What is the neurophysiological substrate of memory?

• Two studies looking at long-term neural changes associated with behavior in– Motor tasks • Running, Reaching task• (Primary motor cortex)

– Sensory tasks• Enriched environment• barrel cortex

Motor learning and novel sensory experience promote rapid dendritic spine formation

Enhanced spine dynamics during adolescent motor training is region- and learning-specific.

A fraction of newly formed spines persists over weeks and correlates with performance after learning.

Novel experience promotes spine elimination..

Maintenance of daily formed new spines and spines formed during early development throughout life.

Spine maintenance in different cell types and cortical layers.

Summary

• New experiences lead to the fast (within 1 hour) formation of new dendritic spines in brain areas used to perform new behavior

• The number of remaining new spines formed during the new experiences predicts the success of newly acquired behaviors.

• Pruning increases after new spine formation to bring back total number of spines to baseline level.

• The remaining spines appear to last long enough to sustain memory across a lifetime.

How applicable are these studies to humans?

• Humans have several types of long-term memory– Implicit: Procedural, classical, priming– Explicit: consciously accessed memory, declarative

and semantic