episodic-like memory episodic-like memory episodic-like memory is the memory system in animals that is comparable to human episodic memory. the term was first described by clayton & dickinson referring to an animal's ability to encode and retrieve information about 'what' occurred during an episode, 'where' the episode took place, and 'when' the episode happened. this ability in animals is considered 'episodic-like' because there is currently no way of knowing whether or not this form of remembering is accompanied by conscious recollection—a key component of endel tulving's original definition of episodic memory. distinction from human episodic memory in order for an animal's memory to qualify as 'episodic-like,' it must meet three behavioural criteria reflecting the content, structure and flexibility of the memory. content refers to recalling what happened, where it happened, and when it happened on the basis of a specific past experience. structure refers to forming an integrated what-where-when representation, and flexibility refers to being able to use the information in a versatile way. in order for an animal to meet these behavioural criteria then, they must be able to not only form what-where-when memories, but integrate the what, where and when of the event into an integrated framework. the assessment of episodic-like memory must rely on these behavioural characteristics because animals do not have the language capabilities to participate in the episodic memory tests developed for humans. evidence of an episodic-like memory system was first provided by clayton & dickinson (1998). they demonstrated that western scrub jays (aphelocoma californica) remember where they cache different types of food, and discriminately recover them depending on the perishability of the item and the amount of time that has passed since caching. recent research has further investigated episodic-like memory in these birds, but has also explored evidence of this memory system in other species such as the rufous hummingbird, pigeons, primates, rats and honeybees. the overall organization and brain structures involved in human episodic memory have also been compared to what exists in the animal brain. many similarities have been found including the role of the medial temporal lobe, a structure including the hippocampus. nonetheless, many have cautioned making comparisons to human episodic memory. many criticisms of this area of research have been made including questioning how accurately we can attain this information simply based on behavioural criteria and non verbal tests. neural mechanisms subdivisions of the hippocampus in a rat brain. information is projected through a path which begins with the dentate gyrus (dg), then to area ca3, ca1, and finally to the subiculum. the ability to encode and retrieve past experiences relies on the circuitry of the medial temporal lobe, a brain structure that includes the hippocampus and other para-hippocampal cortical areas. the organization of these brain areas is largely conserved across mammalian species as are the major pathways that information travels between the medial temporal lobe and the neocortex. because of this strong parallel between animal brain structures and the structures involved in human episodic memory, there is reason to believe that not only do some animals possess the ability to form what-where-when memories, but that this episodic-like system may be more comparable to human episodic memory than once thought. according to eichenbaum (2000), information that is projected from nearly all neocortical areas come together onto one or more subdivisions of the para-hippocampal region which includes the perirhinal cortex, the postrhinal cortex and the enotrhinal cortex. this information is then projected onto subdivisions of the hippocampus which are connected by a path which begins with the dentate gyrus, continuing to area ca3, then ca1, and finally through to the subiculum. information is then directed back to the para-hippocampal region and finally to the same areas of the cerebral cortex that were the source of input to this region. this organization has been observed in primates, rats, and other mammalian species. the hippocampus in particular has an evolutionarily well conserved structure. it contains similar cell types and comparable structural design in humans and non-human primates. its structure in rodents is also remarkably similar although in rodents it contains approximately ten times fewer cells and more connections between hemispheres. animal lesion studies have also provided evidence related to the importance of particular brain structures in episodic-like memory. rats with medial prefrontal cortical lesions showed impairment on the ‘where’ component suggesting that this area contributed to retrieving information on object location. similarly, hippocampal lesions severely impacted all three components (what, where, and when) suggesting that the hippocampus is responsible for detecting new events, stimuli, and places when forming new memories and on retrieving that information later on. research western scrub jays (aphelocoma californica) episodic-like memory was first demonstrated in the western scrub jay (aphelocoma californica). recent research regarding mental time travel and episodic-like memory has focused on determining whether there are any non-human animals that demonstrate future planning and under what conditions they do so. one species that has frequently been considered is the western scrub jay (aphelocoma californica), a member of the corvid family of birds native to western north america. these large-brained, long-lived, and highly social birds hide food caches for future consumption and rely on memory to recover their caches of hidden food at a later date, typically weeks if not months into the future. they show an ability to form what-where-when memories characteristic of episodic memory as they remember the spatial location and contents of their caches as well as recalling which conspecifics were watching during caching. flexibility within episodic-like memory has been demonstrated within a study by clayton et al. involving the caching of perishable and non-perishable foods. the jays were allowed to cache perishable and non-perishable items but then discovered, in the interval between caching and recovery, that the perishable food type degraded more quickly than originally thought. they reasoned that, if the birds do use a flexible declarative memory system, they should be able to update their knowledge about the rate of perishability of the food and change their search behaviour at recovery accordingly, even though the