Doctors have some answers for why Perry didn't

The stammer. The furrowed brow. The inability to spit out a basic fact that you've been carrying around in your head for weeks.

Call it a brain freeze or a senior moment - the sort of lapse that befell Texas Gov. Rick Perry in a GOP presidential debate this week can happen to anyone.

Except not, in most cases, on the unforgiving stage that is live national television.

Physicians say multiple factors can contribute to this kind of mental fumble, and as a 61-year-old on a rugged campaign schedule, Perry was subject to more than one.

Age, fatigue, and stress all can play a role, said H. Branch Coslett, interim chair of the neurology department at the University of Pennsylvania's Perelman School of Medicine. With the names of things, in particular, the brain becomes less efficient over the years at summoning them forth, as connections between brain cells weaken, he said.

"It's more likely to happen at 61 than at 31," Coslett said. "And it's more likely to happen at 91 than at 61."

Then the more you try to think of the elusive name, the harder it gets with mounting stress, the physician added. Stop trying to think of it, and the answer bubbles forth.

In Perry's case, he tried Wednesday to name three federal agencies that he wanted to eliminate, and came up with only two - the Departments of Education and Commerce. Given a second chance moments later in the debate, he stumbled in naming even the first two.

Laughter was followed by painful silence before he admitted defeat.

"And let's see. I can't - the third one - I can't. Sorry," Perry said. "Oops."

Salman Akhtar, a professor of psychiatry at Thomas Jefferson University, agreed that fatigue and the rigors of campaigning could have been involved in the high-profile gaffe.

In theory, Akhtar added, some internal conflict also could have tripped up the candidate. For example, Perry might have been thinking that axing those federal agencies would entail the loss of thousands of jobs, the professor said.

"He must feel a little guilt," said Akhtar, a psychoanalyst.

Memory difficulties become even more common in people with mild cognitive impairment, but Akhtar and Coslett said this would be unlikely in someone of Perry's age.

As for that elusive third agency, it was revealed to be the Department of Energy. At least his campaign had fun with it. A poll on Perry's website asked:

"What part of the Federal Government would you like to forget about the most?"