Washington, Nov 13 Newborn neurons in the brain make room for new memories by moving out the old ones, concludes a new mice study.

The study provides some of the first evidence that new neurons sprouted in the hippocampus (a brain region associated with learning and memory) cause the decay of short-term fear memories in that brain region, without an overall memory loss.

Study's lead author Kaoru Inokuchi of The University of Toyama in Japan and colleagues say the discovery shows a more important role than many would have anticipated for the erasure of memories.

They propose that the birth of new neurons promotes the gradual loss of memory traces from the hippocampus as those memories are transferred elsewhere in the brain for permanent storage.

Although they examined this process only in the context of fear memory, Inokuchi says he "thinks all memories that are initially stored in the hippocampus are influenced by this process."

In effect, the new results suggest that failure of neurogenesis will lead to problems because the brain's short-term memory is literally full.

In Inokuchi's words, we may perhaps experience difficulties in acquiring new information because the storage capacity of the hippocampus is "occupied by un-erased old memories."

Of course, Inokuchi added, "our finding does not necessary deny the important role of neurogenesis in memory acquisition."

He says hippocampal neurogenesis could have a dual role, in both erasing old memories and acquiring new ones.

The study has been reported in the November 13th issue of the journal Cell, a Cell Press publication. (ANI)