Mechanisms underlying satiation of feeding behavior of the mollusc Aplysia

Animals filled almost to satiation by nonnutritive bulk do not satiate when they ingest a small amount of seaweed. This suggests that satiation is not triggered by chemostimulation of an anteriorly located "hot spot." Inflation of a balloon placed in the gut of the animal results in satiation as reflected in a number of different parameters of feeding behavior. The suppressive effect of a relatively brief inflation is rapidly and fully reversible, although repeated inflation and deflation appeared to produce slowly reversible or irreversible effects. The parameters of the changes in feeding during gut inflation are comparable to those of normal animals that are slowly fed individual pieces of food. The inflation volume needed to satiate the animal is a function of the rate of inflation--more rapid inflations requiring larger volumes. Cutting of the esophageal nerves results in a significant increase in the volume needed to satiate the animals, but nevertheless they eventually cease feeding and generally do not show a burst gut. The evidence indicates that the satiation that eventually occurs in nerve-sectioned animals, at least in part, is due to depression of feeding following very prolonged sensory stimulation. The data suggest that for a rapidly consumed meal, satiation results primarily due to distension-related gut signals conveyed by the esophageal nerves, whereas for very slowly consumed meals, the former factor interacts with a process associated with sensory stimulation, such as receptor adaptation. The current results indicate that balloon distension can serve as a reasonable stimulus in experiments in simplified preparations in which the nervous system can be studied.     

Mechanisms of resurgence II: Response-contingent reinforcers can reinstate a second extinguished behavior

Three experiments with rat subjects examined resurgence of an extinguished instrumental response using the procedure introduced by Epstein (1983) with pigeons. There were three phases: (1) initial acquisition of pressing on a lever (L1) for pellet reward, (2) extinction of L1, and (3) a test session in which a second lever (L2) was inserted, briefly reinforced, and then extinguished. Experiment 1 confirmed that if pressing L2 delivered 20 pellets followed by extinction, rats would resume L1 responding in the final test. Experiment 2 compared the effects of response-contingent and non-contingent rewards delivered upon insertion of L2. Although insertion of L2 alone did not increase L1 responding, response-contingent and non-contingent rewards led to comparable increases in L1 responding. Experiment 3 found that the delivery of non-contingent pellets during extinction of L1, which would be expected to reduce the ability of pellets to set the occasion for the L1 response, also reduced the effects of both response-contingent and non-contingent rewards during the final test. The results indicate that in this method, the resurgence treatment leads to an increase in L1 pressing due to simple presentation of the pellet; delivering the reinforcer after extinction of L1 reinstates L1 responding by setting the occasion for the L1 response.     

Mechanisms revisited

This paper defends an interventionist treatment of mechanisms and contrasts this with Waskan (forthcoming). Interventionism embodies a difference-making conception of causation. I contrast such conceptions with geometrical/mechanical or “actualist” conceptions, associating Waskan’s proposals with the latter. It is argued that geometrical/mechanical conceptions of causation cannot replace difference-making conceptions in characterizing the behavior of mechanisms, but that some of the intuitions behind the geometrical/mechanical approach can be captured by thinking in terms of spatio-temporally organized difference-making information.     

Mechanisms of imagery-perception interaction

A number of different research findings have shown that mental imagery can affect the perceptual processing of stimuli. The present research was aimed at characterizing the representations and processes underlying imagery-perception interactions. In four experiments, subjects mentally projected images of letters into the visual field, and either detected or detected and localized point threshold stimuli that fell on or off the image. Stimuli falling on the image were detected more often than stimuli falling off the image, consistent with the hypothesis that the representations at the interface between imagery and perception have an array format. When the facilitation was analyzed in terms of signal detection theory, it was found to consist only of criterion lowering, and not of enhanced sensitivity. The local criterion-lowering effect of imaged letters was then compared with the effect of perceiving a letter and attending to a letter. Perceiving a letter had no discernible effect on stimulus detection, whereas attending to the letter caused the same local criterion lowering, without sensitivity changes, as imaging the letter. This is consistent with the claims of Neisser (1976) and others that imagery is an attentional state.     

Mechanisms of attentional priority

When a single abrupt onset occurs in a multielement visual display, it captures attention, possibly by generating an attentional interrupt that designates onsets as being of high priority. In 3 experiments, the mechanisms subserving attentional priority setting were investigated. Subjects searched for a prespecified target letter among multiple distractor letters, half of which had abrupt onsets and half of which did not. The target, when present, was equally often an onset element and a no-onset element. Several models for attentional priority, differing in how many onset elements have priority over no-onset elements, were assessed. The data support a model in which approximately 4 onset stimuli are processed before any no-onset stimuli are processed. Two attentional priority mechanisms are proposed: (a) queuing of a limited number of high-priority elements and (b) temporally modulated decay of attentional priority tags.     

