Hippocampal damage and exploratory preferences in rats: memory for objects, places, and contexts

Rats have a natural tendency to spend more time exploring novel objects than familiar objects, and this preference can be used as an index of object recognition. Rats also show an exploratory preference for objects in locations where they have not previously encountered objects (an index of place memory) and for familiar objects in contexts different from those in which the objects were originally encountered (an index of context memory). In this experiment, rats with cytotoxic lesions of the hippocampal formation were tested on all three versions of the novelty-preference paradigm, with a 5-min retention interval between the familiarization and test phases. Rats with sham lesions displayed a novelty preference on all three trial types, whereas the rats with hippocampal lesions displayed a novelty preference on Object trials but did not discriminate between the objects on Place trials or Context trials. The findings indicate that hippocampal damage impairs memory for contextual or spatial aspects of an experience, whereas memory for objects that were part of the same experience are left relatively intact.     

Role of CA3 and CA1 subregions of the dorsal hippocampus on temporal processing of objects

Previous research in the dorsal CA1 and dorsal CA3 subregions of the hippocampus has been shown to play an important role in mediating temporal order memory for spatial location information. What is not known is whether the dorsal CA3 and dorsal CA1 subregions of the hippocampus are also involved in temporal order for visual object information. Rats with dorsal CA1, dorsal CA3 or control lesions were tested in a temporal order task for visual objects using an exploratory paradigm. The results indicated that the controls and the dorsal CA3 lesioned rats preferred the first rather then the last object they had explored previously, indicating good memory for temporal order of object presentation. In contrast, rats with dorsal CA1 lesions displayed a profound deficit in remembering the order of the visual object presentations in that they preferred the last object rather than the first. All three groups of rats preferred a novel object compared to a previously explored object suggesting normal detection of visual object novelty. The results suggest that only the dorsal CA1, but not dorsal CA3, region is critical for processing temporal information for visual objects without affecting the detection of new visual objects.     

Olfactory discrimination, reversal learning, and stimulus control in rats.

Rats were trained to discriminate lights, tones, or odors and then given a series of discrimination reversals. Only rats trained with odors showed positive transfer on the first reversal and acquisition of a reversal set. Other experiments demonstrated that rats preferentially attend to odors when presented in compound with lights or tones; that odors exert more discriminative control than tones in tests using compound stimuli of competing sign; and that after pretraining on the positive stimulus, acquisition of an odor but not a light discrimination occurs with virtually no errors. These results demonstrate the importance of stimulus modality in the establishment of stimulus control and the need for more careful analysis of stimulus factors in cross-species comparisons of learning ability.     

新颖性图像加工的时间进程

采用ERPs技术,考察了个体新颖性图像加工的时间进程。行为结果表明: 新颖性图像的判断时间更长。ERPs结果显示:新颖与非新颖图像在刺激呈现后190–340ms诱发出明显的前额区N190–340,但在波幅上无显著差异;在400–600ms以及600–1000ms,新颖性图像在顶区与额–中央区, 特别在右侧半球诱发出更大的正性偏移(P400–600和LPC)。研究表明: 图像新颖性属性的识别主要发生在涉及图像特征融合、图像记忆编码等多项认知活动参与的晚期加工阶段,并存在半球右侧化效应。     

Competitive short-term and long-term memory processes in spatial habituation

Exposure to a spatial location leads to habituation of exploration such that, in a novelty preference test, rodents subsequently prefer exploring a novel location to the familiar location. According to Wagner's (1981) theory of memory, short-term and long-term habituation are caused by separate and sometimes opponent processes. In the present study, this dual-process account of memory was tested. Mice received a series of exposure training trials to a location before receiving a novelty preference test. The novelty preference was greater when tested after a short, rather than a long, interval. In contrast, the novelty preference was weaker when exposure training trials were separated by a short, rather than a long interval. Furthermore, it was found that long-term habituation was determined by the independent effects of the amount of exposure training and the number of exposure training trials when factors such as the intertrial interval and the cumulative intertrial interval were controlled. A final experiment demonstrated that a long-term reduction of exploration could be caused by a negative priming effect due to associations formed during exploration. These results provide evidence against a single-process account of habituation and suggest that spatial habituation is determined by both short-term, recency-based memory and long-term, incrementally strengthened memory.     

