Rhesus monkeys (Macaca mulatta) demonstrate robust memory for what and where, but not when, in an open-field test of memory

The function of episodic memory in animals

The best-known example of episodic memory in animals came from food-storing birds. One of the beauties of the food-storing system was that inherent in the behaviour were the elements that (at the time) made up episodic memory: what, where and when. While there were then already plenty of data on animals' ability to put together what and where, the addition of the time element in animals' memory and its testing was one that was both new and experimentally challenging. It has, however, led to an increasing variety of examples showing that animals can put together all three informational components. If episodic memories can be described as those memories that make any one of us who we are, why should non-human animals have such memories? Here, we argue that episodic memories play a significant functional role in the lives of real animals, in particular, enabling them to make decisions about how they might or should act in their future. We support our argument with data from a range of examples, focussing on data from the field.This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Of popsicles and crackers: when spatio-temporal memory is not integrated into children's decision-making

Prior research has used innovative paradigms to show that some non-human animal species demonstrate behavioural choices (i.e. foraging for a food item at a specific location, and at a time that guarantees it has not yet decayed), reflecting episodic-like or 'WWW' memory (memory for 'what' happened, 'where' and 'when'). These results raised the question of whether similar approaches could be used to examine memory in young children in order to reduce verbal demands. The present research examines the extent to which children's WWW memory aligns with memory-based choices in 3- to 5-year-olds (n = 95; study 1) and in 7- to 11-year-olds and adults (n = 168; study 2). Results indicate that preschoolers' struggle with choice-based tasks probably reflects difficulty integrating their WWW memory with an understanding that certain items decay over time. Moreover, a convergence between verbal recall measures and choice-based measures is observable in 7-year-olds and beyond, reflecting a stronger integration of memory signals, understanding of state transformation, and decision-making. This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Episodic-like memory in wild free-living blue tits and great tits

Episodic-like memory in non-human animals represents the behavioral characteristics of human episodic memory-the ability to mentally travel backward in time to "re-live" past experiences. A focus on traditional model species of episodic-like memory may overlook taxa possessing this cognitive ability and consequently its evolution across species. Experiments conducted in the wild have the potential to broaden the scope of episodic-like memory research under the natural conditions in which they evolved. We combine two distinct yet complementary episodic-like memory tasks (the what-where-when memory and incidental encoding paradigms), each targeting a different aspect of human episodic memory, namely the content (what-where-when) and process (incidental encoding), to comprehensively test the memory abilities of wild, free-living, non-caching blue tits (Cyanistes caeruleus) and great tits (Parus major). Automated feeders with custom-built programs allowed for experimental manipulation of spatiotemporal experiences on an individual-level basis. In the what-where-when memory experiment, after learning individualized temporal feeder rules, the birds demonstrated their ability to recall the "what" (food type), "where" (feeder location), and "when" (time since their initial visit of the day) of previous foraging experiences. In the incidental encoding experiment, the birds showed that they were able to encode and recall incidental spatial information regarding previous foraging experiences ("where" test), and juveniles, but not adults, were also able to recall incidentally encoded visual information ("which" test). Consequently, this study presents multiple lines of converging evidence for episodic-like memory in a wild population of generalist foragers, suggesting that episodic-like memory may be more taxonomically widespread than previously assumed.

Temporal foundations of episodic memory

A fundamental question in the development of animal models of episodic memory concerns the role of temporal processes in episodic memory. Gallistel, (1990) developed a framework in which animals remember specific features about an event, including the time of occurrence of the event and its location in space. Gallistel proposed that timing is based on a series of biological oscillators, spanning a wide range of periods. Accordingly, a snapshot of the phases of multiple oscillators provides a representation of the time of occurrence of the event. I review research on basic timing mechanisms that may support memory for times of occurrence. These studies suggest that animals use biological oscillators to represent time. Next, I describe recently developed animal models of episodic memory that highlight the importance of temporal representations in memory. One line of research suggests that an oscillator representation of time supports episodic memory. A second line of research highlights the flow of events in time in episodic memory. Investigations that integrate time and memory may advance the development of animal models of episodic memory.

HIPK2 mediates M1 polarization of microglial cells via STAT3: A new mechanism of depression-related neuroinflammation

This study aimed to investigate the role of protein kinase HIPK2 in depression and its associated mechanism. The chronic unpredictable mild stress (CUSM) model was constructed to simulate mice with depression to detect the mouse behaviors. Moreover, by using mouse microglial cells BV2 as the model. After conditional knockdown of HIPK2, the depressive behavior disorder of mice was improved, meanwhile, neuroinflammation was alleviated, and the M1 cell proportion was reduced. Similar results were obtained after applying the HIPK2 inhibitor tBID or ASO-HIPK2 treatment. HIPK2 was overexpressed in BV2 cells, which promoted M1 polarization of cells, while tBID suppressed the effect of HIPK2 and reduced the M1 polarized level in BV2 cells. Pull-down assay results indicated that HIPK2 bound to STAT3 and promoted STAT3 phosphorylation. We found that HIPK2 can bind to STAT3 to promote its phosphorylation, which accelerates M1 polarization of microglial cells, aggravates the depressive neuroinflammation, and leads to abnormal behaviors. HIPK2 is promising as the new therapeutic target of depression.

