Dragonflies are some of the most efficient and deadly predators in the world due to their extraordinary visual capabilities. In my thesis research, I chose to measure the visual responses of descending neurons in Aeshnid dragonflies with receptive fields directed behind the animal. Backward-looking cells are considered important in warning the dragonfly of incoming predators and dangers. The only previously known backward-looking cell is in the dorsal median tract (DMT1) of the ventral nerve cord. All that is known about this cell is that it lies ipsilateral to the axon and that it responds to visual motion behind the dragonfly. In my experiments, I exposed the ventral nerve cord of the dragonfly for placement of an extracellular hook electrode. The dragonfly was waxed to a metal rod, ventral side up, and was placed in front of a curved rear-projection screen with its head facing away from the screen. Zigzagging target stimuli were played on the screen with varying speeds and target sizes; as well as two different expanding stimuli that simulated approaching objects (looming stimuli). The electrophysiological spiking responses were digitized with Powerlab (AD Instruments) and analyzed with Labchart (AD Instruments) and custom scripts were written in MATLAB (Mathworks). My results showed that there are at least four distinct backward-looking neurons; looming ipsilateral (assumed to be DMT1), looming contralateral, target ipsilateral, and target contralateral. (Ipsilateral and contralateral refer to the side of descending connective in which the neurons were recorded). Looming cells preferred large-sized targets and were multidirectional but showed no preference to speed. Target cells preferred fast moving targets, usually smaller target sizes, and they showed a preference for downward movement. We have not yet identified these four large neurons anatomically, but that is the next important step in this investigation.
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