共查询到20条相似文献,搜索用时 62 毫秒
1.
The wavelet analysis is a powerful tool for analyzing and detecting features of signals characterized by time-dependent statistical
properties, as biomedical signals. The identification and the analysis of the components of these signals in the time–frequency
domain, give meaningful information about the physiological mechanisms that govern them. This article presents the results
of the wavelet analysis applied to the a-wave component of the human electroretinogram. In order to deepen and improve our knowledge about the behavior of the early photoreceptoral
response, including the possible activation of interactions and correlations among the photoreceptors, we have detected and
identified the stable time–frequency components of the a-wave, using six representative values of luminance. The results indicate the occurrence of three frequencies lying in the range
20–200 Hz. The lowest one is attributed to the summed activities of the photoreceptors. The others are weaker and at low luminance
one of them does not occur. We relate them to the response of the rods and the cones whose aggregate activities are non-linear
and typically exhibit self-organization under selective stimuli. The identification of the stable frequency components and
of their times of occurrence helps us to shine light about the complex mechanisms governing the a-wave. The present results are promising toward the assessment of more refined model concerning the photoreceptoral activities. 相似文献
2.
《Electronic Notes in Theoretical Computer Science》1991,80(2):89-93
Pattern visual evoked potentials (VEPs) to transient and steady-state stimulation were recorded in 10 normal subjects at 4 levels of luminance (180, 57, 22 and 11 cd/m2). VEPs were also recorded in 5 patients with optic neuropathy at a fixed luminance (180 cd/m2). The relationship between P100 latency of transient VEPs (T-VEPs) and the phase of steady-state VEPs (S-VEPs) was analyzed. As luminance decreased in normal subjects, P100 latency was prolonged and the phase lag increased. A significant linear relationship between the P100 latency and phase was found. Patients showed both the prolonged P100 latency and the delayed phase. The simple linear regression line of the phase-P100 latency function of normal subjects closely matched the patients' values. These results suggest that changes in the phase may be equivalent to changes in the P100 latency. S-VEPs, therefore, may be clinically useful in assessing visual function. 相似文献
3.
Uri Werner Edith Suss-Toby Ayelet Rom Baruch Minke 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1992,170(4):427-434
Summary Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca2+ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La3+), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca2+ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca2+, but not K+ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La3+. The EGTA experiments suggest that internal Ca2+ is necessary for light excitation of barnacle photoreceptors while the La3+ experiments suggest that La3+-sensitive inward current is necessary to maintain excitation during prolonged light.Abbreviations EGTA
ethylenglyol-bis-(-aminoethylether) N, N, N1, N1-tetraacetate
- BAPTA
bis-(0-aminophenoxy)-ethane-N, N, N1, N1-tetraacetic acid
- DMSO
dimethyl sulfoxide
- trp
transient receptor potential
- nss
no steady state
- ASW
artificial sea water 相似文献
4.
Susan A. Werness S. Dale Fay Kim T. Blackwell Thomas P. Vogl Daniel L. Alkon 《Biological cybernetics》1993,70(1):95-28
A companion paper in a previous issue of this journal presented a resistance-capacitance circuit computer model of the four-neuron visual-vestibular network of the invertebrate marine mollusk Hermissenda crassicornis. In the present paper, we demonstrate that changes in the model's output in response to simulated associative training is quantitatively similar to behavioral and electrophysiological changes in response to associative training of Hermissenda crassicornis. Specifically, the model demonstrates many characteristics of conditioning: sensitivity to stimulus contingency, stimulus specificity, extinction, and savings. The model's learning features also are shown to be devoid of non-associative components. Thus, this computational model is an excellent tool for examining the information flow and dynamics of biological associative learning and for uncovering insights concerning associative learning, memory, and recall that can be applied to the development of artificial neural networks. 相似文献
5.
