Scientists then tested a class of drugs called histone deacetylase, or HDAC, inhibitors on the mice.

BBC: NEWS | Health | Scientists 'reverse' memory loss

Appears this is regulated in part through the reactivation of polycomb repressor complexes by novel histone demethylases.

FORBES: SciCafe: Snapshots of four Hot Boston Labs

The change is suggested to be the result of a "histone code" - a process that sees genetic changes made to proteins called histones within cells' nuclei.

BBC: Honey bees' genetic code unlocked

Polycomb repressor complex modulation by histone demethylases .

FORBES: SciCafe: Snapshots of four Hot Boston Labs