Marian Diamond; neuroscientist

Marian Diamond, a pathbreaking neuroscientist whose research — including a study of Albert Einstein's preserved brain — showed that the body's three-pound seat of consciousness was a dynamic structure of beautiful complexity, capable of development even in old age, died July 25 at an assisted-living community in Oakland, California. She was 90.

A daughter, Ann Diamond, confirmed her death but did not know the cause.

Diamond, a professor emerita of integrative biology at the University of California at Berkeley, was long known on campus as the woman with the hat box. Decorated on the outside with a floral print and carried by a bright blue string, it contained a preserved human brain, the crucial prop for her lesson that the brain was, as she once wrote, "the most complex mass of protoplasm on this earth and, perhaps, in our galaxy."

Diamond was considered a foundational figure in modern neuroscience. She provided the first hard evidence demonstrating the brain's plasticity — its ability to develop, to grow, even in adulthood. "In doing so," her colleague George Brooks said in a statement, "she shattered the old paradigm of understanding the brain as a static and unchangeable entity that simply degenerated as we age."

Her breakthrough occurred in the early 1960s, when — building on the work of psychologist Donald Hebb — she began studying the brains of lab rats. Rats that were raised alone, in small and desolate cages, had more trouble navigating a maze than did rats that were raised in "enriched" cages, with toys and rat playmates.