SACRAMENTO, Calif. — Size does matter after all when it comes to sexual satisfaction, according to Dr. Daniel Amen.

Forget those enlargement offers in your e-mail inbox: We're talking about the Big B — the Brain.

"In order to have a great sex life, you have to have a great brain," Amen says during a phone interview from Newport Beach, Calif., where he lives.

Brain greatness, he explains, requires avoiding activities that can literally shrink the brain, including abusing drugs and alcohol.

Amen is a clinical psychiatrist and brain-imaging expert who also brings a single guy's interest to the topic.

"I like to look, that's all I can say," he says, savoring the double-entendre of expressing his love of the view inside the skull. Since 1989, he has opened four Amen Clinics, including one in Fairfield, where brain scans are key to evaluation. (You can check out hundreds of brain scans and more at www.amenclinic.com.)

Drawing on his work, Amen has written books about dealing with such hardships as Alzheimer's disease, anxiety, depression and attention deficit disorder.

His latest book, "Sex on the Brain: 12 Lessons To Enhance Your Love Life" (Harmony Books, $24, 278 pages), falls into his growing catalog of writing about how to enhance the good life, as author of the "Head Check" column in Men's Health magazine and in books such as "Change Your Brain, Change Your Life" and "Making a Good Brain Great."

"It just seemed like nobody was putting the brain right in the middle of our sex lives," Amen says.

The way he looks at it, sex largely occurs in your brain. Specifically, it appears that the right temporal lobe may be called the B Spot, the part of the brain that is "the seat of orgasms."

Amen's interest in his latest topic is more than just professional. "In large part, I did this book for me; there's a lot of me in it," he says.

Amen is 52, and the way to his heart is definitely through his brain.

"I'm just always looking for the perfect brain," he says. "If I date someone long enough, they get scanned."

His daughters — who are 19, 24 and 30 years old — are used to Daddy offering to scan their dates. Such scans, he writes, provide telling information, akin to "meeting someone's parents or taking them on vacation."

He feels pretty good about his own brain's sex appeal.

"At 52, my brain is better than it was at 37," Amen says.

He says evaluating the brain's physical condition can provide relationship-saving clues. He recounts one case where a husband suddenly turned into a colossal jerk, which almost led to divorce. Brain imaging uncovered evidence that the man was suffering brain damage from chemical exposure on the job. Once the exposure was stopped, his brain's health — and his marital happiness — were restored.

The moral of such stories, Amen says, is that taking care of your brain physically is key to a satisfying romantic life. Like your body, your brain's good health requires aerobic exercise, a healthy diet and avoidance of harmful chemicals, including too much alcohol and caffeine.

Amen also says a little reasoning and neuro-knowledge is needed to override the differences in the way men's and women's brains operate.

"Male-female communication styles are radically different, brain-based and hard-wired," Amen writes.

Men, Amen says, would be well-served by remembering to listen without feeling compelled to jump in with solutions.

He says women would be best served by being direct in expressing their desires, without getting too wordy or expecting men to read any subtle cues about how they're feeling.

"Women want guys to read them like their girlfriends, and it just causes great pain," he says. "Repetition and good coaching is how men learn. So help 'em out."