TORONTO - Gaps in short-term memory in people with amnesia are most noticeable when a person tries to recall new information that is unfamiliar, while information that is familiar because of repetition is more likely to be retained, a new study shows.
A young woman who has had amnesia since birth has shown scientists at Baycrest's Rotman Research Institute that she is impaired when it comes to retaining unfamiliar faces, but when she is shown a photo of someone familiar, such as a Hollywood celebrity, she can more easily recall it a few seconds later.
The 22-year-old woman, known as "HC," has amnesia as a result of developing only half the normal volume of the hippocampus in her brain because of oxygen deprivation during her first week of life. The hippocampus is a part of the brain that plays an important role in consolidating information from short- and long-term memory.
HC functions relatively normally despite her impairment and is a "good sport" about taking part in research, said lead investigator Nathan Rose, a post-doctoral fellow in cognitive neuroscience at the institute.
"She has participated in research for a while now, and she really enjoys it. She's eager to come in and help us out, and she sort of views doing these tasks as little games."
In one experiment, she and a control group of 20 undergraduate students were shown 40 famous faces and 40 non-famous faces and asked to recognize them after a short delay.
"We showed a picture of a famous face very briefly, just for a second, and then there was a brief delay, either one or eight seconds, and then we showed two faces, and just said, 'Which one did you just see?'" Rose explained in an interview.
"And the two faces, one was the exact match, and one was a morphed version of that face — a different face."
HC scored 70 per cent in accuracy compared to the control group's 81 per cent on non-famous faces. But her recognition of famous faces was 85 per cent — the exact same as for the control group.
HC is a film buff and celebrity watcher. When researchers showed her a photo of Paris Hilton and asked her a few seconds later whether she recognized the face, she had no problem remembering the Hollywood party girl.
In another short-term memory task, participants were presented with a single word — a high-frequency common word, a low-frequency word, or a non-word. Then the person had to do a counting exercise for several seconds, and recall the word.
"In the case of high-frequency words, HC was able to do it pretty well, but for the non-words, she was just hopeless," Rose said.
The single case study, which was done in collaboration with the University of Toronto, is considered important for understanding the nuanced workings of short-term memory in people with a memory disorder such as amnesia.
People with amnesia have deficits in long-term memory, yet often seem to function fine by relying on their short-term memory, which has traditionally been thought to be intact. However, a growing body of research, including this latest study, shows that "working memory" is also impaired in this population.
"Our findings add to the growing evidence that short-term memory is not intact in amnesia," Dr. Fergus Craik, a Baycrest scientist who collaborated on the study, said in a release. "However, to my knowledge, we are the first to directly test the hypothesis that short-term memory functions better if the information has some past familiarity to the person."
That may explain why individuals with amnesia are often able to compensate for their profound memory deficit in social settings by seeking out familiar cues to support short-term memory.
Rose said it helps illustrate how important it is to have things in a familiar context when an older adult has a serious memory problem.
The person can navigate around their home city or apartment relatively well, he noted, "but then you move them to a nursing home or something, they have a really hard time figuring out how to get around."
The study was posted online in the science journal Neuropsychologia, ahead of the print publication.