Spatial selection via feature-driven inhibition of distractor locations

The allocation of spatial attention was measured with detection probes at different locations. Response times were faster for probes at the location of the target digit, which subjects reported, than at the locations of distractor digits, which they ignored. Probes at blank locations between stimuli produced fast responses, indicating that selection was accomplished by inhibiting distractor locations but not other areas. Unlike earlier studies using location cuing with simpler stimuli, these experiments showed no attentional differences across horizontal or vertical midlines. Attention varied little with distance from the target, although blank locations far from the target were somewhat less attended than were those near the target, and attention was only slightly affected by expectations for stimulus location. This task demonstrates a form of feature-driven spatial attention, in which locations with objects lacking target features are inhibited.     

Integrated memory for objects, places, and temporal order: evidence for episodic-like memory in mice

Human episodic memory refers to the recollection of an unique past experience in terms of what happened, and where and when it happened. Factoring out the issue of conscious recollection, episodic memory, even at the behavioral level, has been difficult to demonstrate in non-human mammals. Although, it was previously shown that rodents can associate what and when or what and where information given on unique trials, it proved to be difficult to demonstrate memory for what, where, and when simultaneously in mammals, without using extensive training procedures, which might induce semantic rather than episodic memory recall. Towards the goal of an animal model of human episodic memory we designed an three-trial object exploration task in which different versions of the novelty-preference paradigm were combined to subsume (a) object recognition memory, (b) the memory for locations in which objects were explored, and (c) the temporal order memory for object presented at distinct time points. We found that mice spent more time exploring two "old familiar" objects relative to two "recent familiar" objects, reflecting memory for what and when and concomitantly directed more exploration at a spatially displaced "old familiar" object relative to a stationary "old familiar" object, reflecting memory for what and where. These results suggest that during a single test trial the mice were able to (a) recognize previously explored objects, (b) remember the location in which particular objects were previously encountered, and (c) to discriminate the relative recency in which different objects were presented. According to the currently discussed behavioral criteria for episodic-like memory in animals, our results suggest that mice are capable to form such higher order memories.     

Multivariate analysis of putative measures of activity, exploration, emotionality, and spatial behavior in the hooded rat (Rattus norvegicus)

Hooded rats were tested in six situations representing the variables of activity, exploration, emotionality, and spatial preference, detection of change, and learning. The activity, exploration, and emotionality variables and spatial variables were analyzed in separate multivariate analyses, followed by an analysis of the entire set. The first of these resulted in four components: activity, exploration and emotionality, reactivity to handling, and autonomic reactivity (defecation). Four components, defined by the following variables, emerged from the spatial analysis: (a) the tendency to circle, circling direction, and spatial learning; (b) heading error in spatial learning and reversal and open-field directional preference; (c) spatial reversal and direction of turn to escape restraint; and (d) detection of change in spatial arrangement and directional preference in the detection task. The final analysis investigated relations between the activity, exploration, and emotionality variables and the spatial variables, finding only two. The clear dimensionality of these behavioral repertoires emphasizes how important it is to recognize the distinctions among them.     

Are space and time automatically integrated in episodic memory?

The aim of the present study was to determine to what extent spatial and temporal features are automatically integrated during encoding in episodic memory. Both nameable and non-nameable stimuli were presented sequentially at different locations on a computer screen. Mixed and pure blocks of trials were used. In the mixed blocks participants were instructed to focus either on the spatial or the temporal order of the objects, as on the majority of the trials recall of this feature was tested (expected trials). However, on a few trials participants had to reproduce the other feature (unexpected trials). In the pure blocks either the spatial or the temporal order of the objects was tested on all trials. More errors were made on unexpected than on expected trials of the mixed blocks. Moreover, no primacy or recency effects were found when performance on the spatial task was plotted as a function of the temporal position. These results suggest that spatial information and temporal order information rely on separate encoding processes.     

Are space and time automatically integrated in episodic memory?

The aim of the present study was to determine to what extent spatial and temporal features are automatically integrated during encoding in episodic memory. Both nameable and non-nameable stimuli were presented sequentially at different locations on a computer screen. Mixed and pure blocks of trials were used. In the mixed blocks participants were instructed to focus either on the spatial or the temporal order of the objects, as on the majority of the trials recall of this feature was tested (expected trials). However, on a few trials participants had to reproduce the other feature (unexpected trials). In the pure blocks either the spatial or the temporal order of the objects was tested on all trials. More errors were made on unexpected than on expected trials of the mixed blocks. Moreover, no primacy or recency effects were found when performance on the spatial task was plotted as a function of the temporal position. These results suggest that spatial information and temporal order information rely on separate encoding processes.     

