Fig. 2. Dynamic encoding and mixed selectivity in individual units.

a–e Mean response to the non-singleton (solid curves) and singleton (dashed curve; not present in all sessions) offers ± s.e.m. (shading) is shown as a function of time from onset of the offer period (double arrows) for five example units. Averages include all choices. Dynamics varied from rapid and transient (a, c) to slow and sustained (b). The sign of encoding could be positive (a, b) or negative (i.e., firing less for larger offers (c)), or reversing mid-trial (d). Further stratifying by accept (green) and reject (blue) choices (e) showed selectivity for both benefit and choice. While the encoding of offer size appeared to reverse sign for unit (e), this was an artifact of the greater response for reject than accept choices later in the trial combined with more frequent rejections for smaller offers. In contrast, the reversal observed for unit (d) did not depend on choice (not shown).