Labelling and optical erasure of synaptic memory traces in the motor cortex

Dendritic spines are the major loci of synaptic plasticity and are considered as possible structural correlates of memory. Nonetheless, systematic manipulation of specific subsets of spines in the cortex has been unattainable, and thus, the link between spines and memory has been correlational. We developed a novel synaptic optoprobe, AS-PaRac1 (activated synapse targeting photoactivatable Rac1), that can label recently potentiated spines specifically, and induce the selective shrinkage of AS-PaRac1-containing spines. In vivo imaging of AS-PaRac1 revealed that a motor learning task induced substantial synaptic remodelling in a small subset of neurons. The acquired motor learning was disrupted by the optical shrinkage of the potentiated spines, whereas it was not affected by the identical manipulation of spines evoked by a distinct motor task in the same cortical region. Taken together, our results demonstrate that a newly acquired motor skill depends on the formation of a task-specific dense synaptic ensemble. A new light-activated probe that targets recently active neuronal spines for manipulation induces shrinkage of recently potentiated spines following a motor learning task; spine shrinkage disrupted learning, suggesting a causal relationship between the specific subset of targeted spines and the learned behaviour. Memory tracked using synaptic optogenetics It has long been speculated that changes in spine stability and potentiation are the structural correlates of memory, but tools to help link these structural changes to specific memories have not been available. Akiko Hayashi-Takagi et al . have developed a new light-activated probe that targets recently active spines for manipulation. Optically induced shrinkage of recently potentiated spines following a motor learning task is seen to disrupt learning, suggesting a causal relationship between the specific subset of targeted spines and the learned behaviour.