TIME COURSE OF EYE POSITION INFLUENCE IN PRIMATE INFERIOR COLLICULUS.
R.R.Metzger*1,2; A.M.Underhill1,2; J.M.Groh1,2 1. Psychological &
Brain Sciences, Dartmouth College, Hanover, NH, USA; 2. Ctr. for
Cognitive Neurosci., Dartmouth College, Hanover, NH, USA

Because the visual and auditory systems initially employ different
spatial frames of reference that can shift with respect to one another
when the eyes move, knowledge of eye position is an important
component of visual-auditory integration. We previously reported that
eye position modulates the auditory responses of approximately one
third of neurons in the primate inferior colliculus (IC; Neuron (2001)
29: 509), and the reference frame of these auditory responses appears
to be intermediate between head- and eye-centered. Here we explore the
time course of the effect of eye position on the responses of IC
neurons to sounds of 500 ms duration. Two monkeys were trained to
fixate visual stimuli at 3 locations while noise bursts were presented
from speakers at up to 15 azimuthal locations (90o left to 90o
right). The reference frame employed by the population of IC neurons
was stable throughout the 500 ms stimulus period. Sensitivity to both
eye position and sound location reached their maximum values within
150 ms of sound onset, and showed a similar time course
overall. Sensitivity to eye position was generally not present in the
spontaneous activity of IC neurons prior to sound onset. The presence
of an immediate effect of eye position on the auditory response
suggests that the eye position signal is available to IC neurons
without delay. The lack of sensitivity to eye position in the absence
of sound is further evidence that eye position modulates the acoustic
inputs to these neurons, but does not alter the activity of these
neurons in the absence of sound. Supported by: Sloan, McKnight,,
Whitehall, John Merck, ONR YIP, NIH 17778-19 to JMG