Impaired Visuospatial Recognition Memory but Normal Object Novelty Detection and Relative Familiarity Judgments in Adult Mice Expressing the APPswe Alzheimer's Disease Mutation.

The present study examined the effects of a human APPswe mutation on object recognition memory in adult Tg2576 mice. The results showed that 14-month old Tg2576 mice were able to detect object novelty as well as control mice, even with delays of up to 24 hr. In addition, transgenic mice showed a normal recency effect and explored the most recently encountered object significantly less than an object encountered earlier in a trial. However, adult Tg2576 mice showed impairments in detecting a change in the relative positions of an array of familiar objects. The results suggest that the formation of representations involving a combination of object identity and spatial information are particularly sensitive to amyloid pathology in adult APPswe mutant mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced recognition memory following glycine transporter 1 deletion in forebrain neurons.

Selective deletion of glycine transporter 1 (GlyT1) in forebrain neurons enhances N-methyl-D-aspartate receptor (NMDAR)-dependent neurotransmission and facilitates associative learning. These effects are attributable to increases in extracellular glycine availability in forebrain neurons due to reduced glycine re-uptake. Using a forebrain- and neuron-specific GlyT1-knockout mouse line (CamKIIαCre; GlyT1tm1.2fl/fI), the authors investigated whether this molecular intervention can affect recognition memory. In a spontaneous object recognition memory test, enhanced preference for a novel object was demonstrated in mutant mice relative to littermate control subjects at a retention interval of 2 hr, but not at 2 min. Furthermore, mutants were responsive to a switch in the relative spatial positions of objects, whereas control subjects were not. These potential procognitive effects were demonstrated against a lack of difference in contextual novelty detection: Mutant and control subjects showed equivalent preference for a novel over a familiar context. Results therefore extend the possible range of potential promnesic effects of specific forebrain neuronal GlyT1 deletion from associative learning to recognition memory and further support the possibility that mnemonic functions can be enhanced by reducing GlyT1 function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition between the conditioned rewarding effects of cocaine and novelty.

Access to novelty might provide an alternative learning history that competes with conditioned drug reward. We tested this suggestion in rats using a place conditioning procedure with cocaine and novelty. In Experiment 1, rats were conditioned with cocaine to prefer one side of an apparatus. In a subsequent phase, cocaine exposure continued; however, on the unpaired side, separate group of rats had access to novel objects, cocaine injections, or saline with no objects. Pairings with novel objects or cocaine shifted a preference away from the cocaine-paired environment during drug-free and drug-challenge tests. Experiment 2 tested novelty's impact when cocaine exposure was discontinued. The identical procedures were used except drug exposure ceased on the cocaine-paired side during the second phase. Both groups expressed a preference for the cocaine compartment. This preference was maintained for rats that did not have novel objects; however, rats that experienced novelty spent similar amounts of time in both compartments during both tests. Overall, the conditioned rewarding effects of novelty competed with those of cocaine as evidenced by a change in choice behaviors motivated by drug reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of age on object exploration, habituation, and response to spatial and nonspatial change.

To measure their ability to detect novel arrangements in a given environment, young (6 months old) and senescent (22-24 months old) male F344 rats were repeatedly exposed to a given spatial configuration of objects contained in an open field. After the rats were habituated to the novel environment (1 trial with no objects, followed by 3 trials with 5 salient objects), the spatial arrangement of the objects was modified (2 trials), and object novelty was tested (2 trials) by substituting a familiar object with a new one at the same location (nonspatial change). The results indicated that the senescent rats explored old objects less than young rats, particularly on Trial 2. On the 1st trial with displaced objects (Trial 5), the senescent rats explored the displaced objects less than the young rats. However, when a new object was placed in the field (Trials 7-8), there were no age differences in new object exploration. These results Suggest that senescent rats have decrements in the ability to build spatial representations of the environment and to use this information to detect such changes, even though object recognition is not impaired with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pattern separation deficits may contribute to age-associated recognition impairments.

