Rapid strengthening of thalamo-amygdala synapses mediates cue-reward learning

What neural changes underlie individual differences in goal-directed learning? The lateral amygdala (LA) is important for assigning emotional and motivational significance to discrete environmental cues, including those that signal rewarding events. Recognizing that a cue predicts a reward enhances an animal's ability to acquire that reward; however, the cellular and synaptic mechanisms that underlie cue-reward learning are unclear. Here we show that marked changes in both cue-induced neuronal firing and input-specific synaptic strength occur with the successful acquisition of a cue-reward association within a single training session. We performed both in vivo and ex vivo electrophysiological recordings in the LA of rats trained to self-administer sucrose. We observed that reward-learning success increased in proportion to the number of amygdala neurons that responded phasically to a reward-predictive cue. Furthermore, cue-reward learning induced an AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole propionic acid)-receptor-mediated increase in the strength of thalamic, but not cortical, synapses in the LA that was apparent immediately after the first training session. The level of learning attained by individual subjects was highly correlated with the degree of synaptic strength enhancement. Importantly, intra-LA NMDA (N-methyl-d-aspartate)-receptor blockade impaired reward-learning performance and attenuated the associated increase in synaptic strength. These findings provide evidence of a connection between LA synaptic plasticity and cue-reward learning, potentially representing a key mechanism underlying goal-directed behaviour.     

基于WGAN的语音增强算法研究

带噪语音可看成由独立的噪声信号和语音信号经某种方式混合而成,传统语音增强方法需要对噪声信号和干净语音信号的独立性和特征分布做出假设,不合理的假设会造成噪声残留、语音失真等问题,导致语音增强效果不佳。此外,噪声本身的随机性和突变性也会影响传统语音增强方法的鲁棒性。针对这些问题,使用生成对抗网络来对语音进行增强,给出一种基于Wasserstein 距离的生成对抗网络(Wasserstein generative adversarial nets, WGAN)的语音增强方法来加快训练速度和稳定训练过程。该方法无需人工提取声学特征,且使语音增强系统的泛化能力得以提升,在匹配噪声集和不匹配噪声集中都有良好的增强效果。实验结果表明,使用训练出的端对端语音增强模型后,语音信号的客观评价标准(perceptual evaluation of speech quality,PESQ)平均得到23.97%的提高。     

抗阻力训练的运动学特征

当前针对各种抗阻力训练对肌肉力量和爆发力的影响,人们进行了大量研究,但对其诱导的机械刺激与肌体适应方面的认识,仍存在严重不足。目前认为,抗阻力训练动力学的变化(力量、收缩持续时间和爆发力等)以及这些变化诱导机体内激素及代谢物的改变,可以影响肌肉力量的获得和爆发力的发展;而对于不同运动学变量之间结合的效果,及其对肌肉适应产生的影响并不清楚。认识机械刺激与肌体适应之间的关系,有助于更科学地把力量训练和爆发力训练结合在一起,提高训练效益。     

Experience with moving visual stimuli drives the early development of cortical direction selectivity

The onset of vision occurs when neural circuits in the visual cortex are immature, lacking both the full complement of connections and the response selectivity that defines functional maturity. Direction-selective responses are particularly vulnerable to the effects of early visual deprivation, but it remains unclear how stimulus-driven neural activity guides the emergence of cortical direction selectivity. Here we report observations from a motion training protocol that allowed us to monitor the impact of experience on the development of direction-selective responses in visually naive ferrets. Using intrinsic signal imaging techniques, we found that training with a single axis of motion induced the rapid emergence of direction columns that were confined to cortical regions preferentially activated by the training stimulus. Using two-photon calcium imaging techniques, we found that single neurons in visually naive animals exhibited weak directional biases and lacked the strong local coherence in the spatial organization of direction preference that was evident in mature animals. Training with a moving stimulus, but not with a flashed stimulus, strengthened the direction-selective responses of individual neurons and preferentially reversed the direction biases of neurons that deviated from their neighbours. Both effects contributed to an increase in local coherence. We conclude that early experience with moving visual stimuli drives the rapid emergence of direction-selective responses in the visual cortex.     

Cortical remodelling induced by activity of ventral tegmental dopamine neurons.

