A neural mechanism for working and recognition memory in inferior temporal cortex

Inferior temporal (IT) cortex is critical for visual memory, but it is not known how IT neurons retain memories while new information is streaming into the visual system. Single neurons were therefore recorded from IT cortex of two rhesus monkeys performing tasks that required them to hold items in memory while concurrently viewing other items. The neuronal response to an incoming visual stimulus was attenuated if it matched a stimulus actively held in working memory, even when several other stimuli intervened. The neuronal response to novel stimuli declined as the stimuli became familiar to the animal. IT neurons appear to function as adaptive mnemonic "filters" that preferentially pass information about new, unexpected, or not recently seen stimuli.     

Complementary neural mechanisms for tracking items in human working memory

Recognition of a specific visual target among equally familiar distracters requires neural mechanisms for tracking items in working memory. Event-related functional magnetic resonance imaging revealed evidence for two such mechanisms: (i) Enhanced neural responses, primarily in the frontal cortex, were associated with the target and were maintained across repetitions of the target. (ii) Reduced responses, primarily in the extrastriate visual cortex, were associated with stimulus repetition, regardless of whether the stimulus was a target or a distracter. These complementary neural mechanisms track the status of familiar items in working memory, allowing for the efficient recognition of a currently relevant object and rejection of irrelevant distracters.     

Dynamic shifts of limited working memory resources in human vision

Our ability to remember what we have seen is very limited. Most current views characterize this limit as a fixed number of items-only four objects-that can be held in visual working memory. We show that visual memory capacity is not fixed by the number of objects, but rather is a limited resource that is shared out dynamically between all items in the visual scene. This resource can be shifted flexibly between objects, with allocation biased by selective attention and toward targets of upcoming eye movements. The proportion of resources allocated to each item determines the precision with which it is remembered, a relation that we show is governed by a simple power law, allowing quantitative estimates of resource distribution in a scene.     

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.     

Phototaxis and sensory transduction in Euglena

The accumulation of Euglena gracilis in an illuminated region is brought about by two main mechanisms: orientation and subsequent directed movement (positive phototaxis) toward light scattered from particles in the illuminated zone; and by the trapping of cells in this region because of shock reactions experienced upon the cells encountering a sudden decrease of light intensity at the light-dark boundary (inverse photophobic responses).Phototactic orientation is mediated by inverse photophobic reactions which occur when the shadow of the stigma periodically falls upon the photoreceptor proper. Euglena also exhibits shock reactions when an already high light intensity is increased further (direct photophobic responses). The expression of both types of phobic responses depends upon stimulus intensity and adaptation of the sensory system in a seemingly complex way. A definition of the minimum components of the stimulus transduction system and a systems analytical approach to the study of input-output relationships enables one to construct an electronic analog of the cell's signal processing system that converts the photoreceptor input to commands which activate or inhibit flagellar reorientation. Computer simulation studies show that this model has considerable predictive value. It is hoped that with the approach presented in this article, a generalized model has become available for dealing with the questions of sensory transduction in aneural systems. Certainly, at this point more questions have been raised than have been answered. Where is the processing device located? Are its kinetic properties determined by electrical processes or by the rates of chemical reactions? Is the processor, and thereby the behavior of the orgamism, modulated by natural environmental parameters, and can it be modified permanently through more drastic chemical treatment of the cell? Is the system capable of permanent or transitory modification through repeated response, that is, does it exhibit phenomena analogous to learning and memory in higher organisms? These are only a few of the problems that require study in the future.     

The role of working memory in visual selective attention

The hypothesis that working memory is crucial for reducing distraction by maintaining the prioritization of relevant information was tested in neuroimaging and psychological experiments with humans. Participants performed a selective attention task that required them to ignore distractor faces while holding in working memory a sequence of digits that were in the same order (low memory load) or a different order (high memory load) on every trial. Higher memory load, associated with increased prefrontal activity, resulted in greater interference effects on behavioral performance from the distractor faces, plus increased face-related activity in the visual cortex. These findings confirm a major role for working memory in the control of visual selective attention.     

Retrograde amnesia produced by electroconvulsive shock after reactivation of a consolidated memory trace

Rats had a memory loss of a fear response when they received an electroconvulsive shock 24 hours after the fear-conditioning trial and preceded by a brief presentation of the conditioned stimulus. No such loss occurred when the conditioned stimulus was not presented. The memory loss in animals given electroconvulsive shock 24 hours after conditioning was, furthermore, as great as that displayed in animals given electroconvulsive shock immediately after conditioning. This result throws doubt on the assertion that electroconvulsive shock exerts a selective amnesic effect on recently acquired memories and thus that electroconvulsive shock produces amnesia solely through interference with memory trace consolidation.     

