Neuronal circuits that control motor behaviors orchestrate multiple tasks, including the inhibition of self-generated sensory signals. Are these multiple targets under the radial control of the central pattern generator (CPG) responsible for motor control?
In the leech, T mechanosensory neurons respond to light touch on the skin and also to pressure caused by contraction of the body wall. In the isolated nervous system this sensory neuron shows phase-dependent inhibitory postsynaptic potentials (IPSPs) during dopamine-induced fictive crawling. The timing and magnitude of the T-IPSPs are highly correlated with motoneuron activity in the contraction phase. These results indicate that the central network responsible for crawling sends a reafferent inhibitory signal onto the T cells, concomitant with the signal to the motoneurons.
NS neurons are premotor neurons, at the center of a vast recurrent inhibitory network that affects all the motoneurons in the leech. During crawling NS is subjected to IPSPs tuned to the motor pattern.
In the present investigation we explore the temporal coincidence between signals delivered to motor, premotor and the sensory neurons and the underlying network architecture. While motoneuron activity controls motor contraction, recurrent inhibition sets a limit onto motoneuron activity, and reafferent inhibition precludes spurious sensory activation. Are these different functions controlled directly by the CPG or do they depend on the motor output?