Researchers gain new insight into memory

A new study shows bigger role for brain structure when it comes to memory.

The brain's memory-processing center may guide both specific recollection and more general familiarity, a new study shows.

Memory specialists say that recollection is defined by the ability to call up specific details about a past event, while familiarity is simply knowing that someone or something has been encountered before, but with no particulars.

For instance, recollection is seeing a friend across a room and remembering his or her name; familiarity is seeing someone across the room you've seen before, but not recalling any details on where or when you've encountered the person, or exactly who the person is.

Researchers have long known that the hippocampus is critical for processing specific memories, but have generally assumed that familiarity was the job of adjacent areas in the medial temporal lobes of the brain.

Memory is impaired, often severely, in people whose hippocampus has been damaged by disease, such as Alzheimer's, or by trauma, such as oxygen deprivation following a heart attack or stroke.

But the latest research, published today in the journal Neuron, which looked more closely at a small group of patients who had suffered hippocampal damage, points strongly to a bigger role for the brain structure.

"Psychologists and neuroscientists have jumped at the notion that the hippocampus is critical only for the recollection component of recognition and that the adjacent cortical areas take care of familiarity only. But our findings suggest that conclusion may have been premature," said John Wixted, chairman of the University of California-San Diego psychology department and senior co-author of the study.

Wixted, Larry Squire, a professor of psychiatry and neuroscience at UCSD and the San Diego Veterans Affairs Health System, and colleagues compared six memory-impaired patients in whom brain imaging showed that damage was localized to the brains of six healthy subjects of the same age.

All the subjects were given lists of common words to study. After a short wait, they were given a list containing both the old and new words, and asked to go over them and rate their confidence that each word was new or old.

The researchers used a statistical model that is able to establish whether both familiarity and recollection memory functions were in play.

After controlling for memory strength -- that is, giving the brain-damaged patients shorter word lists than those used by the controls -- the researchers found that the recognition accuracy of both groups was almost identical.

The similarity suggests that recollection, along with familiarity, was operative even in patients with extensive hippocampal damage.

And that means, the researchers write, that both the familiarity and recollection processes appear to be supported by the hippocampus and adjacent structures.

"This work is helping us piece together how the brain accomplishes learning and memory, and this is important in efforts to develop treatments for memory disorders," Squire said.