Normal aging is associated with impairments in stimulus recognition. In the current investigation, object recognition was tested in adult and aged rats with the standard spontaneous object recognition (SOR) task or two variants of this task. On the standard SOR task, adult rats showed an exploratory preference for the novel object over delays up to 24 h, whereas the aged rats only showed significant novelty discrimination at the 2-min delay. This age difference appeared to be because of the old rats behaving as if the novel object was familiar. To test this hypothesis directly, rats participated in a variant of the SOR task that allowed the exploration times between the object familiarization and the test phases to be compared, and this experiment confirmed that aged rats falsely “recognize” the novel object. A final control examined whether or not aged rats exhibited reduced motivation to explore objects. In this experiment, when the environmental context changed between familiarization and test, young and old rats failed to show an exploratory preference because both age groups spent more time exploring the familiar object. Together these findings support the view that age-related impairments in object recognition arise from old animals behaving as if novel objects are familiar, which is reminiscent of behavioral impairments in young rats with perirhinal cortical lesions. The current experiments thus suggest that alterations in the perirhinal cortex may be responsible for reducing aged animals' ability to distinguish new stimuli from ones that have been encountered previously. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interpreting visual preferences in the visual paired-comparison task.

Performance on the visual paired-comparison (VPC) task has typically been interpreted with E. Sokolov's (1963) comparator model of the orienting response; novelty preferences are interpreted as evidence of retention, whereas null preferences are interpreted as evidence of forgetting. Here the authors capitalized on the verbal nature of human adults to clarify the interpretation of visual preferences in VPC performance. In 2 experiments, adults were tested on either the VPC task or a forced-choice recognition task after delays of 3 min to 12 months. In Experiment 1, adults tested on the VPC task exhibited novelty preferences after short delays, null preferences after intermediate delays, and familiarity preferences after long delays. In Experiment 2, adults tested on the forced-choice recognition task exhibited high levels of accuracy irrespective of delay, but the latency with which they recognized the stimuli increased systematically over the retention interval. These data are inconsistent with a simple Sokolovian interpretation of VPC performance and instead suggest that memory may be expressed as a novelty preference, null preference, or familiarity preference depending on the accessibility of the representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition between novelty and cocaine conditioned reward is sensitive to drug dose and retention interval.

The conditioned rewarding effects of novelty compete with those of cocaine for control over choice behavior using a place conditioning task. The purpose of the present study was to use multiple doses of cocaine to determine the extent of this competition and to determine whether novelty’s impact on cocaine reward was maintained over an abstinence period. In Experiment 1, rats were conditioned with cocaine (7.5, 20, or 30 mg/kg ip) to prefer one side of an unbiased place conditioning apparatus relative to the other. In a subsequent phase, all rats received alternating daily confinements to the previously cocaine paired and unpaired sides of the apparatus. During this phase, half the rats had access to a novel object on their initially unpaired side; the remaining rats did not receive objects. The ability of novelty to compete with cocaine in a drug free and cocaine challenge test was sensitive to cocaine dose. In Experiment 2, a place preference was established with 10 mg/kg cocaine and testing occurred after 1, 14, or 28 day retention intervals. Findings indicate that choice behaviors mediated by cocaine conditioning are reduced with the passing of time. Taken together, competition between cocaine and novelty conditioned rewards are sensitive to drug dose and retention interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Similarities and differences in spatial learning and object recognition between young male C57Bl/6J mice and Sprague-Dawley rats.

Mice and rats are often used interchangeably in neuroscience research. However, species differences in brain structure and connectivity exist within the medial temporal lobe circuits that contribute to learning and memory. The hippocampus in particular contributes to both spatial learning and recognition memory, but the extent to which rats and mice are comparable in these two cognitive domains remains unclear. To evaluate potential species differences in spatial memory and object recognition, young adult male Sprague–Dawley rats and male C57Bl/6J mice were tested in the water maze and novel object recognition tasks. Following six days of training, with four trials per day, there was no difference in the ability of rats and mice to learn the location of a hidden platform. However, rats performed better than mice on the probe trial, indicative of superior retention. In the novel object preference test, no species differences in recognition memory were detected, although rats spent more time exploring the arena and took longer to approach the objects. These observations suggest that while species differences in spatial memory retention are present, they do not correlate with differences in object recognition memory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Young children associate novel words with complex objects rather than salient parts.

How do children learn associations between novel words and complex perceptual displays? Using a visual preference procedure, the authors tested 12- and 19-month-olds to see whether the infants would associate a novel word with a complex 2-part object or with either of that object's parts, both of which were potentially objects in their own right and 1 of which was highly salient to infants. At both ages, children's visual fixation times during test were greater to the entire complex object than to the salient part (Experiment 1) or to the less salient part (Experiment 2)--when the original label was requested. Looking times to the objects were equal if a new label was requested or if neutral audio was used during training (Experiment 3). Thus, from 12 months of age, infants associate words with whole objects, even those that could potentially be construed as 2 separate objects and even if 1 of the parts is salient. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manipulating and recognizing virtual objects: Where the action is.

