Activity and structure of movement-signalling (corollary discharge) interneurons in a cockroach

1. Intracellular recordings were taken from interneurons in the thoracic nervous system of partly restrained American cockroaches during voluntary or imposed leg movements. 2. Two pairs of interganglionic interneurons were found which fired action potentials during voluntary extension movements of one segment of one leg, but rarely during imposed leg extensions or during other voluntary movements (Figs. 4, 5). Because these interneurons were active during a movement driven by specific muscles, they are designated corollary discharge (CD) neurons. 3. Intracellular staining of these CD interneurons showed that the soma and dendritic arbor of each were located in the ganglion that controlled the leg whose movement accompanied firing of the neuron. Furthermore, the soma was situated in and the dendritic arbor was confined to the half ganglion ipsilateral to the same leg, and each cell's axon left the ganglion in the ipsilateral connective (Figs. 7, 8). No other neurons having different physiological characteristics were found with these structural features. 4. It is suggested that such CD neurons may be common in insects and may help coordinate movements, and that they may represent a distinct class, possibly recognizable on structural grounds alone.