ABSTRACT
In chapter 2 of this book, Beninger and Olmstead review behavioural experiments indicating that the dopaminergic input to the striatum conveys a reward or incentive signal, which either reinforces behaviour with motivationally favourable consequences, or makes approach responses more likely towards stimuli associated with fulfilment of motivational demands. In chapter 4, Wickens, presents data obtained from intracellular studies in cortico-striatal slice preparations, which suggest that such reinforcement seen at the behavioural level is mediated by dopamine-dependent synaptic change in cortico-striatal synapses. Chapter 1 by Hyland complements these accounts, by describing single unit physiological experiments
which investigate the circumstances in which midbrain dopamine neurones fire in the freemoving animal: specifically, when a stimulus with incentive value occurs unpredictably, it generates in midbrain dopamine neurones a brief high-frequency burst of action potentials. Putting all these lines of evidence together one can build a scheme for reward-or incentivemediated learning in which the midbrain dopamine neurones discharge a burst of impulses when they receive signals about motivationally favourable changes in the environment; activity in such neurones causes a brief pulsatile release of dopamine in the striatum; this strengthens synapses which have been active immediately preceding the motivationally favourable change; and this effect, in turn, is expressed as reinforcement of the behaviour which led to the motivationally favourable change (see Figure 5.1).
