Representation of sound source direction in the superior colliculus of the guinea pig in a virtual auditory
environment.
S.J. Sterbing,K. Hartung & K.-P. Hoffmann
Experimental Brain Research, 142: 570-577, 2002
- The deep layers of the superior colliculus (SC) receive visual, auditory, and somatosensory input. A major
function of the SC is the control of orientation movements of the eye, head, and pinna. While a topographical map
for sound source direction remains elusive in primary auditory structures of mammals, such a map for azimuthal
sound source directions has been reported in the deep layers of the SC. Moreover, a gradient of elevation tuning
has been also seen in the SC of ferrets and cats. Here we demonstrate that a virtual auditory environment can be
used to reveal azimuthal and elevational topography for auditory spatial receptive fields in neurons in the SC
of guinea pigs. Individual, head-related transfer functions (HRTF) were measured in ten guinea pigs for 122 directions
in the upper hemispheric field and convolved with white noise. Many neurons (39%) in the deep layers showed robust
responses to these virtual sounds, and the majority of these neurons had small spatial receptive fields that were
restricted to the contralateral hemifield. Best directions varied from 0 degree to 135 degree azimuth along the
contralateral side and from -10 degree to 60 degree elevation. Like previous studies using free-field stimulation,
a gradient of best azimuth direction was found along the rostral-caudal axis, with rear directions represented
caudally and front directions rostrally. The topographical organization for best elevations had not been studied
previously in the guinea pig. We found that it roughly followed the mediolateral axis, with preference for high
elevations represented medially and low elevations laterally. A similar organization using free-field stimulation
has been reported in the ferret.
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