Atractylenolide I improves behaviors in mice with depression-like phenotype by modulating neurotransmitter balance via 5-HT2A

To explore the antidepressant effects and targets of atractylenolide I (ATR) through a network pharmacological approach. Relevant targets of ATR and depression analyzed by network pharmacology were scored (identifying 5-HT2A targets). Through elevated plus maze, open field, tail suspension, and forced swimming tests, the behavioral changes of mice with depression (chronic unpredictable mild stress [CUMS]) were examined, and the levels of neurotransmitters including serotonin, dopamine, and norepinephrine (5-HT, DA, and NE) were determined. The binding of ATR to 5-HT2A was verified by small molecular-protein docking. ATR improved the behaviors of CUMS mice, elevated their levels of neurotransmitters 5-HT, DA, and NE, and exerted a protective effect on their nerve cell injury. After 5-HT2A knockout, ATR failed to further improve the CUMS behaviors. According to the results of small molecular-protein docking and network pharmacological analysis, ATR acted as an inhibitor by binding to 5-HT2A. ATR can improve the behaviors and modulate the neurotransmitters of CUMS mice by targeting 5-HT2A.

Learning of object-in-context sequences in freely-moving macaques

Flexible learning is a hallmark of primate cognition, which arises through interactions with changing environments. Studies of the neural basis for this flexibility are typically limited by laboratory settings that use minimal environmental cues and restrict interactions with the environment, including active sensing and exploration. To address this, we constructed a 3-D enclosure containing touchscreens on its walls, for studying cognition in freely moving macaques. To test flexible learning, two monkeys completed trials consisting of a regular sequence of object selections across four touchscreens. On each screen, the monkeys had to select by touching the sole correct object item ('target') among a set of four items, irrespective of their positions on the screen. Each item was the target on exactly one screen of the sequence, making correct performance conditioned on the spatiotemporal sequence rule across screens. Both monkeys successfully learned multiple 4-item sets (N=14 and 22 sets), totaling over 50 and 80 unique, conditional item-context memoranda, with no indication of capacity limits. The enclosure allowed freedom of movements leading up to and following the touchscreen interactions. To determine whether movement economy changed with learning, we reconstructed 3D position and movement dynamics using markerless tracking software and gyroscopic inertial measurements. Whereas general body positions remained consistent across repeated sequences, fine head movements varied as monkeys learned, within and across sequence sets, demonstrating learning set or "learning to learn". These results demonstrate monkeys' rapid, capacious, and flexible learning within an integrated, multisensory 3-D space. Furthermore, this approach enables the measurement of continuous behavior while ensuring precise experimental control and behavioral repetition of sequences over time. Overall, this approach harmonizes the design features that are needed for electrophysiological studies with tasks that showcase fully situated, flexible cognition.

Antcin K targets NLRP3 to suppress neuroinflammation and improve the neurological behaviors of mice with depression

AIM

We aimed to explored the role of Antcin K in resisting depression and its targets.

METHODS

LPS/IFN-γwas used to induce the activation of microglial BV2 cells. Following Antcin K pretreatment, the proportion of M1 cells was determined using flow cytometry (FCM), the expression of cytokines was measured through ELISA, and that of CDb and NLRP3 was analyzed by cell fluorescence staining. The protein levels were detected by Western-blot assay. After NLRP3 was knocked down in BV2 cells (BV2-nlrp3^-/-), the M1 polarization level was detected with Antcin K treatment. The targeted binding relation of Antcin K with NLRP3 was confirmed through small molecule-protein docking and co-immunoprecipitation assay. The chronic unpredictable stress model (CUMS) was constructed to mimic the depression mice. After the administration of Antcin K, the neurological behavior of CUMS mice were detected by open-field test (OFT), elevated plus maze, forced swimming test (FST), and tail suspension test (TST). In addition, the expression of CD11b and IBA-1 was detected through histochemical staining, and the tissue pathological changes were detected by H&E staining.

RESULTS

Antcin K suppressed the M1 polarization of BV2 cells and reduced the expression of inflammatory factors. Meanwhile, NLRP3 exhibited targeted binding relation with Antcin K, and Antcin K lost its effect after NLRP3 knockdown. In the CUMS mouse model, Antcin K improved the depression status and neurological behaviors in mice, and decreased central neuroinflammation and microglial cell polarization.

CONCLUSION

Antcin K targets NLRP3 to suppress microglial cell polarization, alleviate central inflammation in mice and improve their neurological behaviors.

Assessing episodic memory in rodents using spontaneous object recognition tasks

Models of episodic memory are successfully established using spontaneous object recognition tasks in rodents. In this review, we present behavioral techniques devised to investigate this type of memory, emphasizing methods based on associations of places and temporal order of items explored by rats and mice. We also provide a review on the areas and circuitry of the medial temporal lobe underlying episodic-like memory, considering that a large number of neurobiology data derived from these protocols. Although spontaneous recognition tasks are commonplace in this field, there is need for careful evaluation of factors affecting animal performance. Such as the ongoing development of tools for investigating the neural basis of memory, efforts should be put in the refinement of experimental designs, in order to provide reliable behavioral evidence of this complex mnemonic system.

