| Abstract #862, Date 2/17/99, Session Y6, Poster (B127) |
| Lateral inhibition in frequency tuning of bat central auditory neurons |
| *Y. Lu (University of Missouri, Columbia, Missouri); Q.C. Chen (Central China Normal University, Wuhan, P.R.China); P.H.-S. Jen (University of Missouri, Columbia, Missouri) |
During sensory signal processing, signals are synaptically integrated and sharpened with excitation and inhibition. One type of inhibition is the lateral inhibition which accounts for certain perceptual phenomena like the Mach band contour enhancement. In auditory signal processing, the lateral inhibition sharpens frequency tuning and reduces the ambiguity in encoding frequency at high stimulus intensities. Using two-tone inhibition method, we studied the lateral inhibition in frequency tuning of neurons in the inferior colliculus (IC) and the auditory cortex (AC) of the big brown bat, Eptesicus fuscus. Excitatory frequency tuning curves of central auditory neurons were either simple V shaped, upper threshold, or double-peaked. Inhibitory frequency tuning curves can be measured at one flank or both flanks of the excitatory frequency tuning curve. Most inhibitory minimum thresholds were higher than excitatory minimum thresholds by 10-40 dB. Whereas lateral inhibition sharpened frequency tuning, neurons with two-flank lateral inhibitory areas had sharper tuning curves and smaller excitatory areas than neurons with one-flank inhibitory areas. The closer the inhibitory area was to the excitatory area, the sharper the frequency tuning became. The degree of lateral inhibition increased with the intensity of inhibitory tone. Lateral inhibition only occurred within an effective temporal window within which the degree of lateral inhibition changed with the interval between the excitatory and inhibitory tones. During the maximal lateral inhibition, IC and AC neurons had minimal number of impulses and longest response latencies. Bicuculline application changed excitatory frequency tuning curves into simple V shaped. Post drug excitatory frequency tuning curves either completely or partially covered the predrug inhibitory frequency tuning curves. AC neurons were organized in columns and all excitatory and inhibitory frequency tuning curves sequentially isolated within orthogonally penetrated electrodes were similar. |