Response Characteristics of Four Wide-Field Motion-Sensitive Descending Interneurones IN Apis Melufera

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Abstract
The anatomical projections and directional tuning of four descending interneurones sensitive to wide-field motion over the compound eyes are described. The cells are slow to adapt, resistant to habituation and their responses are dependent on the contrast frequency of the periodic patterns used as stimuli. Two of the cells (DNIV2 and DNIV4) are maximally stimulated by movement around the longitudinal axis of the bee (simulated roll), one (DNII2) by movement around the horizontal axis (simulated pitch) and one (DNVI1) by movement around the vertical axis (simulated yaw). The cells are binocular, their directional response being shaped by the interaction of the inputs from each eye. The cells which respond predominantly to roll (DNIV2 and DNIV4) have their arborizations restricted to the ipsilateral side of the brain and thoracic ganglia, i.e. the side which contains the cell soma. The cell responding to pitch (DNII2) has its arborizations distributed bilaterally, invading similar regions of the neuropile in both sides of the brain and thoracic ganglia. The cell which responds to yaw (DNVI1) has its major dendritic field in the ipsilateral side of the brain and descends into the thoracic ganglia in the contralateral side. The majority of its arborizations in the thoracic ganglia are confined to the contralateral neuropile.