Wednesday, August 21, 2013

How the brain shifts between purpose and habit.

Gremel et al. do a nice explication of the brain's upstairs/downstairs story, illustrating with direct electrical recordings how the mouse brain switches between different action strategies (goal-directed and habitual). Goal directed action recruits the frontal cortex while habitual action correlates more with activity in a deeper subcortical structure, the striatum. More indirect imaging data show the story is almost surely same for us. It is the upstairs stuff that is more susceptible to aging, and most of us find it more of an effort to do novel versus habitual actions as we age.
Shifting between goal-directed and habitual actions allows for efficient and flexible decision making. Here we demonstrate a novel, within-subject instrumental lever-pressing paradigm, in which mice shift between goal-directed and habitual actions. We identify a role for orbitofrontal cortex (OFC) in actions following outcome revaluation, and confirm that dorsal medial (DMS) and lateral striatum (DLS) mediate different action strategies. Simultaneous in vivo recordings of OFC, DMS and DLS neuronal ensembles during shifting reveal that the same neurons display different activities depending on whether presses are goal-directed or habitual, with DMS and OFC becoming more and DLS less engaged during goal-directed actions. Importantly, the magnitude of neural activity changes in OFC following changes in outcome value positively correlates with the level of goal-directed behavior. Chemogenetic inhibition of OFC disrupts goal-directed actions, whereas optogenetic activation of OFC specifically increases goal-directed pressing. These results also reveal a role for OFC in action revaluation, which has implications for understanding compulsive behavior.

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