Handheld devices such as mobile phones and tablet computers have become widespread with thousands of available software applications. Recently, handhelds are being proposed as part of medical imaging solutions, especially in emergency medicine, where immediate consultation is required. However, handheld devices differ significantly from medical workstation displays in terms of display characteristics. Moreover, the characteristics vary significantly among device types. We investigate the image quality characteristics of various handheld devices with respect to luminance response, spatial resolution, spatial noise, and reflectance. We show that the luminance characteristics of the handheld displays are different from those of workstation displays complying with grayscale standard target response suggesting that luminance calibration might be needed. Our results also demonstrate that the spatial characteristics of handhelds can surpass those of medical workstation displays particularly for recent generation devices. While a 5 mega-pixel monochrome workstation display has horizontal and vertical modulation transfer factors of 0.52 and 0.47 at the Nyquist frequency, the handheld displays released after 2011 can have values higher than 0.63 at the respective Nyquist frequencies. The noise power spectra for workstation displays are higher than 1.2×10−5 mm2 at 1 mm−1, while handheld displays have values lower than 3.7×10−6 mm2. Reflectance measurements on some of the handheld displays are consistent with measurements for workstation displays with, in some cases, low specular and diffuse reflectance coefficients. The variability of the characterization results among devices due to the different technological features indicates that image quality varies greatly among handheld display devices. 相似文献
6.
Peter M. O’Day Juan Bacigalupo Cecilia Vergara Joan E. Haab 《Molecular neurobiology》1997,15(1):41-63
Investigation of phototransduction in invertebrate photoreceptors has revealed many physiological and biochemical features
of fundamental biological importance. Nonetheless, no complete picture of phototransduction has yet emerged. In most known
cases, invertebrate phototransduction involves polyphosphoinositide and cyclic GMP (cGMP) intracellular biochemical signaling
pathways leading to opening of plasma membrane ion channels. Excitation is Ca2+-dependent, as are adaptive feedback processes that regulate sensitivity to light. Transduction takes place in specialized
subcellular regions, rich in microvilli and closely apposed to submicrovillar membrane systems. Thus, excitation is a highly
localized process.
This article focuses on the intracellular biochemical signaling pathways and the ion channels involved in invertebrate phototransduction.
The coupling of signaling cascades with channel activation is not understood for any invertebrate species. Although photoreceptors
have features that are common to most or all known invertebrate species, each species exhibits unique characteristics. Comparative
electrophysiological, biochemical, morphological, and molecular biological approaches to studying phototransduction in these
species lead to fundamental insights into cellular signaling. Several current controversies and proposed phototransduction
models are evaluated. 相似文献
7.
Sei-ichi Tsujimura Kazuhiko Ukai Daisuke Ohama Atsuo Nuruki Kazutomo Yunokuchi 《Proceedings. Biological sciences / The Royal Society》2010,277(1693):2485-2492
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. 相似文献
8.
Roman V. Frolov Esa-Ville Immonen Matti Weckström 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2014,200(3):209-219
The compound eye of the cricket Gryllus bimaculatus contains a specialized dorsal rim area (DRA) populated by distinct blue-sensitive photoreceptors responsible for perception of polarized light. The rest of the eye is dominated by green-sensitive photoreceptors. Using patch clamp we studied dissociated ommatidia of nocturnal adults and diurnal eight-instar nymphs with the goals (1) of characterizing the biophysical properties of cricket photoreceptors in general and (2) describing the functionally dissimilar blue- and green-sensitive photoreceptors in terms of voltage-gated channel composition and signal coding. Despite different lifestyles, adult and nymph photoreceptors were indistinguishable. No significant circadian changes were observed in K+ currents. In contrast, prominent differences were seen between blue- and green-sensitive photoreceptors. The former were characterized by relatively low absolute sensitivity, high input resistance, slow quantum bumps with long latencies, small light-induced and K+ currents and low steady-state depolarization. Information rate, a measure of photoreceptor performance calculated from voltage responses to bandwidth-limited white noise-modulated light contrast, was 87 ± 8 bits s?1 in green-sensitive photoreceptors vs. 59 ± 14 bits s?1 in blue-sensitive photoreceptors, implying a limited role of DRA in the perception of visual contrasts. In addition, evidence of electrical coupling between photoreceptors is presented. 相似文献
9.
