretations are discussed.