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PubMed2003

Astroglial swelling in the neuronal depolarization ensemble.

The coupling between neuronal depolarization and astroglial swelling was examined. First, previous in vitro data for the swelling of cultured neurons (N18; rat neuroblastoma) and astroglia (C6; rat astroglyoma) upon exposure to a hypoosmotic solution were reappraised. Neurons swelled rapidly, forming blisters, and easily burst. whereas astroglia resisted swelling and slowly assumed a large full-moon shape. The time constant of swelling was 35.2 +/- 7.8 s for N18 and 594.8 +/- 554.0 s for C6. The glial plasmic membrane was found to be much stronger than the neuronal one, presumably due to a well-developed cytoskeleton. To overcome such neuronal membranous weakness, strong astroglial processes need to cover the neurons including the cell body and synapses, as demonstrated electron-microscopically. Next, in situ astroglial swelling was investigated in rats. During K(+)-induced cortical spreading depression, increases or decreases of a wave-ring spread of light (550 nm) transmission through a 1 mm-thick cerebral cortical layer was observed. The moving local optical density decrease in the cortex was attributable to local vascular bed compression induced by astroglial swelling, since concomitant occurrence of colocated dynamic capillary flow stall was confirmed by a hemodilution technique. Astroglial swelling may occur in an ensemble acting during neuronal depolarization, suggesting that neurons and astroglia behave like a unit complex.

Animals↗
PubMed1995

Structure refinement with molecular dynamics and a Boltzmann-weighted ensemble.

Time-averaging restraints in molecular dynamics simulations were introduced to account for the averaging implicit in spectroscopic data. Space- or molecule-averaging restraints have been used to overcome the fact that not all molecular conformations can be visited during the finite time of a simulation of a single molecule. In this work we address the issue of using the correct Boltzmann weighting for each member of an ensemble, both in time and in space. It is shown that the molecular- or space-averaging method is simple in theory, but requires a priori knowledge of the behaviour of a system. This is illustrated using a five-atom model system and the small cycle peptide analogue somatostatin. When different molecular conformers that are separated by energy barriers insurmountable on the time scale of a simulation contribute significantly to a measured NOE intensity, the use of space- or molecule-averaged distance restraints yields a more appropriate description of the measured data than conventional single-molecule refinement with or without application of time averaging.

Algorithms↗
PubMed1995

Cooperative effects of neuronal ensembles.

Electrophysiological properties of neurons as the basic cellular elements of the central nervous system and their synaptic connections are well characterized down to a molecular level. However, the behavior of complex noisy networks formed by these constituents usually cannot simply be derived from the knowledge of its microscopic parameters. As a consequence, cooperative phenomena based on the interaction of neurons were postulated. This is a report on a study of global network spike activity as a function of synaptic interaction. We performed experiments in dissociated cultured hippocampal neurons and, for comparison, simulations of a mathematical model closely related to electrophysiology. Numeric analyses revealed that at a critical level of synaptic connectivity the firing behavior undergoes a phase transition. This cooperative effect depends crucially on the interaction of numerous cells and cannot be attributed to the spike threshold of individual neurons. In the experiment a drastic increase in the firing level was observed upon increase of synaptic efficacy by lowering of the extracellular magnesium concentration, which is compatible with our theoretical predictions. This "on-off" phenomenon demonstrates that even in small neuronal ensembles collective behavior can emerge which is not explained by the characteristics of single neurons.

Animals↗
PubMed1986

Ensemble noise and current relaxation analysis of K+ current in single isolated salivary acinar cells from rat.

The K+ channel in rat parotid gland acinar cells were investigated by ensemble current noise analysis in single isolated cells employing the giga-seal whole cell current recording mode. Sets of 20-40 identical de- and hyperpolarization voltage steps were applied and the resultant current records were processed by computer to obtain the mean and the variance of the current. The time-course of the mean current could be fitted by the sum of two exponentials, suggesting a 3-state model. The simplest plausible hypothesis is a model with one open and two closed states. Assuming this model, the relationship between the variance (sigma 2) and the mean current (I) could be fitted by the function sigma 2/I = i--I/N. The estimated single channel i/V-relations were similar to those taken from single channel current recordings, and the size of the population of channels per cell (N) was 76 +/- 26 (n = 12). The validity of the model was tested by a successful simulation of the time-course of the variance.

Animals↗
PubMedDate not supplied

Role of inhibition in the formation of a dynamic mosaic of neuronal ensembles in the cerebral cortex.

