The Journal of Neuroscience, February 1, 1999, 19(3):1149-1163
Interaural Intensity Difference Processing in Auditory Midbrain
Neurons: Effects of a Transient Early Inhibitory Input
Jeffrey P.
Oswald,
Achim
Klug, and
Thomas J.
Park
The Neurobiology Group, Department of Biological Sciences and The
Biological Resource Laboratory, University of Illinois at Chicago,
Chicago, Illinois 60607
Interaural intensity differences (IIDs) are important cues that
animals use to localize high-frequency sounds. Neurons sensitive to
IIDs are excited by stimulation of one ear and inhibited by stimulation
of the other ear, such that the response magnitude of the cell depends
on the relative strengths of the two inputs, which in turn depends on
the sound intensities at the ears. In the auditory midbrain nucleus,
the inferior colliculus (IC), many IID-sensitive neurons have response
functions that decline steeply from maximum to zero spikes as a
function of IID. However, there are also many neurons with much more
shallow response functions that do not decline to zero spikes. We
present evidence from single-unit recordings in the Free-tailed bat's
IC that this partially inhibited response pattern is a result of the
inhibitory input to these cells being very brief (~2 msec). Of the
cells sampled, 54 of 137 (40%) achieved partial inhibition when tested
with 60 msec tones, and the inhibition to these 54 cells occurred
primarily during the first few milliseconds of the excitatory response. Consequently, the initial component of the response was highly sensitive to IIDs, whereas the later component was primarily
insensitive to IIDs. Each of the 54 "partially inhibited" cells was
able to reach complete inhibition with very short stimuli, such as
simulated bat echolocation calls that invoked only the initial,
IID-sensitive component. Local application of inhibitory transmitter
antagonists disabled the short inhibitory input, indicating that this
response pattern is created within the IC.
Key words:
interaural intensity difference; inferior colliculus; sound localization; inhibition; auditory processing; binaural
Copyright © 1999 Society for Neuroscience 0270-6474/99/1931149-15$05.00/0