Repeated exposure to objects and peers in a play setting

Two hypotheses were contrasted. One posed a positive relationship between mere repeated exposure and preference for stimulus of concern; the other predicted that preference for stimuli would be modulated by their relative novelty and complexity. These hypotheses were tested within the context of a naturalistic play situation in which 40 4- to 5-year-old children were repeatedly exposed to and interacted with play settings differing in complexity. Overt preference for play objects declined with repeated exposure, the rate of decline being inversely determined by the complexity of the play stimuli. Preference for peers, however, increased as a function of repeated exposure, with the amount of increase being an inverse function of the complexity of the external setting.     

空间参照系建立的时间特征*

通过2个实验来探讨空间记忆参照系建立的时间特征。被试学习一个由7个物体组成的场景,场景中的物体以随机的方式序列呈现。一个能够标明物体位置且具有对称结构的场景分别在被试进行物体位置学习之前或之后呈现。研究结果发现:当被试在学习物体位置之前短暂呈现场景结构,场景结构能够决定空间参照系的建立;但被试学习物体位置之后再短暂呈现场景结构,场景结构不能决定空间参照系的建立。以上结果表明:空间参照系是在学习物体位置之前建立,并且建立之后不能被改变。     

Young children's use of temporal and spatial order information in short-term memory

Encoding and retrieval of temporal and spatial order information was investigated in the free recall and probed recognition performance of 3-, 4-, 5-, and 6-year-olds. In both tasks, three line drawings of familiar objects were presented successively in different spatial locations, so that temporal order was not confounded with spatial order. Subjects of all ages revealed an organization for the stimulus display based on the temporal sequence of presentation. With increasing age, subjects began recall more often with the first item so as to take advantage of this sequential organization. In the probed recognition task, subjects were asked questions requiring the use of temporal or spatial order information. Performance by the older subjects indicated that information about temporal and spatial order could be simultaneously encoded. The results are discussed in terms of a context theory derived from Estes's hierarchical association model.     

A behavioral study of alpha-1b adrenergic receptor knockout mice: increased reaction to novelty and selectively reduced learning capacities

Knockout mice lacking the alpha-1b adrenergic receptor were tested in behavioral experiments. Reaction to novelty was first assessed in a simple test in which the time taken by the knockout mice and their littermate controls to enter a second compartment was compared. Then the mice were tested in an open field to which unknown objects were subsequently added. Special novelty was introduced by moving one of the familiar objects to another location in the open field. Spatial behavior and memory were further studied in a homing board test, and in the water maze. The alpha-1b knockout mice showed an enhanced reactivity to new situations. They were faster to enter the new environment, covered longer paths in the open field, and spent more time exploring the new objects. They reacted like controls to modification inducing spatial novelty. In the homing board test, both the knockout mice and the control mice seemed to use a combination of distant visual and proximal olfactory cues, showing place preference only if the two types of cues were redundant. In the water maze the alpha-1b knockout mice were unable to learn the task, which was confirmed in a probe trial without platform. They were perfectly able, however, to escape in a visible platform procedure. These results confirm previous findings showing that the noradrenergic pathway is important for the modulation of behaviors such as reaction to novelty and exploration, and suggest that this is mediated, at least partly, through the alpha-1b adrenergic receptors. The lack of alpha-1b adrenergic receptors in spatial orientation does not seem important in cue-rich tasks but may interfere with orientation in situations providing distant cues only.     

Exploratory behavior as a function of environmental novelty and complexity in male and female rats

Laboratory rats show a positive response to low- and nonstressful novel events. The novel event may involve a number of aspects of the stimulus field. It is usually associated with a change in amount of environmental complexity. Most studies concerning novelty-related behavior involve the introduction of novel objects or the rearrangement of familiar objects. The present purpose was to measure exploratory behavior in response to environments of increased and decreased complexity. Both directions of environmental change are conditions of novelty. A two-way manipulation of increasing and decreasing the complexity of the environment was used. Rats of both sexes showed increased exploration to exposure to novelty, no matter which manipulation was applied; however, female and male rats behaved differently to the two types of novelty. Males responded more to novelty from the introduction of an unfamiliar object. The results indicate novel stimulation, whether of increasing or decreasing complexity, has reward properties. Perhaps the male-specific behavior directed toward unfamiliar objects may serve an adaptive function.     

