Apparatus for electrostimulation of a test subject, comprising a plurality of electrodes that can be applied to the human brain to trigger specific stimuli on the human brain, - wherein a control unit comprising a stimulation unit is provided, with which electrical stimuli can be applied to the individual or multiple electrodes, - wherein the control unit comprises a measuring unit connected downstream of the electrodes for determining voltages applied to the individual electrodes, where appropriate after specification of different mental activities to the test person, - wherein the control unit comprises an analysis unit, which analyses the individual measurement signals detected by measuring electrodes, - wherein the analysis unit is configured, in the context of a preselection, on the basis of the detected measurement signals, to select individual electrodes for the output of a stimulus, - wherein the analysis unit is configured to examine, during the preselection, the measurement signals at the measurement electrodes, in particular exclusively, for the presence of signal powers or signal energies in the range of 60 Hz to 1 kHz, in particular between 60 Hz and 180 Hz, and - wherein the control unit comprises a, in particular human-actuatable, selection and actuation unit, for selection of one or more electrodes from the electrodes preselected by the analysis unit, and for the output by the stimulation unit of a predetermined electrical stimulus to the electrode(s) so selected, which selection and actuation unit is connected downstream of the analysis unit and upstream of the stimulation unit, characterised in that - the control unit is configured to carry out a base measurement by means of the analysis unit, during which the test subject carries out a reference activity, and to store the analysis results thereby obtained - associated with the respective measuring electrode - as reference values or reference signals in a reference memory and to keep them available, and - the analysis unit comprises a comparison unit, which compares the individual detected analysis values with the stored reference values, wherein the analysis result for each individual electrode indicates by how much the detected analysis values differ from the reference values associated with the respective electrode. - wherein a control unit comprising a stimulation unit is provided, with which electrical stimuli can be applied to the individual or multiple electrodes, - wherein the control unit comprises a measuring unit connected downstream of the electrodes for determining voltages applied to the individual electrodes, where appropriate after specification of different mental activities to the test person, - wherein the control unit comprises an analysis unit, which analyses the individual measurement signals detected by measuring electrodes, - wherein the analysis unit is configured, in the context of a preselection, on the basis of the detected measurement signals, to select individual electrodes for the output of a stimulus, - wherein the analysis unit is configured to examine, during the preselection, the measurement signals at the measurement electrodes, in particular exclusively, for the presence of signal powers or signal energies in the range of 60 Hz to 1 kHz, in particular between 60 Hz and 180 Hz, and - wherein the control unit comprises a, in particular human-actuatable, selection and actuation unit, for selection of one or more electrodes from the electrodes preselected by the analysis unit, and for the output by the stimulation unit of a predetermined electrical stimulus to the electrode(s) so selected, which selection and actuation unit is connected downstream of the analysis unit and upstream of the stimulation unit, characterised in that - the control unit is configured to carry out a base measurement by means of the analysis unit, during which the test subject carries out a reference activity, and to store the analysis results thereby obtained - associated with the respective measuring electrode - as reference values or reference signals in a reference memory and to keep them available, and - the analysis unit comprises a comparison unit, which compares the individual detected analysis values with the stored reference values, wherein the analysis result for each individual electrode indicates by how much the detected analysis values differ from the reference values associated with the respective electrode.