Long-term dynamics of amygdalo-motor circuit support the learning of incentive-motivated behaviors

The basolateral amygdala (BLA), traditionally known for its role in associative fear learning, may also play a role in self-initiated, incentive-motivated behaviors. However, it is unclear how the BLA contributes to learning to initiate neutral actions for a positive outcome. In particular, while the mouse secondary motor cortex (M2), a key region involved in spontaneous action initiation, is a major target of BLA glutamatergic output, it is unknown whether and how BLA-M2 communication is involved in the self-initiation of incentive-motivated actions. To address these questions, we trained head-fixed mice to press two initially neutral levers to obtain a water reward. Suppression of BLA-M2 synaptic signaling by tetanus toxin expression reveals its critical role in rapid behavioral learning. Consistently, we characterized how this synaptic communication scales with learning speed using two-photon microscopy of BLA axonal boutons in M2 during the task. We found functional assemblies of boutons that were activated during different steps of the behavior, suggesting well-separated roles: 1) controlling press initiation, 2) discriminative reporting of lever pressing, and 3) reporting licking. Longitudinal imaging of the same axons showed that single bouton activity remained stable for more than two weeks. Finally, when the preferred lever was devalued, the mice learned to reverse their lever preference, with the preparatory activity for pressing scaling with the preference of the chosen lever. These results suggest that BLA-M2 communication not only facilitates initial incentive-motivated behavioral learning but also contributes to value-based action selection.