Animal studies have shown which of the following to be true?

1) Impoverished environments can actually help shield a young brain from damage caused by teratogens.

2) Enriched environments, unfortunately, have no influence on brains damaged by a mother's drug use during pregnancy.

3) Enriched environments help the young overcome brain damage by increasing myelinization.

4) Enriched environments can help the young brain overcome damage caused by some teratogens.