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Rats are highly intelligent, capable of problem solving and deduction. Their intelligence is one of the reasons they make such popular pets. Rats have the neural capacity to remember an owner, but the likelihood of a captive rat remembering his owner after a long absence depends on various factors.
A number of studies have sought to determine for certain whether rats have the capacity for episodic memory, but no conclusive evidence existed as recently as as of October 2013. One 2006 study, "Episodic-Like Memory in the Rat", conducted at the University of Georgia did find that rats have the cognitive machinery to form memories of events. The study proved that rats could remember whether certain places in a maze had an availability of food. This distinguishes them from less intelligent creatures that simply form associations between stimuli and outcomes. The ability to remember events suggests that pet rats may store memories of their owners for retrieval later.
Capacity for Recollection
The ability to recollect is distinct from the ability to store memories. Numerous studies on rats have shown they have a capacity for recollection, but in this scenario, the owner is remembered as a stimulus rather than as a person. The rat may see an owner and recollect that when last exposed to that particular physical stimulus -- the owner’s presence -- that he received a treat. This doesn’t necessarily mean that the rat identifies the owner as the same person who walks past the cage and did nothing, because the outcome of the exposure to that stimulus was different. The owner at feeding time represents one stimulus. The same owner walking past might not, especially if he doesn't smell like food when he passed by.
Sense of Familiarity
As well as having conscious recollection, rats are capable of experiencing familiarity, meaning that rats can form neural associations with objects and people through prolonged exposure. Once exposure ends, rats are capable of retaining a sense of familiarity. It is most probable that a pet rat who has not seen his owner for a long time will experience a sense of familiarity rather than have a specific recollection of that person.
Rats very much live in the moment. They are instinctive and are driven by their survival mechanisms. But this doesn’t preclude them from retrieving memories, provided there is a trigger stimulus. Without a trigger stimulus, it is unlikely that a rat will retrieve a memory. In practical terms, that means a rat will most likely not stop what he’s doing to reminisce about his owner but he may, upon seeing or being held by his owner, retrieve a memory of a specific event involving that owner.
Periods of Absence
It is unclear for how long a rat may hold onto a memory or sense of familiarity, but it is highly probable that the longer the period of time between the event occurring and the reintroduction of the relevant stimulus -- the presence of the owner -- the less likely it becomes that the rat will recollect. In cases of former owners coming by to visit, a pet rat may experience a sense of familiarity with that person, but the intensity of that familiarity is governed by the recency of the last encounter and the period of exposure. So, a rat who spent years with a former owner may be familiar with that person after an absence -- but a rat who had little contact with a former owner or a long time ago may not.
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