PREMOTOR INTERNEURONS IN GENERATION OF ADAPTIVE LEG REFLEXES AND VOLUNTARY MOVEMENTS IN STICK INSECTS

We investigated the role of local nonspiking interneurons involved in motor control of legs in the stick insect, Carausius morosus. In a pre paration that allowed the animals to perform active leg movements such as adaptive tactile reflexes, proprioceptive reflexes, and walking, w e gathered the following results. Almost all tested nonspiking interne urons that provide synaptic drive onto motoneurons of the proximal leg muscles contribute to all of the motor programs underlying tactile re flexes and voluntary leg movements such as walking, searching, and roc king. Most of them are also involved in the generation of propriocepti ve reflexes. All motor programs for coactivation, avoidance reflexes, resistance reflexes, and voluntary leg movements result from parallel pathways including nonspiking interneurons that support and others tha t oppose the motoneuronal activity. The contribution of a single inter neuron to the different motor programs is specific: it can be supporti ng for one motor program but opposing for the other. Even for the same motor program, for example, coactivation, the contribution of an indi vidual interneuron can depend on the stimulus site from where the resp onse is elicited. Our results support the idea that the different moto r patterns for adaptive tactile reflexes, resistance reflexes, and vol untary leg movements emerge from a multifunctional neuronal circuit th at is reorganized corresponding to the motor behavior performed. The a ctual motor pattern is then shaped by distributed information processi ng in parallel supporting and opposing pathways. (C) 1996 John Wiley & Sons, Inc.