Sensory feedback can coordinate the swimming activity of the leech.

Previous studies showed that sensory feedback from the body wall is important and sometimes critical for generating normal, robust swimming activity in leeches. In this paper, we evaluate the role of sensory feedback in intersegmental coordination using both behavioral and physiological measurements. We severed the ventral nerve cord of leeches in midbody and then made video and in situ extracellular recordings from swimming animals. Our electrophysiological recordings unequivocally demonstrate that active intersegmental coordination occurs in leeches with severed nerve cords, refuting earlier conclusions that sensory feedback cannot coordinate swimming activity. Intersegmental coordination can in fact be achieved by sensory feedback alone, without the intersegmental interactions conveyed by the nerve cord.