Born with only half a brain, Mack can speak normally, graduated from high school and has an uncanny knack for dates.
At 27, doctors determined that the right side of her brain had essentially rewired itself to make up for function that was likely lost during a pre-birth stroke. But her childhood and young adult years were fraught with frustration.
Ten years ago, Dr. Jordan Grafman, chief of the Cognitive Neuroscience Section at the National Institutes of Health, finally diagnosed the problem. Video Watch how Mack's brain healed itself »
An MRI scan revealed she was missing nearly all the left side of her brain. While it was clear Mack has some problems, Grafman said he and the family were shocked by the extent of the damage.
"We were surprised to see the extent of the lesion in her brain, which basically took away the left side of her brain," said Grafman. "There's some very deep structures remaining, but the surface of her brain, the cortex is 95 percent gone and some of the deeper structures, structures that control movement, are missing. These are all structures that are important for movement, behavior, cognition."
The only answer, Grafman said, was that Mack's brain has rewired itself. The remaining half took over some of the essential functions that are normally done by the left, such as speaking and reading. That rewiring, however, came at a cost.
"Michelle has fairly normal language abilities, certainly basic language abilities, she can construct a sentence, she can understand instructions, she can find words when she's talking, but actually she has some trouble in some aspects of visual-spatial processing," said Grafman.
"It's quite possible that in her learning, in her development, when the right hemisphere either took over or developed some of the language abilities that it cost her in some of the skills that are normally mediated by the right side of the brain," added Grafman.
In the 10 years since Grafman first diagnosed Mack, she has seen some intellectual functions improve, the doctor said. Recovery has not been perfect, however. Mack still struggles with abstract concepts and becomes easily lost in unfamiliar surroundings.
The diagnosis explained why Mack had experienced a lifetime of difficulty controlling her emotions.
"He's helped us understand the reason why I tend to throw fits, temper tantrums," she said. "It was because I was missing half my brain."
Mack will always have some problems, but dad Wally Mack said that Grafman's diagnosis and treatment answered a lot of questions and gave him hope.
"Dr. Grafman explained that the right hemisphere is taking over, and it might take her a little while longer to get there with all the rewiring that has to take place," he said. "But that told us all these bad days are behind us and there are nothing but good days ahead."
Michelle Mack is now 37 and lives with her mother and father. She works from home doing data entry for her church. She is fairly independent, pays rent and can do most household chores. She realizes she'll need help for the rest of her life but wanted to tell her story to make it clear that she is not helpless.
"I wanted to do this so people like producers, photographers and security guards and police officers learn about people like me," she said, "that I'm normal but have special needs, and that there are a lot people like me, so that they could be more understanding."