Ben Katz Olaf Voolstra Hanan Tzadok Bushra Yasin Elisheva Rhodes-Modrov Jonas-Peter Bartels 《Channels (Austin, Tex.)》2017,11(6):678-685
Drosophila photoreceptors respond to oscillating light of high frequency (~100 Hz), while increasing the oscillating light intensity raises the maximally detected frequency. Recently, we reported that dephosphorylation of the light-activated TRP ion channel at S936 is a fast, graded, light-, and Ca2+-dependent process. We further found that this process affects the detection limit of high frequency oscillating light. Accordingly, transgenic Drosophila, which do not undergo phosphorylation at the S936-TRP site (trpS936A), revealed a short time-interval before following the high stimulus frequency (oscillation-lock response) in both dark- and light-adapted flies. In contrast, the trpS936D transgenic flies, which mimic constant phosphorylation, showed a long-time interval to oscillation-lock response in both dark- and light-adapted flies. Here we extend these findings by showing that dark-adapted trpS936A flies reveal light-induced current (LIC) with short latency relative to trpWT or trpS936D flies, indicating that the channels are a limiting factor of response kinetics. The results indicate that properties of the light-activated channels together with the dynamic light-dependent process of TRP phosphorylation at the S936 site determine response kinetics. 相似文献
10.
There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light whereas cones operate continuously under rapidly changing bright light conditions. Absorption of light by rod- and cone-specific visual pigments in the outer segments of photoreceptors triggers a phototransduction cascade that eventually leads to closure of cyclic nucleotide-gated channels on the plasma membrane and cell hyperpolarization. This light-induced change in membrane current and potential can be registered as a photoresponse, by either classical suction electrode recording technique1,2 or by transretinal electroretinogram recordings (ERG) from isolated retinas with pharmacologically blocked postsynaptic response components3-5. The latter method allows drug-accessible long-lasting recordings from mouse photoreceptors and is particularly useful for obtaining stable photoresponses from the scarce and fragile mouse cones. In the case of cones, such experiments can be performed both in dark-adapted conditions and following intense illumination that bleaches essentially all visual pigment, to monitor the process of cone photosensitivity recovery during dark adaptation6,7. In this video, we will show how to perform rod- and M/L-cone-driven transretinal recordings from dark-adapted mouse retina. Rod recordings will be carried out using retina of wild type (C57Bl/6) mice. For simplicity, cone recordings will be obtained from genetically modified rod transducin α-subunit knockout (Tα-/-) mice which lack rod signaling8. 相似文献
11.
Russell G. Foster Alan Roberts 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1982,145(3):413-419
Summary Behavioural experiments demonstrate that embryos and young larval stages ofXenopus laevis when exposed to a sudden drop in light intensity may show locomotor activity. Recordings from motoneurone axons demonstrate that the integrity of the pineal eye photoreceptors are essential for this response to occur. Thus the pineal has a direct excitatory effect on behaviour.The pineal eye arises embryologically as a single dorsal vesicular evagination of the diencephalon and anatomically it is very similar to that of other developing amphibians.Recording from the pineal eye using a suction electrode demonstrates that suddenly lowering the light intensity evokes a burst of impulses followed by a raised firing frequency. Conversely, increasing the light intensity leads to a lowered firing frequency. With prolonged exposure to white light at a range of intensities, the frequency of spike discharge is dependent upon the light intensity. The pineal eye can therefore act as a luminance detector.The pineal photoreceptors are most sensitive to light of a wavelength near 520 nm, this probably enables maximum sensitivity to the wavelengths of light that penetrate the freshwater environment.The possible role of the pineal eye in controlling locomotor activity is discussed.Abbreviations
HRP
horse raddish peroxidase
-
SEM
scanning electron microscopy 相似文献
12.