episodic information about what they cached where and when was encoded before gaining the new knowledge about the decay rates. results confirmed this reasoning demonstrating that these birds possess a flexible episodic like memory system where they can update their information after the time of encoding. an experiment conducted by dally et al. examined the importance of social living in scrub jays by testing whether storer birds remember the status of the observer bird who watched them during caching – adding a 'who' to the what-where-when memory framework. they found that, as predicted, storer birds' adjusted their behaviour during the initial caching period according to the rank of the observer bird. in the dominant observer bird condition, where they experienced the highest risk of cache theft, storers cached predominantly in the tray farthest away from the observer bird and recached the greatest proportion of items during the recovery period. in a second part of this study, they tested whether scrub jays remember which particular individual was present when they made specific caches. birds cached in front of observer birds as they did the first part of this study, but then hours later were separated into three conditions where they either recovered their caches in private, in front of an observer bird that watched them cache initially, or in front of a new control bird. they found that the proportion of caches that were recached at recovery differed significantly between conditions and significantly more caches were recached during the observed condition relative to the control condition. this suggests that during the recovery stage, storer birds remember whether the observer bird watching them recover their cache was the same bird who watched them cache initially and engage in additional behaviours to prevent cache theft. hummingbirds a study of the rufous hummingbird found they were able to learn and remember which flowers in an arrangement contained a nectar reward. although visual cues such as the type and colour of flower increased how quickly the locations were learned, they weren't necessary for learning. hummingbirds could remember that only the center flower contained a reward even in arrangements of identical flowers. artificial flowers were created using small cardboard disks painted in unique colours, the center of which contained a syringe tip filled with a small amount of sucrose solution. when spacing between the flowers was increased, hummingbirds still remembered the relative locations of the flowers in arrangement. when the arrangements of artificial flowers were moved, the hummingbirds remembered which flowers contained nectar, even when the new location of the arrangement placed an empty flower in the location previously occupied by a reward flower. hummingbirds demonstrate the ability to recall where certain flowers were located and how recently they were visited. rufous hummingbirds are also able to adjust their foraging strategies based on when they've last visited flowers and how often the flower's nectar is renewed. artificial flowers were refilled in either ten- or twenty-minute intervals upon being emptied. the hummingbirds were able to distinguish between the types of flower and adjust their foraging strategies accordingly. over time the hummingbirds learned the schedule of renewal and visited the flowers renewed every ten minutes much more frequently than the flowers renewed every twenty minutes. this implies planning on the part of the hummingbird in order to avoid redundant trips and avoid wasting energy. similar cognitive abilities and foraging strategies were also observed in a study of the green-backed firecrown, another species of hummingbird. pigeons pigeons have been shown to think back on past experience to generate positive future outcomes. the pigeon has also been shown to exhibit qualities similar to episodic-like memory. pigeons respond to a stimulus shown before the presentation of food by thereafter pecking future examples of the stimulus. in the event that a stimulus is presented without food, pigeons will choose not to peck at future presentations of the stimulus. a study at the university of kentucky aimed to determine whether pigeons could recall their previous actions with regard to certain hues presented either with or without food. the first phase of the experiment involved training the pigeons to peck in response to one stimulus (vertical lines) and refrain from pecking for at least four seconds in response to another stimulus (horizontal lines). the presented stimuli were then followed by both a red and green key. pecking the green key following a pecking stimulus (vertical lines) resulted in a food reward, as did pecking the red stimulus following a non-pecking stimulus (horizontal lines). this allowed the experimenters to effectively pose questions to the pigeons on their past actions. the pigeons were required to recall what the previous stimulus had been and how they had reacted in order to formulate a correct response and receive a reward. this differs from other memory tasks where the aim was simply to determine whether a stimulus and response could be paired as a learned association and then testing the memory for that association. this experiment showed a clear use of episodic memory or a similar construct, pigeons were shown to think back on past experience to generate a positive future outcome. primates due to their similarities to humans, researchers have been interested in looking into the episodic memory abilities of non-human primates. however, little uncritisized research has previously been done. for example, schwartz performed an experiment with gorillas in a task requiring the animal to select the appropriate card that represented the food he had just eaten and who had given it to him. while the gorilla appropriately identified the food items and trainer, it is unclear if he recalled the event or chose the answer most familiar to him. menzel also showed evidence of episodic memory in apes, however, an alternative explanation is that the chimpanzees were displaying spatial semantic memory. furthermore, hampton had mixed results when testing rhesus monkeys; while demonstrating memory for the location and type of food, they lacked sensitivity to when they acquired the knowledge. thus, more research was required for this type of memory in non-human primates. humans and primates may possess some of the same information encoding and storage mechanisms related to episodic memory. chimpanzees and orangutans were tested using an adapted design by clayton and colleagues for experimenting with scrub jays. after five minutes and again at