For the first time, researchers have found that animals can retrieve and replay past events from memory. The ultimate goal of the study, which was conducted by a team of neuroscientists at Indiana University, is to develop new medications to treat Alzheimer’s disease.
“The reason we’re interested in animal memory isn’t only to understand animals, but rather to develop new models of memory that match up with the types of memory impaired in human diseases such as Alzheimer’s disease,” said lead author Jonathon Crystal.
The majority of clinical trials have been focused on how potential Alzheimer’s drugs impact spatial memory in animals. However, the type of memory loss that causes the most debilitating effects in Alzheimer’s patients is episodic memory.
“If your grandmother is suffering from Alzheimer’s, one of the most heartbreaking aspects of the disease is that she can’t remember what you told her about what’s happening in your life the last time you saw her,” said study first author Danielle Panoz-Brown.
“We’re interested in episodic memory – and episodic memory replay – because it declines in Alzheimer’s disease, and in aging in general.”
Episodic memory is the ability to recall specific experiences and events. The capacity to place certain events in chronological order is referred to as “episodic memory replay.”
People would not be able to make sense of most scenarios if they could not remember the order in which they occurred, explained Professor Crystal.
Over the course of a year, the research team trained 13 rats to memorize a list of up to 12 different odors. Ultimately, the rats showed that they were able to identify odors based on the order of the list and not just by the scent itself.
According to Professor Crystal, the rats successfully completed their tasks in the correct order around 87 percent of the time, which strongly indicates that the animals were utilizing episodic memory replay.
Further analysis showed that the rats’ memories were long-lasting and resistant to the interference of other memories. In addition, the study revealed that brain activity was stimulated in the hippocampus, which is the brain region that controls episodic memory.
New genetic tools are making it possible to create rats with neurological conditions similar to Alzheimer’s disease, and not just mice. This creates an urgent need to find reliable methods of studying episodic memory replay in rats.
“We’re really trying push the boundaries of animal models of memory to something that’s increasingly similar to how these memories work in people,” said Professor Crystal. “If we want to eliminate Alzheimer’s disease, we really need to make sure we’re trying to protect the right type of memory.”
The study is published in the journal Current Biology.