Elizabeth Preston, writing at Inkfish:
How good are you at remembering something you learned two weeks earlier? What if during the intervening 14 days, your head was removed? One flatworm isn’t bothered by this scenario. After growing back its entire head and brain, it picks off pretty much where it left off.
The flatworms here are planarians, a nonparasitic genus. Their brains are incredibly simple, so simple in fact that they’re perhaps better described as ganglia, or bundles of nerves. That may help explain why, after their heads were removed and regrew, the flatworms could still remember the simple training researchers put them through before the “incident.” Planarian memories may reside not just in the brain, but elsewhere in the body.
But where? The scientists aren’t certain, but they suspect epigenetics—heritable changes in gene function that don’t change the underlying DNA sequence—may have something to do with the curious finding.