Berkeley brain researcher Marian Diamond has studied millions of brain cells, but this time was different. This time, she was looking at cells taken from the 20th century's most celebrated clump of human intelligence -- Albert Einstein's brain.

Nearly 30 years after the great physicist's death, Diamond was peering through a microscope and counting Einstein's neurons and other brain cells. She cannot find words to describe the experience.

"You feel special and thrilled and excited," she says. "I mean, there's no descriptive adjective to say what you really feel."

Four sections of Einstein's brain -- each the size of a sugar cube -- had been sent to her in a jar of preservative by Dr. Thomas Harvey, the pathologist who had performed the autopsy on Einstein. He died at 76 in Princeton Hospital in 1955.

For several years, Diamond and a team of researchers at Berkeley have been trying to find out what keeps the aging brain healthy. They had a growing body of data from studies on rat brains suggesting that animals who live in an "enriched environment" -- with lots of sensory stimulation -- have healthier brains.

In other words, an active brain is a healthy brain, says Diamond, professor of anatomy at the University of California at Berkeley.

Diamond's research focused on two types of brain cells: glial cells and neurons. Glial cells support and nourish neurons, which handle most of brain's mental "work." She hypothesized on the basis of earlier findings that an active, healthy brain might have more glial cells per neuron than an inactive brain.

Diamond already had glial-cell data from extensive studies on 11 brains from men aged 49 to 80.

"Then we heard that Einstein's brain was sitting in a cardboard box in Kansas," she recalls. "We saw a chance to study the most highly evolved brain available in our lifetime."

She called a colleague in Kansas and confirmed that Harvey, who now works in Weston, Mo., still had the brain. Before Einstein's cremation, in accordance with his wish, his brain was removed for research and entrusted to Harvey.

Diamond negotiated with Harvey, explaining her previous research and her wish to compare her data with samples taken from Einstein's brain. Harvey agreed to send her four samples cut from the right and left frontal lobes and the right and left lower parietal lobes -- the parts of the brain associated with abstract thinking.

They came in the mail -- four "superbly preserved" three-quarter-inch squares of tissue in fluid, Diamond said, "like little sugar cubes. That's all we needed." She and coworkers removed the brain tissue and cut slices -- six thousandths of a millimeter thick -- to study under the microscope.

It's what Diamond calls "old-fashioned research," the kind of methodical laboratory data-collection that can be tedious -- unless the brain you're studying happen to be Albert Einstein's. They took the ultrathin slices of brain tissue, stained them with a dye to make the glial cells stand out from the neurons, put them under a microscope and began counting cells.

Then they tallied the ratio of glial cells to neurons in Einstein's brain and compared that with the other 11 brains they already had tested. The ratio in Einstein's brain was higher than average for all four samples, but the difference, by the most conservative statistical standard, was deemed significant in only one sample -- the one from the left lower parietal lobe.

That is the part of the brain most involved with higher mathematical and language abilities, Diamond says.

Diamond summarized her findings last month at the Winter Conference on Brain Research in Vail, Colo. An article titled "The Brain of a Scientist: Albert Einstein," has been accepted for publication in the Journal of Experimental Neurology.

"The belief is that glial cells nourish the neurons, and there being more in a given person might indicate that that person has a more active brain," says pathologist Harvey, coauthor of the article.

Asked where the rest of Einstein's brain is, Harvey says: "It's in a number of places." But he declined to be more specific or say how many researchers are studying it. He has never published research on Einstein's brain, of which he once remarked: "It looks just like anybody else's."

Diamond suggests that the above-average concentration of glial cells in the part of Einstein's brain involved with abstract reasoning is consistent with Einstein's statements about his own thinking.

"When I examine myself and my methods of thought I come to the conclusion that the gift of fantasy has meant more to me than my talent for absorbing positive knowledge," Einstein once said.

But the role of glial cells in thinking is not fully understood. And the extra glial cells might be related to aging, says Dr. Janice Stevens, staff psychiatrist at the neuropsychiatry branch of the National Institute of Mental Health.

"As we get old, unfortunately, the nerve cells decrease and the glial cells take their place," Stevens says. "But that didn't seem to hamper Einstein too much.

The human brain loses nerve cells steadily from the time of birth, even as it nearly quadruples in size by adulthood. The loss of cells is more than offset by growth of the "wiring diagram" -- the brain connections that, as Stevens puts it, "make us smart."

Stevens calls Diamond's finding interesting, but cautions that no one knows exactly how -- or even whether -- glial cells help the brain think.

"In general, more glial cells is bad news, not good news," she says, because they're scar tissue and skeletal structure, not thought-producing cells.

"Many idiots have big brains loaded with glial cells," she says.

Whatever the results of research such as Diamond's, however, the fascination with Einstein's brain is bound to continue.

Stevens tells a possibly apocryphal story about the time researchers at Princeton did an electroencephalogram (EEG) on Einstein. They were measuring the alpha wave, which indicates the brain's "idling activity." Alpha wave activity disappears with arousal or intense brain activity.

The researchers started the EEG, and Einstein, so the story goes, was calmly solving quadratic equations in his head. His alpha wave, indicating mental idling, was very high.

All of a sudden, the alpha wave went flat. Alarmed, the researchers rushed in and asked Einstein what was wrong.

"I hear it's raining outside," said the world's greatest scientist. "and I've left my rubbers at home."