A recent study of REM Sleep Behavior Disorder, in which people act out their dreams while sleeping, found that those suffering from it have violent dreams far more often than healthy people. The researchers suggest this may indicate the "purpose" of dreams: to rehearse threatening situations.

A rat study recently reported in Nature sheds some light on what we all know: that habits are hard to break and easily re-kindled. Maybe this will help us work out the important next step: how to stop that being so!