Rats, like humans, experience infantile amnesia-adults of both species don't remember the events that happen to them as infants. But a study in February's Behavioral Neuroscience (Vol. 120, No. 1) suggests that those early memories don't entirely disappear; instead, it's the ability to retrieve them that's the problem. And, the study finds, reducing the activity of the neurotransmitter GABA in a rat's brain can help it recover otherwise lost infant memories.
In a classic Pavlovian conditioning setup, psychologist Rick Richardson, PhD, and colleagues at the University of New South Wales in Australia paired bursts of white noise with electric shocks so that 18-day-old infant rats would learn to fear the white noise. Although adult rats would retain that memory of fear, infant rats tested 10 days later had already forgotten it. When the researchers played the white noise, a control group of these 28-day-old rats seldom exhibited the classic fear response of freezing in place.
A test group of the rats, though, received an injection of a compound called FG7142 before the 10-day test, and those rats were significantly more likely to freeze in fear.
In one sense this wasn't a surprise, according to Richardson. FG7142 reduces the activity of the neurotransmitter GABA, which has been found to suppress memories in adult rats. So FG7142 has been
found to facilitate remembering, he notes.
"It's kind of like GABA is a brake, and with FG7142 we're removing the brake," Richardson says.
But, for many years, researchers have debated whether infantile amnesia is qualitatively different than other forms of forgetting, or whether the same biological mechanisms are at work in both.
Now, Richardson says, his study suggests that some of the same systems that govern forgetting in adults may also be responsible for infantile amnesia.
"Infantile amnesia is such an overpowering effect that people have thought there must be a difference between it and other types of forgetting," Richardson says. "But that difference may be quantitative rather than qualitative."