BOX 5.1 Making Rats Smarter How do rats learn? Can rats be "educated?" In classic studies, rats are placed in a complex communal environment filled with objects that provide ample opportunities for exploration and play (Greenough, 1976). The objects are changed and rearranged each day, and during the changing time, the animals are put in yet another environment with another set of objects. So, like their real-world counterparts in the sewers of New York or the fields of Kansas, these rats have a relatively rich set of experiences from which to draw information. A contrasting group of rats is placed in a more typical laboratory environment, living alone or with one or two others in a barren cage--which is obviously a poor model of a rat's real world. These two settings can help determine how experience affects the development of the normal brain and normal cognitive structures, and one can also see what happens when animals are deprived of critical experiences.      After living in the complex or impoverished environments for a period from weaning to rat adolescence, the two groups of animals were subjected to a learning experience. The rats that had grown up in the complex environment made fewer errors at the outset than the other rats; they also learned more quickly not to make any errors at all. In this sense, they were smarter than their more deprived counterparts. And with positive rewards, they performed better on complex tasks than the animals raised in individual cages. Most significant, learning altered the rats' brains: the animals from the complex environment had 20-25 percent more synapses per nerve cell in the visual cortex than the animals from the standard cages (see Turner and Greenough, 1985; Beaulieu and Colonnier, 1987). It is clear that when animals learn, they add new connections to the wiring of their brains--a phenomenon not limited to early development (see, e.g., Greenough et al., 1979).