The extent to which these specific memory systems exist in nonhumans is debated. The distinction between episodic and semantic memory in humans is central in cognitive neuroscience and has been well-established by the combination of behavioral studies, neuroimaging studies, and studies of patients with brain damage. You may know that monkeys have tails, but probably do not remember the occasion on which you learned this fact. By contrast, semantic memories lack contextual details. In this case, contextual information about where and when you formed a memory is useful in discriminating facts learned reading tabloids from facts learned during a trip to the botanical gardens. For example, you might remember loading ripe tomatoes and watermelon for a barbecue on the supermarket checkout belt while reading about the anti-cancer properties of a plant in a tabloid headline. One type of memory is episodic memory (EM), which enables use of contextual information about distinct episodes from one’s personal past to guide behavior. These distinct systems have evolved because they each serve specialized functions that have promoted survival and reproduction. Our apparently seamless experiences of remembering result from the combined action of cognitively and neurobiologically distinguishable systems in the brain. Investigators that have refined their approach from asking the naïve question “do nonhuman animals have episodic memory” to instead asking “what aspects of episodic memory are shared by humans and nonhumans” are making progress. The most productive way forward is likely a combination of neurobiology and sophisticated cognitive testing that identifies the mental representations present in episodic memory.
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However, defining memory types on the basis of the brain structures involved rather than on identified cognitive mechanisms risks missing the most crucial functional aspects of episodic memory, which are ultimately behavioral. Some investigators have attempted to use neurobiological parallels to bridge this gap. It is therefore a significant challenge for investigators to agree on objective behavioral criteria that can be applied in nonhumans and still capture features of memory thought to be critical in humans. Focus on phenomenal experience in human memory, such as the sense of “having been there” has resulted in conceptualizations of episodic memory that are difficult or impossible to apply to nonhumans. Episodic memories differ from other types of memory because they represent aspects of the past not present in other memories, such as the time, place, or social context in which the memories were formed.