Philip H.-S. Jen
Div. of Biological Sciences, Univ. of Missouri, Columbia, MO 65211
The influence of sound direction on frequency tuning of 64 inferior collicular neurons of the big brown bat was studied by comparing the best frequency and Q[inf 10-dB], Q[inf 30-dB], and Q[inf 50-dB] values of each neuron determined from five sound directions between (plus or minus)70(degrees) in azimuth. Sound direction did not affect the BF of all but three neurons by more than 5 kHz but it affected at least one Q value of 51 (80%) neurons by more than 50%. Whereas sound direction affected all three Q values of 9 (14%) neurons, it afected no more than two Q values of the remaining 42 (66%) neurons. Sound direction also affected the shape of frequency tuning curves in 21 (32.8%) neurons. Frequency tuning of 30 collicular neurons to different sound directions was also studied before and after ionophoretical application of bicuculline to each recorded neuron. Bicuculline application not only lowered the minimum threshold of 20 (67%) neurons in all sound directions, it also shifted the lowest MT of 10 (33%) neurons to a different sound direction. In addition, it reduced the Q[inf 10-dB] values of 18 (60%) neurons and changed the shape of the frequency tuning curves of 21 (70%) neurons.