Cataplexy versus REM sleep atonia: a neurophysiological study

Narcolepsy is a disorder of the central nervous system, characterised by
excessive daytime sleepiness and transient episodes of muscle weakness. These
attacks are called 'cataplexy' and are induced by emotions. At the present, it
is unclear what mechanism is responsible for these attacks. Treatment is
therefore only available on empirical base.
The current theory is that cataplexy is equivalent to the paralysis every
individual has during dreaming, the so-called REM sleep atonia. During this
state, the neuron in the spinal cord, responsible for muscle tone, is
temporarily inhibited.
Whether this is due to pre- or postsynaptic influences, is not known.

Is the muscle weakness during cataplexy due to pre- or postsynaptic inhibition?
In other words: what happens with the H-reflex and Magnetic Evoked Potential
during REM sleep and cataplexy?

In an experimemtal setting, one of the nerves in the leg will be stimulated
with an electrical current in order to measure the H-reflex. At the same time,
a certain area of the brain that is responsible for movements of the legs, will
be stimulated with a strong magnet. Both techniques will be performed during
sleep in all subjects, in narcoleptic patients also during cataplexy. In this
way, data can be obtained about the excitability of the alpha motor neuron in
the spinal cord.

Both techniques have been used worldwide for years and are safe. The burden for
the subjects will be a disturbed sleep as awakening upon the magnetic stimulus
is likely. Since the narcoleptics using medication must stop this during two
weeks, they have the risk of the cataplexy getting worse. However, this is
reversible as soon as the medication is restarted with no risk of permanent
damage whatsoever.