Both Hebbian plasticity and neuromodulation essential to memory formation

The influential Hebbian plasticity hypothesis suggests that an increase in the strength of connections between neurons whose activity is correlated produces memories. Other theories, however, propose that neuromodulatory systems need to be activated together with Hebbian plasticity mechanisms to engage memory formation.

The present work published in the journal PNAS provides direct in vivo evidence supporting the idea that a parallel mechanism involving neuromodulation and Hebbian processes is both necessary and sufficient to trigger synaptic strengthening and behavioral associative memory formation. This parallel process may represent a general mechanism used by many learning systems in the brain.