A hearing aid comprises an amplifier (303, 309, 317), an input transducer (301), an output transducer (824) and a signal processing device (825). The amplifier (303, 309, 317) and the signal processing device (825) are connected. The hearing aid further comprises at least two electrodes (201-205) adapted for detecting electrical signals such as brain waves, the at least two electrodes (201-205) being connected to a differential amplifier (303, 309, 317), which in turn is connected to the signal processing device, and means for modifying the operation of said hearing aid in dependence of the detected signals. The invention further provides a method for adaptation of a hearing aid.