Journal of Neuroscience, Vol 15, 5152-5168, Copyright © 1995 by Society for Neuroscience
Binaural tuning of auditory units in the forebrain archistriatal gaze fields of the barn owl: local organization but no space map
YE Cohen and EI Knudsen
Department of Neurobiology, Stanford University School of Medicine, California 94305-5401, USA.
We identified a region in the archistriatum of the barn owl forebrain that
contains neurons sensitive to auditory stimuli. Nearly all of these neurons
are tuned for binaural localization cues. The archistriatum is known to be
the primary source of motor-related output from the avian forebrain and, in
barn owls, contributes to the control of gaze, much like the frontal eye
fields in monkeys. The auditory region is located in the medial portion of
the archistriatum, at the level of the anterior commissure, and is within
the region of the archistriatum from which head saccades can be elicited by
electrical microstimulation (see preceding companion article, Knudsen et
al., 1995). Free-field measurements revealed that auditory sites have
large, spatial receptive fields. However, within these large receptive
fields, responses are tuned sharply for sound source location. Dichotic
measurements showed that auditory sites are tuned broadly for frequency and
that the majority are tuned to particular values of interaural time
differences and interaural level differences, the principal cues used by
barn owls for sound localization. The tuning of sites to these binaural
cues is essentially independent of sound level. The auditory properties of
units in the medial archistriatum are similar to those of units in the
optic tectum, a structure that also contributes to gaze control. Unlike the
optic tectum, however, the auditory region of the archistriatum does not
contain a single, continuous auditory map of space. Instead, it is
organized into dorsoventral clusters of sites with similar binaural
(spatial) tuning. The different representations of auditory space in
closely related structures in the forebrain (archistriatum) and midbrain
(optic tectum) probably reflect the fact that the forebrain contributes to
a wide variety of sensorimotor tasks more complicated than gaze control.
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