The mammalian locomotor CPG: revealing the contents of the black box.

It has long been known that a neural circuit situated in the spinal cord of mammals is independently capable of generating and modulating locomotor movements. Following its initial discovery over a century ago, a great deal of research has been focused on characterizing this neural circuit to determine how it is able to elicit movement. For much of the 20th century, difficulty in identifying individual component interneurons that comprised this neural circuit resulted in it being considered a powerful but mysterious "black box." In this article, we will review the development of a number of innovative experimental approaches that have brought us to the current state of research in the field, where we are able to identify populations that comprise this neural circuit, pinpoint their specific function, and image their activity in real time during a locomotor task.