The researchers used extremely high-resolution functional magnetic resonance imaging (fMRI) and software developed at UCLA's Ahmanson-Lovelace Brain Mapping Center to study blood flow within the hippocampus as 10 human volunteers learned to associate names with faces.
The study identified areas within the hippocampus -- the cornu ammonis and the dentate gyrus -- as highly active only during encoding of the face-name pairs. This activity decreased as associations were learned. The subiculum, another area of the hippocampus, was active primarily during the retrieval of the face-name associations. Activity in the subiculum also decreased as retrieval became more practiced.
Previous studies have demonstrated the importance of the hippocampus in forming memories. However, no studies until now have directly examined how activity patterns within specific substructures change during learning.
"Our findings demonstrate that memory formation is a dynamic process, with subdivisions within the hippocampus making distinct but changing contributions as learning takes place," said lead author Michael M. Zeineh, a Brain Mapping Center researcher and student in the David Geffen School of Medicine's Medical Scientist Training Program. "Brain activity increases as information is introduced, then diminishes as the new information becomes better learned.
"As knowledge about the brain's complex circuitry grows, neuroscientists will be better able to understand and address a host of debilitating neurological disorders, from Alzheimer's disease to epilepsy to damage caused by head injuries," Zeineh said.