The brain is quite the circus act: It constantly juggles
the complex job of processing a daily barrage of new
experiences with the equally daunting task of storing
memories. But scientists never understood how it managed
to pull this off. Now, two studies published in June reveal
it’s because neurons, brain cells that transmit messages, alter
their DNA constantly.
The trick is methylation and demethylation — adding
and removing chemical tags called methyl groups to specific
locations on DNA that turn genes on and off without editing
the genetic code itself.
Researchers recently discovered that adult mouse neurons
methylate and demethylate — startling, since experts thought
methylation happened only during brain development
and then became permanent, to establish cells’ identities.
Given these findings, University of Alabama at Birmingham
neurobiologist David Sweatt and Johns Hopkins University
neurobiologist Hongjun Song wondered if methyl groups
affected long-term memory formation.
The researchers knew that neurons fire at a steady
rate to form memories but also that new experiences can
overstimulate them. To mimic a learning experience and see
how neurons keep their activity in check, each team tweaked
rat or mouse neurons’ firing rates, genetically or with drugs.
To cope, the neurons used methylation and demethylation
like a volume knob, constantly adjusting the signal strength
of connected neurons by turning on or off the genes that
make the signal receptors. This knowledge brings us one
step closer to understanding memory at the molecular level.