The organization of exteroceptive sensory inputs to interneurons of the flight neuropil in locusts

Abstract

1. Thirty-seven pairs of mesothoracic interneurons respond selectively to visual or ocellar stimuli corresponding to deviations from course in flight, expressed as angular rotation around the three spatial axes. 2. Sensitivities to roll and yaw are very strongly associated. All interneurons showing a directional preference for yaw rotations showed the same preference for roll rotations. A few roll-sensitive cells were not directionally sensitive to yaw. Some interneurons respond exclusively to pitch rotations, most to both pitch and roll/yaw. 3. Approximately equal numbers of interneurons prefer pitch up, pitch down, roll/yaw to the ipsilateral side and roll/yaw to the contralateral side. All four possible combinations of pitch (up or down) with roll/yaw (ipsilateral or contralateral) preferences occur with equal probability. 4. No relationship between neuronal structure and directional properties could be discerned. 5. The average latency of the ocellar EPSPs recorded in the interneurons is not significantly different from the average latency of the ocellar spike in the descending neurons (at the same temperature and in the same ganglion). The average ocellar IPSP latency is 8.5 ms longer. The data support the hypothesis that most EPSPs are derived from monosynaptic inputs from the DNs, and most IPSPs from polysynaptic inputs. A few EPSPs are also derived from polysynaptic inputs. 6. Most of these neurons are sensitive to wind, at least some directionally so, in a manner functionally compatible with their visual or ocellar directionality, and most are excited. Two neurons respond to movement of small objects in the visual field, and 5 to high frequency sound.