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Abstract:
Many neurons in the barn owl's inferior colliculus (IC) exhibit auditory motion-direction sensitivity (MDS), i.e., they respond more to motion of a
sound source in one direction than to motion in the opposite direction. We investigated the cellular mechanisms underlying the phenomenon of auditory MDS
by microiontophoretically applying gamma-aminobutyric acid (GABA) or the GABA-antagonist bicuculline methiodide (BMI) while recording from
neurons in the owl's midbrain. In most cases GABA reduced the overall firing rate, whereas BMI increased it. In addition, 29 of the
motion-direction-sensitive cells completely lost their selectivity for the direction of auditory movement during administration of BMI. It had been proposed
that auditory MDS in the owl is due to inhibition. The present results show that GABAergic inhibition plays a role in the strengthening of MDS. We discuss
the data within the framework of the acoustic motion detector and with respect to microiontophoretic studies on visual motion detection and on inhibitory
mechanisms in the inferior colliculus.
