"'Concussion' means a violent shaking. If the brain moves inside the skull, like an egg yolk inside an egg, you're at risk [of symptoms]," says Collins, who works with athletes at the high school and college levels on up through big-time professionals like Pittsburgh Penguins center Sidney Crosby and Minnesota Twins slugger Justin Morneau.

(Another question many ask: why do football players seem to be able to return days or weeks after concussions, while some baseball and hockey players are out far longer? Collins' theory: Head impact is so common in football that players susceptible to the injury are weeded out before reaching the NFL, leaving a concussion-resistant population at the top.)

Roberts began learning such facts two weeks after the Fenway incident. He was and remains more than happy with the treatment he has received from Oriole physicians, he says, but at the suggestion of his agent, he decided to contact Collins, a Ph.D. in neuropsychology whose department at the University of Pittsburgh is the world's largest research and clinical program devoted to evaluating and managing sports-related traumatic brain injury.

Collins says it took a him a few moments on the phone to determine he'd have good news and bad news for the player.

"Brian's symptoms indicated a specific kind of concussion, and we've learned a great deal about how to treat that type," he says.

But it was worst kind for an athlete to have — and the one that calls for the longest period of recovery.

Retraining the brain

Then and later, what Collins told Roberts helped clarify what the Oriole veteran had been going through. It framed what he'd be doing, painful and hopeful, over the next few difficult months.

And now that Roberts is beginning preparations for the coming year, and he and his doctor expect a fully healthy return for spring training, it suggests answers to a question fans always ask when an athlete disappears for months to deal with a concussion: What's taking so long?

Collins told Roberts he had suffered damage to his vestibular system, the part of the brain (located in the brain stem) that processes sensory cues, turning them into eye movement, balance and motion.

No region could be more crucial to an athlete, particularly one, like Roberts, whose agility is basic to his success.

"Look at Brian's swing. It's a thing of beauty," says Collins, a former ballplayer at the University of Southern Maine who competed in the 1989 College World Series. "The vestibular system is his money-maker."

It's also a system that consumes vast amounts of energy in any human being.

The brain contains billions of cells called neurons, he explains, and each is connected to an axon. It's energy passing across that network that causes human behavior.

A concussion sparks unwanted chemical reactions, though, releasing materials from those cells, including potassium, and causing the absorption of calcium. The changes constrict vessels and muddle transmission.

"The cells aren't working as they should. You get reduced blood flow to the brain. And you get this energy crisis," he says.

A vestibular concussion, it turns out, involves a high-functioning system most of us take for granted, the part of the brain that allows a person to move his or her eyes, take in visual information, and channel it into appropriate bodily movement.

That's why Roberts couldn't do seemingly simple things like going to the store or driving without getting sick — they demand frequent and rapid eye adjustments and plenty of integration.

"I was doing these things every day that aggravated the condition, and I had no idea," Roberts says.

Research has shown that simple head-and-eye exercises, eventually coordinated with body motion, can re-establish the neural pathways that control vestibular functions, and that this retraining of the brain reduces symptoms.