POSSIBLE FUNCTIONS OF A POPULATION OF DESCENDING NEURONS IN THE HONEYBEES VISUO-MOTOR PATHWAY

An identified population of honeybee descending neurons (DNs) responds to wide-field motion over the compound eyes. They give non-habituatin g, directionally selective responses which adapt to continued motion. Contrast sensitivity functions show the responses depend on luminance, contrast, spatial and temporal frequency. The distribution of the DNs ' outputs in the thoracic ganglia is consistent with changes in muscul ar activity required for particular compensatory movements. These feat ures suggest the DNs lie along the optomotor pathway. The DNs' respons es have different time-courses. This might reflect distinctions in the ir putative inputs and between pathways implicated in different aspect s of visually mediated flight control. The responses of horizontal DNs to contraction and expansion and to unidirectional motion were compar ed revealing differences in the way they integrate the monocular compo nents of binocular flow-fields and how velocity and spatial structure effects this integration. It is possible the DNs are convergence site( s) for substrates underlying different behaviours each triggered by sp ecific optical flow templates.