共查询到20条相似文献,搜索用时 15 毫秒
1.
Ryan C. Kelly Matthew A. Smith Robert E. Kass Tai Sing Lee 《Journal of computational neuroscience》2010,29(3):567-579
Multineuronal recordings have revealed that neurons in primary visual cortex (V1) exhibit coordinated fluctuations of spiking
activity in the absence and in the presence of visual stimulation. From the perspective of understanding a single cell’s spiking
activity relative to a behavior or stimulus, these network fluctuations are typically considered to be noise. We show that
these events are highly correlated with another commonly recorded signal, the local field potential (LFP), and are also likely
related to global network state phenomena which have been observed in a number of neural systems. Moreover, we show that attributing
a component of cell firing to these network fluctuations via explicit modeling of the LFP improves the recovery of cell properties.
This suggests that the impact of network fluctuations may be estimated using the LFP, and that a portion of this network activity
is unrelated to the stimulus and instead reflects ongoing cortical activity. Thus, the LFP acts as an easily accessible bridge
between the network state and the spiking activity. 相似文献
2.
3.
Alberto Mazzoni Henrik Lindén Hermann Cuntz Anders Lansner Stefano Panzeri Gaute T. Einevoll 《PLoS computational biology》2015,11(12)
Leaky integrate-and-fire (LIF) network models are commonly used to study how the spiking dynamics of neural networks changes with stimuli, tasks or dynamic network states. However, neurophysiological studies in vivo often rather measure the mass activity of neuronal microcircuits with the local field potential (LFP). Given that LFPs are generated by spatially separated currents across the neuronal membrane, they cannot be computed directly from quantities defined in models of point-like LIF neurons. Here, we explore the best approximation for predicting the LFP based on standard output from point-neuron LIF networks. To search for this best “LFP proxy”, we compared LFP predictions from candidate proxies based on LIF network output (e.g, firing rates, membrane potentials, synaptic currents) with “ground-truth” LFP obtained when the LIF network synaptic input currents were injected into an analogous three-dimensional (3D) network model of multi-compartmental neurons with realistic morphology, spatial distributions of somata and synapses. We found that a specific fixed linear combination of the LIF synaptic currents provided an accurate LFP proxy, accounting for most of the variance of the LFP time course observed in the 3D network for all recording locations. This proxy performed well over a broad set of conditions, including substantial variations of the neuronal morphologies. Our results provide a simple formula for estimating the time course of the LFP from LIF network simulations in cases where a single pyramidal population dominates the LFP generation, and thereby facilitate quantitative comparison between computational models and experimental LFP recordings in vivo. 相似文献
4.
Carlo R. Laing Thomas Frewen Ioannis G. Kevrekidis 《Journal of computational neuroscience》2010,28(3):459-476
Binocular rivalry occurs when two very different images are presented to the two eyes, but a subject perceives only one image
at a given time. A number of computational models for binocular rivalry have been proposed; most can be categorised as either
“rate” models, containing a small number of variables, or as more biophysically-realistic “spiking neuron” models. However,
a principled derivation of a reduced model from a spiking model is lacking. We present two such derivations, one heuristic
and a second using recently-developed data-mining techniques to extract a small number of “macroscopic” variables from the
results of a spiking neuron model simulation. We also consider bifurcations that can occur as parameters are varied, and the
role of noise in such systems. Our methods are applicable to a number of other models of interest. 相似文献
5.
The aim of the investigation was to explore the influence of levodopa therapy on the regularity of the structural variations
present in the lower extremity joints of individuals with Parkinson’s disease (PD). Ten participants with PD walked on a treadmill
during the states of “off” and “on” levodopa. Approximate entropy was used to quantify the regularity of the structural variations
present in the joint kinematics. Additionally, a pseudo-periodic surrogation analysis was used to evaluate if changes in the
regularity of the joint’s movement were associated with a noisy or deterministic motor process. This investigation provided
two key findings. The first was that the structural variations present in ankle joint were more regular with levodopa therapy.
