1. A method of displaying the activity of a brain, the method including the steps of: (i) obtaining an electroencephalogram (EEG) signal from the brain; (ii) segmenting said EEG signal with a processor into either contiguous or overlapping segments comprised of a sequential number of samples of said EEG signal; (iii) representing said EEG segments as a fixed order autoregressive moving average (ARMA) signal representation with an autoregressive order between 8 and 13 and a moving average order between 5 and 11; (iv) rewriting in z-domain notation said fixed order ARMA signal representation to obtain a z-domain representation; (v) generating AR coefficient data and MA coefficient data for said segments of said EEG signal for said fixed order ARMA signal representation; (vi) determining the poles of said z-domain representation for said segments of said EEG signal by substituting said coefficient data for said segments of said EEG signal into said z-domain representation; (vii) determining the sum of said poles ( z p ) for said segments of said EEG signal as either; (a) the sum of the number of poles determined in step (vi); or (b) the first autoregressive AR coefficient of said coefficient data for said fixed order ARMA signal representation; (viii) determining the mean pole location for said segments of said EEG signal by dividing the sum of said poles ( z p ) by the number of said poles; (ix) determining an index value representing the activity of the brain for said segments of said EEG signal by applying a discriminating function to either the sum of the poles ( z p ) or the mean pole location for said segments of said EEG signal; and (x) displaying said index value on display means.