My favorite topic in psychology has always been memory. It gives everyone the ability to relive extreme emotions by replaying scenarios in their own mind like a personal movie. Without this function in our brains, we wouldn't be able to gain knowledge and further our intelligence or relive our wedding day and remember the intense emotions that tag along with it.
Visual, Acoustic and Semantic memories combine together to allow us to absorb information around us.
To me, one of the most crippling diseases is Alzheimer's. Having the ability taken away to recall how to drive a car or even remember your own family is heartbreaking. One can only hope that researchers continue to make great strides in preventing or curing this disease.