The Journal of Neuroscience, November 1, 2001, 21(21):8586-8593
A Topographic Instructive Signal Guides the Adjustment of the
Auditory Space Map in the Optic Tectum
Peter S.
Hyde and
Eric I.
Knudsen
Department of Neurobiology, Stanford University School of Medicine,
Stanford, California 94305
Maps of auditory space in the midbrain of the barn owl (Tyto
alba) are calibrated by visual experience. When owls are raised wearing prismatic spectacles that displace the visual field in azimuth,
the auditory receptive fields of neurons in the optic tectum shift to
compensate for the optical displacement of the visual field. This shift
results primarily from a shift in the tuning of tectal neurons for
interaural time difference. The visually based instructive
signal that guides this plasticity could be based on a topographic,
point-by-point comparison between auditory and visual space maps or on
a foveation-dependent visual assessment of the accuracy of auditory
orienting responses. To distinguish between these two possibilities, we
subjected owls to optical conditions that differed in the center of
gaze and the visual periphery. A topographic signal would cause the
portions of the space map representing the central and peripheral
regions of visual space to adjust differently, according to the optical
conditions that exist in each region. In contrast, a foveation-based
signal would cause both portions of the map to adjust similarly,
according to the optical conditions that exist at the center of gaze.
In six of seven experiments, adaptive changes were as predicted by a
topographic instructive signal. Although the results do not rule out
the possible contribution of a foveation-based signal, they demonstrate
that a topographic instructive signal is, indeed, involved in the
calibration of the auditory space map in the barn owl optic tectum.
Key words:
supervised learning; superior colliculus; multimodal
maps; instructive signal; plasticity; barn owl
Copyright © 2001 Society for Neuroscience 0270-6474/01/21218586-08$05.00/0
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