When Susan Brandt, 66, of Miami, saw her parents starting to lose their memory, she turned to online games at a website called Lumosity in an attempt to sharpen her mind.

Related: Seven tricks to improve your memory.

"The single biggest thing I'm afraid of - and [it] is not getting cancer, not having rheumatism, not being able to walk around - it is losing your mind," she said. "It is being senile."

When Brandt started forgetting people's names, she turned to a Lumosity game called Familiar Faces.

"I don't have to feel quite so guilty when I'm sitting there at 1 a.m. playing a computer game," Brandt said.

Lumosity, with 60 million users, is the most popular of several online brain training programs created by neuroscientists that promise to improve brainpower.

The games are modeled after the concept of a personal trainer to teach a person how to bulk up the brain like a muscle. Each session lasts about 15 minutes per day, and according to studies, after about 10 hours, thousands of people report improvement in their memory and problem solving.

In an October interview with the Pittsburgh Post-Gazette, Teresa Heinz Kerry, Secretary of State John Kerry's wife, touted Lumosity for helping her brain to recover after she was taken to the hospital following "seizure-like" symptoms during the summer.

Related: Experts remain skeptical as brain games get popular.

Dan Hurley, 56, of Montclair, N.J., said he became a fan after he found that he'd gotten smarter after using Lumosity to train his brain for 3.5 months.

"Things like crossword puzzles and reading and other things that we all do, they're great for keeping you at the level you're at, for maintaining, but if you want to expand your abilities, you have to do things that progressively get harder," said Hurley, a science journalist and author of " Smarter: The New Science of Building Brain Power."

He said he not only became more effective in daily life but also became better at multitasking.

"According to my performance on a test of intelligence, my intellectual abilities increased 16 percent," Hurley said. "These games are challenging and if they're not challenging, they're not working."

ABC News' Maggy Patrick contributed to this piece.