One popular model suggest that PFo, in particular, represents value in a common currency. A common value system would allow comparison of different goods (e.g., apples and oranges), and would constitute an important mechanism for making advantageous choices. We propose to test the idea that PFo and PFm compute value in a common currency. On this view, orbitomedial prefrontal cortex is a summing junction for positive and negative value, used for decision making. This currency would be independent of the sensory modality and would become apparent when there are multiple competing outcomes, as opposed to only one type and quantity of reward. Under these conditions, according to this idea, orbitomedial prefrontal cortex would become more active and more important. ? ? We propose to examine neuronal activity in PFo and PFm related to predicted outcome for different types of stimulus-outcome mappings. We will also monitor an array of autonomic functions as subjects perform behavioral tasks. The study will focus on amygdala interactions with PFo and PFm. Because the amygdala plays a role in both positive and negative affect our study will involve a comparison of neuronal activity in relation to both positive and negative secondary reinforcers. To date, neurophysiologists studying PFo and PFm have concentrated almost exclusively on positive outcomes, so the proposed experiment is expected to uncover new information regarding the representation of negative outcomes. In addition, some research has suggested that PFo contains functional subdivisions, such that lateral regions represent negative values and medial regions represent positive values. If such subdivisions exist, we should see a spatial segregation of neurons coding for positive and negative values. Finally, neuropsychological and neurophysiological findings suggest that value is encoded in the PFo with the help of the amygdala, and that, in the absence of the amygdala, the associative encoding linking stimuli with outcomes is disrupted. Recordings will be made from PFo and PFm before and after selective excitotoxic amygdala lesions or inactivations. If associative encoding requires the amygdala, then before amygdala lesions, neural activity in PFo and PFm during the stimulus presentation period should reflect the expected outcome, but after amygdala lesions this activity should disappear.
| Rudebeck, Peter H; Murray, Elisabeth A (2008) Amygdala and orbitofrontal cortex lesions differentially influence choices during object reversal learning. J Neurosci 28:8338-43 |
| Murray, Elisabeth A; O'Doherty, John P; Schoenbaum, Geoffrey (2007) What we know and do not know about the functions of the orbitofrontal cortex after 20 years of cross-species studies. J Neurosci 27:8166-9 |
