69���˵���

A 22-year-old woman who has had amnesia since birth has demonstrated she can’t hold a single face or word in short-term memory – unless the information is familiar to her.

When presented with a face such as Hollywood celebrity Paris Hilton and asked to recognize the face a few seconds later, the woman, known as HC, could remember the A-list party girl. However, she was unable to remember novel, unfamiliar faces as well as healthy age, education and IQ- matched control participants. HC’s short-term memory was even impaired for faces that were famous, but whom HC did not know, such as former U.S. first lady Hillary Clinton.
 
The single case study with the woman was led by Baycrest’s Rotman Research Institute, in collaboration with the University of Toronto. The study is posted online in the science journal Neuropsychologia, in advance of print publication.

The finding is important for understanding the nuanced workings of short-term memory in people with a devastating memory disorder such as amnesia. The study provides the first strong evidence that the short-term memory deficit in individuals with amnesia is most apparent only when the individual is trying to recall new information that is “unfamiliar” to them. When information is already “familiar” from past repetitive exposure, it is more likely to be retained in short-term memory, also known as “working memory.”

Despite HC’s severe memory impairment – the result of experiencing hypoxia (loss of oxygen) in the first week of life – she is a relatively normal functioning individual and college graduate, who is an avid film buff and celebrity watcher.

“This woman is missing 50 percent of the normal volume of her hippocampus with no obvious damage to other parts of her brain. This provides an extraordinary opportunity to generate new insights about how this crucial memory centre of the brain affects both short-term and long-term memory,” said lead investigator Nathan Rose, a post-doctoral fellow in Cognitive Neuroscience at Baycrest’s Rotman Research Institute. Rose conducted the study with  Fergus Craik, a University of Toronto emeritus professor, and York University professor Shayna Rosenbaum.

“We wanted to test if HC’s short-term memory was impaired, and, if so, whether this impairment only existed for novel stimuli. That is exactly what we found.”

Amnestic individuals have profound deficits in long term memory and yet many seem to function fine by relying on their short-term memory which has traditionally been thought to be intact. However, a growing body of scientific evidence, including this latest study, is showing 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. 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,” said Craik, a collaborator on the study and co-editor of the Oxford Handbook of Memory.

The findings 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.

Single cases with a clear pattern of specific brain deficits, such as HC, are incredibly rare and important for neuroscience. These cases enable researchers to generate more precise data that demonstrates a specific brain area is necessary for certain memory functions. Most individuals with amnesia typically present with diffuse damage in the brain which can complicate brain imaging and behavioural data interpretation.