Carotenoids can be found in such vegetables as carrots, pumpkins, peppers, tomatoes, potatoes, oranges, kale, spinach, and peas.
For their study, the researchers included 43 adults aged between 65 and 86 years. They asked to learn and remember pairs of unrelated words while undergoing through functional MRI. The assessed the level of lutein and zeaxanthin (kinds of carotenoids) in the retina.
Scientists found that higher levels of lutein and zeaxanthin were associated with a lower signal in several areas of the brain. This indicated lower brain activity in individuals with higher levels of carotenoids, which meant they had not had to work as hard to complete the task.
More information about the research here.