The processing of mechanosensory information by spiking local interneurons in the locust

The responses and receptive fields of a group of spiking local interneurons in the metathoracic ganglion of the locust were defined by making intracellular recordings from them while moving joints of a hindleg and stimulating external mechanoreceptors. Some interneurons respond both to inputs from internal mechanoreceptors (proprioceptors) at particular joints and to inputs from an array of external mechanoreceptors. The effects of both types of receptor can be excitatory or inhibitory. Other interneurons respond to proprioceptive input alone. There is a spectrum of responses. At one extreme are interneurons that respond tonically, the frequency of their spikes being determined by the angle of a particular joint. At the other extreme are interneurons that respond phasically to imposed movements of a joint in any direction. Inbetween are interneurons that respond with either a rapidly or a more slowly adapting change in the frequency of their spikes to the displacement of a joint in only one direction. Each movement of a particular joint excites or inhibits several interneurons with a range of different response characteristics. An interneuron typically receives inputs from only one joint, though some are excited by both femoral and tibial receptors. The interneurons spike during active movements of a leg elicited by direct stimulation of individual motor neurons, and during movements elicited by tactile stimulation of other parts of the body.