The second was that changes in the structural variations were related to a deterministic motor process. This indicated that
the variations present in the walking patterns of individuals with PD most likely arose from higher-order neural couplings
rather than noise in the motor process. Monitoring the regularity of the structural variations present in gait may help improve
the management of PD. 相似文献
6.
A “probabilistic” rather than a “deterministic” approach to the theory of neural nets is developed. Neural nets are characterized
by certain parameters which give the probability distributions of different kinds of synaptic connections throughout the net.
Given a “state” of the net (i.e., the distribution of firing neurons) at a given moment, an equation for the state at the
next moment of quantized time is deduced. Certain very special cases involving constant distributions are solved. A necessary
condition for a steady state is deduced in terms of an integral equation, in general non-linear. 相似文献
7.
Whitley R 《Culture, medicine and psychiatry》2011,35(4):519-535
This article is propelled by recent theory positing that ‘social defeat’ is a common experience for people with severe mental
illness, potentially affecting course and outcome. The primary objective is to investigate how far fear of crime and violence
contributes toward ‘social defeat’ among people with mental illness. This is done through examining 6 years of ethnographic
data collected from a sample of urban-dwelling people with severe mental illness, all securely-housed in apartments located
in small scale “recovery communities.” Findings suggest that many participants living in the highest crime neighborhoods report
that they deliberately restrict their temporal and spatial movement as a consequence of such crime. This hinders aspects of
their recovery. Nevertheless, participants actively confront the nefarious affects of neighborhood crime by engaging in various
empowering strategies of resistance. These include confronting disruptive people, fortifying homes, moving around the neighborhood
in small groups and carrying objects such as umbrellas and canes that can be used in self-defense. Some reported that fear
of crime directly contributed to the development of a rich and gratifying domestic life, centered on hospitality and religion.
I conclude that participants partake in valiant and durable “social resistance,” and may better be perceived as imaginative
and resourceful resistors, rather than passive victims of “social defeat.” An influential factor fostering such resistance
is the “recovery community’ itself, which creates secure and reliable housing within a micro-community in which participants
could thrive. 相似文献
8.
Brada B 《Culture, medicine and psychiatry》2011,35(2):285-312
This essay argues that what makes “global health” “global” has more to do with configurations of space and time, and the claims
to expertise and moral stances these configurations make possible, than with the geographical distribution of medical experts
or the universal, if also uneven, distribution of threats to health. Drawing on a study of public–private partnerships supporting
Botswana’s HIV/AIDS treatment program, this essay demonstrates ethnographically the processes by which “global health” and
its quintessential spaces, namely “resource-limited” or “resource-poor settings,” are constituted, reinforced, and contested
in the context of medical education and medical practice in Botswana’s largest hospital. Using Silverstein’s work on orders
of indexicality, I argue that the terms of “global health” are best understood as chronotopic, and demonstrate how actors
orient themselves and others spatio-temporally, morally, and professionally by using or refuting those terms. I conclude by
arguing that taking “global health” on its own terms obscures the powerful forces by which it becomes intelligible. At stake
are the frames within which medical anthropologists understand their objects of study, as well as the potential for the spaces
of “global health” intervention to expand ever outward as American medical personnel attempt to calibrate their experiences
to their expectations. 相似文献
9.
10.
The notion of “pressure” as an evolutionary “force” that “causes” evolution is a pervasive linguistic feature of biology textbooks,
journal articles, and student explanatory discourse. We investigated the consequences of using a textbook and curriculum that
incorporate so-called force-talk. We examined the frequency with which biology majors spontaneously used notions of evolutionary
“pressures” in their explanations, students’ definitions and explanations of what they meant when they used pressures, and
the structure of explanatory models that incorporated evolutionary pressures and forces. We found that 12–20 percent of undergraduates
spontaneously used “pressures” and/or “forces” as explanatory factors but significantly more often in trait gain scenarios
than in trait loss scenarios. The majority of explanations using “force-talk” were characterized by faulty evolutionary reasoning.
