Behavioural report of single neuron stimulation in somatosensory cortex

Understanding how neural activity in sensory cortices relates to perception is a central theme of neuroscience. Action potentials of sensory cortical neurons can be strongly correlated to properties of sensory stimuli and reflect the subjective judgements of an individual about stimuli. Microstimulation experiments have established a direct link from sensory activity to behaviour, suggesting that small neuronal populations can influence sensory decisions. However, microstimulation does not allow identification and quantification of the stimulated cellular elements. The sensory impact of individual cortical neurons therefore remains unknown. Here we show that stimulation of single neurons in somatosensory cortex affects behavioural responses in a detection task. We trained rats to respond to microstimulation of barrel cortex at low current intensities. We then initiated short trains of action potentials in single neurons by juxtacellular stimulation. Animals responded significantly more often in single-cell stimulation trials than in catch trials without stimulation. Stimulation effects varied greatly between cells, and on average in 5% of trials a response was induced. Whereas stimulation of putative excitatory neurons led to weak biases towards responding, stimulation of putative inhibitory neurons led to more variable and stronger sensory effects. Reaction times for single-cell stimulation were long and variable. Our results demonstrate that single neuron activity can cause a change in the animal's detection behaviour, suggesting a much sparser cortical code for sensations than previously anticipated.     

Attention modulates synchronized neuronal firing in primate somatosensory cortex

A potentially powerful information processing strategy in the brain is to take advantage of the temporal structure of neuronal spike trains. An increase in synchrony within the neural representation of an object or location increases the efficacy of that neural representation at the next synaptic stage in the brain; thus, increasing synchrony is a candidate for the neural correlate of attentional selection. We investigated the synchronous firing of pairs of neurons in the secondary somatosensory cortex (SII) of three monkeys trained to switch attention between a visual task and a tactile discrimination task. We found that most neuron pairs in SII cortex fired synchronously and, furthermore, that the degree of synchrony was affected by the monkey's attentional state. In the monkey performing the most difficult task, 35% of neuron pairs that fired synchronously changed their degree of synchrony when the monkey switched attention between the tactile and visual tasks. Synchrony increased in 80% and decreased in 20% of neuron pairs affected by attention.     

Ocular dominance plasticity in adult cat visual cortex after transplantation of cultured astrocytes

During a critical restricted period of postnatal development, the visual cortical circuitry is susceptible to modifications that are dependent on experience. If vision is restricted to only one eye during this period, the territories innervated by the deprived eye shrink considerably, whereas those innervated by the non-deprived eye expand, and the deprived eye loses the ability to influence almost all of the cells in the cortex. Thus, changes in ocular dominance are paralleled and possibly mediated by synapse elimination and axonal sprouting. Hypotheses about the mechanisms underlying ocular-dominance plasticity assume the activation of NMDA (N-methyl-D-aspartate) receptors and subsequent calcium influx as a trigger of synaptic modifications. In addition, plasticity relies on functional neuromodulatory afferents. On the basis of immunocytochemical studies, it was recently proposed that the presence of immature astrocytes is a prerequisite for visual cortical plasticity, and that the end of the critical period is causally linked to the maturation of astrocytes. Here we report, in support of this hypothesis, that resupplementation of the visual cortex of adult cats with astrocytes cultured from the visual cortex of newborn kittens reinduces ocular-dominance plasticity in adult animals.     

Long-term sensory deprivation prevents dendritic spine loss in primary somatosensory cortex

A substantial decrease in the number of synapses occurs in the mammalian brain from the late postnatal period until the end of life. Although experience plays an important role in modifying synaptic connectivity, its effect on this nearly lifelong synapse loss remains unknown. Here we used transcranial two-photon microscopy to visualize postsynaptic dendritic spines in layer I of the barrel cortex in transgenic mice expressing yellow fluorescent protein. We show that in young adolescent mice, long-term sensory deprivation through whisker trimming prevents net spine loss by preferentially reducing the rate of ongoing spine elimination, not by increasing the rate of spine formation. This effect of deprivation diminishes as animals mature but still persists in adulthood. Restoring sensory experience after adolescent deprivation accelerates spine elimination. Similar to sensory manipulation, the rate of spine elimination decreases after chronic blockade of NMDA (N-methyl-D-aspartate) receptors with the antagonist MK801, and accelerates after drug withdrawal. These studies of spine dynamics in the primary somatosensory cortex suggest that experience plays an important role in the net loss of synapses over most of an animal's lifespan, particularly during adolescence.     