Synaptic theory of working memory

It is usually assumed that enhanced spiking activity in the form of persistent reverberation for several seconds is the neural correlate of working memory. Here, we propose that working memory is sustained by calcium-mediated synaptic facilitation in the recurrent connections of neocortical networks. In this account, the presynaptic residual calcium is used as a buffer that is loaded, refreshed, and read out by spiking activity. Because of the long time constants of calcium kinetics, the refresh rate can be low, resulting in a mechanism that is metabolically efficient and robust. The duration and stability of working memory can be regulated by modulating the spontaneous activity in the network.     

生活经验与工作记忆容量对条件推理的影响

选取5种条件命题的4种推理形式作为实验材料,采用经典的OSPAN任务测得被试的工作记忆容量,考察了生活经验与工作记忆容量对条件推理的影响.研究表明:生活经验会决定问题空间的表征,从而影响条件推理过程;工作记忆容量对条件推理没有影响;生活经验和工作记忆容量没有交互作用.此外,研究还表明在条件推理中,人们倾向于使用启发式策略,较少用到分析式策略.     

p53 dynamics control cell fate

Cells transmit information through molecular signals that often show complex dynamical patterns. The dynamic behavior of the tumor suppressor p53 varies depending on the stimulus; in response to double-strand DNA breaks, it shows a series of repeated pulses. Using a computational model, we identified a sequence of precisely timed drug additions that alter p53 pulses to instead produce a sustained p53 response. This leads to the expression of a different set of downstream genes and also alters cell fate: Cells that experience p53 pulses recover from DNA damage, whereas cells exposed to sustained p53 signaling frequently undergo senescence. Our results show that protein dynamics can be an important part of a signal, directly influencing cellular fate decisions.     

1GNF-200施肥旋耕机的设计与研究

该施肥旋耕机是为４０．４～５８．８ｋＷ轮式拖拉机配套的新型施肥、整地联合作业机具,可在作物播种前的旋耕整地过程中,完成化肥的条状深施。经设计方案、总体配置、主体结构和机组配套性能等的分析研究,以及机具田间工作性能测试表明,此机具设计合理,性能可靠,作业质量满足农艺要求。     

Optical imaging of neuronal populations during decision-making

We investigated decision-making in the leech nervous system by stimulating identical sensory inputs that sometimes elicit crawling and other times swimming. Neuronal populations were monitored with voltage-sensitive dyes after each stimulus. By quantifying the discrimination time of each neuron, we found single neurons that discriminate before the two behaviors are evident. We used principal component analysis and linear discriminant analysis to find populations of neurons that discriminated earlier than any single neuron. The analysis highlighted the neuron cell 208. Hyperpolarizing cell 208 during a stimulus biases the leech to swim; depolarizing it biases the leech to crawl or to delay swimming.     

Distinguishing the direct and indirect products of a gas-surface reaction

It has long been postulated that gas-surface chemical reactions can occur by means of two distinct mechanisms: direct reaction on a single gas-surface encounter or reaction between two adsorbed species. It is shown here that these mechanisms have distinct dynamical signatures, as illustrated by the reaction of hydrogen with chlorine on gold(111). The direct reaction product leaves the surface with a high kinetic energy in a narrow angular distribution that displays a "memory" of the direction and energy of the incident hydrogen atom. The indirect reaction product has a near-thermal energy distribution and an angular distribution that is close to that of a cosine function.     

Uniform inhibition of dopamine neurons in the ventral tegmental area by aversive stimuli

Dopamine neurons play a key role in reward-related behaviors. Reward coding theories predict that dopamine neurons will be inhibited by or will not respond to aversive stimuli. Paradoxically, between 3 and 49% of presumed dopamine neurons are excited by aversive stimuli. We found that, in the ventral tegmental area of anesthetized rats, the population of presumed dopamine neurons that are excited by aversive stimuli is actually not dopaminergic. The identified dopamine neurons were inhibited by the aversive stimulus. These findings suggest that dopamine neurons are specifically excited by reward and that a population of nondopamine neurons is excited by aversive stimuli.     

