Date of Award

6-2016

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Robert Olberg

Language

English

Keywords

angular, spike, time, expansion, values

Abstract

The Target Selective Descending Neurons (TSDNs) DIT3 and MDT3 in the Aeshnid dragonfly have been shown to respond best to expanding visual stimuli that appear to be approaching, also called looming stimuli. The ratio between the length of the object (L) and the absolute approach velocity (V) completely determines the time course of angular expansion of the object’s image. This study investigated how these neurons responded to the change in expansion of the stimuli, along with which properties of the looming stimuli (target angle, angular expansion rate, or angular acceleration) excite DIT3 and MDT3, respectively. In this experiment, we dissected the animal to expose the nerve cord and then drove a microelectrode into individual axons. We distinguished between DIT3 and MDT3 by displaying a raster stimulus; the response to different areas of the visual field allowed us to determine which neuron we had penetrated. DIT3 has been shown to prefer visual stimuli in the contralateral portion of the visual field, while MDT3 prefers stimuli in the ipsilateral portion of the visual field. We then exposed the animal to stimuli with different looming properties to test for variations in response. We found that these neurons are most sensitive to looming stimuli with large L/V values. The spikes for DIT3 and MDT3 occurred earlier as the L/V values of the stimuli successively increased. We also found that both DIT3 and MDT3 respond to a consistent angular expansion rate, while the other parameters resulted in inconsistent spike times relative to changing L/V values. This implies that these TSNDs encode information regarding angular velocity down the nerve cord, information that may be important for the animal to intercept its prey.

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