The discovery puzzled the team that conducted the new investigation

Jun 7, 2012 12:54 GMT  ·  By
Stanford researchers have shown that two rhythms could be summed to produce a third rhythm, determining the type of brain activity that leads to arm movements
   Stanford researchers have shown that two rhythms could be summed to produce a third rhythm, determining the type of brain activity that leads to arm movements

A group of investigators at the Stanford University argues that the movements of the human body are driven by motor neurons that relay basic, rhythmic electrical patterns down the spine. Before this study, scientists believed that specific external information relayed via these neurons was controlling motion.

External data refers to information such as velocity, direction and distance. Experts believed that this knowledge is centralized in the brain, and then relayed to muscles in charge of controlling movement.

But apparently these neurons serve no such function. What the investigation suggests is that the patterns in which they relay basic, rhythmic electrical impulses down the spine is what drives movement, both in humans and other species.

The new model was made possible by the fact that predicting the actions of motor neurons is not an easy task. Thus far, establishing a one-to-one relationship between the behavior of a motor neural fiber and a specific muscle behavior (activity or velocity) has proven to be impossible.

What the new study does is provide an elegant explanation of some of the most mysterious aspects related to how motor neurons control arm movements. Details of their work appear in the June 3 online issue of the top scientific journal Nature.

The researchers say that their theory represents a significant departure from conventional wisdom on the topic. The work was carried out by a collaboration of neuroscientists and electrical engineers.

The group managed to demonstrate that neural activity controlling arm movements does not encode or carry external spatial information, such as researchers proposed some time ago. However, they did find that the neurons fired in inherent rhythmic patterns.

Electrical engineering associate professor Krishna Shenoy conducted the study together with post-doctoral researchers Mark Churchland (Columbia University) and John Cunningham (Washington University in St. Louis).

“If you saw a piston or a spark plug by itself, would you be able to explain how it makes a car move? Motor-cortex neurons are like that, too, understandable only in the context of the whole,” Cunningham says of the complexity of the research he and his team are conducting.

“The brain has had an evolutionary goal to drive movements that help us survive. The primary motor cortex is key to these functions. The patterns of activity it displays presumably derive from evolutionarily older rhythmic motions such as swimming and walking. Rhythm is a basic building block of movement,” Churchland concludes.