During middle adulthood, crystallized intelligence tends to , and fluid intelligence tends to .

During middle adulthood, crystallized intelligence tends to improve upon or maintained, and fluid intelligence tends to declines.

Explanation:

Crystallized intelligence refers to the capacity of a brain to recall the knowledge that was stored in it through learning and experience. While fluid intelligence is the ability of also a dedicated part of the brain to think, solve problems at hand without having to make use of past learning and experience. Middle adulthood, from the question, signifies the period between early adulthood and late adulthood. This varies among cultures, life expectancy also differs too among cultures, however, this age might be between 40 to 65 years.