Chimpanzees (Pan troglodytes) navigate to find hidden fruit in a virtual environment

Almost all animals navigate their environment to find food, shelter, and mates. Spatial cognition of nonhuman primates in large-scale environments is notoriously difficult to study. Field research is ecologically valid, but controlling confounding variables can be difficult. Captive research enables experimental control, but space restrictions can limit generalizability. Virtual reality technology combines the best of both worlds by creating large-scale, controllable environments. We presented six chimpanzees with a seminaturalistic virtual environment, using a custom touch screen application. The chimpanzees exhibited signature behaviors reminiscent of real-life navigation: They learned to approach a landmark associated with the presence of fruit, improving efficiency over time; they located this landmark from novel starting locations and approached a different landmark when necessary. We conclude that virtual environments can allow for standardized testing with higher ecological validity than traditional tests in captivity and harbor great potential to contribute to longstanding questions in primate navigation, e.g., the use of landmarks, Euclidean maps, or spatial frames of reference.

A review of behavioral methods for the evaluation of cognitive performance in animal models: Current techniques and links to human cognition

INTRODUCTION

Memory is defined as the ability to store, maintain and retrieve information. Learning is the acquisition of information that changes behavior and memory. Stress, dementia, head trauma, amnesia, Alzheimer's, Huntington, Parkinson's, Wernicke-Korsakoff syndrome (WKS) may be mentioned among the diseases in which memory and learning are affected. The task of understanding deficits in memory and learning in humans is daunting due to the complexity of neural and cognitive mechanisms in the nervous system. This job is made more difficult for clinicians and researchers by the fact that many techniques used to research memory are not ethically acceptable or technically feasible for use in humans. Thus, animal models have been necessary alternative for studying normal and disordered learning and memory. This review attempts to bridge these domains to allow biomedical researchers to have a firm grasp of "memory" and "learning" as constructs in humans whereby they may then select the proper animal cognitive test.

RESULTS AND CONCLUSION

Various tests (open field habituation test, Y-maze test, passive avoidance test, step-down inhibitory avoidance test, active avoidance test, 8-arms radial maze test, Morris water maze test, radial arm water maze, novel object recognition test and gait function test) have been designed to evaluate different kinds of memory. Each of these tests has their strengths and limits. Abnormal results obtained using these tasks in non-human animals indicate malfunctions in memory which may be due to several physiological and psychological diseases of nervous system. Further studies by using the discussed tests can be very beneficial for achieving a therapeutic answer to these diseases.

Mandrills learn two-day time intervals in a naturalistic foraging situation

Primates display high efficiency in finding food in complex environments. Knowledge that many plant species produce fruit simultaneously, can help primates to anticipate fruit finding at the start of fruiting seasons. Knowledge of elapsed time can help primates decide when to revisit food trees to find ripened fruit and to return before competitors find these fruits. To investigate whether mandrills are able to learn time intervals of recurring food, we recorded the foraging choices of captive mandrills in a group setting. We used a procedure with renewable food rewards that could be searched for: carrots and grapes, hidden underground in specific places with different renewal intervals (2 and 5 days, respectively). We monitored the first choice of location for individuals, if other individuals had not already searched at the same location, to exclude possible effects of individuals following others rather than relying on memory. Throughout the study, the mandrills became increasingly likely to first search at carrot locations on carrot days, while the probability of them searching at carrot locations decreased on days without carrot. Due to model instability, our results were inconclusive about an effect of grape days on the choice of the mandrills. Cues provided by conspecifics indicating the availability of simultaneously emerging food rewards did not affect the choice of the mandrills. We conclude that mandrills can take into account elapsed time in a foraging context. Thereby, this study indicates how mandrills can use temporal cognitive abilities to overcome temporal challenges of food-finding in a group setting.

Location and temporal memory of objects declines in aged marmosets (Callithrix jacchus)

Episodic memory decline is an early marker of cognitive aging in human. Although controversial in animals and called “episodic-like memory”, several models have been successfully developed, however they rarely focused on ageing. While marmoset is an emerging primate model in aging science, episodic-like memory has never been tested in this species and importantly in aged marmosets. Here, we examined if the recall of the what-when and what-where building blocks of episodic-like memory declines in ageing marmosets. We developed a naturalistic approach using spontaneous exploration of real objects by young and old marmosets in the home cage. We implemented a three-trial task with 1 week inter-trial interval. Two different sets of identical objects were presented in sample trials 1 and 2, respectively. For the test trial, two objects from each set were presented in a former position and two in a new one. We quantified the exploratory behaviour and calculated discrimination indices in a cohort of 20 marmosets. Young animals presented a preserved memory for combined what-where, and what-when components of the experiment, which declined with aging. These findings lead one to expect episodic-like memory deficits in aged marmosets.

Do primates flexibly use spatio-temporal cues when foraging?

