Electrical stimulation is also rapid acting, with the effect being observed in seconds. Finally, electrical stimulation can be applied safely. Methods for delivering current to biological tissue have been determined through careful science and testing. Safe stimulating waveforms that employ bi-directional pulses with charge densities below established limits are well tolerated by the tissue. Thus, electrical stimulation is an extraordinarily versatile, effective, and safe tool for manipulation of activity of the nervous system.
Electrical stimulation impacts neural rehabilitation in many ways and at different time scales.
For example, in a neuroprosthetic device, stimulation generates the desired force and movement when applied, and the force generation ends when the stimulation is turned off. However, this stimulation can also result in longer-term changes in muscle physiology and chemistry, bone density, and spinal cord circuitry. The situation is similar in the cochlear implant, in which stimulation results in not only the generation of a percept but also in remodeling of the auditory system and in neuroprotection of the fibers of the auditory nerve. In deep brain stimulation, electrical stimulation appears to act by blocking the input from a dysfunctional circuit of the motor-control pathway. However, the effects of stimulation on tremor have a different time course than the effects on bradykinesia, which suggests different mechanisms are responsible.