Provocative new research suggests the learning process could mean that old memories are forgotten because of the need to reorganize brain circuits.
Drs. Paul Frankland and Sheena Josselyn, neuroscientists at the University of Toronto, argue that formation of new neurons in the hippocampus — a brain region known for its importance in learning and remembering — could cause forgetting of old memories by fostering a reorganization that clears old memories, reduces interference and increases the capacity for new learning.
The new theory may help to explain longstanding medical mysteries.
Researchers have long known of the phenomenon of infantile amnesia: This refers to the absence of long-term memory of events occurring within the first 2-3 years of life, and little long-term memories for events occurring until about 7 years of age.
Studies have shown that though young children can remember events in the short term, these memories do not persist.
This new study shows that this amnesia is associated with high levels of new neuron production — a process called neurogenesis — in the hippocampus, and that more permanent memory formation is associated with a reduction in neurogenesis.
Frankland and Josselyn’s research looked at the retention of memories in young mice in which they suppressed the usual high levels of neurogenesis in the hippocampus (thereby replicating the circuit stability normally observed in adult mice).
They also studied older mice in which they stimulated increased neurogenesis (thereby replicating the conditions normally seen in younger mice).
From the findings, researchers were able to show a cause-and-effect relationship between a reduction in neurogenesis and increased remembering, and the converse, decreased remembering when neurogenesis increased.
Researchers believe the study provides insight on why we have no memories from our earliest years.