Top-down gain control of the auditory space map by gaze control circuitry in the barn owl

High-level circuits in the brain that control the direction of gaze are intimately linked with the control of visual spatial attention. Immediately before an animal directs its gaze towards a stimulus, both psychophysical sensitivity to that visual stimulus and the responsiveness of high-order neurons in the cerebral cortex that represent the stimulus increase dramatically. Equivalent effects on behavioural sensitivity and neuronal responsiveness to visual stimuli result from focal electrical microstimulation of gaze control centres in monkeys. Whether the gaze control system modulates neuronal responsiveness in sensory modalities other than vision is unknown. Here we show that electrical microstimulation applied to gaze control circuitry in the forebrain of barn owls regulates the gain of midbrain auditory responses in an attention-like manner. When the forebrain circuit was activated, midbrain responses to auditory stimuli at the location encoded by the forebrain site were enhanced and spatial selectivity was sharpened. The same stimulation suppressed responses to auditory stimuli represented at other locations in the midbrain map. Such space-specific, top-down regulation of auditory responses by gaze control circuitry in the barn owl suggests that the central nervous system uses a common strategy for dynamically regulating sensory gain that applies across modalities, brain areas and classes of vertebrate species. This approach provides a path for discovering mechanisms that underlie top-down gain control in the central nervous system.     

Horizontal and vertical components of head movement are controlled by distinct neural circuits in the barn owl

To generate behaviour, the brain must transform sensory information into signals that are appropriate to control movement. Sensory and motor coordinate frames are fundamentally different, however: sensory coordinates are based on the spatiotemporal patterns of activity arising from the various sense organs, whereas motor coordinates are based on the pulling directions of muscles or groups of muscles. Results from psychophysical experiments suggest that in the process of transforming sensory information into motor control signals, the brain encodes movements in abstract or extrinsic coordinate frames, that is ones not closely related to the geometry of the sensory apparatus or of the skeletomusculature. Here we show that an abstract code underlies movements of the head by the barn owl. Specifically, the data show that subsequent to the retinotopic code for space in the optic tectum yet before the motor neuron code for muscle tensions there exists a code for head movement in which upward, downward, leftward and rightward components of movement are controlled by four functionally distinct neural circuits. Such independent coding of orthogonal components of movement may be a common intermediate step in the transformation of sensation into behaviour.     

Incremental training increases the plasticity of the auditory space map in adult barn owls

The plasticity in the central nervous system that underlies learning is generally more restricted in adults than in young animals. In one well-studied example, the auditory localization pathway has been shown to be far more limited in its capacity to adjust to abnormal experience in adult than in juvenile barn owls. Plasticity in this pathway has been induced by exposing owls to prismatic spectacles that cause a large, horizontal shift of the visual field. With prisms, juveniles learn new associations between auditory cues, such as interaural time difference (ITD), and locations in visual space, and acquire new neurophysiological maps of ITD in the optic tectum, whereas adults do neither. Here we show that when the prismatic shift is experienced in small increments, maps of ITD in adults do change adaptively. Once established through incremental training, new ITD maps can be reacquired with a single large prismatic shift. Our results show that there is a substantially greater capacity for plasticity in adults than was previously recognized and highlight a principled strategy for tapping this capacity that could be applied in other areas of the adult central nervous system.     

A disinhibitory microcircuit for associative fear learning in the auditory cortex

Learning causes a change in how information is processed by neuronal circuits. Whereas synaptic plasticity, an important cellular mechanism, has been studied in great detail, we know much less about how learning is implemented at the level of neuronal circuits and, in particular, how interactions between distinct types of neurons within local networks contribute to the process of learning. Here we show that acquisition of associative fear memories depends on the recruitment of a disinhibitory microcircuit in the mouse auditory cortex. Fear-conditioning-associated disinhibition in auditory cortex is driven by foot-shock-mediated cholinergic activation of layer 1 interneurons, in turn generating inhibition of layer 2/3 parvalbumin-positive interneurons. Importantly, pharmacological or optogenetic block of pyramidal neuron disinhibition abolishes fear learning. Together, these data demonstrate that stimulus convergence in the auditory cortex is necessary for associative fear learning to complex tones, define the circuit elements mediating this convergence and suggest that layer-1-mediated disinhibition is an important mechanism underlying learning and information processing in neocortical circuits.     

