Cataplexy: 'tonic immobility' rather than 'REM-sleep atonia'?
BACKGROUND
Cataplexy, a sudden loss of muscle tone in response to strong emotions, is the most specific symptom of narcolepsy. It is currently thought to be due to disturbed rapid eye movement (REM) sleep regulation, and portrayed as REM sleep atonia occurring at the wrong time. However, there are several arguments against including cataplexy in the 'state boundary control' hypothesis. It does not explain why cataplexy is triggered by emotions, and recent studies in narcoleptic dogs showed that REM sleep regulatory mechanisms were in fact intact in these animals.


METHODS
We review the literature on the REM sleep dissociation theory, discuss the merits and demerits of the theory, and propose an alternative hypothesis explaining cataplexy.


RESULTS
Cataplexy may represent an atavism (recurrence of an ancestral characteristic) of tonic immobility. Tonic immobility (TI) denotes a condition in which an animal is rendered immobile when faced with danger. Arguments in favor of the TI hypotheses are that it explains the emotional triggering. Furthermore, centers regulating narcolepsy and TI are both located in the lateral hypothalamic area. Finally, several drugs known for their ameliorating effect on cataplexy reduce the frequency and duration of TI in animals.


CONCLUSIONS
Cataplexy may be due to a mechanism different from the other clinical symptoms of narcolepsy.
Department of Neurology & Clinical Neurophysiology, Leiden University Medical Centre, P.O. Box 9600, 2300 RC Leiden, The Netherlands.
Sebastiaan
S
Overeem
Gert Jan
GJ
Lammers
J Gert
JG
van Dijk