We discuss the conceptual similarity between faulty notions of evolutionary pressures and linguists’ force-dynamic models
of everyday reasoning and ultimately question the appropriateness of force-talk in evolution education. 相似文献
11.
Andrei Belitski Stefano Panzeri Cesare Magri Nikos K. Logothetis Christoph Kayser 《Journal of computational neuroscience》2010,29(3):533-545
Studies analyzing sensory cortical processing or trying to decode brain activity often rely on a combination of different
electrophysiological signals, such as local field potentials (LFPs) and spiking activity. Understanding the relation between
these signals and sensory stimuli and between different components of these signals is hence of great interest. We here provide
an analysis of LFPs and spiking activity recorded from visual and auditory cortex during stimulation with natural stimuli.
In particular, we focus on the time scales on which different components of these signals are informative about the stimulus,
and on the dependencies between different components of these signals. Addressing the first question, we find that stimulus
information in low frequency bands (<12 Hz) is high, regardless of whether their energy is computed at the scale of milliseconds
or seconds. Stimulus information in higher bands (>50 Hz), in contrast, is scale dependent, and is larger when the energy
is averaged over several hundreds of milliseconds. Indeed, combined analysis of signal reliability and information revealed
that the energy of slow LFP fluctuations is well related to the stimulus even when considering individual or few cycles, while
the energy of fast LFP oscillations carries information only when averaged over many cycles. Addressing the second question,
we find that stimulus information in different LFP bands, and in different LFP bands and spiking activity, is largely independent
regardless of time scale or sensory system. Taken together, these findings suggest that different LFP bands represent dynamic
natural stimuli on distinct time scales and together provide a potentially rich source of information for sensory processing
or decoding brain activity. 相似文献
12.
This paper is about how cortical recurrent interactions in primary visual cortex (V1) together with feedback from extrastriate
cortex can account for spectral peaks in the V1 local field potential (LFP). Recent studies showed that visual stimulation
enhances the γ-band (25–90 Hz) of the LFP power spectrum in macaque V1. The height and location of the γ-band peak in the LFP spectrum were correlated with visual stimulus size. Extensive spatial summation, possibly mediated by
feedback connections from extrastriate cortex and long-range horizontal connections in V1, must play a crucial role in the
size dependence of the LFP. To analyze stimulus-effects on the LFP of V1 cortex, we propose a network model for the visual
cortex that includes two populations of V1 neurons, excitatory and inhibitory, and also includes feedback to V1 from extrastriate
cortex. The neural network model for V1 was a resonant system. The model’s resonance frequency (ResF) was in the γ-band and varied up or down in frequency depending on cortical feedback. The model’s ResF shifted downward with stimulus size,
as in the real cortex, because increased size recruited more activity in extrastriate cortex and V1 thereby causing stronger
feedback. The model needed to have strong local recurrent inhibition within V1 to obtain ResFs that agree with cortical data.
Network resonance as a consequence of recurrent excitation and inhibition appears to be a likely explanation for γ-band peaks in the LFP power spectrum of the primary visual cortex. 相似文献
13.
Victoria N. Alexander 《Biosemiotics》2009,2(1):77-100
Hackles have been raised in biosemiotic circles by T. L. Short’s assertion that semiosis, as defined by Peirce, entails “acting
for purposes” and therefore is not found below the level of the organism (2007a:174–177). This paper examines Short’s teleology and theory of purposeful behavior and offers a remedy to the disagreement.
