Invariant visual representation by single neurons in the human brain

It takes a fraction of a second to recognize a person or an object even when seen under strikingly different conditions. How such a robust, high-level representation is achieved by neurons in the human brain is still unclear. In monkeys, neurons in the upper stages of the ventral visual pathway respond to complex images such as faces and objects and show some degree of invariance to metric properties such as the stimulus size, position and viewing angle. We have previously shown that neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects or scenes. Here we report on a remarkable subset of MTL neurons that are selectively activated by strikingly different pictures of given individuals, landmarks or objects and in some cases even by letter strings with their names. These results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories.     

Corridors of migrating neurons in the human brain and their decline during infancy

The subventricular zone of many adult non-human mammals generates large numbers of new neurons destined for the olfactory bulb. Along the walls of the lateral ventricles, immature neuronal progeny migrate in tangentially oriented chains that coalesce into a rostral migratory stream (RMS) connecting the subventricular zone to the olfactory bulb. The adult human subventricular zone, in contrast, contains a hypocellular gap layer separating the ependymal lining from a periventricular ribbon of astrocytes. Some of these subventricular zone astrocytes can function as neural stem cells in vitro, but their function in vivo remains controversial. An initial report found few subventricular zone proliferating cells and rare migrating immature neurons in the RMS of adult humans. In contrast, a subsequent study indicated robust proliferation and migration in the human subventricular zone and RMS. Here we find that the infant human subventricular zone and RMS contain an extensive corridor of migrating immature neurons before 18 months of age but, contrary to previous reports, this germinal activity subsides in older children and is nearly extinct by adulthood. Surprisingly, during this limited window of neurogenesis, not all new neurons in the human subventricular zone are destined for the olfactory bulb--we describe a major migratory pathway that targets the prefrontal cortex in humans. Together, these findings reveal robust streams of tangentially migrating immature neurons in human early postnatal subventricular zone and cortex. These pathways represent potential targets of neurological injuries affecting neonates.     

Glycine potentiates the NMDA response in cultured mouse brain neurons

Transmitters mediating 'fast' synaptic processes in the vertebrate central nervous system are commonly placed in two separate categories that are believed to exhibit no interaction at the receptor level. The 'inhibitory transmitters' (such as glycine and GABA) are considered to act only on receptors mediating a chloride conductance increase, whereas 'excitatory transmitters' (such as L-glutamate) are considered to activate receptors mediating a cationic conductance increase. The best known excitatory receptor is that specifically activated by N-methyl-D-aspartate (NMDA) which has recently been characterized at the single channel level. The response activated by NMDA agonists is unique in that it exhibits a voltage-dependent Mg block. We report here that this response exhibits another remarkable property: it is dramatically potentiated by glycine. This potentiation is not mediated by the inhibitory strychnine-sensitive glycine receptor, and is detected at a glycine concentration as low as 10 nM. The potentiation can be observed in outside-out patches as an increase in the frequency of opening of the channels activated by NMDA agonists. Thus, in addition to its role as an inhibitory transmitter, glycine may facilitate excitatory transmission in the brain through an allosteric activation of the NMDA receptor.     

一氧化氮合酶阳性神经元在鱼脑的分布

应用还原型尼克酰胺腺苷二核苷酸—黄递酶组化法，研究了一氧化氮合酶阳性神经元在鱼脑内的分布。结果显示，一氧化氮合酶阳性神经元存在于硬骨鱼纲的鳙鱼脑内不同部位，数量较少，集中分布；胞体呈圆形或三角形，着色较深，发出突起。由此可见，低等脊椎动物鱼类脑中也存在一氧化氮合酶阳性神经元，较哺乳动物而言分布集中且数量少，表明一氧化氮的存在与动物脑的进化有一定的关系。     

GABA regulates synaptic integration of newly generated neurons in the adult brain

