Neuronal adaptation and optimal coding in economic decisions

During economic decisions, neurons in orbitofrontal cortex (OFC) encode the values of offered and chosen goods. Importantly, their responses adapt to the range of values available in any given context. A fundamental and open question is whether range adaptation is behaviorally advantageous. Here we develop a theoretical framework to assess optimal coding for economic decisions and we examine the activity of offer value cells in non-human primates. We show that firing rates are quasi-linear functions of the offered values. Furthermore, we demonstrate that if response functions are linear, range adaptation maximizes the expected payoff. This is true even if adaptation is corrected to avoid choice biases. Finally, we show that neuronal responses are quasi-linear even when optimal tuning functions would be highly non-linear. Thus value coding in OFC is functionally rigid (linear responses) but parametrically plastic (range adaptation with optimal gain). While generally suboptimal, linear response functions may facilitate transitive choices.