The present invention regards an in-ear stimulation device comprising at least one in-ear sensor, a control unit, and an output transducer. The in-ear stimulation device is configured to be worn at or on an ear of a human user and at least partly in an ear canal of the user. The at least one in-ear sensor is arranged and configured to measure electrical activity signals indicative of an electroencephalogram (EEG) of a user wearing the device. The control unit is configured to receive the electrical activity signals and to detect a presence of a slow oscillation, which is in a frequency range between 0.5 Hz and 1 Hz, in the electrical activity signals. The control unit is further configured to trigger, in response to detecting the presence of a slow oscillation, a generation of at least one stimulus impulse. The output transducer is configured to receive the at least one stimulus impulse and to generate a corresponding output sound.