Foraging in seasonal environments can be cognitively demanding. Comparative studies have associated large brain size with a frugivorous diet. We investigated the ability of three semi-free-ranging primate species with different degrees of frugivory (N_trials: Macaca tonkeana = 419, Macaca fascicularis = 197, Sapajus apella = 346) in developing a mental representation of the spatio-temporal distribution of food using foraging experiments. Forty-two boxes were fixed on trees, and each week ("season"), some of them were filled with fruits which were either highly preferred, or less preferred. Spatial (geometrical panels) and temporal (peel skin of the available fruit) cues were present at each season to indicate where (food location), what (which food) was available, and when. To test the flexible use of the cues in primate foraging behaviour, we first removed the spatial and temporal cues one at a time, and then, we manipulated the "seasonal" order of the available fruit. We compared the foraging performances in the absence and the presence of the cues and during the usual and unusual seasonal order. The average proportion of baited boxes chosen by the subjects in presence of both cues was high (between 73% and 98%) for all species. The primates seemed to remember the spatio-temporal food availability (or used other cues) because no difference was found between trials with or without our spatial and temporal cues. When the usual seasonal pattern was changed, they flexibly adjusted the feeding choice by using the provided temporal cues. We discuss these results also in view of a possible experimental bias.

Acetylcholine and Spontaneous Recognition Memory in Rodents and Primates

Whilst acetylcholine has long been linked to memory, there have been significant questions about its specific role. In particular, the effects of cholinergic manipulations in primates and rodents has often been at odds. Here, we review the work in primates and rodents on the specific function of acetylcholine in memory, and episodic memory in particular. We propose that patterns of impairment can best be understood in terms of a role for hippocampal acetylcholine in resolving spatial interference and we discuss the benefits of new tasks of episodic memory in animals allowing clearer translation of findings to the clinic.

Are There Differences in "Intelligence" Between Nonhuman Species? The Role of Contextual Variables

We review evidence for Macphail’s (1982, 1985, 1987)Null Hypothesis, that nonhumans animals do not differ either qualitatively or quantitatively in their cognitive capacities. Our review supports the Null Hypothesis in so much as there are no qualitative differences among nonhuman vertebrate animals, and any observed differences along the qualitative dimension can be attributed to failures to account for contextual variables. We argue species do differ quantitatively, however, and that the main difference in “intelligence” among animals lies in the degree to which one must account for contextual variables.

Wild common marmosets (Callithrix jacchus) employ spatial cognitive abilities to improve their food search and consumption: an experimental approach in small-scale space

The ability of an animal to integrate and retain spatial information of resources often depends on the spatial memory and the speed at which this memory crystallizes. These become especially important once foragers reach their target area. However, very little is known about how wild common marmosets encode spatial information when feeding rewards are near to each other in a small-scale space. With this in mind, we performed field experiments to test foraging decisions related to a small-scale space setting. Specifically, we tested the (i) short- and (ii) long-term spatial memory, as well as (iii) the ability to remember the spatial location of resources after a single visit (one-trial spatial learning). The study was conducted with four groups of wild common marmosets (Callithrix jacchus) living in a semiarid Caatinga environment. We observed that individuals were able to retain spatial information of food sources on both a short- and long-term basis and to learn the spatial location of these resources after a single visit. We suggest that such abilities during foraging can improve the search for scattered resources with fluctuations of food availability. Presumably, this would be particularly advantageous in Caatinga, with its vegetation exhibiting asynchronous phenological patterns. Altogether, our results demonstrate that common marmosets employ all three studied spatial cognitive abilities to improve their food search and consumption.

Are the roots of human economic systems shared with non-human primates?

We review and analyze evidence for an evolutionary rooting of human economic behaviors and organization in non-human primates. Rather than focusing on the direct application of economic models that a priori account for animal decision behavior, we adopt an inductive definition of economic behavior in terms of the contribution of individual cognitive capacities to the provision of resources within an exchange structure. We spell out to what extent non-human primates' individual and strategic decision behaviors are shared with humans. We focus on the ability to trade, through barter or token-mediated exchanges, as a landmark of an economic system among members of the same species. It is an open question why only humans have reached a high level of economic sophistication. While primates have many of the necessary cognitive abilities (symbolic and computational) in isolation, one plausible issue we identify is the limits in exerting cognitive control to combine several sources of information. The difference between human and non-human primates' economies might well then be in degree rather than kind.

Hippocampal damage attenuates habituation to videos in monkeys

Monkeys with selective damage to the hippocampus are often unimpaired in matching-to-sample tests but are reportedly impaired in visual paired comparison. While both tests assess recognition of previously seen images, delayed matching-to-sample may engage active memory maintenance whereas visual paired comparison may not. Passive memory tests that are not rewarded with food and that do not require extensive training may provide more sensitive measures of hippocampal function. To test this hypothesis, we assessed memory in monkeys with hippocampal damage and matched controls by providing them the opportunity to repeatedly view small sets of videos. Monkeys pressed a button to play each video. The same 10 videos were used for six consecutive days, after which 10 new videos were introduced in each of seven cycles of testing. Our measure of memory was the extent to which monkeys habituated with repeated presentations, watching fewer videos per session over time. Monkeys with hippocampal lesions habituated more slowly than did control monkeys, indicating poorer memory for previous viewings. Both groups dishabituated each time new videos were introduced. These results, like those from preferential viewing, suggest that the hippocampus may be especially important for memory of incidentally encoded events.

