A device and a method for detecting a brain response state of a subject id disclosed. The detection comprises repeatedly presenting the subject with a sound stimulus for evoking a brain response. Detecting the evoked brain response signal related to each of said sound stimulus. Determining a window having a time width covering at least partly an area of at least one neuron's evoked response in the brain response signal. Calculating an average response signal over the window and comparing the at least one neuron's evoked response with the average response signal for determining a cellular variance and/or volatility.
