... daily consumption of beverages sweetened with high-fructose corn syrup or sucrose can impair the ability to learn and remember information, particularly when consumption occurs during adolescence.
Both adult and adolescent rats were given daily access to sugar-sweetened beverages that mirror sugar concentrations found in common soft drinks. Adult rats that consumed the sugar-sweetened beverages for one month performed normally in tests of cognitive function; however, when consumption occurred during adolescence the rats were impaired in tests of learning and memory capability.
... consuming sugar-sweetened drinks is ... interfering with our brain's ability to function normally and remember critical information about our environment, at least when consumed in excess before adulthood."
In addition to causing memory impairment, adolescent sugar-sweetened beverage consumption also produced inflammation in the hippocampus, an area of the brain that controls many learning and memory functions. [emphasis mine]