What, where and when: spatial foraging decisions in primates

When exploiting the environment, animals have to discriminate, track, and integrate salient spatial cues to navigate and identify goal sites. Actually, they have to know what can be found (e.g. what fruit), where (e.g. on which tree) and when (in what season or moment of the year). This is very relevant for primate species as they often live in seasonal and relatively unpredictable environments such as tropical forests. Here, we review and compare different approaches used to investigate primate spatial foraging strategies: from direct observations of wild primates to predictions from statistical simulations, including experimental approaches on both captive and wild primates, and experiments in captivity using virtual reality technology. Within this framework, most of these studies converge to show that many primate species can (i) remember the location of most of food resources well, and (ii) often seem to have a goal-oriented path towards spatially permanent resources. Overall, primates likely use mental maps to plan different foraging strategies to enhance their fitness. The majority of studies suggest that they may organise spatial information on food resources into topological maps: they use landmarks to navigate and encode local spatial information with regard to direction and distance. Even though these studies were able to show that primates can remember food quality (what) and its location (where), still very little is known on how they incorporate the temporal knowledge of available food (when). Future studies should attempt to increase our understanding of the potential of primates to learn temporal patterns and how both socio-ecological differences among species and their cognitive abilities influence such behavioural strategies.

Sleep-dependent consolidation patterns reveal insights into episodic memory structure

Episodic memory formation is considered a genuinely hippocampal function. Its study in rodents has relied on two different task paradigms, i.e. the so called "what-where-when" (WW-When) task and "what-where-which" (WW-Which) task. The WW-When task aims to assess the memory for an episode as an event bound into its context defined by spatial and distinct temporal information, the WW-Which task lacks the temporal component and introduces, instead, an "occasion setter" marking the broader contextual configuration in which the event occurred. Whether both tasks measure episodic memory in an equivalent manner in terms of recollection has been controversially discussed. Here, we compared in two groups of rats the consolidating effects of sleep on episodic-like memory between both task paradigms. Sampling and test phases were separated by a 90-min morning retention interval which did or did not allow for spontaneous sleep. Results show that sleep is crucial for the consolidation of the memory on both tasks. However, consolidating effects of sleep were stronger for the WW-Which than WW-When task. Comparing performance during the post-sleep test phase revealed that WW-When memory only gradually emerged during the 3-min test period whereas WW-Which memory was readily expressed already from the first minute onward. Separate analysis of the temporal and spatial components of WW-When performance showed that the delayed episodic memory on this task originated from the temporal component which also did not emerge until the third minute of the test phase, whereas the spatial component already showed up in the first minute. In conclusion, sleep differentially affects consolidation on the two episodic-like memory tasks, with the delayed expression of WW-When memory after sleep resulting from preferential coverage of temporal aspects by this task.

Effects of the Extremely Low Frequency Electromagnetic Fields on NMDA-Receptor Gene Expression and Visual Working Memory in Male Rhesus Macaques

Introduction

The present research aimed to examine Visual Working Memory (VWM) test scores, as well as hormonal, genomic, and brain anatomic changes in the male rhesus macaques exposed to Extremely Low Frequency Magnetic Field (ELF-MF).

Methods

Four monkeys were exposed to two different ELF-MF frequencies: 1 Hz (control) and 12 Hz (experiment) with 0.7 μT (magnitude) 4 h/d for 30 consecutive days. Before and after the exposure, VWM test was conducted using a coated devise on a movable stand. About 10 mL of the animals' blood was obtained from their femoral vain and used to evaluate their melatonin concentration. Blood lymphocytes were used for assaying the expressions of N-Methyl-D-aspartate NMDA-receptor genes expression before and after ELF exposure. Anatomical changes of hippocampus size were also assessed using MRI images.

Results

Results indicated that VWM scores in primates exposed to 12 Hz frequency ELF increased significantly. Plasma melatonin level was also increased in these animals. However, these variables did not change in the animals exposed to 1 Hz ELF. At last, expression of the NMDA receptors increased at exposure to 12 Hz frequency. However, hippocampal volume did not increase significantly in the animals exposed to both frequencies.

Conclusion

In short, these results indicate that ELF (12 Hz) may have a beneficial value for memory enhancement (indicated by the increase in VWM scores). This may be due to an increase in plasma melatonin and or expression of NMDA glutamate receptors. However, direct involvement of the hippocampus in this process needs more research.

From minutes to days-The ability of sows (Sus scrofa) to estimate time intervals

Time estimation helps allocating time to different tasks and to plan behavioural sequences. It may also be relevant to animal welfare if it enables animals assessing the duration of a negative situation. Here, we investigated the ability of dry sows to estimate short and long time periods. We used a variant of the peak-interval procedure and the choice between 2 resources of different quality and replenishment rates to assess time periods in the order of minutes and days, respectively. In the minute-experiment, the sows were trained to expect an interruption while feeding at the end of an interval. Heart rate and heart rate variability slightly and continuously increased and decreased, respectively, towards the end of that interval. In the day-experiment, lasting about 60days, the sows were increasingly more likely to open the door to a high food reward on the correct day when this food reward was presented every fifth day. We conclude that the sows learnt to estimate time intervals of 5days after lengthy training but did not accurately learn intervals in the range of minutes. Therefore, they might re-visit replenishing resources after several days, but may not base short-term decisions solely on the passing of time.