J. M. Hemmi R. F. Mark 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(3):379-387
The visual acuity of the tammar wallaby was estimated using a behavioural discrimination task. The wallabies were trained
to discriminate a high-contrast (86%) square-wave grating from a grey field of equal luminance (1000–6000 cd m−2). Visual-evoked cortical potentials were used to measure the complete contrast sensitivity function. The stimulus was a sinusoidal
phase reversal of a sinusoidally modulated grating of various spatial frequencies and contrasts with a mean luminance of 40 cd m−2. The behavioural acuity was estimated to be about 4.8 cycles/deg. The contrast sensitivity peaked at about 0.15 cycles/deg
and declined towards both lower and higher spatial frequencies. The cut-off frequency of the contrast sensitivity function
is slightly lower than the behaviourally measured acuity at about 2.7 cycles/deg. The retinal magnification factor was estimated
anatomically from laser lesions to be about 0.16 mm/deg. Based on the known ganglion cell density and the retinal magnification
factor, an anatomical upper limit to visual acuity of about 6 cycles/deg can be calculated. The differences in estimates of
visual acuity between the behavioural and anatomical methods on the one side and physiology on the other side are discussed.
Accepted: 28 May 1998 相似文献
13.
Background
When we are viewing natural scenes, every saccade abruptly changes both the mean luminance and the contrast structure falling on any given retinal location. Thus it would be useful if the two were independently encoded by the visual system, even when they change simultaneously. Recordings from single neurons in the cat visual system have suggested that contrast information may be quite independently represented in neural responses to simultaneous changes in contrast and luminance. Here we test to what extent this is true in human perception.Methodology/Principal Findings
Small contrast stimuli were presented together with a 7-fold upward or downward step of mean luminance (between 185 and 1295 Td, corresponding to 14 and 98 cd/m2), either simultaneously or with various delays (50–800 ms). The perceived contrast of the target under the different conditions was measured with an adaptive staircase method. Over the contrast range 0.1–0.45, mainly subtractive attenuation was found. Perceived contrast decreased by 0.052±0.021 (N = 3) when target onset was simultaneous with the luminance increase. The attenuation subsided within 400 ms, and even faster after luminance decreases, where the effect was also smaller. The main results were robust against differences in target types and the size of the field over which luminance changed.Conclusions/Significance
Perceived contrast is attenuated mainly by a subtractive term when coincident with a luminance change. The effect is of ecologically relevant magnitude and duration; in other words, strict contrast constancy must often fail during normal human visual behaviour. Still, the relative robustness of the contrast signal is remarkable in view of the limited dynamic response range of retinal cones. We propose a conceptual model for how early retinal signalling may allow this. 相似文献14.
We analyze the dynamic properties of a neural network model for on-off spiking neurons recorded in the first optic chiasm
of the fly visual system. The model consists of two parallel pathways and three sequential processing stages. The first stage
models photoreceptors. At the second stage, the signal is segregated into on- and off-pathways. These pathways are proposed
to correspond to two populations of amacrine cells. At the third stage, the on- and off-pathways converge to on-off neurons.
Furthermore, according to the model, on-off neurons interact via recurrent connections. This stage is proposed to correspond
to lamina L4 neurons. In response to luminance increments and decrements, the model exhibits a three-component response and
suggests pathways for each of the components. When stimulated by a train of pulses, the model exhibits fast adaptation for
frequencies higher than about 5 Hz. Furthermore, adaptation to on- and off-pulses occurs independently. When the frequency
of stimulation is reduced, the unit recovers rapidly from its adapted state. The temporal modulation transfer function has
its peak around 7 Hz. The phase characteristics show a phase lead for low temporal frequencies changing to a phase lag for
high frequencies. These model predictions are compared with data from Jansonius and van Hateren (1991).
Received: 26 May 1997 / Accepted in revised form: 19 February 1998 相似文献
15.
Phototransduction is a process which links the absorption of photons by a rod or cone to the modulation of voltage across
the cell membrane. An important feature of many vertebrate photoreceptors is a mechanism that adjusts the sensitivity and
dynamics of the response to light according to the level of illumination.
