Compression method for raw data u 1 (t N) of measurements of electrocorticographic signals which evolve over time and are acquired using a set of electrodes arranged in direct contact with a cortex, each electrode being characterised by a different whole identification index i and a position r(i) at the surface of the cortex, the index i varying from 1 to L and L denoting the total number of electrodes, the raw electrocorticographic time signal u i ( t) acquired by the electrode having the index i being sampled at successive times t N, N being a whole number denoting the succession rank of a sample of the signal over time, as a sampled raw signal u i (t N) whose amplitude encoding forms the raw data of the raw electrocorticographic signal acquired at the sampling time t N, the compression method being characterised in that it comprises an effective step of compression pre-processing of the sampled raw electrocorticographic time signal u i (t N) before entropic encoding involving: for i varying from 1 to L and at each successive sampling time tN from a rank N 0, converting the raw signal u i (t N) acquired via the electrode i observed into a pre-processed signal ε i (t N) equal to the difference between a first term and a second term, the first term being equal to the raw signal u i (t N) acquired at the electrode i at the current time tN, and the second term being a prediction function fi which has no loss of information and which can be calculated in real time and which is temporally dependent on raw signals u σ i ( j) ( t N-k), u i ( t N-k) observed in the recent past up to the time t N-p(i), p(i) designating an entire rank which is not equal to zero of the most distant past relative to the rank N of the current time associated with the observed electrode i, k being a whole number varying from 1 to p(i), in at least one whole number m(i), different from L, of electrodes σ i (j) adjacent to the observed electrode i and at most in the whole number m(i) of electrodes σ i (j) adjacent to the observed electrode i and in the observed electrode i, σ i being a proximity function of the observed electrode i and σ i (j) denoting the indexes of the m(i) electrodes adjacent to the observed electrode i, j being a travel index of the proximity function σ i varying from 1 to m(i). for i varying from 1 to L and at each successive sampling time tN from a rank N 0, converting the raw signal u i (t N) acquired via the electrode i observed into a pre-processed signal ε i (t N) equal to the difference between a first term and a second term, the first term being equal to the raw signal u i (t N) acquired at the electrode i at the current time tN, and the second term being a prediction function fi which has no loss of information and which can be calculated in real time and which is temporally dependent on raw signals u σ i ( j) ( t N-k), u i ( t N-k) observed in the recent past up to the time t N-p(i), p(i) designating an entire rank which is not equal to zero of the most distant past relative to the rank N of the current time associated with the observed electrode i, k being a whole number varying from 1 to p(i), in at least one whole number m(i), different from L, of electrodes σ i (j) adjacent to the observed electrode i and at most in the whole number m(i) of electrodes σ i (j) adjacent to the observed electrode i and in the observed electrode i, σ i being a proximity function of the observed electrode i and σ i (j) denoting the indexes of the m(i) electrodes adjacent to the observed electrode i, j being a travel index of the proximity function σ i varying from 1 to m(i).