Capuchins, space, time and memory: an experimental test of what-where-when memory in wild monkeys

There is considerable controversy about the existence, extent and adaptive value of integrated multimodal memory in non-human animals. Building on prior results showing that wild capuchin monkeys in Argentina appear to recall both the location and amount of food at patches they had previously visited, I tested whether they also track and use elapsed time as a basis for decisions about which feeding patches to visit. I presented them with an experimental array of eight feeding sites, at each of which food rewards increased with increasing elapsed time since the previous visit, similar to the pattern of ripe fruit accumulation in natural feeding trees. Over the course of 68 days, comprising two distinct renewal rate treatments, one group repeatedly visited sites in the feeding array, generating 212 valid choices between sites. Comparison of observations against simulated movements and multinomial statistical models shows that the monkeys' choices were most consistent with dynamic memory for elapsed time specific to each of the eight sites. Thus, it appears that capuchin monkeys possess and use integrated memories of prior food patch use, including where the patch is relative to their current location, how productive the patch is and how long it has been since they last visited the patch. Natural selection to use such integrated memories in foraging tasks may provide an ecologically relevant basis for the evolution of complex intelligence in primates.

Dissociating memory traces and scenario construction in mental time travel

There has been a persistent debate about how to define episodic memory and whether it is a uniquely human capacity. On the one hand, many animal cognition studies employ content-based criteria, such as the what-where-when criterion, and argue that nonhuman animals possess episodic memory. On the other hand, many human cognition studies emphasize the subjective experience during retrieval as an essential property of episodic memory and the distinctly human foresight it purportedly enables. We propose that both perspectives may examine distinct but complementary aspects of episodic memory by drawing a conceptual distinction between episodic memory traces and mental time travel. Episodic memory traces are sequential mnemonic representations of particular, personally experienced episodes. Mental time travel draws on these traces, but requires other components to construct scenarios and embed them into larger narratives. Various nonhuman animals may store episodic memory traces, and yet it is possible that only humans are able to construct and reflect on narratives of their lives - and flexibly compare alternative scenarios of the remote future.

Wild chacma baboons (Papio ursinus) remember single foraging episodes

Understanding animal episodic-like memory is important for tracing the evolution of the human mind. However, our knowledge about the existence and nature of episodic-like memory in non-human primates is minimal. We observed the behaviour of a wild male chacma baboon faced with a trade-off between protecting his stationary group from aggressive extra-group males and foraging among five out-of-sight platforms. These contained high-priority food at a time of natural food shortage. In 10 morning and eight evening trials, the male spontaneously visited the platforms in five and four different sequences, respectively. In addition, he interrupted foraging sequences at virtually any point on eight occasions, returning to the group for up to 2 h. He then visited some or all of the remaining platforms and prevented revisits to already depleted ones, apparently based on his memory for the previous foraging episode about food value, location, and time. Efficient use of memory allowed him to keep minimal time absent from his group while keeping food intake high. These findings support the idea that episodic-like memory offers an all-purpose solution to a wide variety of problems that require flexible, quick, yet precise decisions in situations arising from competition for food and mates in wild primates.

What did you choose just now? Chimpanzees' short-term retention of memories of their own behavior

Many recent comparative studies have addressed "episodic" memory in nonhuman animals, suggesting that birds, rodents, great apes, and others can remember their own behavior after at least a half-day delay. By contrast, despite numerous studies regarding long-term memory, few comparable studies have been conducted on short-term retention for own behavior. In the current study, we addressed the following question: Do chimpanzees remember what they have just done? Four chimpanzees performed matching-to-sample and visual search tasks on a routine basis and were occasionally (every four sessions) given a "recognition" test immediately after their response during visual search trials. Even though these test trials were given very rarely, all four chimpanzees chose the stimulus they selected in the visual search trials immediately before the test trial significantly more frequently than they chose the stimulus they selected in another distractor trial. Subsequent experiments ruled out the possibility that preferences for the specific stimuli accounted for the recognition test results. Thus, chimpanzees remembered their own behavior even within a short-term interval. This type of memory may involve the transfer of episodic information from working memory to long-term episodic-like memory (i.e., an episodic buffer).

What, where and when: deconstructing memory

The ability of animals to remember the what, where and when of a unique past event is used as an animal equivalent to human episodic memory. We currently view episodic memory as reconstructive, with an event being remembered in the context in which it took place. Importantly, this means that the components of a what, where, when memory task should be dissociable (e.g. what would be remembered to a different degree than when). We tested this hypothesis by training hummingbirds to a memory task, where the location of a reward was specified according to colour (what), location (where), and order and time of day (when). Although hummingbirds remembered these three pieces of information together more often than expected, there was a hierarchy as to how they were remembered. When seemed to be the hardest to remember, while errors relating to what were more easily corrected. Furthermore, when appears to have been encoded as a combination of time of day and sequence information. As hummingbirds solved this task using reconstruction of different memory components (what, where and when), we suggest that similar deconstructive approaches may offer a useful way to compare episodic and episodic-like memories.

