Multiple Decision-Making Systems and the Common Currency Hypothesis

The ‘common currency’ hypothesis proposes that selecting between choices requires a centralized neural representation of value which combines the attributes of choice into a single metric of comparison. Conversely, the multiple decision-making systems theory posits competing decision-making algorithms that separately identify actions to take. These two theories have increasingly become central to how neuroscientists understand decision-making. However, these theories appear incompatible with each other, at least on the surface. This Perspective addresses how these theories interact with each other and points to unanswered questions about the intricacies of action selection. We find that it is unlikely that a single common currency arbitrates between decision systems, but that some algorithms can be described as containing a common currency mechanism. However, others are unlikely to be compatible with a common currency hypothesis. We also find that computational differences between individual common currency representations may have measurable effects neurophysiologically and behaviorally.