Long-term in vivo imaging of experience-dependent synaptic plasticity in adult cortex

Do new synapses form in the adult cortex to support experience-dependent plasticity? To address this question, we repeatedly imaged individual pyramidal neurons in the mouse barrel cortex over periods of weeks. We found that, although dendritic structure is stable, some spines appear and disappear. Spine lifetimes vary greatly: stable spines, about 50% of the population, persist for at least a month, whereas the remainder are present for a few days or less. Serial-section electron microscopy of imaged dendritic segments revealed retrospectively that spine sprouting and retraction are associated with synapse formation and elimination. Experience-dependent plasticity of cortical receptive fields was accompanied by increased synapse turnover. Our measurements suggest that sensory experience drives the formation and elimination of synapses and that these changes might underlie adaptive remodelling of neural circuits.     

Naturalistic experience transforms sensory maps in the adult cortex of caged animals

Much of what is known about the functional organization and plasticity of adult sensory cortex is derived from animals housed in standard laboratory cages. Here we report that the transfer of adult rats reared in standard laboratory cages to a naturalistic habitat modifies the functional and morphological organization of the facial whisker representation in the somatosensory 'barrel' cortex. Cortical whisker representations, visualized with repeated intrinsic signal optical imaging in the same animals, contracted by 46% after four to six weeks of exposure to the naturalistic habitat. Acute, multi-site extracellular recordings demonstrated suppressed evoked neuronal responses and smaller, sharper constituent receptive fields in the upper cortical layers (II/III), but not in the thalamic recipient layer (IV), of rats with naturalistic experience. Morphological plasticity of the layer IV barrel field was observed, but on a substantially smaller scale than the functional plasticity. Thus, transferring animals to an environment that promotes the expression of natural, innate behaviours induces a large-scale functional refinement of cortical sensory maps.     

胃大部切除术后功能性排空障碍的处理

目的探讨对胃大部切除术后功能性排空障碍的治疗措施.方法对1996年9月至2005年9月收治的16例胃大部切除术后功能性排空障碍者进行临床分析.结果16例患者经对症处理,3-8周后均治愈.结论胃大部切除术后功能性排空障碍非机械性梗阻,一经诊断明确应行保守治疗,切忌再次手术.     

胃大部切除术后功能性排空障碍的处理

目的探讨对胃大部切除术后功能性排空障碍的治疗措施.方法对1996年9月至2005年9月收治的16例胃大部切除术后功能性排空障碍者进行临床分析.结果16例患者经对症处理,3-8周后均治愈.结论胃大部切除术后功能性排空障碍非机械性梗阻,一经诊断明确应行保守治疗,切忌再次手术.     

Ketamine-xylazine anaesthesia blocks consolidation of ocular dominance changes in kitten visual cortex

In the visual cortex of mammals, response properties of single neurons can be changed by restricted visual experience during early postnatal development. Covering one eye for four to eight hours when kittens are at the peak of the sensitive period is sufficient to weaken the influence of the occluded eye on cortical neurons resulting in a noticeable shift of ocular dominance towards the open eye. The underlying changes in synaptic connections do not occur so readily when a kitten is anaesthetized and paralysed. We report here that an ocular dominance shift is prevented in alert kittens that receive repeated brief monocular exposures when these are followed by ketamine-xylazine anaesthesia. This retrograde effect on cortical plasticity suggests that the process by which synaptic activity is converted into structural changes has been disturbed.     

Adaptive immune responses in acute and chronic hepatitis C virus infection

The hepatitis C virus (HCV) persists in the majority of infected individuals and is a significant cause of human illness and death globally. Recent studies have yielded important insights into immunity to HCV, in particular revealing the central role of T cells in viral control and clearance. Other key features of adaptive immune responses remain obscure, including mechanisms by which T cells control HCV replication, the role of antibodies in conferring protection and how cellular and humoral immunity are subverted in persistent infection.     

树干液流对环境变化响应研究的整合分析

【目的】从生态系统和全球尺度上考察了树干液流和生物及非生物因子之间的关系,将影响因子参数化以进行全球树干液流的估计,量化比较人为控制环境试验对液流的影响。【方法】采用数据整合分析方法,收集2001—2019年树干液流相关研究数据,从森林生态系统和全球尺度上研究树干液流密度(Fd)对生物和非生物因子的响应,并对树干液流与年平均温度(MAT)、年平均降水量(MAP)、饱和水汽压亏缺(VPD)、光合有效辐射(PAR)、土壤含水率(ρ)等主要影响因子的关系进行多元回归分析。【结果】胸径(DBH)和叶面积指数(LAI)都与Fd在生物群落和全球尺度上高度相关;VPD与Fd呈负相关关系;通过MAT、MAP、VPD、DBH和土壤体积含水率建立参数化模型可以估算树干液流密度;不同控制试验通过影响环境因子,进而影响森林蒸腾。【结论】树干液流主要受到自身生物因子和环境因子的影响并且影响程度因生态系统而异,人为活动可导致环境因子改变进而影响树干液流及蒸腾。