What do Charlize Theron, Jim Carey and Nicole Kidman have in common besides memorizing scripts, learning lines and making movies? They all have dual citizenship: Ms. Theron is a dual citizen of South Africa/USA; Jim Carey, Canada/USA; and Ms. Kidman, Australia/USA.

If you want to double up your brainpower so you can memorize lines or just a shopping list, researchers at Johns Hopkins say dual learning is the key. Their recommendation: a program called "Dual N-Back" that strengthens your working memory by up to 30 percent.

Dr. Mike has long been a proponent of Double Decision, a brain game that improves brain-processing speed. (Research has shown that it can decrease dementia in 73-to 83-year-olds by over 33 percent when practiced for five weeks.) Dual N-Back is an excellent complement to that. It works on a similar principal of exercising your short-term memory and challenging your recall. As you progress through Dual N-Back, the levels become more and more difficult, just like Double Decision, and your brain becomes more and more used to flexing its muscles in your prefrontal cortex.

So, to improve your sharpness and upgrade your executive function (it manages learning and decision-making), check out these intriguing programs. The demos for both are free, but Double Decision has a small maintenance fee. You can explore it at www.brainhq.com. The Dual N-Back program carries no charge unless you want to contact the developers and customize your own scalable features into the program. Check it out at https://dual-nback.io/.

Mehmet Oz, M.D., is host of "The Dr. Oz Show," and Mike Roizen, M.D., is chief wellness officer and chair of Wellness Institute at Cleveland Clinic. To live your healthiest, tune into "The Dr. Oz Show" or visit www.sharecare.com.

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