Memories formed in one part of the brain are replayed and
transferred to a different area of the brain during rest, according
to a new UCL study in rats.
The finding suggests that replay of previous experiences during
rest is important for memory consolidation, a process whereby the
brain stabilises and preserves memories for quick recall in the
future. Understanding the physiological mechanism of this is
essential for tackling amnesiac conditions such as Alzheimer's
disease, where memory consolidation is affected.
Lead researcher, Dr Freyja Ólafsdóttir (UCL Cell &
Developmental Biology), said: "We want to understand how a healthy
brain stores and accesses memories as this will give us a window
into how conditions such as Alzheimer's disease disrupt the
process. We know people with Alzheimer's have difficulty recalling
the recent past but can often readily remember childhood memories,
which seem more resilient. The parts of the brain we studied are
some of the first regions affected in Alzheimer's and now we know
they are also involved in memory consolidation."
The study investigated the role of sleep in memory consolidation
by simultaneously studying two areas of the brain as the rats
rested following activity.
Six rats each ran for 30 minutes on a six metre long track
before resting for 90 minutes. During rest, the team studied the
responses of place cells in the hippocampus, where memories are
formed, and grid cells in the entorhinal cortex, where the memories
were found to transfer to.
The response of the place cells showed that the rats re-ran the
track in their minds as they rested but did so at speeds 10-20
times faster than they experienced in reality. The same replay
happened almost simultaneously, with a 10 millisecond delay, in
grid cells located in a different part of the brain, suggesting
that the rats' memories transferred from one part of the brain to
another.
Study supervisor, Dr Caswell Barry (UCL Cell & Developmental
Biology), said: "This is the first time we've seen coordinated
replay between two areas of the brain known to be important for
memory, suggesting a filing of memories from one area to another.
The hippocampus constantly absorbs information but it seems it
can't store everything so replays the important memories for long
term storage and transfers them to the entorhinal cortex, and
possibly on to other areas of the brain, for safe-keeping and easy
access."
The scientists plan to investigate memory transfer to other
areas of the brain and replay in rats with Alzheimer's disease to
better understand the memory consolidation mechanism and the link
between quality of sleep and amnesiac conditions.
The paper, Coordinated grid and place cell replay during rest, is
published in the Nature Neuroscience.