"Learning and memory can occur at synapses.  Regardless of the species, brain location and memory type, many of the underlying mechanisms appear to be universal.  Events are represented first as changes in the electrical activity of the brain, then as second messenger molecules, and next as modifications of existing synaptic proteins.  These temporary changes are converted to permanent ones—long-term memory—by altering the structure of the synapse."—from Mark F. Bear, Barry W. Connors, & Michael A. Paradiso in Neuroscience:  Exploring the Brain, Lippincott Williams & Wilkins,2001, p.792