Representations of sensory stimuli in the cerebral cortex can undergo progressive remodelling according to the behavioural importance of the stimuli. The cortex receives widespread projections from dopamine neurons in the ventral tegmental area (VTA), which are activated by new stimuli or unpredicted rewards, and are believed to provide a reinforcement signal for such learning-related cortical reorganization. In the primary auditory cortex (AI) dopamine release has been observed during auditory learning that remodels the sound-frequency representations. Furthermore, dopamine modulates long-term potentiation, a putative cellular mechanism underlying plasticity. Here we show that stimulating the VTA together with an auditory stimulus of a particular tone increases the cortical area and selectivity of the neural responses to that sound stimulus in AI. Conversely, the AI representations of nearby sound frequencies are selectively decreased. Strong, sharply tuned responses to the paired tones also emerge in a second cortical area, whereas the same stimuli evoke only poor or non-selective responses in this second cortical field in naive animals. In addition, we found that strong long-range coherence of neuronal discharge emerges between AI and this secondary auditory cortical area.     

Visual discrimination of target displacement remains after damage to the striate cortex in humans

Damage to the striate cortex usually causes blindness in those regions of the visual field which map to the area of neural damage. Nonetheless, there are reports that some patients with such damage can localize and perform certain visual discriminations between light stimuli presented within the 'blind' area of the visual field. Experiments on animals with different brain areas ablated suggest that visual function is served by two principal projection pathways from the retina. That to the striate cortex is primarily responsible for fine discrimination between stimulus parameters such as colour and spatial pattern, whereas that to the superior colliculus in the midbrain is responsible for visual localization of stimuli. The residual visual functions in patients with cortical damage are usually attributed to the non-striate retinal projection to the superior colliculus. We now present measurements of spatial discrimination in two observers with large visual field defects (scotomata) caused by damage to the striate cortical region. Both exhibit a near normal ability to discriminate displacements of targets when two lights are flashed sequentially in their defective visual field, but they are unable to discriminate spatial pattern or size. We argue that these results are consistent with the 'two visual systems' interpretation of ablation studies on non-human species.     

Adaptive coding of visual information in neural populations

Our perception of the environment relies on the capacity of neural networks to adapt rapidly to changes in incoming stimuli. It is increasingly being realized that the neural code is adaptive, that is, sensory neurons change their responses and selectivity in a dynamic manner to match the changes in input stimuli. Understanding how rapid exposure, or adaptation, to a stimulus of fixed structure changes information processing by cortical networks is essential for understanding the relationship between sensory coding and behaviour. Physiological investigations of adaptation have contributed greatly to our understanding of how individual sensory neurons change their responses to influence stimulus coding, yet whether and how adaptation affects information coding in neural populations is unknown. Here we examine how brief adaptation (on the timescale of visual fixation) influences the structure of interneuronal correlations and the accuracy of population coding in the macaque (Macaca mulatta) primary visual cortex (V1). We find that brief adaptation to a stimulus of fixed structure reorganizes the distribution of correlations across the entire network by selectively reducing their mean and variability. The post-adaptation changes in neuronal correlations are associated with specific, stimulus-dependent changes in the efficiency of the population code, and are consistent with changes in perceptual performance after adaptation. Our results have implications beyond the predictions of current theories of sensory coding, suggesting that brief adaptation improves the accuracy of population coding to optimize neuronal performance during natural viewing.     

Neural correlates of short-term perceptual learning in orientation discrimination indexed by event-related potentials

The current work investigated the neural correlates of visual perceptual learning in grating orientation discrimination by recording event-related potentials (ERPs) from human adults. Subjects were trained with a discrimination task of grating orientation in three consecutive training sessions within 2 h. While reaction times (RTs) were shortened gradually across training sessions, the N1 was decreased and the P2 was increased over the parietal and occipital areas. A broadly distributed P3 was increased along with more practices. In addition, the time course of learning reflected in the P2 and P3 amplitudes was in line with the changes of reaction times and exhibited a stable level during later training. The impli- cations of these results to the neural mechanisms subserving perceptual learning were discussed.     

