The hippocampus (a part of the brain associated with memory function) supports both recollection and familiarity memories when these memories are strong, contrary to current thinking, University of California, San Diego researchers report. The study has implications for the design of a neural prosthesis.

Recollection memory involves remembering specific details about a learning episode, such as where and when the episode occurred. Familiarity memory refers to remembering an item as previously encountered, but without any recall of specific details, such as recognizing someone’s face but recalling nothing else about that person.

Current thinking is that these two types of memories involve different regions in the brain’s medial temporal lobe: the hippocampus for recollection, the adjacent perirhinal cortex for familiarity.

The researchers developed a novel method that combined functional magnetic resonance imaging of the brain with a test in which study participants looked at a series of words and judged on a 20-point confidence scale if each word had been studied earlier or not. The data showed that the hippocampus was actively involved in both types of memories, contrary to earlier research.

The discovery peels away another layer of complexity in human memory, said researcher Larry R. Squire, PhD, a Research Career scientist at the VA Medical Center, San Diego and professor of psychiatry, neurosciences, and psychology at UC San Diego,. “If we really want to know how the brain works, the best guide is to think of it in terms of neuroanatomy. Psychological descriptions got us started, but a fundamental map and understanding will require a deeper biological foundation.” The findings may also help in diagnosing and treating patients with memory problems, he said.

For example, the findings suggest that an electronic neural prosthesis for the hippocampus (see Electronic hippocampal system turns long-term memory on and off, enhances cognition) may also be useful for familiarity-based memories (instead of treating two separate areas of the brain).

Ref.: Christine N. Smith, John T. Wixted, and Larry R. Squire, The Hippocampus Supports Both Recollection and Familiarity When Memories Are Strong, The Journal of Neuroscience, 2011; [DOI:10.1523/JNEUROSCI.3438-11.2011]

Ref.: Zhuang Song, Annette Jeneson, and Larry R. Squire, Medial Temporal Lobe Function and Recognition Memory: A Novel Approach to Separating the Contribution of Recollection and Familiarity, The Journal of Neuroscience, 2011; [DOI:10.1523/JNEUROSCI.3012-11.2011]