Visual behaviour mediated by retinal projections directed to the auditory pathway

An unresolved issue in cortical development concerns the relative contributions of intrinsic and extrinsic factors to the functional specification of different cortical areas. Ferrets in which retinal projections are redirected neonatally to the auditory thalamus have visually responsive cells in auditory thalamus and cortex, form a retinotopic map in auditory cortex and have visual receptive field properties in auditory cortex that are typical of cells in visual cortex. Here we report that this cross-modal projection and its representation in auditory cortex can mediate visual behaviour. When light stimuli are presented in the portion of the visual field that is 'seen' only by this projection, 'rewired' ferrets respond as though they perceive the stimuli to be visual rather than auditory. Thus the perceptual modality of a neocortical region is instructed to a significant extent by its extrinsic inputs. In addition, gratings of different spatial frequencies can be discriminated by the rewired pathway, although the grating acuity is lower than that of the normal visual pathway.     

Change in pattern of ongoing cortical activity with auditory category learning

Humans are able to classify novel items correctly by category; some other animals have also been shown to do this. During category learning, humans group perceptual stimuli by abstracting qualities from similarity relationships of their physical properties. Forming categories is fundamental to cognition and can be independent of a 'memory store' of information about the items or a prototype. The neurophysiological mechanisms underlying the formation of categories are unknown. Using an animal model of category learning, in which frequency-modulated tones are distinguished into the categories of 'rising' and 'falling' modulation, we demonstrate here that the sorting of stimuli into these categories emerges as a sudden change in an animal's learning strategy. Electro-corticographical recording from the auditory cortex shows that the transition is accompanied by a change in the dynamics of cortical stimulus representation. We suggest that this dynamic change represents a mechanism underlying the recognition of the abstract quality (or qualities) that defines the categories.     

基于奥米亚棕蝇听觉定向机制声定位系统仿生学设计

在研究奥米亚棕蝇定位机制的基础上,首先运用传递函数方法设计了一种仿生三维声定位电学装置,为此搭建了4种电路原型,电路原型由测量单元与耦合单元组成,最后讨论并优化了与提高灵敏度相关的参数。理论分析和仿真结果表明,所设计的声定位电学装置与其他装置相比,具有尺寸小、定位精度高等优点,可为进一步研究奥米亚棕蝇这种精确感知声源的能力及其对波达角的高精度定位应用提供参考。     

指导学生参加2009年全国职业院校技能大赛之我见

全国职业院校技能大赛已经成为每年一次的重大赛事,每所职业院校对此极大关注和高度重视。通过分析2009年大赛(高职组)"产品造型设计及快速成型"项目,总结了指导学生训练的有效方法:"四个阶段","学中做,做中学"全面提升学生技能和素质。     

A neurofibromatosis-1-regulated pathway is required for learning in Drosophila

The tumour-suppressor gene Neurofibromatosis 1 (Nf1) encodes a Ras-specific GTPase activating protein (Ras-GAP). In addition to being involved in tumour formation, NF1 has been reported to cause learning defects in humans and Nf1 knockout mice. However, it remains to be determined whether the observed learning defect is secondary to abnormal development. The Drosophila NF1 protein is highly conserved, showing 60% identity of its 2,803 amino acids with human NF1 (ref. 12). Previous studies have suggested that Drosophila NF1 acts not only as a Ras-GAP but also as a possible regulator of the cAMP pathway that involves the rutabaga (rut)-encoded adenylyl cyclase. Because rut was isolated as a learning and short-term memory mutant, we have pursued the hypothesis that NF1 may affect learning through its control of the Rut-adenylyl cyclase/cAMP pathway. Here we show that NF1 affects learning and short-term memory independently of its developmental effects. We show that G-protein-activated adenylyl cyclase activity consists of NF1-independent and NF1-dependent components, and that the mechanism of the NF1-dependent activation of the Rut-adenylyl cyclase pathway is essential for mediating Drosophila learning and memory.     

