Sensorimotor pathways processing vibratory signals from the femoral chordotonal organ of the stick insect

The femoral chordotonal organ of stick insects senses position and velocity of movements in the femur-tibia joint, as well as tibial vibration. While sensory information about large-scale tibial movements is processed by a we ll-known neuronal network and elicits resistance reflexes in extensor and f lexor tibiae motoneurons, it is not yet known how sensory information about vibration of the tibia is processed. We investigated the transmission of v ibration stimuli to tibial extensor motoneurons and their premotor interneu rons. Vibration stimuli applied to the femoral chordotonal organ evoked res ponses in tibial extensor and flexor muscles. During ongoing vibration this response adapted rapidly. This adaptation had no effect on the motoneurona l response to large-scale tibial movements. Recording from premotor interne urons revealed that vibratory signals were processed in part by the same in terneuronal pathways as (large-scale) velocity and position information. Wh ile only certain parts of the interneuronal reflex pathways showed little o r no response during vibration stimuli, most neurons responded to both posi tion or velocity stimuli and vibration at the femoral chordotonal organ. We conclude that sensory information about vibration of the tibia shares part of the interneuronal pathways that transmit sensory information about larg e-scale tibial movements to the motoneurons.