Rob R. de Ruyter van Steveninck, 3

The problem of neural coding is to understand how sequences of action potentials (spikes) are related to sensory stimuli, motor out-puts, or (ultimately) thoughts and intentions. One clear question is whether the same coding rules are used by dierent neurons, or by corresponding neurons in dierent individuals. We present a quantitative formulation of this problem using ideas from informa-tion theory, and apply this approach to the analysis of experiments in the y visual system. We nd signicant individual dierences in the structure of the code, particularly in the way that tempo-ral patterns of spikes are used to convey information beyond that available from variations in spike rate. On the other hand, all the ies in our ensemble exhibit a high coding eÆciency, so that every spike carries the same amount of information in all the individuals. Thus the neural code has a quantiable mixture of individuality and universality.