基于深度学习GRU网络的UWB室内定位优化

为减少信号传输质量和距离估计算法等因素对定位精度的影响,将深度学习应用于超宽带（ultra wide band,UWB）室内定位系统,利用门控循环单元（gated recurrent unit,GRU）网络代替传统UWB室内定位系统中的三边测量过程,以提高UWB室内定位精度。在得到定位标签到基站的距离信息后,将距离信息输入GRU网络中,输出最终位置坐标。GRU作为循环神经网络（recurrent neural network,RNN）的变种,既含有RNN处理时序数据的优势,又解决了RNN中的长程依赖问题。对GRU网络模型中不同学习率、优化器、批量大小、网络层数、隐藏神经元数量参数进行调整和训练。结果表明,基于GRU网络模型的UWB室内定位系统显著提高了定位精度,平均定位误差为6.8 cm。     

Projection neurons within a vocal motor pathway are born during song learning in zebra finches

Many birds learn song during a restricted 'sensitive' period. Juveniles memorize a song model, and then learn the pattern of muscle contractions necessary to reproduce the song. Of the neural changes accompanying avian song learning, perhaps the most remarkable is the production of new neurons which are inserted into the hyperstriatum ventralis pars caudalis (HVc), a region critical for song production. We report here that in young male zebra finches many of the new neurons incorporated into the HVc innervate the robust nucleus of the archistriatum (RA) which projects to motor neurons controlling the vocal musculature. Furthermore, far fewer of these new neurons are incorporated into the HVc of either adult males that are beyond the sensitive learning period, or young females (who do not develop song). Thus, a major portion of the vocal motor pathway is actually created during song learning. This may enable early sensory experience and vocal practice to not only modify existing neuronal circuits, but also shape the insertion and initial synaptic contacts of neurons controlling adult song.     

粮仓补冷空调风管布置方案的CFD模拟

基于低温储粮节能技术研究,文章初步设计了粮仓补冷空调风管布置的3种方案.以计算流体力学CFD模拟软件为工具,对其通风效果进行模拟研究,并对结果进行分析比较,得出最佳风管布置方案.     

脑发育期甲状腺激素对大鼠听觉中潜伏期反应和学习记忆的影响

目的:探讨脑发育期甲状腺激素对大鼠听觉中潜伏期反应(MLR)和学习记忆的影响效应.方法:孕鼠从孕第1天至仔鼠生后30 d饮含质量浓度为0.3 g/L甲硫咪唑的自来水诱发甲状腺功能低下仔鼠,每天腹腔注射质量分数为0.02 mg/kg左旋甲状腺素(L-T4)进行替代治疗.分为H组(甲低)、RP1组(生后1～30 d替代治疗...     

Prediction of auditory spatial acuity from neural images on the owl's auditory space map

The owl can discriminate changes in the location of sound sources as small as 3 degrees and can aim its head to within 2 degrees of a source. A typical neuron in its midbrain space map has a spatial receptive field that spans 40 degrees--a width that is many times the behavioural threshold. Here we have quantitatively examined the relationship between neuronal activity and perceptual acuity in the auditory space map in the barn owl midbrain. By analysing changes in firing rate resulting from small changes of stimulus azimuth, we show that most neurons can reliably signal changes in source location that are smaller than the behavioural threshold. Each source is represented in the space map by a focus of activity in a population of neurons. Displacement of the source causes the pattern of activity in this population to change. We show that this change predicts the owl's ability to detect a change in source location.     

刺激大鼠杏仁外侧核对听皮层神经元调频声反应的影响

采用在体细胞外单细胞记录方法,研究电刺激杏仁外侧核对调频声所诱发的听皮层神经元反应的影响.实验在34只乌拉坦麻醉的SD大鼠上进行,在皮层41区记录了113个对调频声有反应的细胞电活动.观察发现,这些神经元对调频声刺激的反应可分为ON反应,OFF反应,ON-OFF反应,持续性反应和给声抑制反应几种类型.在观察对其中42个神经元的声反应时给予了杏仁外侧核电刺激,其中22%的神经元反应被易化,48%的神经元反应受到了抑制,另外30%神经元的声反应未受杏仁外侧核刺激的影响.这些影响进一步表明,杏仁复合体可在皮层水平参与听觉上传信息的处理,包括听觉信息的加工与整合.同时也表明杏仁核在上传听觉信息的筛选中可能具有重要的作用.