Both phase coding and rate coding can solve the working memory task.

We found two qualitatively different solutions. A) In the first solution (panels A to C), we find that single unit activity codes for stimulus information by relative phase: We plot the rates tanh(xi) of 4 example units i, as a function of the reference oscillation phase θ. We find that single unit activity oscillates, with the phase relative to the reference oscillation depending on stimulus identity (colors). B) Projecting x to the κ1, κ2 plane reveals that population activity lies on overlapping cycles in this plane. Here, the black dots denote θ = 0. C) In the full phase space , the trajectories are non-overlapping, but the cycles are linked. D) In the second solution (Panels D to F), we find that stimulus identity does not modulate the phase of single units, but rather their mean activity. E) This rate-code corresponds to two cycles separated in the κ1, κ2 plane. F) These cycles are also separated in the full phase space.