Remediation becomes possible when the issue is reframed in the terms of the complexity sciences, which allows intentionality
to be understood as the interplay between local and global aspects of a system within a system. What is called “acting for
purposes” is not itself a type of behavior so much as a relationship between a dynamic system that “exists for a purpose”
and its microprocesses that “serve purposes.” The “intentional object” of philosophy is recast here as the holistic self-organized
dynamics of a system, which exists for the purpose of self-maintenance, and that constrains the parts’ behaviors, which serve
the purpose of forming the system. (A “system” can be any emergent, e.g. an abiotic form, an adapted species, a self, a conditioned response, thought, or a set of ideas.) The self-organized whole,
which is represented to the parts in their own constrained behaviors, assumes the guiding function so long attributed to the
mysterious “intentional object.” If emergent self-causation is not disallowed, creative originality, as well as directionality, becomes part of the definition of purposeful behavior. Thus, key tools used here, required for understanding emergence, come
from poetics rather than semoitics. In the microprocesses of self-organization, I find what I call “accidental” indices and
icons — which are poetic in the sense that they involve mere metonymic contiguity and metaphoric similarity — and which are
preferentially selected under constrained conditions allowing radically new connections to habituate into an “intentional”
self-organized system that, not coincidentally, has some of the emergent characteristics of a conventional symbolic system.
相似文献
Victoria N. AlexanderEmail: |
14.
Y. Li G. L. Sattler H. C. Pitot 《In vitro cellular & developmental biology. Animal》1995,31(11):867-870
Summary The presence of optimal nutritional elements in cell culture medium is very important in studies of cultured cells. For this
reason, several researchers have experimented with adding or increasing the concentration of one or more amino acids to the
medium they were using to determine “essential” amino acids and optimal concentrations. We studied how leaving out one amino
acid at a time from Dulbecco’s modified Eagle’s medium would affect epidermal growth factor-induced DNA synthesis in primary
hepatocytes of the rat. Our “modified” DMEM contained only eight amino acids: arginine, cysteine, isoleucine, leucine, lysine,
phenylalanine, tryptophan, and valine. Proline was found to be an essential amino acid in normal DMEM but not in the modified
DMEM, and some other amino acids reduced DNA synthesis in this medium. This study showed that perhaps no single amino acid
such as proline can be called “essential,” but rather an optimal balance of amino acids is required for each major function
of each cell type cultured. 相似文献
15.
Although the traditional “lie detector” test is used frequently in forensic contexts, it has (like most test of deception)
some limitations. The concealed knowledge test (CKT) focuses on participants’ recognition of privileged knowledge rather than
lying per-se and has been studied extensively using a variety of measures. A “guilty” suspect’s interaction with and memory
of crimescene items may vary. Furthermore, memory for crimescene items may diminish over time. The interaction of encoding
quality and test delay on CKT efficiency has been previously implied, but not yet demonstrated. We used a response-time based
CKT to detect concealed knowledge from shallow and deep study procedures after 10-min, 24-h, and 1-week delays. Results show
that more elaborately encoded information afforded higher detection accuracy than poorly encoded items. Although classification
accuracy following deep study was unaffected by delay, detection of poorly elaborated information was initially high, but
compromised after 1 week. Thus, choosing optimal test items requires considering both test delay and initial encoding level. 相似文献
16.
I. N. Konareva 《Neurophysiology》2006,38(3):201-208
Modifications of different EEG rhythms induced by a single neurofeedback session (by the EEG characteristics) directed toward
an increase in the ratio of the spectral powers (SPs) of the α vs θ oscillations were compared with the psychological characteristics of the tested subjects (the group included 30 persons).
A generally accepted neurofeedback technique was used; the intensity of acoustic white noise served as the feedback signal.
