A process for analysing an electroencephalogram signal representative of activity of a brain, including: i) generating coefficient data for a signal representation of a portion of said signal; ii) generating first gain data representing an average amplitude of an output signal generated based on said signal representation and said coefficient data; iii) generating second gain data representing an average amplitude of said portion; and iv) generating, based on said first gain data and said second gain data, brain state data representing subcortical activity of said brain.