THE LOCUST DCMD, A MOVEMENT-DETECTING NEURON TIGHTLY TUNED TO COLLISION TRAJECTORIES

A Silicon Graphics computer was used to challenge the locust descendin g contralateral movement detector (DCMD) neurone with images of approa ching objects. The DCMD gave its strongest response, measured as eithe r total spike number or spike frequency, to objects approaching on a d irect collision course. Deviation in either a horizontal or vertical d irection from a direct collision course resulted in a reduced response , The decline in the DCMD response with increasing deviation from a co llision course was used as a measure of the tightness of DCMD tuning f or collision trajectories. Tuning was defined as the half-width of the response when it had fallen to half its maximum level. The response t uning, measured as averaged mean spike number versus deviation away fr om a collision course, had a halfwidth at half-maximum response of 2.4 degrees-3.0 degrees for a deviation in the horizontal direction and 3 .0 degrees for a deviation in the vertical direction. Mean peak spike frequency showed an even sharper tuning, with a halfwidth at half-maxi mum response of 1.8 degrees for deviations away from a collision cours e in the horizontal plane.