Building Mental Bridges: Episodic Memory In Animals

I have had my cat, Tiger, for nine years and often I wonder how much of the nine years he remembers. Being able to remember our past is one of the many attributes that makes us unique as humans but one has to wonder: do animals have memories? There is no doubt that animals-especially house pets- can remember certain things, such as tricks to receive treats and the time of day in which they are fed, but can they use these memories as advantages for the future? This phenomenon, first coined episodic memory in 1972 by Canadian psychologist Endel Tulving, is defined as “a type of long term memory…characteristically stored as information about specific experiences and events…and affords a sense of personal continuity and familiarity with the past” [1]. When Tulvig first conducted experiments on episodic memory, he made the conclusion that this subcategory of memory is uniquely human because there had never been evidence of conscious experience without the presence of language [2]; and a linguistic element is something that non-human animals essentially do not have. While Tulving’s argument may have some truth to it, who is to say that animals cannot recall their past and apply it to the present?

In order to relate episodic memory to animals, it is important to recognize how human memory works in general. A human’s memory can be divided into many sub-groups; but the two main categories have been defined as declarative and non-declarative memory. Non-declarative memory has been characterized by its “inaccessibility to conscious recalls and is demonstrated by phenomena such as priming and simple forms of classical conditioning” [3] while declarative memory has been further categorized into semantic and episodic memory. While conducting his experiments, Tulving was careful to define episodic and semantic memory in terms of remembering and knowing for “episodic memory is concerned with specific personal experiences, whereas semantic memory mediates what one knows in the world” [3]. Episodic memory is further unique from semantic memory because it is developed later in a human’s life- around the age of four- and because of its fragile nature; it is also the first type of memory to be lost in Alzheimer’s and other brain diseases [4]. Episodic memory could also be explained simply in terms of familiarity; for example, I can remember where the train station near my home is located but not recall the first time I was there. Tulvig also identified episodic recall as “ the retrieval of information about ‘where’ a unique event or episode took place, ‘what’ occurred during the episode and ‘when’ the episode happened” [3] and this is precisely the starting point for the most important experiment conducted that tested episodic memory in animals, namely food-storing scrub jays.

The groundbreaking experiment conducted in 1998 by Nicola Clayton, a professor of comparative cognition at the University of Cambridge in England, proved to be at the forefront of evidence that can prove that animals may possess episodic memory. Clayton, along with Anthony Dickinson and Daniel Griffiths, chose to use a type of bird called scrub jay because of their food-caching behavior: they tended to stash food to recover later [5]. Utilizing Tulvig’s definition of episodic recall, the experiment involving the scrub jays “tested their ability to remember what, where and when they cached a particular foodstuff, based on a trial-unique experience of caching” [3] Clayton ran the experiment using moth larvae and peanuts and observed the scrub jays hide both types of food and a few days later, observe if they remembered where they hid the food. In the majority of the trials, the scrub jay did. Time also affected which kind of food the scrub jay dug up, if too much time passed the bird would avoid the rotten larvae and dig up the peanuts instead. The innovative results of this experiment relate back to Tulvig’s identification because in fact, the scrub jays appeared to remember the “what-where-and-when of specific caching events in the past” [2]. Although these experiments were conducted to test whether these birds possessed episodic memory, the results only proved that the scrub jays had ‘episodic- like’ memory. It was concluded that scrub jays have ‘episodic-like’ memory because one essential part of the research was missing: the evidence that the birds are actually recalling their past events and as aforementioned, the birds would not be able to prove this without the use of language.

Upon the publication of these results, scientists began to test for episodic memory in various animals such as laboratory mice and cebus monkeys, while other scientists still remained skeptical about this mental connection between humans and non-human animals. Thomas Suddendorf, a comparative psychologist at the University of Queensland, concluded, “Animals seem to be living very much in the present…episodic memory also depends on many other faculties that have only been clearly documented in the human mind” [6]. One important phenomenon of episodic memory that has been defined as uniquely human is mental time travel. Mental time travel occurs when we mentally travel back in time to remember a certain event and can use these memories to imagine the future. Suddenhorf argues that mental time travel evolved at least 1.6 million years ago during the time of the hominids [6], which proves that episodic memory is uniquely human.

One can conclude that animals do have ‘episodic-like’ memory because even if they remember where they hid their food some days before, there is no linguistic evidence that they recalled past events to remember where the food was located. It could be true that animals simply do take actions that benefit them in the moment and not so much in the future, but tests are still being conducted to find a way to legitimately prove that non-human animals have a form of episodic memory. Reflecting on the behavior of my own non-human cat, I know that he lives in the moment when he meows for food but exhibits a ‘episodic-like’ memory simply because he knows what time of day he is fed. When following the debate on whether human-defined episodic memory can be applied to the memories of non-human animals, it is important to recognize this point made by anthropologist Charles Mendel of Georgia State University: “animals are using something related to episodic memory, but not necessarily the same as in humans…animal memory systems have always been underestimated---the upper limits are not really known” [5]. It is true that the memories of non-human animals are still being explored but because of the obvious language barrier, the extent to which their memories reach may never be unearthed.

Works Cited

[1] http://www.encyclopedia.com/doc/1O87~episodicmemory.html

[2] http://en.wikipedia.org/wiki/Episodic_memory

[3] http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VH9-3Y868JN-C&_user=400777&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000018819&_version=1&_urlVersion=0&_userid=400777&md5=4352a458dd48c6bd83ac2fc830fe84fa

[4] http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRT-4N97NYR-6&_user=400777&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000018819&_version=1&_urlVersion=0&_userid=400777&md5=e2f30dd3d1c7ac39281d0fc3f37c02c7

[5] http://news.nationalgeographic.com/news/2003/08/0822_030822

[6] http://www.nytimes.com/2007/04/03/science/03time.html