Alzheimer's, Dementia & Mental Health
Finding Rats Remember When Things Happened Opens
Door to Research on Human Memory Loss
New testing with rats may help the understanding of
how Alzheimer’s robs patients of episodic memory
May 19, 2009 – Many have believed only humans have
“episodic memory,” which allows humans to not only recall an event but
also where and when it happened. A new study has found, however, that
rats have such memory, which opens the door to possible new ways to
study the devastating memory loss for humans from Alzheimer’s disease
and other dementias.
The belief that only humans have episodic memory
may have limited approaches to studying the problem, because of the lack
of animals for proper experimentation.
The just-published research from scientists at the
University of Georgia is offering new insights into how this kind of
memory works. The study, published this week in the online edition of
The Proceedings of the National Academy of Sciences, shows that
laboratory rats have "episodic-like memory" and could open novel ways to
study life-robbing loss of memory in humans.
"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," 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.
"These experiments provide insight into the memory
system that retains the time of occurrence of earlier events."
Co-author of the paper was Wenyi Zhou, a doctoral
student in Crystal's laboratory. The work was supported by a grant from
the National Institute of Mental Health.
Memory loss in humans can be caused by an array of
diseases, such as Parkinson's and Huntington's, but the great destroyer
of memory is Alzheimer's disease, which is progressive and, at least for
the present, irreversible. Drugs used to treat cancer can cause memory
loss, as can certain forms of mental illness or traumatic brain
injuries. Memory loss often ends an independent life for those who
suffer it, and researchers around the world are looking for ways to slow
or stop damage to memory, especially through pharmaceuticals.
Still, much remains unknown about the disorder, and
so having an effective animal model of memory will be critical to
understanding how and why memory fades.
Crystal argues in this PNAS paper, however, that
behavioral experiments can show that rats do have such memory. If
confirmed, the implications are considerable because it would give
researchers 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," he said. "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."
The experiment reported this week 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," she
said.
"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 problem at hand for those studying human memory
loss isn't as simple as "Where did I leave my car keys?" The question at
hand is more like, "What happened to me yesterday?" Until researchers
understand memory more—through studies such as this one—memory loss will
remain the great thief of human love.
