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Scientists at Pitt Neurobiology and Systems Neuroscience Institute just broke the code used by the brain’s primary motor cortex to control movements. A long-standing debate has existed concerning the output signals from the brain to the spinal cord. Some have argued that the brain encodes force. Others have suggested that the brain encodes movement direction. In a paper published in Science, Darcy Griffin, Donna Hoffman and Peter Strick (University of Pittsburgh Systems Neuroscience Institute and CNBC) investigated the corticomotoneuronal (CM) contribution to the movement. CM cells are a subset of primary motor cortex neurons that make direct monosynaptic connections with spinal motor neurons. The authors found that this subset of neurons were “functionally tuned”. In other words, individual CM cells encoded a single muscle function. When we move, individual muscles are used for many functions; as agonists to generate force, fixators to prevent unwanted joint movement and as antagonists to brake movement. This exciting finding shows that the brain uses a population of CM cells, which are connected to the same muscle, to control different functions of that muscle. Thus, the primary motor cortex encodes the functional use of a muscle. The paper is available here.