Choice coding in frontal cortex during stimulus-guided or action-guided decision-making.

To optimally obtain desirable outcomes, organisms must track outcomes predicted by stimuli in the environment (stimulus-outcome or SO associations) and outcomes predicted by their own actions (action-outcome or AO associations). Anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) are implicated in tracking outcomes, but anatomical and functional studies suggest a dissociation, with ACC and OFC responsible for encoding AO and SO associations, respectively. To examine whether this dissociation held at the single neuron level, we trained two subjects to perform choice tasks that required using AO or SO associations. OFC and ACC neurons encoded the action that the subject used to indicate its choice, but this encoding was stronger in OFC during the SO task and stronger in ACC during the AO task. These results are consistent with a division of labor between the two areas in terms of using rewards associated with either stimuli or actions to guide decision-making.

Dynamic encoding of responses and outcomes by neurons in medial prefrontal cortex.

Medial prefrontal cortex (MPFC) and lateral prefrontal cortex (LPFC) both contribute to goal-directed behavior, but their precise role remains unclear. Several lines of evidence suggest that MPFC is more important than LPFC for outcome-guided response selection. To examine this, we trained two subjects to perform a task that required them to monitor the specific outcome associated with a specific response on a trial-by-trial basis. While the subjects performed this task, we recorded the electrical activity of single neurons simultaneously from MPFC and LPFC. There were marked differences in the neuronal properties of these two areas. Neurons encoding the response were present in both areas, but in MPFC, there were also neurons that encoded the outcome. In particular, neurons encoded the subject's intended response and how preferable the received outcome was. Thus, only in MPFC was all the information necessary to solve the task encoded. In addition, largely separate populations of MPFC neurons encoded the response and the outcome. Neurons encoding the outcome were in the anterior parts of MPFC: posterior to the corpus callosum, there was a marked drop in their incidence. Our results suggest differences in the contribution of MPFC and LPFC to action control. MPFC neurons encode the desirability of the outcome produced by a specific response on a trial-by-trial basis. This capability may contribute to several of the functions of MPFC, such as action valuation, error detection, and decision making.

Predicting odor pleasantness from odorant structure: pleasantness as a reflection of the physical world.

Although it is agreed that physicochemical features of molecules determine their perceived odor, the rules governing this relationship remain unknown. A significant obstacle to such understanding is the high dimensionality of features describing both percepts and molecules. We applied a statistical method to reduce dimensionality in both odor percepts and physicochemical descriptors for a large set of molecules. We found that the primary axis of perception was odor pleasantness, and critically, that the primary axis of physicochemical properties reflected the primary axis of olfactory perception. This allowed us to predict the pleasantness of novel molecules by their physicochemical properties alone. Olfactory perception is strongly shaped by experience and learning. However, our findings suggest that olfactory pleasantness is also partially innate, corresponding to a natural axis of maximal discriminability among biologically relevant molecules.