A first aspect provides, in a device for processing biomedical data obtained from a body, a method of determining brain activity. The method comprises obtaining neuron oscillation signal data of a first part of a brain over a period of time. The oscillation signal data is apportioned in timeslots within the period and per time slot, based on the oscillation data for the timeslot, an amplitude value and variation value representing data values in the timeslot are obtained. A correlation value is determined between the amplitude values and the corresponding variation values over at least a substantial part of the first time period; and the correlation value is provided as an output. The correlation value may optionally be used for estimating a ratio between excitation and inhibition activity of the brain under scrutiny.