"It was previously known that the hippocampus processes recent memory, but that the hippocampus did not store memories permanently. We were able to determine that it is the anterior cingulate cortex where older, or lifelong, memories are stored and recalled," said Dr. Paul Frankland, the study's co-lead author, a scientist in the Sick Kids Research Institute, and assistant professor of physiology at the University of Toronto.
The formation of new memories is thought to involve the strengthening of synaptic connections between groups of neurons. Remembering involves the reactivation of the same group, or network, of neurons. As memories age, the networks gradually change. Initially, memories for everyday life events appear to depend on networks in the region of the brain called the hippocampus. However, over time, these memories become increasingly dependent upon networks in the region of the brain called the cortex.
"We believe there is active interaction between the hippocampus and cortex, and that the transfer process of memories between these two regions in the brain occurs over several weeks, and likely during sleep," added Dr. Frankland, holder of the Canada Research Chair in Cognitive Neurobiology.
The researchers used a series of strategies with mice, including a mouse model with an altered form of a gene called CaMkinase II, which eliminates the ability to recall old memories, to identify the role of the anterior cingulate cortex.
"Most people define memory as their collective lifetime experiences. These memories colour who we are, yet until now, we've been mystified by how the brain saves and retrieves them," said Dr. Alcino Sliva, the study's principal investigator and professor of neurobiology, psychiatry and psychology at the David Geffen School of Medicine at UCLA. "Now that we know where to look, we're one step closer to developing drugs to target genes or processes of the brain that may be related to memory disorders."
Other authors on the paper include Dr. Bruno Bontempi, co-lead author, Dr. Lynn Talton, and Dr. Leszek Kaczmarek. The US National Institute on Aging funded the study.
The Hospital for Sick Children, affiliated with the University of Toronto, is Canada's most research-intensive hospital and the largest centre dedicated to improving children's health in the country. Its mission is to provide the best in family-centred, compassionate care, to lead in scientific and clinical advancement, and to prepare the next generation of leaders in child health. For more information, please visit www.sickkids.ca.