Releasing the brakes before pressing the gas pedal

Making a simple movement requires preparatory activity in a number of brain areas. Much of this preparation is concerned with selecting and then sending an appropriate pattern of excitation to the spinal cord so that muscles are activated in the correct order and by the appropriate amount at the right time. In this issue of Neurology, Reynolds and Ashby1 report on how the internal workings of one particular area, the primary motor cortex, change in the 100 msec or so just before the onset of a movement. They find that movement involves not only increasing the amount of excitation in parts of the motor cortex, but also reducing the amount of inhibition, and that the two processes seem to be quite separate. At least in this part of the motor system, movement control really does seem to work like a car: it has separate brake and gas pedals. Investigation of the motor cortex in healthy individuals has been made possible by the advent of transcranial magnetic stimulation (TMS). A …