Justin Morneau said his body has healed from an injury-plagued 2011 season. The question now, the 2006 American League most valuable player said, is whether his brain has, too.

"The only thing right now that I'm worrying about coming back, or bothering me as we go along, is the concussion stuff," he said Friday. "That's something that's just so unknown."

Morneau has been shut down during the past two seasons because of concussions, suffered just more than a year apart. And as he started spring training at the Lee County Sports Complex, he acknowledged the possibility that concussions could end his career prematurely.

That reality tempered an otherwise positive day for the Twins first baseman.

Morneau, 30, took batting practice in the cage and on the field, and went through infield drills with teammates in the first full-squad workout of the year. Considering what he's been through in just the past 12 months, that in itself was an accomplishment. In addition to the concussion, Morneau had surgeries to repair a pinched nerve in his neck, to stabilize his left wrist, to remove a cyst from his right knee and clean his left foot of bone spurs.

"The foot, the knee, the wrist, I don't see that limiting me at all going forward," he said.

It's the mystery of the brain that is tempering his enthusiasm, even if it's only slightly. Though science knows more about concussions than ever, treating them is still something of an art form. Recovery