Reward expectancy-related prefrontal neuronal activities: Are they neural substrates of affective working memory?

Primate prefrontal delay neurons are involved in retaining task-relevant cognitive information in working memory (WM). Recent studies have also revealed primate prefrontal delay neurons that are related to reward/omission-of-reward expectancy. Such reward-related delay activities might constitute affective WM (Davidson, 2002). Affective and cognitive WM are both concerned with representing not what is currently being presented, but rather what was presented previously or might be presented in the future. However, according to the original and widely accepted definition, WM is the temporary storage and manipulation of information for complex cognitive tasks. Reward/omission-of-reward expectancy-related neuronal activity is neither prerequisite nor essential for accurate task performance; thus, such activity is not considered to comprise the neural substrates of WM. Also, affective WM might not be an appropriate usage of the term WM. We propose that WM- and reward/omission-of-reward expectancy-related neuronal activity are concerned with representing which response should be performed in order to attain a goal (reward) and the goal of the response, respectively. We further suggest that the prefrontal cortex (PFC) plays a crucial role in the integration of cognitive (for example, WM-related) and motivational (for example, reward expectancy-related) operations for goal-directed behaviour. The PFC could then send this integrated information to other brain areas to control the behaviour.