Putting one foot in front of the other seems like a simple concept to us, but the brain's ability to initiate and send rhythmic movement signals to the body is no small feat. Researchers have just described the precise brain cells involved in this process in simple vertebrates.

"These findings address the longstanding question of how locomotion is initiated following sensory stimulation and, for the first time in any vertebrate, define in detail a direct pathway responsible," study researcher Edgar Buhl, of the University of Bristol in the United Kingdom, said in a statement. "They could thus be of great evolutionary interest and could also open the path to understanding initiation of locomotion in other vertebrates."

Experiments in the 1970s identified areas of the brain responsible for starting locomotion, the precise neuron-by-neuron pathway has not been described in any vertebrate — until Buhl and colleagues studied the movements of the Xenopus frog tadpole. The research is published today, May 16, in the Journal of Physiology.

They found that the pathway to initiate swimming consists of just four types of neurons. The scientists identified nerve cells that detect the touch on the skin, two types of brain nerve cells which pass on the signal, and the motor nerve cells that control the swimming muscles.

When mechanisms in the brain that initiate locomotion break down — for example, in people with Parkinson's disease — beginning to walk becomes a real problem. Therefore, understanding the initiation of swimming in tadpoles could be a first step towards understanding the initiation of locomotion in more complex vertebrates, including people, and may eventually have implications for treating movement disorders such as Parkinson's.