Just like electrical charge can be used to train muscles, it can also have a nasty side effect, namely, the brain can get into haptic feedback mode,where part of the electric pulses sent to the muscles by a device, are stored within the brain, only to be released at a later time.
The user will feel his muscles spasm, under several lower tension impulses. This could be problematic when doing this to the center of a brain where not only that part of the brain is that connects to the muscles, but a whole bunch of other braincells.
Applying electrical current to the brain that gets stored, and released could be very similar to having an epileptic seizures,and could potentially even lead to death,if those electric currents are released or short-circuiting the part of the brain that is responsible for us being alive (and that part that controls automatic functions like heartbeat and lungs.