For enrichment (environmental) effects to work, the animal must actively explore the environment, not simply passively watch it. These brain alterations are no matter of tinkering. Many billions of synapses can be made or lost this way, a capacity that lasts to some extent across the life span. (Quartz, Steven R., PhD, and Terrence J. Sejnowski PhD. Liars, Lovers, and Heroes. NY: HarperCollins Publishers Inc., 2002, p 236)