When the motor cortex (i.e. the area of the brain that controls muscle contractions) is strongly stimulated with TMS during a voluntary muscle contraction, both excitatory and inhibitory effects can be observed in the muscle the targeted cortical area controls. The inhibitory effect entails a transient interruption of neural drive to the muscle. This interruption, called the "silent period", lasts for less than half a second and results in the relaxation of the muscle. Muscle activity and control quickly return to normal after the silent period.