Scientists at the University of Georgia have revealed that rats can be used as nonhuman models to study how "episodic-like memory" works. This development could help open new ways to study how Alzheimer's disease causes loss of memory in man.
"This research shows that rats remember the time at which they encounter a distinctive event, in addition to what the event was and where it happened.
These experiments provide insight into the memory system that retains the time of occurrence of earlier events," said Jonathon Crystal, an associate professor in the Department of Psychology's Neuroscience and Behavior Program in UGA's Franklin College of Art and Sciences.
In episodic memory, unique past events are recalled and can be placed in time and at a specific location.
While scientists believed it for many years that only humans have episodic memory, behavioral experiments have shown that rats do have such memory.
If these findings are replicated in further experiments, they will provide scientists with a way to study this type of memory in a nonhuman model.
"It has been argued that retrieval of episodic memories is analogous to traveling back in time. Recent studies with nonhuman animals suggest that animals remember specific episodes from their past, but there has been controversy over whether episodic-like memory in rodents is the same as it is in humans," said the researchers.
They have revealed that their experiment involved setting up a situation in which rats were "asked" to remember the time of day at which they encountered a distinctive event, in addition to what occurred and where it happened.
The event was the feeding of chocolate-flavored pellets-chocolate being a flavor that rats, like humans, crave.
The rats were fed in the morning and afternoon on separate days, but chocolate was available at only one time and place. Rats adjusted their revisits to the chocolate location by using the time of day rather than how long ago the event occurred.
"Our results suggest that at the time of memory assessment, rats remember when a recent episode occurred, similar to human episodic memory," said Crystal.
Zhou agrees: "As a memory system that is late to develop in childhood and is the first to decline in old age, episodic memory has attracted intensive attention in the scientific community recently.
Because there are many limitations in human studies, I think the development of a rodent model of episodic memory will provide an invaluable tool for understanding the underlying mechanisms. It will also bridge the gap between studies of memory in humans and animals."
The study has been published in the online edition of The Proceedings of the National Academy of Sciences.