The spatial-temporal organization of neuronal responses in the rat visual cortex was investigated during the action on the retina of light stimuli of various size. It was shown that a leading role in the formation of a dynamic mosaic of neuronal ensembles belongs to inhibition. Two systems of inhibition are distinguished, involved in differing degree in the organization of the operating mechanisms of the brain during the action of various stimuli.

Animals↗
PubMed2003

Human GH pulsatility: an ensemble property regulated by age and gender.

Age and gender impact the full repertoire of neurohormone systems, including most prominently the somatotropic, gonadotropic and lactotropic axes. For example, daily GH production is approximately 2-fold higher in young women than men and varies by 20-fold by sexual developmental status and age. Deconvolution estimates of 24-h GH secretion rates exceed 1200 microg/m2 in adolescents and fall below 60 microg/m2 in aged individuals. The present overview highlights plausible factors driving such lifetime variations in GH availability, i.e., estrogen, aromatizable androgen, hypothalamic peptides and negative feedback by GH and IGF-I. In view of the daunting complexity of potential neuromodulatory signals, we underline the utility of conceptualizing a simplified three-peptide regulatory ensemble of GHRH, GHRP (ghrelin) and somatostatin. The foregoing signals act as individual and conjoint mediators of adaptive GH control. Regulation is enforced at 3-fold complementary time scales, which embrace pulsatile (burst-like), entropic (orderly) and 24-h rhythmic (nycthemeral) modes of GH release. This unifying platform offers a convergent perspective of multivalent control of GH outflow.

Adolescent↗
PubMed2001

Neuronal responses in the frontal cortico-basal ganglia system during delayed matching-to-sample task: ensemble recording in freely moving rats.

Electrophysiological recording of single neuron activity has been conducted in rats to investigate the patterns of distributed neuronal responses in the frontal cortico-basal ganglia system that code information during a spatial-delayed matching-to-sample task (DMTSt). Rats were trained to press one of the two retractable levers presented randomly as a sample response. The first valid nose-poke after a delay resulted in the presentation of both levers. Pressing the same lever as the sample lever led to a water reward (match to sample), whereas pressing the lever opposite the sample lever resulted in a time-out (house light turned off). One hundred seventy-one neurons in the medial prefrontal cortex (mPFC), 51 in the dorsal striatum (STR), and 93 in the nucleus accumbens (NAc) were recorded during DMTSt. Different patterns of neuronal responses were observed during different behavioral episodes (sample, delay, and match phases) in all three recording areas. Space-related neuronal responses specific to the side of the lever pressed were more often found in the sample phase than in the match phase in all three areas studied. Neuronal responses specific to either correct or error trials were observed with similar percentages in the mPFC and the NAc, while the incidence of correct/error-coded activity in the STR was lower. Ensemble neuronal activity that coded sample versus match lever presses was observed in three out of five rats in sets of trials with similar speed and trajectory of lever press. The results reveal specific patterns of neural responses in the frontal cortico-basal ganglia system in rats during the DMTSt and suggest the existence of specific neuronal coding for different behavioral events associated with a learned short-term memory process.

Action Potentials↗
PubMed2006

Multimodal fusion imaging ensemble for targeted sentinel lymph node management: initial results of an innovative promising approach for anatomically difficult lymphatic drainage in different tumour entities.

PURPOSE: There are situations where exact identification and localisation of sentinel lymph nodes (SLNs) are very difficult using lymphoscintigraphy, a hand-held gamma probe and vital dye, either a priori or a posteriori. We developed a new method using a simultaneous injection of two lymphotropic agents for exact topographical tomographic localisation and biopsy of draining SLNs. The purpose of this prospective pilot study was to investigate the feasibility and efficacy of this method ensemble. METHODS: Fourteen patients with different tumour entities were enrolled. A mixture of (99m)Tc-nanocolloid and a dissolved superparamagnetic iron oxide was injected interstitially. Dynamic, sequential static lymphoscintigraphy and SPECT served as pathfinders. MR imaging was performed 2 h after injection. SPECT, contrast MRI and, if necessary, CT scan data sets were fused and evaluated with special regard to the topographical location of SLNs. The day after injection, nine patients underwent SLN biopsy and, in the presence of SLN metastasis, an elective lymph node dissection. RESULTS: Twenty-five SLNs were localised in the 14 patients examined. A 100% fusion correlation was achieved in all patients. The anatomical sites of SLNs detected during surgery showed 100% agreement with those localised on the multimodal fusion images. SLNs could be excised in 11/14 patients, six of whom had nodal metastasis. CONCLUSION: Our novel approach of multimodal fusion imaging for targeted SLN management in primary tumours with lymphatic drainage to anatomically difficult regions enables SLN biopsy even in patients with lymphatic drainage to obscure regions. Currently, we are testing its validity in larger patient groups and other tumour entities.

