BOX 8-1

Experience, Learning, “Exercise,” and the Brain

Some neuroscientists are trying to understand learning at the level of the nerve cells and the synaptic connections through which they communicate. As noted in the text, early work found that rats reared in a complex environment exhibited substantial increases in the numbers of synapses in various parts of the brain. These studies have shown, however, that formation of new synapses is probably one of the mechanisms underlying memory. Follow-up studies examining motor skill learning in adult rats found that animals that performed a lot of effortful exercise without significant learning formed new blood vessels in their brains but no new synapses. If they learned motor skills, with minimal exercise, they formed synapses but not new blood vessels (Black et al., 1990). This shows both that (1) there are components to the brain's adaptation to the environment beyond neurons and synapses and that (2) making new synapses is associated with learning. In addition, this research has shown that the ability to add synapses in response to housing in a complex environment or learning something new is a lifelong property of the brain—not something lost at an early age—which is precisely what we would expect for memory.

time if the rats were removed from the environment. The intervention provided by the complex cages thus functioned more like the tetanus vaccine, which requires regular boosters, than the smallpox vaccine, which inoculates against disease with a single injection. As this book shows, most early interventions for humans act more like the tetanus than the smallpox vaccine.

Studies of complex environments in rats have also revealed the role that such environments can play in processes of recovery. For example, the detrimental behavioral effects of prenatal exposure to low to moderate levels of alcohol in rats (e.g., motor dysfunction and impairments in learning spatial tasks) can be greatly attenuated by raising the animals in a complex environment (Hannigan et al., 1993). A program of forced motor skill training in alcohol-exposed rats nearly eliminated motor dysfunction, and it also increased synapse number in their cerebellar cortex (Klintsova et al., 1997, 1998). Finally, increasing the complexity of the environment before or after brain damage in developing and adult rats enhanced recovery from the impairments produced by damage to various brain areas, probably through mechanisms that involve the development of alternative strategies rather than the direct recovery of lost functions (see Kolb and Whishaw, 1998).

This research on complex environments certainly suggests that better

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