What Can Different Brains Do with Reward?

Excerpt

In what follows, we first sketch some current thinking on the evolution of some of the brain structures that deal with reward, with emphasis on those that likely appeared at three times during the history of animals (Figure 4.1): with early vertebrates, with early mammals, and during primate evolution. Next we use clues from laboratory research, mainly from studies of rats and rhesus monkeys, to paint a picture of structure-function relationships in each of these three clades. We recognize the hazards of this approach. Rats and rhesus monkeys are crown species, each with a long, separate evolutionary history and a complex suite of adaptations and specializations. The preferred way to understand the role of structures in early vertebrates or early mammals would involve the study of a diversity of animals in each group, selected according to the principles of evolutionary biology. Although a limited amount of such research is available, the literature from comparative psychology has not yet reached a point where we can use the preferred approach effectively. Accordingly, we use what hints come from rat and monkey research, in the context of comparative neuroanatomy, to explore what we have inherited from various ancestors. In doing so, we assume that structure-function relationships do not change haphazardly during evolution. Our approach will perhaps seem most peculiar when we use insights gained from the study of macaque monkeys and humans to explore the function of dopamine neurons and the basal ganglia in Section 4.3: “What Can Vertebrate Brains Do With Reward?” We adopt this approach because the original work was based on monkey research, and because we believe that the principles discerned from that research apply to other vertebrates as well. Our assumption is that such principles are highly conserved, although future work on a broad array of vertebrates is needed to confirm that view.