In an earlier report (K. L. Harman, G. K. Humphrey, and M. A. Goodale, 1999), the authors demonstrated that Os who actively rotated 3-dimensional (3-D) novel objects on a computer screen later showed faster visual recognition of these objects than did Os who had passively viewed exactly the same sequence of images of these virtual objects. In Exp 1 of the present study, using 24 18–30 yr olds, the authors show that compared to passive viewing, active exploration of 3-D object structure led to faster performance on a "mental rotation" task involving the studied objects. They also examined how much time Os concentrated on particular views during active exploration. As found in the previous report, Os spent most of their time looking at the "side" and "front" views ("plan" views) of the objects, rather than the 3-quarter or intermediate views. This preference for the plan views of an object led to the examination of the possibility in Exp 2 that restricting the studied views in active exploration to either the plan views or the intermediate views would result in differential learning. 24 18–28 yr olds were used in Exp 2. It was found that recognition of objects was faster after active exploration limited to plan views than after active exploration of intermediate views. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Role of Hippocampal Subregions in Detecting Spatial Novelty.

Previous literature suggests that the hippocampus subserves processes associated with the encoding of novel information. To investigate the role of different subregions of the hippocampus, the authors made neurotoxic lesions in different subregions of the dorsal hippocampus (i.e., CA1, dentate gyrus [DG], or CA3) of rats, followed by tests using a spontaneous object exploration paradigm. All lesion groups explored normally an object newly introduced in a familiar location. However, when some of the familiar objects were moved to novel locations, both DG and CA3 lesion groups were severely impaired in reexploring the displaced objects, whereas the CA1 lesion group was only mildly impaired in reexploration. The results suggest that the DG-CA3 network is essential in detecting novelty for spatial, but not for individual object, information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of semantic context and memory in the acquisition of novel nouns

Three studies assessed the ability of 2-year-olds to use semantic context to infer the meanings of novel nouns and to retain those meanings a day later. In the first experiment, 24 2-year-olds heard novel nouns in sentences that contained semantically constraining verbs (e.g., "Mommy feeds the ferret"). They chose from a set of four novel object pictures to indicate the referent. Children learned a majority of the novel words. However, they occasionally failed to choose the correct object even when they understood the verb. Experiment 2 examined whether this was due to an inability to identify some of the pictures of novel objects. Experiment 3 tested 24 2-year-olds' memory for the newly learned nouns following a 24 hr delay and found significant retention. Results are discussed in terms of learning mechanisms that facilitate vocabulary acquisition in young children.     

Impaired "episodic-like" object memory in adult APPswe transgenic mice.

An early clinical symptom of Alzheimer's disease is impaired episodic memory. However, the precise pathological event(s) that underpins this deficit remains unclear. In the present study, the authors examined whether wild-type mice and Tg2576 mice expressing an amyloid precursor protein (APP) mutation are able to form an integrated memory of the spatio-temporal context in which objects are presented. In Experiment 1, wild-type mice, but not Tg2576 mice that were 10-12 months old, explored objects presented in a novel location. In Experiment 2, wild-type mice explored an object that was presented both earlier in a sequence and in a different location relative to other objects that possessed only one of these properties (i.e., memory for "what," "where," and "when" items were presented). In contrast, the behavior of adult Tg2576 mice was influenced only by the temporal order in which objects were presented. These results demonstrate that wild-type, but not APP-mutant, mice are able to form an "episodic-like" memory of the spatio-temporal properties of objects and support the hypothesis that aberrant APP processing contributes to impairments in event memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The "Swedish" mutation of the amyloid precursor protein (APPswe) dissociates components of object-location memory in aged Tg2576 mice.

Aged Tg2576 mice show abnormalities in hippocampal morphology and physiology and display behavioral deficits in spatial navigation tasks consonant with a deficit in the functional properties of the hippocampus. However, the nature of the spatial representations disrupted by the "Swedish" mutation of the amyloid precursor protein (APPswe) is unclear. In an effort to characterize the memory deficits in Tg2576 mice, the spontaneous object exploration paradigm was used to interrogate spatial and object memory in mice. With object arrays of comparable size, 16-month-old Tg2576 mice showed a normal object familiarity/novelty effect but impaired memory for the location of objects when 2 objects exchanged locations (topological transformation; Experiment 1). In contrast, Tg2576 mice showed preferential exploration of familiar objects when they were moved to previously unoccupied locations (Experiment 2), irrespective of whether the transformation altered the metric properties of the object array (Experiments 3). These results suggest that Tg2576 mice are able to form representations of the identity of objects and a memory of the spatial organization of objects in an arena. In contrast, conjunctive memory for specific object-location associations is severely impaired in aged Tg2576 mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seeing through sound: Dolphins (Tursiops truncatus) perceive the spatial structure of objects through echolocation.

