Maturity Brings Richer Memories

Photo: Noa Ofen, a post-doc in the McGovern Institute for Brain Research and MIT's Department of Brain and Cognitive Sciences, and Professor John Gabrieli, co-director of the Clinical Research Center in the same department, sit by a monitor displaying an image of a child's brain, which was taken using the MRI scanning machine behind them. Photo courtesy of Donna Coveney, MIT

Cambridge, MA - August 5, 2007 -- McGovern Institute neuroscientists exploring how memory formation differs between children and adults have found that although the two groups have much in common, maturity brings richer memories.

In the August 5 advance online edition of Nature Neuroscience, John Gabrieli and colleagues report that children rival adults in forming basic memories, but adults do better at remembering the rich, contextual details of that information.

"This study takes an important step forward in our understanding of the neural basis of memory development," comments Daniel Schacter, an expert on memory at Harvard University who was not associated with the study. "It provides new insights into how children learn that are not only theoretically important, but could inform practical learning in everyday settings.

The ability to remember factual information - who, what, where, when - emerges gradually during childhood, and plays a critical role in education. The brain systems underlying it have been extensively studied in adults, but until now little was known about how they mature during child development, partly because of the difficulty of working with young children in a magnetic resonance imaging (MRI) scanner.

The new study indicates that a more developed prefrontal cortex (PFC) - an area of the brain long associated with higher-order thinking, planning, and reasoning - may be responsible for creating richer memories in adults.

"Activation in the PFC follows an upward slope with age in contextual memories. The older the subjects, the more powerful the activation in that area, explains Gabrieli, an associate member of MIT's McGovern Institute for Brain Research and the Grover Hermann Professor in Health Sciences and Technology and Cognitive Neuroscience, Department of Brain and Cognitive Sciences, Harvard-MIT Division of Health Sciences and Technology.

"That makes sense, because there's been a convergence of evidence that the PFC develops later than other brain regions, both functionally and structurally, and it is still developing during the teenage years. But this is the first study that asks how this area matures and contributes to learning."

For the study, Noa Ofen, a postdoctoral associate in Gabrieli's lab, forewarned 49 healthy volunteers ranging in age from eight to 24 that they would be tested on their recognition of 250 common scenes, such as a kitchen, shown to them as they lay in a functional magnetic resonance imaging scanner. She recorded their brain responses as the volunteers tried to commit each picture to memory. Shortly after the volunteers left the scanner, she showed them twice as many scenes. Had they seen each one before, and if so, how vividly did they recall the scene?

Ofen then went back to the brain activation patterns. In both children and adults, several areas in the PFC and the medial temporal lobe (MTL) showed higher activation at the time when subjects studied a scene they would later remember. No age-related differences showed up in the activation patterns of the MTL regions in children and adults, but differences did appear in the PFC when looking at pictures that were later correctly recognized.

Those age-related differences related to the quality of the volunteers' memories. The older the volunteers, the more frequently their correct answers were enriched with contextual detail. Going back to the brain scans, Ofen found that the enriched memories also correlated with more intense activation in a PFC area known to neuroscientists as Brodmann's Area 9.

"We found no change with age for memories without context," Ofen explains. "All the maturation is in memories with context. Our findings suggest that as we mature, we are able to create more contextually rich memories, and that ability evolves with a more mature PFC."

The team also used voxel-based morphometry to measure the concentration of gray matter in the activated brain regions. (A voxel is analogous to a 3-dimensional pixel.) The same PFC regions that showed age-related activation for the formation of contextual memory showed the strongest age-related structural changes. Counter-intuitively for non-neuroscientists, the gray matter in this region continuously shrinks rather than increases with maturity, most likely a result of the brain's pruning and fine-tuning the connectivity among neurons during development.

These findings indicate that different parts of the brain involved in declarative memory develop on different time scales. By age 8, most of the areas involved with basic declarative memory formation (the hippocampus and other areas of the MTL, and parts of the PFC) are on par with adults in both size and function. However, the area of the PFC associated with the contextual memory that is so important in higher learning is still developing and honing its skills into early adulthood.

"We also see that teenagers remain intermediaries and their PFCs are still developing," Gabrieli comments. "This region continues to grow between 16 and 17 year olds about to enter college and those young adults who are finishing college." He and Ofen are currently conducting studies including adults up to the age of 30, using a wider range of memory processes. The researchers hope that future studies about functional brain development in memory can benefit educational efforts to help children learn more effectively, perhaps by encouraging more attention to context.

Susan Whitefield-Gabrieli, a research associate at MIT's McGovern Institute, contributed to this research, in addition to scientists from Harvard University, New York University, and the University of California, Berkeley.

The study was funded by the National Institute of Mental Health.

Graphic: Subsequent memory activation in children, adolescents, and young adults: Activation in the Medial Temporal Lobe (MTL, lower brain scans) remains constant while activation in the Prefrontal Cortex (PFC, upper brain scans) increases from childhood to adulthood when successfully memorizing pictures with rich detail.

Image courtesy Julian Wong (independent artist) and Noa Ofen (McGovern Institute)