EEG potentials were recorded from the C3 and C4 leads. Psychological testing was carried out using Eysenck’s (EPQ), Rusalov’s
(OST), and (16 PF) questionnaires. The directions of changes in the SPs of EEG frequency components were found to significantly
correlate with some individuality-related peculiarities of the tested subjects. The SP of the δ rhythm correlated with the
EPQ scale “neuroticism,” OST scale “social plasticity,” and 16 PF factors H (“parmia”), I (“premsia”), and Q3 (“self-control of behavior”). The SP of the θ component demonstrated correlations with the OST scales “ergisity,” “plasticity,”
and “social temp” and with 16 PF factors M (“autia”), Q4 (“frustration”), and Q1 (“exvia”). The SP of the α rhythm correlated with 16 PF factors Q3 (“self-control of behavior”), G (“strength of superEgo”), O (“hypothymia”), L (“protension”), and N (“shrewdness”). The SP
of the β rhythm correlated with the OST scale “emotionality,” while that of the γ rhythm showed correlations with the 16 PF
indices L (“protension”) and M (“autia”). Changes in the ratio of the α vs θ SPs correlated with the EPQ scale “neuroticism.” Thus, our data confirm the statement that a high individual variability
of the results of a single (first in the series) neurofeedback session is to a great extent related to peculiarities of the
individual psychological pattern of the subject.
Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 239–247, May–June, 2006. 相似文献
17.
Jesse A. Gillis Liang Zhang Frances K. Skinner 《Journal of computational neuroscience》2010,29(3):521-532
Local field potential (LFP) multielectrode recordings of spontaneous rhythms in an isolated whole hippocampal preparation
are characterized with respect to their spatial variability within the hippocampus, and their frequency properties. Using
simulated data, we categorize potential relationships between frequency variation over time in LFP recordings and spatial
variability between electrodes. We then use data recorded from the intact preparation to distinguish between our theoretical
categories. We find that the LFP recordings have a close to spatially invariant frequency distribution (not phase) across
the hippocampus, and differ in frequency only in a component that may be seen as physiological noise. From these facts, we
conclude that the isolated hippocampal LFP recordings represent a single signal and may be regarded as a unitary circuitry.
We additionally examine phase differences across our recording sites. We use our characterization of the hippocampal isolate’s
properties to predict its spatial coherence in response to high frequency stimulation. We find that there is a finely tuned
inverse relationship between temporal variability in the hippocampal isolate’s LFP recordings and their spatial coherence. 相似文献
18.
Gilligan’s (1982) refinement of Kohlberg’s theory on moral development operates on two theses: (1) females, more so than males,
reach moral decisions based on the personalities of the relevant individuals; and (2) female behaviors stemming from moral
decisions are based upon “care” and “responsibility for others.” This article accepts the first thesis but argues that the
second is incorrect. That is, self-interest—i.e., aiding “blood” kin and/or carefully monitoring reciprocity—rather than “altruism”
is argued to be the operant dynamic in forging distaff morality and resultant behavior. Six empirical examples are presented
as contraindicative of Gilligan’s second thesis. Finally, it is suggested that selection for the psychological traits of independence
and the mastery of subtle social chess yielded ancestral females who had more descendants—us—than did females with alternative
profiles.
Nancy S. Coney is a professor at Western Illinois University and is interested in both clinical and nonclinical aspects of
women’s psychology.
Wade C. Mackey is interested in biocultural anthropology and has authored two books on fathering:Fathering Behaviors (Plenum, 1995) andThe American Father (Plenum, 1996). 相似文献
19.
Mackay AL 《Journal of biosciences》2003,28(5):539-546
Conclusion We must conclude that the sub-title of Bernal’s “The Social Function of Science” — “What science does: what science could
do” is still the relevant challenge and indicates Bernal’s chief contribution, besides the foundation of molecular biology
to our civilization. It is manifest that resources spent on armaments are a monstrous pathological symptom of our social structure.
The ancient problem of “what is property” and what may be “owned” and by whom or by what organs of society is awakening. 相似文献
20.
On the mathematical theory of rumor spread 总被引:1,自引:0,他引:1
The applicability of the theory of random nets to the theory of rumor spread is shown. In particular the “weak connectivity”
of the net appears as the saturation fraction of “knowers” in a thoroughly mixed population through which a message diffuses
where each knower tells the message to a finite average number of individuals. Further it is shown how the time course equation
of rumor spread, where time is measured by the number of “removes” from the starters, can be translated into an ordinary continuous
time course equation if the distribution of the telling intervals is known. 相似文献