Imaging cortical correlates of illusion in early visual cortex

Exploring visual illusions reveals fundamental principles of cortical processing. Illusory motion perception of non-moving stimuli was described almost a century ago by Gestalt psychologists. However, the underlying neuronal mechanisms remain unknown. To explore cortical mechanisms underlying the 'line-motion' illusion, we used real-time optical imaging, which is highly sensitive to subthreshold activity. We examined, in the visual cortex of the anaesthetized cat, responses to five stimuli: a stationary small square and a long bar; a moving square; a drawn-out bar; and the well-known line-motion illusion, a stationary square briefly preceding a long stationary bar presentation. Whereas flashing the bar alone evoked the expected localized, short latency and high amplitude activity patterns, presenting a square 60-100 ms before a bar induced the dynamic activity patterns resembling that of fast movement. The preceding square, even though physically non-moving, created gradually propagating subthreshold cortical activity that must contribute to illusory motion, because it was indistinguishable from cortical representations of real motion in this area. These findings demonstrate the effect of spatio-temporal patterns of subthreshold synaptic potentials on cortical processing and the shaping of perception.     

Rapid developmental switch in the mechanisms driving early cortical columnar networks

The immature cerebral cortex self-organizes into local neuronal clusters long before it is activated by patterned sensory inputs. In the cortical anlage of newborn mammals, neurons coassemble through electrical or chemical synapses either spontaneously or by activation of transmitter-gated receptors. The neuronal network and the cellular mechanisms underlying this cortical self-organization process during early development are not completely understood. Here we show in an intact in vitro preparation of the immature mouse cerebral cortex that neurons are functionally coupled in local clusters by means of propagating network oscillations in the beta frequency range. In the newborn mouse, this activity requires an intact subplate and is strongly synchronized within a cortical column by gap junctions. With the developmental disappearance of the subplate at the end of the first postnatal week, activation of NMDA (N-methyl-D-aspartate) receptors in the immature cortical network is essential to generate this columnar activity pattern. Our findings show that during a brief developmental period the cortical network switches from a subplate-driven, gap-junction-coupled syncytium to a synaptic network acting through NMDA receptors to generate synchronized oscillatory activity, which may function as an early functional template for the development of the cortical columnar architecture.     

Auditory cortical responses in the cat to sounds that produce spatial illusions.

Humans and cats can localize a sound source accurately if its spectrum is fairly broad and flat, as is typical of most natural sounds. However, if sounds are filtered to reduce the width of the spectrum, they result in illusions of sources that are very different from the actual locations, particularly in the up/down and front/back dimensions. Such illusions reveal that the auditory system relies on specific characteristics of sound spectra to obtain cues for localization. In the auditory cortex of cats, temporal firing patterns of neurons can signal the locations of broad-band sounds. Here we show that such spike patterns systematically mislocalize sounds that have been passed through a narrow-band filter. Both correct and incorrect locations signalled by neurons can be predicted quantitatively by a model of spectral processing that also predicts correct and incorrect localization judgements by human listeners. Similar cortical mechanisms, if present in humans, could underlie human auditory spatial perception.     

Selective responses of visual cortical cells do not depend on shunting inhibition

Theoretical analyses of the electrical behaviour of the highly branched processes of nerve cells has focused attention on the possibility that single cells perform complex logical operations rather than simply summing their synaptic inputs. In particular, it has been suggested that the orientation and direction selectivity of cells in the visual cortex results from the action of a nonlinear 'shunting' inhibition that emulates an AND-NOT logical operation. The characteristic biophysical feature of this proposed inhibitory mechanism is that it evokes a large and relatively sustained increase in the conductance of the neuronal membrane while leaving the membrane potential unaffected. This shunting mechanism contrasts with linear 'summative' inhibition in which conductance changes are less prominent, and inhibition is achieved by hyperpolarization of the membrane potential. In a direct experimental test of the hypothesis that the selectivity of visual cortical neurons depends on shunting inhibition we found no evidence for the large conductance changes predicted by the theory.     