Wistar rats show episodic-like memory for unique experiences

Human episodic memory refers to the recollection of an unique past experience in terms of its details, its locale, and temporal occurrence. Episodic memory, even in principle, has been difficult to demonstrate in non-verbal mammals. Previously, we provided evidence that mice are able to form an integrated memory for "what," "where," and "when" aspects of single experiences by combining different versions of the novelty-preference paradigm, i.e., object recognition memory, the memory for locations in which objects were explored, and the temporal order memory for objects presented at distinct time points. In the present series of experiments we evaluated whether this paradigm, with minor modifications, also works with rats. We found that rats spent more time exploring an "old familiar" object relative to a "recent familiar" object, suggesting that they recognized objects previously explored during separate trials and remembered their order of presentation. Concurrently, the rats responded differentially to spatial object displacement dependent on whether an "old familiar" or "recent familiar" object was shifted to a location, where it was not encountered previously. These results provide strong evidence that the rats established an integrated memory for "what," "where," and "when." We also found that acute stress impaired the animal's performance in the episodic-like memory task, which, however, could be partially reversed by the N-Methyl-D-aspartate-receptors agonist D-cycloserine.     

Audiotactile temporal order judgments

We report a series of three experiments in which participants made unspeeded 'Which modality came first?' temporal order judgments (TOJs) to pairs of auditory and tactile stimuli presented at varying stimulus onset asynchronies (SOAs) using the method of constant stimuli. The stimuli were presented from either the same or different locations in order to explore the potential effect of redundant spatial information on audiotactile temporal perception. In Experiment 1, the auditory and tactile stimuli had to be separated by nearly 80 ms for inexperienced participants to be able to judge their temporal order accurately (i.e., for the just noticeable difference (JND) to be achieved), no matter whether the stimuli were presented from the same or different spatial positions. More experienced psychophysical observers (Experiment 2) also failed to show any effect of relative spatial position on audiotactile TOJ performance, despite having much lower JNDs (40 ms) overall. A similar pattern of results was found in Experiment 3 when silent electrocutaneous stimulation was used rather than vibrotactile stimulation. Thus, relative spatial position seems to be a less important factor in determining performance for audiotactile TOJ than for other modality pairings (e.g., audiovisual and visuotactile).     

Something old,something new: a developmental transition from familiarity to novelty preferences with hidden objects

Novelty seeking is viewed as adaptive, and novelty preferences in infancy predict cognitive performance into adulthood. Yet 7‐month‐olds prefer familiar stimuli to novel ones when searching for hidden objects, in contrast to their strong novelty preferences with visible objects ( Shinskey & Munakata, 2005 ). According to a graded representations perspective on object knowledge, infants gradually develop stronger object representations through experience, such that representations of familiar objects can be better maintained, supporting greater search than with novel objects. Object representations should strengthen with further development to allow older infants to shift from familiarity to novelty preferences with hidden objects. The current study tested this prediction by presenting 24 11‐month‐olds with novel and familiar objects that were sometimes visible and sometimes hidden. Unlike 7‐month‐olds, 11‐month‐olds showed novelty preferences with both visible and hidden objects. This developmental shift from familiarity to novelty preference with hidden objects parallels one that infants show months earlier with perceptible stimuli, but the two transitions may reflect different underlying mechanisms. The current findings suggest both change and continuity in the adaptive development of object representations and associated cognitive processes.     

MATCHING-TO-SAMPLE PERFORMANCE IN RATS: A CASE OF MISTAKEN IDENTITY?

Three rats had previously acquired a simultaneous matching-to-sample performance with steady and blinking lights. In training, the sample stimulus had always appeared on the middle of three horizontally arranged keys with the comparison stimuli on the side keys. In Experiment 1, the sample stimulus appeared on any of the three keys with the comparison stimuli on the remaining two. The matching-to-sample performance broke down with variable sample and comparison locations; the sample stimulus did not control responding to the comparison stimuli when it appeared on a side key, but it retained control when it appeared on the middle key (as in training). In Experiment 2, the rats were trained with the sample always on the left key. When the sample appeared on either of the trained locations (left or middle key), it retained control for both locations. When the sample then appeared on any of the three keys, as in Experiment 1, sample control did not transfer to the untrained location (right key). The experiments demonstrate that training with fixed sample and comparison locations may establish spatial location as an additional controlling aspect of the stimuli displayed on the keys; stimulus location had become part of the definition of the controlling stimuli. The rats' performance seemed best described as specific discriminations involving the visual stimuli and their spatial locations rather than as identity matching.     

Haptic perception of linear extent.

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.