Robust fractional order controller for irrigation main canal pools with time-varying dynamical parameters

A new method is proposed with which to design a class of robust fractional order controllers - which we denote as FPI controllers since they can be regarded as a generalization of standard PI controllers - for the effective control of water distribution in irrigation main canal pools characterized by time-varying dynamical parameters. The closed loop behavior of the nominal plant is defined by using frequency specifications, which are combined with an optimization procedure that minimizes the IAE (Integral of Absolute Error) - a cost related to the closed loop time response specifications - in the whole range of plant parameter variations. Interest in such robust fractional order controllers is justified by the fact that dynamical parameters of irrigation main canal pools may change drastically according to their operational regimes. Equivalent FPI, PI and PID controllers - in the sense of their exhibiting the same closed loop dynamics for the nominal plant specifications - were simulated for several working conditions, and their behaviors were compared. Additional issues, such as noise rejection or robustness to unmodelled high frequency dynamics have also been considered.     

Dynamics of magnetic domain walls under their own inertia

The motion of magnetic domain walls induced by spin-polarized current has considerable potential for use in magnetic memory and logic devices. Key to the success of these devices is the precise positioning of individual domain walls along magnetic nanowires, using current pulses. We show that domain walls move surprisingly long distances of several micrometers and relax over several tens of nanoseconds, under their own inertia, when the current stimulus is removed. We also show that the net distance traveled by the domain wall is exactly proportional to the current pulse length because of the lag derived from its acceleration at the onset of the pulse. Thus, independent of its inertia, a domain wall can be accurately positioned using properly timed current pulses.     

采用双任务范式使被试将工作记忆信息保存在工作记忆当中并完成选择性注意任务,结果发现:视觉空间工作记忆负荷不能使熟悉面孔的干扰效应消失,语义工作记忆负荷使熟悉面孔的干扰效应在高知觉负荷条件下消失.因此,熟悉面孔在高知觉负荷条件下可能是以语义的方式存储在工作记忆当中,在低知觉负荷条件下可能是同时存储在视觉空间工作记忆和语义工作记忆中.

采用双任务范式使被试将工作记忆信息保存在工作记忆当中并完成选择性注意任务,结果发现:视觉空间工作记忆负荷不能使熟悉面孔的干扰效应消失,语义工作记忆负荷使熟悉面孔的干扰效应在高知觉负荷条件下消失.因此,熟悉面孔在高知觉负荷条件下可能是以语义的方式存储在工作记忆当中,在低知觉负荷条件下可能是同时存储在视觉空间工作记忆和语义工作记忆中.     

两个约束条件下允许外购的多产品报童问题

首先通过形状记忆合金的材性试验研究了其超弹性变形性能,并将其等效拟合为多线性模型,得到其计算参数.然后,提出了一种新型耗能增强型SMA阻尼器,说明了其构造,阐述了其工作原理和设计要点,推导了阻尼器的恢复力模型.最后通过有限元程序对设置该阻尼器的多层钢框架、对角设置SMA拉索的多层钢框架、普通钢框架进行了地震时程分析,对比研究了该阻尼器的消能减震能力.结果表明该阻尼器的滞回环非常饱满,耗能能力强,大震下对结构的位移和层间位移角控制效果显著.     

Toward a universal law of generalization for psychological science

A psychological space is established for any set of stimuli by determining metric distances between the stimuli such that the probability that a response learned to any stimulus will generalize to any other is an invariant monotonic function of the distance between them. To a good approximation, this probability of generalization (i) decays exponentially with this distance, and (ii) does so in accordance with one of two metrics, depending on the relation between the dimensions along which the stimuli vary. These empirical regularities are mathematically derivable from universal principles of natural kinds and probabilistic geometry that may, through evolutionary internalization, tend to govern the behaviors of all sentient organisms.     

反复脑缺血再灌注对小鼠学习记忆和脑内氧化损伤的影响

目的建立血管性痴呆（VD）动物模型,并探讨反复脑缺血再灌注对小鼠认知障碍和脑组织氧化损伤的影响．方法健康的昆明小鼠30只,随机分为3组,即正常组、假手术组、模型组．采用清醒小鼠反复脑缺血再灌注手术方法,应用跳台法、避暗法、Morris水迷宫研究脑缺血再灌注对小鼠行为学的影响;通过HE、尼氏染色观察病理形态学变化;用生化分析方法检测脑组织中SOD活性、MDA的含量．结果与正常组比较,反复脑缺血再灌注能导致小鼠出现明显的学习记忆功能障碍,模型VD小鼠SOD的活性降低（P〈0．01）,MDA的含量增加（P〈0．01）．结论反复脑缺血再灌注能引起小鼠学习记忆功能障碍,这可能与脂质过氧化反应、自由基代谢紊乱有关．