Do different tests of episodic memory produce consistent results in human adults?

A number of different philosophical, theoretical, and empirical perspectives on episodic memory have led to the development of very different tests with which to assess it. Although these tests putatively assess the same psychological capacity, they have rarely been directly compared. Here, a sample of undergraduates was tested on three different putative tests of episodic memory (What-Where-When, Unexpected Question/Source Memory, and Free Recall). It was predicted that to the extent to which these different tests are assessing the same psychological process, performance across the various tests should be positively correlated. It was found that not all tests were related and those relationships that did exist were not always linear. Instead, two tests showed a quadratic relationship, suggesting the contribution of multiple psychological processes. It is concluded that not all putative tests of episodic cognition are necessarily testing the same thing.

Prospective Memory in a Language-Trained Chimpanzee (Pan troglodytes)

Prospective memory involves the encoding, retention, and implementation of an intended future action. Although humans show many forms of prospective memory, less is known about the future oriented processes of nonhuman animals, or their ability to use prospective memory. In this experiment, a chimpanzee named Panzee, who had learned to associate geometric forms called lexigrams with real-world referents, was given a prospective memory test. Panzee selected between two foods the one she wanted to receive more immediately. That food was scattered in an outdoor yard where she could forage for it. Also outdoors were lexigram tokens, one of which represented the food item that remained indoors throughout a 30 minute period, and that could be obtained if Panzee brought in the token that matched that food item. After foraging for the selected food item, Panzee consistently remembered to retrieve and return the correct token when food was available indoors, whereas on control trials involving no indoor food she rarely returned a token. This indicated that Panzee encoded information relevant to the future action of token retrieval after extended delays for one type of food, even when a more immediately preferred food was available.

Animal memory: rats can answer unexpected questions about past events

A new study has found that rats are able to answer, in a hippocampus-dependent manner, unexpected questions about whether they recently ate food or not. The results highlight potential shared mechanisms for remembering personal events in rats and humans, and offer new insights into the nature of animal memory.

Are monkeys able to plan for future exchange?

Whether or not non-human animals can plan for the future is a hotly debated issue. We investigate this question further and use a planning-to-exchange task to study future planning in the cooperative domain in two species of monkeys: the brown capuchin (Cebus apella) and the Tonkean macaque (Macaca tonkeana). The rationale required subjects to plan for a future opportunity to exchange tokens for food by collecting tokens several minutes in advance. Subjects who successfully planned for the exchange task were expected to select suitable tokens during a collection period (5/10 min), save them for a fixed period of time (20/30 min), then take them into an adjacent compartment and exchange them for food with an experimenter. Monkeys mostly failed to transport tokens when entering the testing compartment; hence, they do not seem able to plan for a future exchange with a human partner. Three subjects did however manage to solve the task several times, albeit at very low rates. They brought the correct version of three possible token types, but rarely transported more than one suitable token at a time. Given that the frequency of token manipulation predicted transport, success might have occurred by chance. This was not the case, however, since in most cases subjects were not already holding the token in their hands before they entered the testing compartment. Instead, these results may reflect subjects' strengths and weaknesses in their time-related comprehension of the task.

Cholinergic mechanisms of episodic memory: what specific behavioural tasks can tell us about specific neural mechanisms

Understanding the neural basis of episodic memory is crucial for understanding how to treat memory loss in normal ageing as well as in disorders such as Alzheimer's disease. However, it is only recently that episodic memory has been able to be reliably modelled in animals allowing the biological basis to be fully explored. Here we review studies on the role of the cholinergic basal forebrain on episodic memory, and highlight differences in findings from studies in monkeys and rats. The results highlight the importance of choosing appropriate behavioural models of cognitive processes in order to understand the neural basis of the processes accurately.

Chimpanzees (Pan troglodytes) fail a what-where-when task but find rewards by using a location-based association strategy

Recollecting the what-where-when of an episode, or episodic-like memory, has been established in corvids and rodents. In humans, a linkage between remembering the past and imagining the future has been recognised. While chimpanzees can plan for the future, their episodic-like memory has hardly been investigated. We tested chimpanzees (Pan troglodytes) with an adapted food-caching paradigm. They observed the baiting of two locations amongst four and chose one after a given delay (15 min, 1 h or 5 h). We used two combinations of food types, a preferred and a less preferred food that disappeared at different rates. The subjects had to base their choices on the time elapsed since baiting, and on their memory of which food was where. They could recover either their preferred food or the one that remained present. All animals failed to obtain the preferred or present foods above chance levels. They were like-wise unsuccessful at choosing baited cups above chance levels. The subjects, thus, failed to use any feature of the baiting events to guide their choices. Nonetheless, their choices were not random, but the result of a developed location-based association strategy. Choices in the second half of the study correlated with the rewards obtained at each location in the first half of the study, independent from the choices made for each location in the first half of the study. This simple location-based strategy yielded a fair amount of food. The animals' failure to remember the what-where-when in the presented set-up may be due to the complexity of the task, rather than an inability to form episodic-like memories, as they even failed to remember what was where after 15 minutes.

