Directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, to sounds delivered from selected horizontal and vertical angles.
Under free field stimulation conditions, directional sensitivity of 336 inferior collicular (IC) neurons of 6 Eptesicus fuscus was studied by recording the minimum threshold (MT) and number of impulses of each neuron to a best frequency (BF) sound delivered from selected horizontal and vertical angles. An auditory response center was determined for each neuron by delivering a BF sound from a specific point of the bat's frontal auditory space. At the response center, the neuron had maximal directional sensitivity and lowest MT. Auditory response centers of all 336 IC neurons studied were located in the contralateral frontal auditory space and they shifted from lateral angles toward the midline with increasing BF. Sound direction affected the sharpness of frequency tuning (i.e. Q10-dB value) but not the BF and overall shape of the frequency threshold curve of a neuron. Sound direction also affected the MTs, number of impulses and intensity-rate functions but not the discharge patterns of IC neurons. High BF neurons generally had sharper directional sensitivity than low BF neurons. Bending downward the pinna contralateral to the recording site increased a neuron's MT and shifted its response center downward and toward the midline of the bat's frontal auditory space. The effect of pinna bending on a neuron's MT and impulse directional curves can be explained on the basis of variation of its auditory response area and its MT.
Jen
P H
PH
Division of Biological Sciences, University of Missouri, Columbia 65211.
Wu
M
M
D000161:Acoustic Stimulation; D000818:Animals; D002685:Chiroptera / Q000502:physiology*; D007245:Inferior Colliculi / Q000502:physiology*; D013017:Sound Localization