Adult neurogenesis, the birth and integration of new neurons from adult neural stem cells, is a striking form of structural plasticity and highlights the regenerative capacity of the adult mammalian brain. Accumulating evidence suggests that neuronal activity regulates adult neurogenesis and that new neurons contribute to specific brain functions. The mechanism that regulates the integration of newly generated neurons into the pre-existing functional circuitry in the adult brain is unknown. Here we show that newborn granule cells in the dentate gyrus of the adult hippocampus are tonically activated by ambient GABA (gamma-aminobutyric acid) before being sequentially innervated by GABA- and glutamate-mediated synaptic inputs. GABA, the major inhibitory neurotransmitter in the adult brain, initially exerts an excitatory action on newborn neurons owing to their high cytoplasmic chloride ion content. Conversion of GABA-induced depolarization (excitation) into hyperpolarization (inhibition) in newborn neurons leads to marked defects in their synapse formation and dendritic development in vivo. Our study identifies an essential role for GABA in the synaptic integration of newly generated neurons in the adult brain, and suggests an unexpected mechanism for activity-dependent regulation of adult neurogenesis, in which newborn neurons may sense neuronal network activity through tonic and phasic GABA activation.     

关于视觉表象的几个争论

表象是感知过的事物不在面前时头脑中出现该事物的形象,从而使人产生在心理面“看”或“听”的体验。由于表象天生地个体私密性而难以研究,目前对于视觉表象本质的解释主要有两类理论：图片理论和虚无假设。双方在理论建构和研究方法上都存在着激烈的争论,如表征形式、表象与知觉的关系、内隐知识、实验者效应等。目前研究中还存在证真偏向严重,忽略表象个体差异和将表象简单化、单一化等问题。     

Tragic Imagery in Hamlet

莎士比亚运用形象这种生动的修辞语言展现了事物、行为或想法。莎翁在《哈姆雷特》中,用夜晚,监狱,疾病和疯癫等形象使得读者深刻的了解到戏剧中人物间激烈的矛盾、哈姆雷特的愤世嫉俗以及剧中人物情感所经历的一切。     

Interactive memory systems in the human brain.

Learning and memory in humans rely upon several memory systems, which appear to have dissociable brain substrates. A fundamental question concerns whether, and how, these memory systems interact. Here we show using functional magnetic resonance imaging (FMRI) that these memory systems may compete with each other during classification learning in humans. The medial temporal lobe and basal ganglia were differently engaged across subjects during classification learning depending upon whether the task emphasized declarative or nondeclarative memory, even when the to-be-learned material and the level of performance did not differ. Consistent with competition between memory systems suggested by animal studies and neuroimaging, activity in these regions was negatively correlated across individuals. Further examination of classification learning using event-related FMRI showed rapid modulation of activity in these regions at the beginning of learning, suggesting that subjects relied upon the medial temporal lobe early in learning. However, this dependence rapidly declined with training, as predicted by previous computational models of associative learning.     

略论审美意象

<正> 崛起于20世纪初英美文坛上的意象派,倡导了西方现代主义文艺运动,在短短的几十年时间内,形成了巨大的影响。但是,意象派作为一个文学流派,其核心概念“意象”却如美本身一样,是一个灵活得让人难以把握的美学术语。人们在运用“意象”理论进行文艺研究和分析作品时,往往众说纷纭而大多失之偏颇。笔者认为,要想挖掘这一文艺美学理论研究的难题,须回到雄踞同期世界美学峰巅的中国古典美学。     

Smell images and the flavour system in the human brain

Flavour perception is one of the most complex of human behaviours. It involves almost all of the senses, particularly the sense of smell, which is involved through odour images generated in the olfactory pathway. In the human brain, the perceptual systems are closely linked to systems for learning, memory, emotion and language, so distributed neural mechanisms contribute to food preference and food cravings. Greater recognition of the role of the brain's flavour system and its connection with eating behaviour is needed for a deeper understanding of why people eat what they do, and to generate better recommendations about diet and nutrition.     

Transcranial magnetic stimulation and the human brain

Transcranial magnetic stimulation (TMS) is rapidly developing as a powerful, non-invasive tool for studying the human brain. A pulsed magnetic field creates current flow in the brain and can temporarily excite or inhibit specific areas. TMS of motor cortex can produce a muscle twitch or block movement; TMS of occipital cortex can produce visual phosphenes or scotomas. TMS can also alter the functioning of the brain beyond the time of stimulation, offering potential for therapy.     