Adult↗
PubMed1997

Sharply tuned cochlear nerve ensemble periodicity responses to sonic and ultrasonic frequencies.

Vertebrates are able to perceive the pitch of a series of harmonics, even when the fundamental frequency has been removed from the acoustic stimulus. Neural periodicity responses corresponding to the "missing fundamental" frequency of sonic stimuli have been observed in the auditory system of several animal species, including our own. This paper examines periodic cochlear neural responses of the gerbil. Periodicity responses to both sonic and ultrasonic stimuli originate within the cochlea of this animal. Acoustic stimuli, consisting of 2-12 successive harmonic frequencies, were used to generate an ensemble cochlear nerve periodicity response that was recorded from the round window of the cochlea. This response had a frequency equal to that of the missing fundamental, and not to those of the harmonic stimuli. Forward masking of the stimuli used to produce the periodicity response was used to generate sharp tuning curves, with tip frequencies corresponding to the harmonics and not to the periodicities. The sharpness of these functions increased as the frequencies of the harmonics increased, up to at least 38 kHz. This property could be related to reception of ultrasonic vocalizations utilized by many rodent species.

Acoustic Stimulation↗
PubMed2006

Decoding spike train ensembles: tracking a moving stimulus.

We consider the issue of how to read out the information from nonstationary spike train ensembles. Based on the theory of censored data in statistics, we propose a 'censored' maximum-likelihood estimator (CMLE) for decoding the input in an unbiased way when the spike activity is observed over time windows of finite length. Compared with a rate-based, moment estimator, the CMLE is proved consistently more efficient, particularly with nonstationary inputs. Using our approach, we show that a dynamical input to a group of neurons can be inferred accurately and with high temporal resolution (50 ms) using as few as about one spike per neuron within each decoding window. By applying our theoretical results to a population coding setting, we then demonstrate that a spiking neural network can encode spatial information in such a way to allow fast and precise tracking of a moving target.

Brain↗
PubMed1990

The accuracy of estimating the thermal insulation of clothing ensembles - the effect of appraisers.

The effect of the appraisers on the estimation of the thermal insulation of clothing ensembles was investigated. Nine appraisers, four experienced and five inexperienced, estimated the total thermal insulation by summing the values for individual garments. Lists of individual garments worn by workers were given during thermal comfort measurements carried out in shops and stores during one winter and summer. The beginners estimated the thermal insulation as accurately as the experienced appraisers. There were, however, great individual differences, for which three main reasons were found. Interpolation between the insulation provided by two garments was insufficient, and the insulation of these garments should be checked in more precise tables. Classification of the garments into heavy, medium and light clothing items was not adequate, and garments not listed by the workers confused the estimation given by different appraisers. The effect of error in thermal insulation on the PMV index is negligible if more than one appraiser estimates the thermal insulation and the mean of the estimates is used.

Journal Article↗
PubMed1984

Ensemble reactions of neurons in the reticular formation of the cat--categorization of inputs and temporal influences.

A method of recording ensemble reactions of reticular neurons was applied in anesthetized cats to obtain information about categorization of inputs and the influence of the time factor upon a pattern of responses, reactions to stimulus intensity changes and to complex stimuli, and temporal influences with their relation to plastic changes induced by iterative stimulation. In spite of some variability of the pattern of responses evoked in the reticular formation (RF) by electrical stimulation of the same source, reactions of the parenchyma of the RF differentiate heterotopic stimuli; reactions evoked from receptor areas situated closely to each other exhibited a similar pattern whereas less resemblance was found in the case of responses evoked from sources with a heterosegmental projection and from contralateral sources. Stimulus intensity changes did not influence substantially the pattern of recordings in the RF. The noticeable effect resulting from the increase of stimulus intensity was enlargement of responses. A complex stimulus (two heterotopic stimuli applied simultaneously) was manifested by a reaction which, in comparison with reactions evoked from each of both sources separately, had a different pattern. A trend of changes in the size of responses evoked in the RF by continuous stimulation (60 stimuli, 0.3 Hz) was observed only in some cases. Abrupt alterations of the stimulation rate (0.3 Hz in equilibrium 1 Hz, 0.3 Hz in equilibrium 2 Hz) resulted in a prompt change in responses. With constant stimulation conditions, this activity was fairly constant with an absence of trends. Persistent changes were observed only in a minority of cases. The neuronal apparatus of the RF computes ongoing effects on the basis of ability to discriminate different inputs and to readily change its function. The extent to which the RF holds information about the antecedent "history" of its functioning and the extent to which intrinsic mechanisms of the RF by itself are responsible for behavioral habituation remains problematical.