Validation of a rodent model of episodic memory

Episodic memory consists of representations of specific episodes that happened in the past. Modeling episodic memory in animals requires careful examination of alternative explanations of performance. Putative evidence of episodic-like memory may be based on encoding failure or expectations derived from well-learned semantic rules. In Experiment 1, rats were tested in a radial maze with study and test phases separated by a retention interval. The replenishment of chocolate (at its study-phase location) depended on two factors: time of day (morning vs. afternoon) and the presence or absence of chocolate pellets at the start of the test phase. Because replenishment could not be decoded until the test phase, rats were required to encode the study episode. Success in this task rules out encoding failure. In Experiment 2, two identical mazes in different rooms were used. Chocolate replenishment was trained in one room, and then they were asked to report about a recent event in a different room, where they had no expectation that the memory assessment would occur. Rats successfully answered the unexpected question, ruling out use of expectations derived from well-learned semantic rules. Our behavioral methods for modeling episodic memory may have broad application for assessments of genetic, neuroanatomical, neurochemical, and neurophysiological bases of both episodic memory and memory disorders such as those that occur in Alzheimer's disease.

Do monkeys think in metaphors? Representations of space and time in monkeys and humans

Research on the relationship between the representation of space and time has produced two contrasting proposals. ATOM posits that space and time are represented via a common magnitude system, suggesting a symmetrical relationship between space and time. According to metaphor theory, however, representations of time depend on representations of space asymmetrically. Previous findings in humans have supported metaphor theory. Here, we investigate the relationship between time and space in a nonverbal species, by testing whether non-human primates show space-time interactions consistent with metaphor theory or with ATOM. We tested two rhesus monkeys and 16 adult humans in a nonverbal task that assessed the influence of an irrelevant dimension (time or space) on a relevant dimension (space or time). In humans, spatial extent had a large effect on time judgments whereas time had a small effect on spatial judgments. In monkeys, both spatial and temporal manipulations showed large bi-directional effects on judgments. In contrast to humans, spatial manipulations in monkeys did not produce a larger effect on temporal judgments than the reverse. Thus, consistent with previous findings, human adults showed asymmetrical space-time interactions that were predicted by metaphor theory. In contrast, monkeys showed patterns that were more consistent with ATOM.

Origins of spatial, temporal and numerical cognition: Insights from comparative psychology

Contemporary comparative cognition has a large repertoire of animal models and methods, with concurrent theoretical advances that are providing initial answers to crucial questions about human cognition. What cognitive traits are uniquely human? What are the species-typical inherited predispositions of the human mind? What is the human mind capable of without certain types of specific experiences with the surrounding environment? Here, we review recent findings from the domains of space, time and number cognition. These findings are produced using different comparative methodologies relying on different animal species, namely birds and non-human great apes. The study of these species not only reveals the range of cognitive abilities across vertebrates, but also increases our understanding of human cognition in crucial ways.

Episodic-like memory in animals

Episodic memory consists of representations of unique past events. It has been argued that episodic memory is grounded in a temporal framework, meaning that we remember when an event occurred. The ability to model the temporal aspects of episodic memory in non-human animals has been challenging and controversial. This article briefly reviews the theoretical perspective in which temporal processing plays a prominent role in episodic memory. Next, the article reviews experimental attempts to identify temporal processes of episodic memory in animals. Recent studies suggest that, at the time of memory assessment, rats remember a unique earlier event, including when it occurred, what happened, and where it took place, referred to as what-where-when memory.

Keeping track of time: evidence for episodic-like memory in great apes

Episodic memory, as defined by Tulving, can be described in terms of behavioural elements (what, where and when information) but it is also accompanied by an awareness of one's past (chronesthesia) and a subjective conscious experience (autonoetic awareness). Recent experiments have shown that corvids and rodents recall the where, what and when of an event. This capability has been called episodic-like memory because it only fulfils the behavioural criteria for episodic memory. We tested seven chimpanzees, three orangutans and two bonobos of various ages by adapting two paradigms, originally developed by Clayton and colleagues to test scrub jays. In Experiment 1, subjects were fed preferred but perishable food (frozen juice) and less preferred but non-perishable food (grape). After the food items were hidden, subjects could choose one of them either after 5 min or 1 h. The frozen juice was still available after 5 min but melted after 1 h and became unobtainable. Apes chose the frozen juice significantly more after 5 min and the grape after 1 h. In Experiment 2, subjects faced two baiting events happening at different times, yet they formed an integrated memory for the location and time of the baiting event for particular food items. We also included a memory task that required no temporal encoding. Our results showed that apes remember in an integrated fashion what, where and when (i.e., how long ago) an event happened; that is, apes distinguished between different events in which the same food items were hidden in different places at different times. The temporal control of their choices was not dependent on the familiarity of the platforms where the food was hidden. Chimpanzees' and bonobos' performance in the temporal encoding task was age-dependent, following an inverted U-shaped distribution. The age had no effect on the performance of the subjects in the task that required no temporal encoding.