Practising orientation identification improves orientation coding in V1 neurons

The adult brain shows remarkable plasticity, as demonstrated by the improvement in fine sensorial discriminations after intensive practice. The behavioural aspects of such perceptual learning are well documented, especially in the visual system. Specificity for stimulus attributes clearly implicates an early cortical site, where receptive fields retain fine selectivity for these attributes; however, the neuronal correlates of a simple visual discrimination task remained unidentified. Here we report electrophysiological correlates in the primary visual cortex (V1) of monkeys for learning orientation identification. We link the behavioural improvement in this type of learning to an improved neuronal performance of trained compared to naive neurons. Improved long-term neuronal performance resulted from changes in the characteristics of orientation tuning of individual neurons. More particularly, the slope of the orientation tuning curve that was measured at the trained orientation increased only for the subgroup of trained neurons most likely to code the orientation identified by the monkey. No modifications of the tuning curve were observed for orientations for which the monkey had not been trained. Thus training induces a specific and efficient increase in neuronal sensitivity in V1.     

A synaptic memory trace for cortical receptive field plasticity

Receptive fields of sensory cortical neurons are plastic, changing in response to alterations of neural activity or sensory experience. In this way, cortical representations of the sensory environment can incorporate new information about the world, depending on the relevance or value of particular stimuli. Neuromodulation is required for cortical plasticity, but it is uncertain how subcortical neuromodulatory systems, such as the cholinergic nucleus basalis, interact with and refine cortical circuits. Here we determine the dynamics of synaptic receptive field plasticity in the adult primary auditory cortex (also known as AI) using in vivo whole-cell recording. Pairing sensory stimulation with nucleus basalis activation shifted the preferred stimuli of cortical neurons by inducing a rapid reduction of synaptic inhibition within seconds, which was followed by a large increase in excitation, both specific to the paired stimulus. Although nucleus basalis was stimulated only for a few minutes, reorganization of synaptic tuning curves progressed for hours thereafter: inhibition slowly increased in an activity-dependent manner to rebalance the persistent enhancement of excitation, leading to a retuned receptive field with new preference for the paired stimulus. This restricted period of disinhibition may be a fundamental mechanism for receptive field plasticity, and could serve as a memory trace for stimuli or episodes that have acquired new behavioural significance.     

Cortical ensemble activity increasingly predicts behaviour outcomes during learning of a motor task

When an animal learns to make movements in response to different stimuli, changes in activity in the motor cortex seem to accompany and underlie this learning. The precise nature of modifications in cortical motor areas during the initial stages of motor learning, however, is largely unknown. Here we address this issue by chronically recording from neuronal ensembles located in the rat motor cortex, throughout the period required for rats to learn a reaction-time task. Motor learning was demonstrated by a decrease in the variance of the rats' reaction times and an increase in the time the animals were able to wait for a trigger stimulus. These behavioural changes were correlated with a significant increase in our ability to predict the correct or incorrect outcome of single trials based on three measures of neuronal ensemble activity: average firing rate, temporal patterns of firing, and correlated firing. This increase in prediction indicates that an association between sensory cues and movement emerged in the motor cortex as the task was learned. Such modifications in cortical ensemble activity may be critical for the initial learning of motor tasks.     

方位辨别知觉学习的眼传递及空间频率调谐特性

为了研究方位辨别知觉学习的神经机制,采用心理物理的方法,研究了方位辨别知觉学习的空间频率调谐与眼传递特性.通过对9个被试在固定空间频率（周期/度）进行方位辨别的训练,并于训练前后在多个空间频率（0.5, 1, 2, 4, 8, 16和32周期/度）测量方位辨别的阈值,发现被试在训练空间频率的方位辨别阈值平均下降了7.01 dB,并且这种学习效应可显著传递到非训练眼.学习效应可分为两个部分：一部分可传递到其他空间频率（4.10 dB）,另外一部分则特异于训练空间频率（2.95 dB）.这些结果说明方位辨别学习可能发生在双眼信息汇聚之后的视皮层,且可能有多种机制参与其中.     

基于时域统计平均预处理的RBF网络发动机气缸压力识别方法

在柴油发动机气缸压力的识别过程中，针对缸盖振动信号的信噪比低且呈非平稳特性，影响神经网络对气缸压力识别的问题，提出了在径向基函数(RBF)网络训练前，对训练样本进行时域统计平均降噪预处理，再对实验样本进行识别．结果表明，时域统计平均有效提高了训练样本的信噪比，RBF网络经训练后，对柴油发动机气缸压力的识别具有计算速度快、识别精度高的优点．     

