Memory tests performed with amnesiacs have enabled researchers to refute a long-held belief in an essential difference between long-and short-term memories.
In the study, researchers from the University of Pennsylvania determined that the hippocampus -- a seahorse shaped structure in the middle of the brain - was just as important for retrieving certain types of short-term memories as it is for long-term memories.
Their findings, published in the Journal of Neuroscience, overturn the established view of the hippocampus and offers insight on how the brain forms and recalls memories by piecing together related bits of experiences.
"For over 40 years, the chief paradigm has been that the hippocampus was important for creating long-term memory but not short-term or working memory," said Ingrid Olson, a member of Penn's Department of Psychology and researcher at Penn's Center for Cognitive Neuroscience. "However, our data show that one type of working memory, working memory for the relationship between bits of information, is dependent on the hippocampus.
According to Olson, how much time has elapsed - or, in other words, the age of the memory -- is less important to the hippocampus than is the requirement to form connections between pieces of information to create a coherent episode of memory.
"I can remember what my keys look like, and I can remember where the coffee table is located, but the critical test of my memory is if I can remember that I left my keys on the coffee table," Olson said.
To study the role of the hippocampus in forming short-term memories, Olson and her colleagues used visual memory tests to study the ability of nine amnesiacs to recall images presented to them on a screen. These subjects all suffered from damage to their hippocampi and related brain structures, and their lives are ruled by the fact that they can no longer form long-term memories, much like characters from the movies "Memento" or "Finding Nemo."