Animals↗
PubMed1991

Stimulus classification by ensembles of climbing fiber receptive fields.

Although the local structure of the cerebellum is fairly uniform and its inputs are often widely shared, outputs from different regions of the cerebellar cortex reach different parts of the cerebellar and vestibular nuclei, which can affect the rest of the nervous system in different ways. In this review, we explain how different ensembles of climbing fiber responses in the anterior lobe and paramedian lobule can be generated by a tactile stimulus to the distal hindpaw. Apart from differing in degree of activation, the cortical regions differ also in the detailed pattern of the activation transmitted. The anterior lobe can distinguish a greater diversity of stimuli to various skin surfaces than can the paramedian median lobule. This differential classification of particular stimulus arrays by the two cerebellar regions could produce distinct patterns of neuronal activity in various corticonuclear compartments.

Animals↗
PubMed1995

The subtleties of ultrasound images of an ensemble of cells: simulation from regular and more random distributions of scatterers.

Significant differences in the backscatter amplitudes which are correlated with different tissue morphology have been observed in ultrasound images of tissue. While many factors could be linked to subtle changes in the images, the purpose of this paper is to explore the possibility that backscatter signals are linked to the organization of the spatial distribution of individual cells that produce an ensemble of scattering sources. Simple one- and two-dimensional simulations of backscatter signals produced by weak scatters separated by << lambda to < lambda in regular, random, and pseudo-random distributions in a "sample" are performed. Both regular and pseudo-random distributions produce large boundary signals, and in the central regions of the sample, the square root of the backscatter power is directly related to the amount of randomization, R, over a large range. Large changes in backscattering intensities are predicted for the same density of scatterers with differing R in different regions of the same sample. Thus, the subtle differences in the scattering distribution should show significant changes in the backscatter images.

Animals↗
PubMed1986

Effects of extracochlear direct current stimulation on the ensemble auditory nerve activity of cats.

The influence of direct current applied by round window stimulation on the whole nerve response of the auditory nerve of the cat has been studied. Effects on acoustically driven activity (CAP) and on the ensemble spontaneous activity of the nerve were observed. Stimulation with positive current suppressed driven and spontaneous activity. The strength and spread of suppressive effects was a function of the applied current level. After a period of positive electrical stimulation, driven and spontaneous activity rapidly returned to normal values. A rebound effect was sometimes observed, marked by a brief increase in spontaneous activity above the normal level. Negative current initially produced an increase in the amplitude of driven and spontaneous responses. Prolonged stimulation with negative current (greater than 30 s) resulted in a subsequent, graded reduction of neural activity, until a profound suppression of spontaneous and evoked neural activity was attained. The amplitude/latency relationship of CAPs was altered during passing of negative currents but not during passing of positive currents. Recovery from the suppression generated by negative currents was commonly prolonged for anything from a few seconds to many minutes; prolongation was dependent on stimulus amplitude, duration and duty cycles.

Acoustic Stimulation↗
PubMed1995

Temporal structure in spatially organized neuronal ensembles: a role for interneuronal networks.

Network oscillations are postulated to be instrumental for synchronizing the activity of anatomically distributed populations of neurons. Results from recent studies on the physiology of cortical interneurons suggest that through their interconnectivity, they can maintain large-scale oscillations at various frequencies (4-12 Hz, 40-100 Hz and 200 Hz). We suggest that networks of inhibitory interneurons within the forebrain impose co-ordinated oscillatory 'contexts' for the 'content' carried by networks of principal cells. These oscillating inhibitory networks may provide the precise temporal structure necessary for ensembles of neurons to perform specific functions, including sensory binding and memory formation.

Animals↗
PubMed2006

Classifier ensembles for protein structural class prediction with varying homology.

Structural class characterizes the overall folding type of a protein or its domain. A number of computational methods have been proposed to predict structural class based on primary sequences; however, the accuracy of these methods is strongly affected by sequence homology. This paper proposes, an ensemble classification method and a compact feature-based sequence representation. This method improves prediction accuracy for the four main structural classes compared to competing methods, and provides highly accurate predictions for sequences of widely varying homologies. The experimental evaluation of the proposed method shows superior results across sequences that are characterized by entire homology spectrum, ranging from 25% to 90% homology. The error rates were reduced by over 20% when compared with using individual prediction methods and most commonly used composition vector representation of protein sequences. Comparisons with competing methods on three large benchmark datasets consistently show the superiority of the proposed method.

Algorithms↗