Science split second late or a few inches off the mark, and few would remember.
Instead, running with his back to the ball, Willie Mays extended his arm and placed his glove squarely under the 420-foot center field drive. The New York Giants win
Game 1 of the 1954 World Series, and Mays, his glove, and “The
Catch” earn their place in history.
Few of our limb movements will ever gain such immortality, but what we accomplish every day is remarkable, nonetheless.
When we catch a tipped wineglass or launch a dart toward a bullseye, hardly a second thought is given to the intricacy of neural circuits that orchestrate such precise movements. How do these circuits control skilled behaviors?
Because rodent limb movements are strikingly similar to those of primates
( 1), and mice provide a means of manipulating neuronal subtypes selectively ( 2), as a postdoc with Tom Jessell I reasoned that a detailed quantification of mouse reaching, together with a genetic dissection of spinal circuits, might help disentangle core features of mammalian skilled motor control ( 3).
Reaching appears simple, but deceptively so. Motor neurons fire, propelling the arm to target. Yet reaching does not arise from an isolated burst of motor output; rather, motor neuron activity is continually tweaked to shape appropriate limb kinematics ( 4– 6). One strategy for updating motor output is to use proprioceptive feedback from muscles to evaluate outcome and correct course. But sensory information is slow in its trek from the periphery to the brain, creating at least two challenges for motor systems: how to achieve faster feedback for rapid movements, and how to prevent sensory feedback delays from destabilizing the limb ( 7) (see the figure, panel A).
INTERNAL COPIES PROVIDE FEEDBACK.
Rapid movements unfold before sensory information arrives ( 8),