自下而上注意的神经机制

由刺激驱动的注意选择即为自下而上注意,又称为瞬时注意或外源性注意。对其神经机制的研究可使我们更好地理解大脑如何产生意识。自下而上选择对注意的分配迅速且高效,但其神经基础一直存在争论。回顾了该研究领域的两大理论模型及其研究证据:基于显著性的注意模型和初级视皮层(V1)显著性模型。最后讨论了该领域未来的研究方向。     

恐惧情绪加工的神经机制

恐惧是一种基本情绪,在人类的生存和适应中具有重要意义.研究者认为对恐惧情绪的加工存在着两种方式——阈上加工和阈下加工,而最近更多的研究者认为对恐惧的加工是需要中枢神经系统参与的阈上加工.在恐惧的形成与表达中,杏仁核、前扣带回、眶额叶皮质等脑区发挥着重要的作用;恐惧记忆的编码与巩固受到海马和各相关脑区的共同影响;前扣带回、内侧前额叶皮质等相关脑区是恐惧情绪调节的高级中枢;在恐惧的消退过程中,内侧前额叶发挥着重要的作用,它影响杏仁核、海马等相关脑区的活动.未来研究应该从恐惧情绪加工过程中脑区的交互机制、恐惧易感性以及发展认知神经科学等角度对恐惧神经机制展开大量研究,力图全方位地理解恐惧加工的神经机制.     

客体连续性的加工机制

把先前和现在遇到的客体视为同一个体的现象就可以称为客体连续性。目前对客体连续性的形成主要存在四种解释机制：相似理论、时空理论、种类理论和因果理论。研究者对时空理论中时空信息和客体表面特征信息, 种类理论和因果理论在此过程中所起的作用存在争论。今后应构建相似、种类、因果理论的实验范式, 改进时空、种类和因果理论实验设计的不足并把客体连续性的研究从视觉领域拓展到到嗅觉、听觉等领域。     

衰老机制的思考

衰老原因和机制极为复杂,是一具有累积性、普遍性、渐进性、内生性和危害性的生命过程.衰老的本质是渐进性的功能减退,各种因素通过引起功能减退加速衰老,减慢功能损害则能延缓衰老.本文笔者认为:衰老机制是非特异性的;理论上,能引起功能减退的因素应能加速衰老.     

刻板印象的认知神经机制

刻板印象是大脑对社会信息的一种自动的类别化加工过程。近期脑成像的研究表明, 刻板印象的注意编码、语义表征以及抑制控制等认知成分可以分别通过相应的ERP成分表现出来; 而基于ERP源定位以及fMRI的研究表明, 杏仁核、前扣带回、大脑前额皮层以及外侧顶叶皮层附近的颞顶联结区可能参与到了它们的认知加工。最后结合已有的研究, 提出了刻板印象可能的认知通道, 并简要分析了当前研究的不足与今后的发展方向。     

衰老机制的思考

衰老原因和机制极为复杂,是一具有累积性、普遍性、渐进性、内生性和危害性的生命过程。衰老的本质是渐进性的功能减退,各种因素通过引起功能减退加速衰老,减慢功能损害则能延缓衰老。本文笔者认为：衰老机制是非特异性的;理论上,能引起功能减退的因素应能加速衰老。     

The Development of Defense Mechanisms

ABSTRACT It is proposed that defense mechanisms may be characterized as forming a hierarchy, from least to most complex, and that the lowest level defenses emerge early in life, while the more complex defenses emerge later in development Three defenses–Denial, Projection and Identification–were chosen to test this assumption A method for assessing the use of these defenses in Thematic Apperception Test (TAT) stories was developed and validated in a study of four age groups preschool, elementary school, early adolescent, and late adolescent The results of the study were consistent with the prediction Denial was used most frequently by preschool children, and decreased in use thereafter Identification was used minimally by preschool children but increased steadily through adolescence The use of Projection was most frequent in the two middle age groups Some evidence for sex differences, based on the internal/external orientation of the defense, also was found     

Multiple Mechanisms of Prime-to-Behavior Effects

Recent research has explored how the activation of social constructs via priming can affect behavior. Multiple mechanisms have received support, including direct activation of behavioral representations, goal activation, biases in person perception, biases in situation perception, and biases in self-perception. We review the evolving complexity of proposed prime-to-behavior mechanisms, discuss the predictions of each mechanism, and suggest some integrative principles that influence how and when primed constructs affect behavior.     

Mechanisms of long-term dark adaptation

It has previously been suggested that long-term dark adaptation is controlled by bleaching signals that regulate the activity of an allosteric, positively cooperative protein (Stabell et al., 1986a, b). Recent biochemical evidence strongly supports this assumption, indicating that the primary regulator of the light-sensitive channels in the plasma membrane of the outer segments of the photoreceptors is a homo-oligomeric, allosteric, positively cooperative protein. In this report, we discuss the possibility that signals from bleached photopigments may control the dark-adaptation process through the allosteric protein of the plasma membrane. It is suggested that the concentrations of the bleached photopigment and of the allosteric effector are reciprocal quantities.     

Mechanisms of short-term saccadic adaptation

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.