Young process fear memories in unique way

SYDNEY, Feb. 13 (UPI) -- Australian researchers have found very young rats process memories of fear differently than more mature rats do.

University of New South Wales researchers said their finding advances the understanding of how fearful memories are learned and unlearned.

Rats 16 and 23 days old, the human equivalent of children and adolescents, were trained first to learn, and then to unlearn, a fearful response to a sound. Then, researchers once again trained the rats to learn, and then unlearn, that response.

In some rats, researchers used anesthesia to temporarily inactivate the amygdala -- a brain structure critical for learning, memory and emotional experiences.

Study co-authors Jee Hyun Kim and Rick Richardson found in both 16- and 23-day-old rats, only those with a functioning amygdala were able to learn and unlearn the fear response the first time. During the second round of training, the researchers found only the 23-day-old rats were able to learn and unlearn the response without the amygdala.

They said their study suggests in the very young, it is primarily the amygdala that extinguishes fearful memories, while mechanisms independent of the amygdala develop later.

The study appeared in the Feb. 6 issue of The Journal of Neuroscience.