Abstract

A free running circadian rest–activity cycle is rare in sighted individuals living in a normal environment. Even more rare is a periodicity shorter than 24 hours, as observed in actigraphic recordings in a female patient during convalescence after a whiplash injury in a car accident. The documented free running period was 22.5 hours for 19 days. During the subsequent weeks re-entrainment occurred following re-establishment by a social zeitgeber, with a slightly early circadian phase of nocturnal melatonin onset relative to a late sleep period. Magnetic resonance imaging and cerebral angiography showed an aneurysm at the bifurcation of the right internal carotid artery, close to the circadian pacemaker structure (the suprachiasmatic nuclei), which was later occluded.