When Marian Diamond was growing up in Southern California, she got her first glimpse of a real brain at Los Angeles County Hospital with her dad, a physician. She was 15. Looking back now, at age 90, Diamond, a Berkeley resident, points to that moment as the start of something profound — a curiosity, wonderment, drive.

“It just blew my mind, the fact that a cell could create an idea,” Diamond said in a recent interview, reflecting on her first encounter with that sinewy purple-tinged mass.

She didn’t know that this was the start of a distinguished legacy that would stretch for decades, touching millions. But today, she’d be one of the first to scientifically equate that adolescent thrill with her life’s work.

Because she helped prove a link.

Brains, we now know, thanks in large part to research by Diamond, thrive on challenge, newness, discovery. With this enrichment, brain cells are stimulated and grow.

This week, Diamond, a UC Berkeley emeritus professor of integrative biology and the first woman to earn a PhD in anatomy at Cal, is being honored by the Berkeley City Council, which is designating March 14 as Marian Diamond Day.

And on March 22, KQED TV will air a new documentary film about her life’s work, My Love Affair With the Brain. (Scroll down to watch the trailer.)

The city’s resolution reads in part: “Dr. Diamond is one of the founders of modern neuroscience, her research established that the human brain can be altered by either enriched or impoverished environments at any age from prenatal to extremely old age, and as a consequence changed the way we think about plasticity of the brain.”

Diamond, who raised four kids in Berkeley, retired from UC Berkeley three years ago after nearly 60 years of teaching. It turned out that her passion for research was matched by a second love, teaching others what she had learned.

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And she was effective.

In addition to earning raves from decades of UC Berkeley classroom students, Diamond became a YouTube teaching superstar. Her online lessons have received 1.7 million hits and counting, making her a global educational sensation.

“My siblings and I have all been teachers and that’s no surprise given that she was so invested in teaching,” said Rick Diamond, one of Marian Diamond’s children and an expert in sustainable energy building design who recently retired from the Lawrence Berkeley National Lab. “It’s so much a part of who she is.”

Diamond’s riveting YouTube lectures, breakthrough brain research, and pioneering status as a woman in science caught the attention of Berkeley documentary film producers Catherine Ryan and Gary Weimberg, of Luna productions.

Ryan had taken what she described as a month-long sabbatical from daily work to immerse herself in UC Berkeley culture and academia in search of film material, sitting in on classes, pouring over her computer. Specifically, after finishing a movie about the Iraq war, Soldiers of Conscience, the team was looking for something a little more upbeat.

“I went online and looked at the first two of [Diamond’s] YouTube anatomy lectures and thought, ‘Wow, science, a woman, good news about anatomy, good news about what’s happening in the brain.’ I was just completely turned on and that’s what launched it,” Ryan said.

Asking around, it didn’t take long for Ryan to find an acquaintance who knew Diamond. They had lunch at the Berkeley Faculty Club, and the project grew roots.

My Love Affair with the Brain has its local PBS debut March 22 (8 p.m., Channel 9) but has screened nationally for about a year, winning numerous awards. The film hits a delightful balance of telling a story about a scientist, and about science. Actress Mayim Bialik, who plays a neuroscientist in the The Big Bang Theory TV show and is a real-life neuroscientist, narrates.

It helps that Diamond, who agreed to the film only when assured it would teach science, Ryan said, is charming, funny, easy to understand, and twinkles with enthusiasm.

Her trademark teaching-tool: an elegant floral hatbox, from which she gently lifts out a pickled brain.

“People come up to us and say ‘my life has changed by watching this film,’” Weimberg said. “They suddenly are more connected to their own brain.”

Being a woman scientist is less significant to Diamond than to many of her admirers, Rick Diamond, Weimberg and Ryan agree. “She doesn’t like being labeled as a woman scientist or a feminist, she just did what she wanted to do,” Rick Diamond said.

Diamond’s research helped prove that the brain can physically change in response to external stimulation, growing cells when exposed to enriching experiences, even in older age. And that without enrichment, the brain can shrink.

This opened the gate to critical new thinking in many arenas including childhood education, senior care, the immune system, and general lifestyle health.

Before this, the accepted scientific belief was that brain growth was predetermined by genetics, static, and not influenced by external elements.

Diamond was also the first scientist to study and publish findings on Einstein’s brain, a chapter that proved controversial for a few reasons, but advanced understanding on the importance of glial cells which surround, protect and nourish neurons, the brain’s activity cells.

The film, which included among its audience-testers 150 Berkeley High students, is also poignant: introducing Diamond as she retires, capturing her contagious joy of teaching and her devotion to using her research to improve lives.

The film and Berkeley proclamation come at a time when Diamond’s health is declining. Yet she is still cheerful, according to her son.

“She really believed and embodied that one person can make a difference,” Rick Diamond said, “Whether as a teacher, researcher, writer or friend.”

My Love Affair with the Brain (60 second promo) from Luna Productions on Vimeo.