Selective collateral elimination in early postnatal development restricts cortical distribution of rat pyramidal tract neurones

The pyramidal tract, comprising those axons which pass from the neocortex to the medulla and spinal cord, is among the most thoroughly studied projections of the mammalian cortex. Recent studies using anterograde axon tracing techniques have provided information concerning the time course of the growth of pyramidal tract fibres, yet much remains to be learned about its development. We have now begun to study the distribution of the neurones of origin of the pyramidal tract during the postnatal development of the rat neocortex using the recently introduced retrogradely transported fluorescent marker, True blue. During the first postnatal week, injections of True blue into the pyramidal decussation result inthe labelling of pyramidal tract neurones which are distributed virtually throughout the tangential extent of layer V of the neocortex, whereas after comparable injections during the fourth postnatal week the distribution of such cells is much more restricted and remains restricted into adult life. This developmental restriction is most dramatic in the occipital cortex: during the first postnatal week many pyramidal tract neurones are found throughout the visual cortex while none is seen in this area of the adult. When True blue is injected into the pyramidal decussation during the first postnatal week and the animals are allowed to survive until the fourth postnatal week, the distribution of pyramidal tract neurones is as widespread as in the immediate postnatal period and includes the entire visual cortex. This implies that many of the neurones in the occipital cortex initially send a collateral into the pyramidal tract which is later eliminated, although the neurones themselves persist. These findings, together with similar recent observations on the development of the callosal connections, indicate that the elimination of axon collaterals may be a general feature of the development of cortical projection systems, and that such transitory collaterals may traverse considerable distances.     

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.     

浅谈怎样培养幼儿的手工兴趣

通过多年的实践探索,总结出一些培养幼儿的手工兴趣的做法,如:引导幼儿积极参与,培养动手动脑的兴趣; 创设丰富多彩的环境,激发孩子的手工兴趣;提供宽松自由的手工氛围,以利于幼儿身心发展;家园互动,激发幼儿手工 兴趣;利用创新教法,培养幼儿手工创意兴趣。     

对河西走廊生态农业可持续发展的战略思考

河西走廊被誉为甘肃的粮仓和全国的商品粮基地之一。本文通过对河西走廊资源、气候、沙尘、风暴、生态环境的现状分析 ,论证了河西走廊现有的资源优势、发展潜力以及制约河西走廊生态农业可持续发展的主要因素是水资源和气候环境因素。而解决这一问题的主要途径是退耕还牧、还林、还草。建设“绿色水库” ,强调森林、草原植被对农业发展的综合作用和稳定性优势。提出建造水源涵养林、节水灌溉、调整产业结构、农牧民搬迁等措施 ,必将彻底改善气候环境、提高降水量、增加经济效益并带动农业和畜牧业生态系统的良性循环和可持续发展 ,最终达到“南拓青龙、中扩绿洲、北退黄龙”的目的     

国外幸福感研究的发展轨迹

国外幸福感在三十多年研究历程中经历了三个主要发展时期,第一阶段幸福感主要研究集中在沿着人口统计学的维度对不同人群幸福感描述和比较;在第二阶段幸福感研究之中,开始探索并建构幸福感理论框架;第三阶段侧重于完善与发展幸福感测量方法以更深入理解幸福感复杂、多样化心理过程.最近新的趋势是走向纵向设计研究、跨文化研究以及幸福感干预实验研究.     

国外幸福感研究的发展轨迹

国外幸福感在三十多年研究历程中经历了三个主要发展时期,第一阶段幸福感主要研究集中在沿着人口统计学的维度对不同人群幸福感描述和比较;在第二阶段幸福感研究之中,开始探索并建构幸福感理论框架;第三阶段侧重于完善与发展幸福感测量方法以更深入理解幸福感复杂、多样化心理过程.最近新的趋势是走向纵向设计研究、跨文化研究以及幸福感干预实验研究.     

关于高等数学课堂教学中如何注重能力培养的研究

高等数学课堂教学在实现能力培养目标过程中,应充分体现教师的主导作用与学生的主体地位,对教学、教学手段和教学方法实行一系列改革,尤其要实行国际上流行的“问题解决”模式,重视数学的实际应用,以提高学生学习的主动性、积极性和创造性。     

关于高等数学课堂教学中如何注重培养的研究

高等数学课堂教学在实现能力培养目标过程中,应充分体现教师的主导作用与学生的主体地位,对教学内容、教学手段和教学方法实行一系列改革,尤其要实行国际上流行的"问题解决"模式,重视数学的实际应用,以提高学生学习的主动性、积极性和创造性.     

浅议学生口译能力在相关课程中的培养

口译能力是一种综合的语言应用能力,其形成非一日之功,因此单凭口译一门课程来培养学生的口译能力是远远不够的。本文对影响口译水平的内在因素进行了简要的分析,探讨了口译基本能力素质在其相关课程中得到充分的系统的训练的必要性和可能性。     

论高校体育课如何开展非智力因素的教学

大学生的学习和成才过程,是一个智力因素与非智能力因素相互影响,而又以非智力因素起决定作用的过程二在高校体育课中开展非智力因素的教学,有利于大学生的健康成长,有助于教学质量的提高,是体育教学工作的出发点和归宿．