论华兹华斯诗歌中的植物意象

华兹华斯以“自然诗人”闻名于世，他的诗歌作品几乎囊括了大自然的全貌．从华兹华斯笔下有关植物的诗篇中，分析其植物意象的构成，探讨植物意象的三层象征意义：在现实层面上，是人类可居的理想家园；在精神层面上，是生命旅程的伴侣，向人揭示生活的哲理；在终极意义上，是神性的直接体现。最后，简要分析了华兹华斯选择这一题材的内在动机。     

A general mechanism for perceptual decision-making in the human brain

Findings from single-cell recording studies suggest that a comparison of the outputs of different pools of selectively tuned lower-level sensory neurons may be a general mechanism by which higher-level brain regions compute perceptual decisions. For example, when monkeys must decide whether a noisy field of dots is moving upward or downward, a decision can be formed by computing the difference in responses between lower-level neurons sensitive to upward motion and those sensitive to downward motion. Here we use functional magnetic resonance imaging and a categorization task in which subjects decide whether an image presented is a face or a house to test whether a similar mechanism is also at work for more complex decisions in the human brain and, if so, where in the brain this computation might be performed. Activity within the left dorsolateral prefrontal cortex is greater during easy decisions than during difficult decisions, covaries with the difference signal between face- and house-selective regions in the ventral temporal cortex, and predicts behavioural performance in the categorization task. These findings show that even for complex object categories, the comparison of the outputs of different pools of selectively tuned neurons could be a general mechanism by which the human brain computes perceptual decisions.     

酒神精神与尼采哲学--浅析《悲剧的诞生》

本文阐述尼采酒神精神产生的渊源，分析了酒神精神的深刻内涵，提出了尼采哲学的重要命题－重估一切价值，超人强力意志。     

Energetics and the evolution of human brain size

The human brain stands out among mammals by being unusually large. The expensive-tissue hypothesis explains its evolution by proposing a trade-off between the size of the brain and that of the digestive tract, which is smaller than expected for a primate of our body size. Although this hypothesis is widely accepted, empirical support so far has been equivocal. Here we test it in a sample of 100 mammalian species, including 23 primates, by analysing brain size and organ mass data. We found that, controlling for fat-free body mass, brain size is not negatively correlated with the mass of the digestive tract or any other expensive organ, thus refuting the expensive-tissue hypothesis. Nonetheless, consistent with the existence of energy trade-offs with brain size, we find that the size of brains and adipose depots are negatively correlated in mammals, indicating that encephalization and fat storage are compensatory strategies to buffer against starvation. However, these two strategies can be combined if fat storage does not unduly hamper locomotor efficiency. We propose that human encephalization was made possible by a combination of stabilization of energy inputs and a redirection of energy from locomotion, growth and reproduction.     

High constitutive activity of native H3 receptors regulates histamine neurons in brain

Some G-protein-coupled receptors display 'constitutive activity', that is, spontaneous activity in the absence of agonist. This means that a proportion of the receptor population spontaneously undergoes an allosteric transition, leading to a conformation that can bind G proteins. The process has been shown to occur with recombinant receptors expressed at high density, and/or mutated, but also non-mutated recombinant receptors expressed at physiological concentrations. Transgenic mice that express a constitutively active mutant of the beta2-adrenergic receptor display cardiac anomalies; and spontaneous receptor mutations leading to constitutive activity are at the origin of some human diseases. Nevertheless, this process has not previously been found to occur in animals expressing normal levels of receptor. Here we show that two isoforms of the recombinant rat H3 receptor display high constitutive activity. Using drugs that abrogate this activity ('inverse agonists') and a drug that opposes both agonists and inverse agonists ('neutral antagonist'), we show that constitutive activity of native H3 receptors is present in rodent brain and that it controls histaminergic neuron activity in vivo. Inverse agonists may therefore find therapeutic applications, even in the case of diseases involving non-mutated receptors expressed at normal levels.