As Pam approached menopause, she thought she was losing her mind.
"Oh my god, it was horrible," said the 57-year-old from Glenwood Springs, N.Y. "I could not remember words. Even a word like 'cat' might not come to mind. I'd have to go through the alphabet to come up with the word. And words I'd spelled all my life, I'd think I spelled them wrong."
Recently, Pam, who did not want her last name used, enrolled in an introductory mortgage class hoping to learn to be a lender. A high-powered business consultant with experience in banking, she thought she'd pass the exam with flying colors.
"I was in the class for one day and I cannot tell you one thing I learned," she told ABCNew.com. "I walked out laughing because everyone else was getting it. It was like Greek to me.
"In the end, I didn't take the test. I said, 'Forget it, no way," said Pam. "It's very upsetting. Normally this would have come easily to me."
For Pam and millions of other women in their 40s and 50s, "brain fog" seems to roll in as their menstrual cycles wane. Many fear it will never lift, signally the end of their professional lives.
Research published this week in the journal Neurology confirms that women do, indeed, lose their intellectual edge in peri-menopause -- the five- or six-year period leading up to the last menstrual cycle. But the ability to learn rebounds in the later phases of menopause.
For four years, University of California Los Angeles (UCLA) researchers looked at 2,362 women between the ages of 42 and 52 who took tests to measure verbal memory, working memory and processing speed at four different points during menopause: pre-menopause, early peri-menopause, late peri-menopause and after menopause.
The Study of Women's Health Across the Nation (SWAN), which is based at seven sites throughout the United States and is funded by the National Institute on Aging, concluded that women taking hormones before their last period improved their cognitive skills, but after that, the hormones had a detrimental effect.
"It looks like the time at which you take hormones matters," said Dr. Gail Greendale, head investigator for the SWAN study at UCLA.
When tested year after year, women in their 40s and 50s "get better each time," she said.
"There's a learning effect," Greendale told ABCNews.com. "But on the test of speed, we found that when you get to late peri-menopause, (learning) takes about an 80 percent hit.
"You're a little off your game," she said. "You're not forgetting your way to the grocery store, but you don't feel as sharp or fast on the uptake."
This latest research is significant because it may clear the way for women in the earliest phases of menopause -- when they are typically younger and at the height of their professional careers -- to safely take estrogen to give them their edge back.
Since then fewer women are turning to hormone replacement therapy, according to doctors.
But comparing the two studies is "apples and oranges," according to Greendale.
The WHI iinvolved postmenopausal women 65 and over and was designed to test the effects of hormone therapy, diet modification, and calcium and vitamin D supplements on heart disease, fractures, and breast and colorectal cancer.