基于频域窄带莱斯噪声消除机制的OFDM网络信号发射精度增强算法

为改善当前OFDM网络信号精度增强算法中难以高效消除频域窄带莱斯噪声,且系统误码率较高的不足,提出了一种基于频域窄带莱斯噪声消除机制的OFDM网络信号精度增强算法.首先,基于128频相移键控调制方法,在获取信号时域特征的基础上,引入快速傅里叶变换,对信号进行离散化,并基于信号投影机制,构建正交星座图,实现信号投影矢量在预发射状态下的正交分层排序,消除了信源状态下频域窄带莱斯噪声对系统的干扰;随后,引入快速傅里叶逆变换,对预发射信号进行加密处理,且通过量化评估模型对信号精度进行优化提升,有效节约了传输带宽,提高了信号发射性能,改善了信道抗衰落效果.仿真实验表明,与当前常见的时间窗消除机制(time window elimination mechanism, TWE)、频率拓扑映射机制(frequency topology mapping, FT)相比,本文算法的误码率更低,且具有更高的信号增益效果.     

Inhibition of climbing fibres is a signal for the extinction of conditioned eyelid responses

A fundamental tenet of cerebellar learning theories asserts that climbing fibre afferents from the inferior olive provide a teaching signal that promotes the gradual adaptation of movements. Data from several forms of motor learning provide support for this tenet. In pavlovian eyelid conditioning, for example, where a tone is repeatedly paired with a reinforcing unconditioned stimulus like periorbital stimulation, the unconditioned stimulus promotes acquisition of conditioned eyelid responses by activating climbing fibres. Climbing fibre activity elicited by an unconditioned stimulus is inhibited during the expression of conditioned responses-consistent with the inhibitory projection from the cerebellum to inferior olive. Here, we show that inhibition of climbing fibres serves as a teaching signal for extinction, where learning not to respond is signalled by presenting a tone without the unconditioned stimulus. We used reversible infusion of synaptic receptor antagonists to show that blocking inhibitory input to the climbing fibres prevents extinction of the conditioned response, whereas blocking excitatory input induces extinction. These results, combined with analysis of climbing fibre activity in a computer simulation of the cerebellar-olivary system, suggest that transient inhibition of climbing fibres below their background level is the signal that drives extinction.     

心理词汇学习策略与英语词汇教学

词汇学习是语言学习的重要组成部分,本文阐述了心理词汇的基本理论及词汇学习策略的基本分类,试图探讨如何将心理词汇与学习策略结合起来,分析在词汇学习策略中心理词汇的指导作用。     

学习策略与学习过程

讨论了学习者的学习技巧和策略。对学习策略基本概念、策略与技巧的区别、学习策略理论、学习策略训练和学习者学习过程的意义进行了探讨。通过对学习者学习过程的研究,使教育者能够意识到学习策略的重要性,进而在教学过程中最大程度上帮助学习者,达到事半功倍的效果。     

分类任务中标签噪声的研究综述

近年来,随着机器学习的发展,分类系统的性能有了很大的飞跃。模型需要大量带标签数据才能使训练结果达到要求,而获取高质量的标注数据费时费力。为了降低成本,出现了众包、自动化系统等方法标注训练数据。但是,这些标注方法往往会产生大量错误标注,即标签噪声。另外,信息不足、专家错误和编码错误等因素,也可能使标签受到污染。训练过程中对标签噪声的处理不当,可能会使预测精度和准确性降低,或者使模型复杂度增加。因此,研究标签噪声对推广机器学习在各领域的应用和降低机器 学习算法的部署成本等方面具有重要意义。通过综述产生标签噪声的原因、影响以及近几年来应对标签噪声的一些技术方法,对标签噪声的研究现状和发展前景进行分析。     

基于互相关和最大似然估计的弱信号检测

弱信号检测一直以来是人们研究的热点，如何从强噪声环境下提取有用的信号非常关键。简单介绍互相关检测的原理及最大似然理论，并在此基础上，提出了将互相关检测与最大似然理论相结合检测弱信号的新方法。仿真结果表明，此方法是可行的。     

应用型本科院校系统辨识课程教学改革探索

结合应用型本科院校的培养目标和学生学习特点，探讨了系统辨识课程理论与实践教学的改革方法。研究指出该课程的理论教学应做到深入浅出，以激发学生的学习兴趣，同时应加强实践教学，以调动学生的学习积极性。理论与实践教学相互补充，易于使学生掌握辨识算法的本质，巩固对算法的理解，从而提高教学质量。