Cover legend: The input–output gain of individual motor neurons, stained for choline acetyltransferase (green) in this saggital view of the ventral horn of spinal cord (down is ventral), is modulated by the premotor interneuron network (red cells stained with Nissl) to optimize the control of muscular force. Image courtesy of Peter C. Petersen, Kristian Jensen, and the core facility for integrative microscopy, University of Copenhagen. For more information, see the article by Vestergaard and Berg (pages 3711–3723).