Redundant Control of Motor Systems in Arthropods

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1)In the intact crayfish, the diverse sensory inputs converge onto the three pairs of nonspiking giant interneurons (G1, G2, G3 ; NGIs) of the brain through both direct excitatory and inhibitory pathways, and that although statocyst inputs potentially have more of an effect on NGI responses, the balance of the response must depend on how different sensory inputs are weighted in neuronal integration. Furthermore, it was found that the compensatory eyestalk movements during walking are not only under the influence of orientation cues, such as gravitational, visual, and substrate inputs, but also under the influence of outputs from walking motor center. 2)In adults with leg contact with the surface of water, intracellular injection of depolarizing current into any one of four dorsal giant interneurons (dGIs) ascending from the terminal abdominal ganglion and eighteen identified interneurons (trigger neurons) descending from the brain initiated swimming behavior. When the legs were not contact with the surface of water, the same current injection initiated flying behavior. In adults whose the brain and suboesophageal ganglion were removed, intracellular injection of depolarizing current into any one of these interneurons initiated flying behavior on the surface of water. Compared with the current injection into a single dGI,the current injection into two dGIs at the same time initiated flight or swimming behavior with short latency and long duration. These results suggest that the suboesophageal ganglion integrates the leg proprioceptive inputs to select the behavioral motor pattern most appropriate to the current external condition. 3)The above-mentioned results imply that the neuronal mechanism of motor control in arthropods might involve considerable functional overlap or "redundancy" to utilize common sets of muscles while operating in "false safe" and "synergic action" modes, and to select specific motor pattern.