The duty of a PWM signal in a power converter is extracted to feed forward to modulate the slope of a linear oscillating ramp signal or the voltage level of an error signal, so as to modulate the duty of the PWM signal, by which the transient response of the power converter and the stability of the PWM loop both are improved. The shaft is provided with an internal longitudinal channel or bore extending to the end face. Detection of epileptiform activity or an electrographic seizure and stimulation of language cortex may be performed by a sensing andor stimulation electrode that is inserted into a subject’s brain and connected to one or more neurostimulation devices for monitoring andor stimulating the language cortex.