Journal of Neuroscience, Vol 5, 317-329, Copyright © 1985 by Society for Neuroscience
Directional asymmetries of optokinetic nystagmus: developmental changes and relation to the accessory optic system and to the vestibular system
J Wallman and J Velez
To investigate the relation of the directional organization of the
accessory optic system (AOS) to that of its principal behavioral output,
optokinetic nystagmus (OKN), we measured the eye velocity during OKN in
response to 14 directions of stimulus motion, including horizontal,
vertical, cyclorotational (rotations about the optic axis), and
intermediate directions in both neonatal and older chickens. We found
substantial and consistent OKN asymmetries between opposite directions of
stimulus motion when the stimuli were viewed monocularly; the asymmetries
were largest to combinations of cyclorotational and vertical stimulus
motion and to horizontal stimulus motion. The highest gain of OKN in the
older animals was in response to two directions of stimulus motion:
horizontal temporal-to-nasal and a combination of excyclorotation and
downward. In addition, OKN to upward moving stimuli was consistently better
than to downward stimuli. The association of high OKN gain in the older
animals with the pattern of visual motion produced by head movements
exciting the contralateral anterior semicircular canal suggests a possible
vestibular organization of the optokinetic system. The response pattern of
the newly hatched chickens differed in three ways from that of the older
animals: in the non- horizontal stimulus directions the best direction was
to upward and excyclorotational stimulus motion; the horizontal asymmetry
was somewhat less strong; and the OKN gain to high velocity horizontal
stimulus motion was lower. The change in directional pattern of OKN over
the first weeks of life appears related to a corresponding change in
anatomy of the AOS.
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