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Abstract:
Nystagmus is a pattern of eye movement characterized by
smooth rotations of the eye in one direction and rapid rotations in
the opposite direction that reset eye position. Periodic
alternating nystagmus (PAN) is a form of uncontrollable nystagmus
that has been described as an unstable but amplitude-limited
oscillation. PAN has been observed previously only in subjects with
vestibulo-cerebellar damage. We describe results in which PAN can
be produced in normal subjects by prolonged rotation in darkness.
We propose a new model in which the neural circuits that control
eye movement are inherently unstable, but this instability is kept
in check under normal circumstances by the cerebellum.
Circumstances which alter this cerebellar restraint, such as
vestibulo-cerebellar damage or plasticity due to rotation in
darkness can lead to PAN.
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