Models of Economic Choice
The “standard model” of economic decisions posits that value itself is computed in the prefrontal cortex such as the orbital or medial prefrontal cortex. Such value information is then transmitted to motor-related brain regions such as the lateral intraparietal cortex and the cingulate cortex where the utility is integrated with effort cost and the final utility is computed, which guides the choice amongst multiple goods. Early evidence challenging this proposal gained support mainly from the observations that neurons in the orbitofrontal cortex (OFC) encode both the pre-and post-decision variables, which suggests that economic decisions may be resolved in the OFC. We are further addressing this question by recording from multiple brain regions simultaneously using a multi-attribute choice task.
Cross Task Representation of Value-based Decisions
In an attempt to propose a unified theory for OFC function, recent studies have suggested that the central role of OFC is building of a “cognitive map” of the task space. It was proposed that the core function of a cognitive map is to “abstract important features of experiences and generalize them to new situations.” Such proposal is consistent with the malleability of the prefrontal cortex in encoding task-related information. However, such property of OFC in reward representation has just begun to be tested. Along this line, we have been investigating whether or how the same population of OFC neurons support value-based decisions in different tasks.
Memory-based Economic Decisions
In choice tasks in which subjective values must be stored in working memory (WM) for subsequent choices, analysis of single-unit spiking activity in the OFC failed to identify value encoding WM signals in the OFC. In an ongoing study, we leverage the power of population decoding to examine whether economic value as WM content can be decoded from OFC and/or the lateral prefrontal cortex (LPFC). We found population-level, parallel value-WM representation in the OFC and LPFC. These results resonate with current views emphasizing the distributed nature of WM, which, in contrast to localized WM, is more robust against perturbation/distraction.
To account for such distributed property of WM, a recent computational work from Xiao-Jing Wang’s laboratory proposed a multi-regional reverberation network model of WM. Applying the mechanism of this computational framework to LPFC-OFC interaction, we predict that due to the strong interaction between cortical areas in the distributed WM scenario, sustained inactivation of LPFC will disrupt value WM in the OFC and thus will affect the animal’s choice pattern. Conversely, transient inactivation of LPFC during the WM period will not impact subsequent WM maintenance and the eventual choice behavior. We are currently carrying out the inactivation study to test this hypothesis
Neuroeconomics and Psychopathology
NMDA receptors are increasingly implicated in psychiatric disorders such as schizophrenia. The NMDA antagonist treatment is considered a mechanistically relevant model for cognitive deficits of schizophrenia. Functional imaging studies suggest that, after systemic administration of NMDA antagonists, the most affected brain region is the prefrontal cortex (PFC). Animal studies also suggest that the PFC is a key region responsible for the expression of behaviors that are relevant to schizophrenia, including working memory and reward processing. Therefore, it is important to understand the impact of this treatment on prefrontal cellular mechanisms that lead to the disruption of these cognitive functions. To this end, under the economic choice task, we will record from the same population of neurons and compare their activities while the animals are ON and OFF acute NMDA antagonist treatment. This project is part of a key science project of which I am a principal investigator (Nonhuman primate whole brain connectome and disease models) funded by the Shanghai Municipality.