We construct a system of ordinary differential equations that models what are currently thought to be the important molecule
mechanisms involved in phototransduction: this includes consideration of both intracellular enzyme kinetics and the properties
of light-insensitive and light-sensitive conductances in the cone membrane. The system contains negative feedback whose functional
form is determined by constraining the steady-state behaviour of the system. Despite the highly nonlinear nature of the system
of ordinary differential equations, our methods permit us to derive an analytic expression for the first-order frequency response
parametric in the steady-state value of only one dynamic variable, the light input. Various unknown kinetic parameters are
found by fitting the model to experimental data on the first-order frequency response of cones measured at several mean light
levels spanning a range of four log units. Good fits are obtained to the data, and the computed shape of the feedback function
agrees qualitatively with recent experiment. Moreover, the model accounts for the dramatic speeding up of the response kinetics
and the decrease in response gain with increasing light level. 相似文献
16.
C Breslin A O''Lenskie 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2001,356(1412):1249-1258
Neuromorphic hardware is the term used to describe full custom-designed integrated circuits, or silicon ''chips'', that are the product of neuromorphic engineering--a methodology for the synthesis of biologically inspired elements and systems, such as individual neurons, retinae, cochleas, oculomotor systems and central pattern generators. We focus on the implementation of neurons and networks of neurons, designed to illuminate structure-function relationships. Neuromorphic hardware can be constructed with either digital or analogue circuitry or with mixed-signal circuitry--a hybrid of the two. Currently, most examples of this type of hardware are constructed using analogue circuits, in complementary metal-oxide-semiconductor technology. The correspondence between these circuits and neurons, or networks of neurons, can exist at a number of levels. At the lowest level, this correspondence is between membrane ion channels and field-effect transistors. At higher levels, the correspondence is between whole conductances and firing behaviour, and filters and amplifiers, devices found in conventional integrated circuit design. Similarly, neuromorphic engineers can choose to design Hodgkin-Huxley model neurons, or reduced models, such as integrate-and-fire neurons. In addition to the choice of level, there is also choice within the design technique itself; for example, resistive and capacitive properties of the neuronal membrane can be constructed with extrinsic devices, or using the intrinsic properties of the materials from which the transistors themselves are composed. So, silicon neurons can be built, with dendritic, somatic and axonal structures, and endowed with ionic, synaptic and morphological properties. Examples of the structure-function relationships already explored using neuromorphic hardware include correlation detection and direction selectivity. Establishing a database for this hardware is valuable for two reasons: first, independently of neuroscientific motivations, the field of neuromorphic engineering would benefit greatly from a resource in which circuit designs could be stored in a form appropriate for reuse and re-fabrication. Analogue designers would benefit particularly from such a database, as there are no equivalents to the algorithmic design methods available to designers of digital circuits. Second, and more importantly for the purpose of this theme issue, is the possibility of a database of silicon neuron designs replicating specific neuronal types and morphologies. In the future, it may be possible to use an automated process to translate morphometric data directly into circuit design compatible formats. The question that needs to be addressed is: what could a neuromorphic hardware database contribute to the wider neuroscientific community that a conventional database could not? One answer is that neuromorphic hardware is expected to provide analogue sensory-motor systems for interfacing the computational power of symbolic, digital systems with the external, analogue environment. It is also expected to contribute to ongoing work in neural-silicon interfaces and prosthetics. Finally, there is a possibility that the use of evolving circuits, using reconfigurable hardware and genetic algorithms, will create an explosion in the number of designs available to the neuroscience community. All this creates the need for a database to be established, and it would be advantageous to set about this while the field is relatively young. This paper outlines a framework for the construction of a neuromorphic hardware database, for use in the biological exploration of structure-function relationships. 相似文献
17.
