Development of the declarative memory system in the human brain

Brain regions that are involved in memory formation, particularly medial temporal lobe (MTL) structures and lateral prefrontal cortex (PFC), have been identified in adults, but not in children. We investigated the development of brain regions involved in memory formation in 49 children and adults (ages 8‐24), who studied scenes during functional magnetic resonance imaging. Recognition memory for vividly recollected scenes improved with age. There was greater activation for subsequently remembered scenes than there was for forgotten scenes in MTL and PFC regions. These activations increased with age in specific PFC, but not in MTL, regions. PFC, but not MTL, activations correlated with developmental gains in memory for details of experiences. Voxel-based morphometry indicated that gray matter volume in PFC, but not in MTL, regions reduced with age. These results suggest that PFC regions that are important for the formation of detailed memories for experiences have a prolonged maturational trajectory. The neural systems mediating declarative or explicit memory (memory for events and facts) in adults have been identified through convergent lesion and functional neuroimaging evidence, but little is known about the normal development of declarative memory systems from childhood through adulthood. In adults, MTL structures, including the hippocampus and surrounding perirhinal and parahippocampal cortices, are essential for the formation of new declarative memories; bilateral MTL injury results in global amnesia that is defined by an inability to form new declarative memories 1,2 . PFC is not essential for memory formation, but PFC lesions impair declarative memory for contextual details of an experience (source memory) 3,4 . Functional neuroimaging studies in healthy adults have found that greater magnitudes of MTL and PFC activation during encoding correlate, on a stimulus-by-stimulus or event-related basis, with successful memory formation, as evidenced by accurate subsequent memory for scenes, words and faces 5‐9 .