Experiment 1 tested a dolphin (Tursiops truncatus) for cross-modal recognition of 25 unique pairings of 8 familiar, complexly shaped objects, using the senses of echolocation and vision. Cross-modal recognition was errorless or nearly so for 24 of the 25 pairings under both visual to echoic matching (V-E) and echoic to visual matching (E-V). First-trial recognition occurred for 20 pairings under V-E and for 24 under E-V. Echoic decision time under V-E averaged only 1.88 s. Experiment 2 tested 4 new pairs of objects for 24 trials of V-E and 24 trials of E-V without any prior exposure of these objects. Two pairs yielded performance significantly above chance in both V-E and E-V. Also, the dolphin matched correctly on 7 of 8 1st trials with these pairs. The results support a capacity for direct echoic perception of object shape by this species and demonstrate that prior object exposure is not required for spontaneous cross-modal recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ebb and flow of infant attentional preferences: evidence for long-term recognition memory in 3-month-olds

Using paired-comparisons, 3-month-olds' (n = 148) recognition of dynamic visual events was investigated after retention intervals of 1 minute, 1 day, and 1 and 3 months (Experiment 1) and 1 minute, 1 day, and 1 week (Experiment 2). Participants were either tested at each retention interval (Multiple Tests) or tested at one interval (Single Test). The proportion of total looking time to the novel event and the length of the longest look to novel and familiar events in the first 15 s of the retention test revealed significant novelty preferences at 1 minute and 1 day and a null preference at 1 week for Multiple- and Single-Test groups. At 1 month, Multiple- (Proportion of Total Looking Time and Longest Look) and Single-Test groups (Longest Look only) preferred the familiar event. The 3-month test revealed a familiarity preference (both measures) for Single- and a null preference for Multiple-Tests groups. This changing pattern of attentional preferences is consistent with models of infant recognition memory in which novelty, familiarity, and null preferences are considered conjointly and hypothesized to reflect the accessibility of novel and familiar event representations in memory.     

Development of orienting to locations and objects in human infants.

Investigated the preference for orienting to novel locations and novel objects in young infants in 2 experiments, by examining the influence of visual signals on subsequent attentional orienting and eye movements. Exp 1 (n?=?12) demonstrates that 3-mo-olds show inhibition of return (IOR) for 10° target eccentricities, but not for 30° target eccentricities. In Exp 2, 14 3-mo-olds and 14 6-mo-olds oriented to 10° targets that varied in location and object identity. Ss of both ages strongly preferred orienting to novel objects at novel locations. At 3 mo, the preference for novel objects was equal to the preference for novel locations, while at 6 mo a tendency to prefer novel objects over novel locations emerged. Overall, findings support separate development of these 2 forms of novelty preference, and suggest that novel location preferences (IOR) relates closely to the eye movement system. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging in rhesus macaques is associated with changes in novelty preference and altered saccade dynamics.

Studies demonstrating recognition deficits with aging often use tasks in which subjects have an incentive to correctly encode or retrieve the experimental stimuli. In contrast to these tasks, which may engage strategic encoding and retrieval processes, the visual paired comparison (VPC) task measures spontaneous eye movements made toward a novel as compared with familiar stimulus. In the present study, seven rhesus macaques aged 6 to 30 years exhibited a dramatic age-dependent decline in preference for a novel image compared with one presented seconds earlier. The age effect could not be accounted for by memory deficits alone, because it was present even when familiarization preceded test by 1 second. It also could not be explained by an encoding deficit, because the effect persisted with increased familiarity of the sample stimulus. Reduced novelty preference did correlate with eye movement variables, including reaction time distributions and saccade frequency. At long delay intervals (24 or 48 hours) aging was paradoxically associated with increased novelty preference. Several explanations for the age effect are considered, including the possible role of dopamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and relative novelty in human perceptual learning.

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty. (PsycINFO Database Record (c) 2011 APA, all rights reserved)