The study of memory in humans and how the brain converts information to short-term and long-term memories is a frequent subject of research. Understanding how memory works can offer clues to neurological problems like Alzheimer’s related dementia, traumatic brain injury and even depression.
In a recent study of lab rats, neuroscientists at Indiana University found that the animals could mentally replay past events, a first for investigating memory in non-humans.
The research was led by IU professor Jonathon Crystal and is published in the journal Current Biology. Dr. Crystal explained, "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."
There are different kinds of memory that the brain processes. When looking at potential treatments for Alzheimer ’s most studies investigate drugs that can affect spatial memory. Remembering how to get to and from work or the grocery store, how to make a cup of tea and where to find food. In Alzheimer’s patients though, episodic memory is often what they lose. Memories of events like weddings, birthdays, or vacations tend to be lost. These are the kinds of memories that are passed down to younger generations. When an Alzheimer’s patient can no longer remember a trip they took or the person they married, they suffer, but so do their family members and loved ones. Danielle Panoz-Brow is the first author of the study and a Ph.D. student at IU. She explained, "We're interested in episodic memory -- and episodic memory replay -- because it declines in Alzheimer's disease, and in aging in general. 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."
It’s not only special times like weddings or birthdays but everyday events as well. Who hasn’t lost their cell phone a few times? When you realize your phone is missing, retracing your steps and remembering where you were and what you did recently can help jog your memory of whatever “episode” of time was happening when it was misplaced. Patients with Alzheimer’s lack the ability to do this.
In the study at IU, the researchers spent almost an entire year working on training 13 lab rats to recognize and memorize 12 distinct odors. They were then placed in an area much like a rat-sized arena where there were several of the odors, and the rats had to sniff out a certain one. The researchers were looking for the rats to be able to sniff out an odor based on its place in the list of twelve, for instance, the second to last scent or the fourth scent. It was about more than just recognizing a smell, but knowing in what order it came. The pattern of how the odors were presented in the arena was changed as well, to tease further out the fact that the rats remembered an episode of time and not just a smell.
The results showed that the rats recalled episodic memory. To further nail it down, some of the animals were induced to have hippocampal function suppressed. The hippocampus is the area of the brain that processes episodic memory. With this ability gone, the rats were not able to recall the order of odors, proving that recalling the sequence was an example of episodic memory in the hippocampus. The research is essential because rats are even more similar to humans regarding brain function than mice. Previously, it was only mice that could be used in cognitive studies, but if rats could be genetically altered to have conditions similar to Alzheimer’s and other forms of dementia, better research would be the result. Very often results from medications tested on animal models do not translate to the same results in human clinical trials. Having lab animals that have similar memory capabilities to humans can only further research into memory loss and dementia. Check out the video to learn more about this study.