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Generating complex movement patterns
What exactly does neuronal activity in the brain's motor cortex encode? In monkeys, Griffin et al. simultaneously recorded from a large number of muscles and from motor cortex cells that project directly to the motor neurons of the spinal cord. Even though the cortical cells had conventional directional tuning curves, different cortical cells were functionally connected to spinal cells with different muscle actions.
Science, this issue p. 667
Abstract
Corticomotoneuronal (CM) cells in the primary motor cortex (M1) have monosynaptic connections with motoneurons. They are one of the few sources of descending commands that directly influence motor output. We examined the contribution of CM cells to the generation of activity in their target muscles. The preferred direction of many CM cells differed from that of their target muscles. Some CM cells were selectively active when a muscle was used as an agonist. Others were selectively active when the same muscle was used as a synergist, fixator, or antagonist. These observations suggest that the different functional uses of a muscle are generated by separate populations of CM cells. We propose that muscle function is one of the dimensions represented in the output of M1.
