transcranial electrostimulation apparatus and method includes a first generator of bipolar pulses of a first predetermined frequency . a source of modulating control signals , producing an output at a second frequency less than the first predetermined frequency , is used to cause the output pulses from the first generator of pulses to vary in amplitude in a predetermined asymmetrical pattern at the frequency of the modulating control signals , with the asymmetrical pattern of signals applied to output electrodes designed to be attached to the scalp of a patient .