Photoreceptors adapt to changes in illumination by altering transduction kinetics and sensitivity, thereby extending their working range. We describe a previously unknown form of rod photoreceptor adaptation in wild-type (WT) mice that manifests as a potentiation of the light response after periods of conditioning light exposure. We characterize the stimulus conditions that evoke this graded hypersensitivity and examine the molecular mechanisms of adaptation underlying the phenomenon. After exposure to periods of saturating illumination, rods show a 10–35% increase in circulating dark current, an adaptive potentiation (AP) to light exposure. This potentiation grows as exposure to light is extended up to 3 min and decreases with longer exposures. Cells return to their initial dark-adapted sensitivity with a time constant of recovery of ∼7 s. Halving the extracellular Mg concentration prolongs the adaptation, increasing the time constant of recovery to 13.3 s, but does not affect the magnitude of potentiation. In rods lacking guanylate cyclase activating proteins 1 and 2 (GCAP−/−), AP is more than doubled compared with WT rods, and halving the extracellular Mg concentration does not affect the recovery time constant. Rods from a mouse expressing cyclic nucleotide–gated channels incapable of binding calmodulin also showed a marked increase in the amplitude of AP. Application of an insulin-like growth factor-1 receptor (IGF-1R) kinase inhibitor (Tyrphostin AG1024) blocked AP, whereas application of an insulin receptor kinase inhibitor (HNMPA(AM)3) failed to do so. A broad-acting tyrosine phosphatase inhibitor (orthovanadate) also blocked AP. Our findings identify a unique form of adaptation in photoreceptors, so that they show transient hypersensitivity to light, and are consistent with a model in which light history, acting via the IGF-1R, can increase the sensitivity of rod photoreceptors, whereas the photocurrent overshoot is regulated by Ca-calmodulin and Ca2+/Mg2+-sensitive GCAPs. 相似文献
18.
The responses of cortical neurons are often characterized by measuring their spectro-temporal receptive fields (STRFs). The STRF of a cell can be thought of as a representation of its stimulus 'preference' but it is also a filter or 'kernel' that represents the best linear prediction of the response of that cell to any stimulus. A range of in vivo STRFs with varying properties have been reported in various species, although none in humans. Using a computational model it has been shown that responses of ensembles of artificial STRFs, derived from limited sets of formative stimuli, preserve information about utterance class and prosody as well as the identity and sex of the speaker in a model speech classification system. In this work we help to put this idea on a biologically plausible footing by developing a simple model thalamo-cortical system built of conductance based neurons and synapses some of which exhibit spike-time-dependent plasticity. We show that the neurons in such a model when exposed to formative stimuli develop STRFs with varying temporal properties exhibiting a range of heterotopic integration. These model neurons also, in common with neurons measured in vivo, exhibit a wide range of non-linearities; this deviation from linearity can be exposed by characterizing the difference between the measured response of each neuron to a stimulus, and the response predicted by the STRF estimated for that neuron. The proposed model, with its simple architecture, learning rule, and modest number of neurons (<1000), is suitable for implementation in neuromorphic analogue VLSI hardware and hence could form the basis of a developmental, real time, neuromorphic sound classification system. 相似文献
19.
AV Avizienis HO Sillin C Martin-Olmos HH Shieh M Aono AZ Stieg JK Gimzewski 《PloS one》2012,7(8):e42772
Efforts to emulate the formidable information processing capabilities of the brain through neuromorphic engineering have been bolstered by recent progress in the fabrication of nonlinear, nanoscale circuit elements that exhibit synapse-like operational characteristics. However, conventional fabrication techniques are unable to efficiently generate structures with the highly complex interconnectivity found in biological neuronal networks. Here we demonstrate the physical realization of a self-assembled neuromorphic device which implements basic concepts of systems neuroscience through a hardware-based platform comprised of over a billion interconnected atomic-switch inorganic synapses embedded in a complex network of silver nanowires. Observations of network activation and passive harmonic generation demonstrate a collective response to input stimulus in agreement with recent theoretical predictions. Further, emergent behaviors unique to the complex network of atomic switches and akin to brain function are observed, namely spatially distributed memory, recurrent dynamics and the activation of feedforward subnetworks. These devices display the functional characteristics required for implementing unconventional, biologically and neurally inspired computational methodologies in a synthetic experimental system. 相似文献
20.
The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l−1) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s−1 m−2 at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s−1 m−2), with fish capturing up to 5 prey larva−1 h−1. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s−1 m−2) exceeding 100 prey larva−1 h−1. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s−1 m−2, remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva−1 h−1) that was independent of larval age. 相似文献