Reinforcement sculpts synaptic ensembles for operant dendritic control

In layer 5 motor cortex of mice, optogenetic reinforcement linked to operant apical dendritic activity selectively strengthens and weakens individual spines, sculpting reproducible synaptic ensembles.

• Why it matters: Reinforcement learning depends on modifying outcome-relevant synapses, but how reinforcement selectively reshapes dendritic inputs into coordinated ensembles is unclear.
• What they did: Using longitudinal two-photon imaging with a closed-loop optical BMI, mice controlled an auditory cursor via selected apical dendrites, while target acquisition triggered optogenetic reinforcement. Plasticity direction depended on activity timing relative to reinforced dendritic events and on pre-existing temporal organization, with enrichment in synergistic versus antagonistic synaptic groups.
• The result: Learning produced increasingly reproducible, selectively recruited, temporally focused synaptic ensembles, including incorporation of newly formed spines; blocking striatal dopamine receptor signaling impaired BMI learning and cortical reorganization of target dendrites.

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