"White Noise" Non-Linear Analysis of Inferior Colliculus Neural Responses in the Little Brown Bat, Myotis Lucifugus

169 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.Echolocation is the primary means by which insectivorous bats orient in flight and capture insect prey. FM bats, whose calls consist of a short (1-5 ms) frequency-modulated (FM) sweep, were chosen for this study. The goal of these experiments was to develop techniques for efficiently characterizing important response properties of auditory neurons from a species of FM bat, Myotis lucifugus. The consistently short (1-5 ms) duration of echolocation calls emitted by the little brown bat, Myotis lucifugus, permitted approximating the sounds heard during hunting with a train of short, constant-duration pulses. In contrast to standard approaches (in which acoustic parameters are changed one at a time), this study used non-linear techniques and measured responses to pulse trains in which both amplitude and inter-pulse gap were randomly varied. "White noise" analysis techniques, including both the calculation of system kernels and new cross-correlational measures, were used. Single-unit activity was recorded from 82 neurons in the inferior colliculus (IC). The power of the techniques is evident from their ability to reveal many different characteristics of the neurons' responses simultaneously. It was found that basic response properties such as latency, threshold, and rate-level function could all be derived at the same time; these responses were generally comparable to those determined using standard methods. In addition, other measures were only possible because of these new techniques. The flat autocorrelation properties of the stimulus made it possible to detect periodic patterns in the neural discharges for 5% of the neurons studied. The techniques also allowed detection of inhibition (despite the use of extracellular recordings) and of delay-sensitive facilitation (in 11% of IC neurons). These response features could not have been determined using standard techniques unless numerous different experiments were carried out to specifically investigate these features. The methods described here therefore provide unique possibilities for the analysis of complex processes such as the auditory processing of echolocation signals.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD