There is both long term and short term memory. For long term memory there are two categories ‘explicit’ and ‘implicit’ memory. Implicit memory are unconscious, procedural memories such as riding a bike, eating, getting dressed, or driving. Explicit memory (or declarative memory), on the other hand, mainly refers to the conscious, intentional recollection of factual information. This can be knowing the capital of a state, It can further be divided into episodic memory and semantic memory.
Implicit memory (or procedural memory) is mainly based on “knowing how” to do. it is normally acquired through repetition and practice. Once these memories are embedded into our brains, we tend to do these actions without thinking about them. The automatic sensorimotor behaviors are repeated so often that we become unaware of them. For example, usually when I commute to school, I spend about 20 minutes on I-95 southbound, I usually doze off and then suddenly realize I am one exist away from the school. Even though I may not fully be paying attention to how far I am driving, i have repeated my commute so often that my implicit memory just takes me to school.
The meme refers to explicit memory and more specifically semantic, which consists of recalling facts, concepts, meanings, and knowledge of the outside world. Although, as we all have learned cramming the night before an exam is usually not the best way to retain information, it is something a lot of us do. Luckily for us, if our exams or quizzes are mainly based on just recalling facts or plain memorization of information, our explicit memory may actually do wonders for us. During a test, these memories, of the information, can me retrieved through associations. I know personally, after I have studied a page or part of my notes so often, when I come across a question that includes that information, I have a short “photographic” memory of those notes. The questions on the test made an association with the notes I have studied. Same can be said with flash cards. If you are asked a question that is based off one of the cards you studied, you are likely to remember the card you studied. Even after all that cramming, I do get surprised that I was actually able to remember and recall the information studied.
One of the most famous studies conducted to understand the difference between explicit and implicit memory was on a patient named “H.M.”. He had parts of his medial temporal lobe, hippocampus and amygdala removed in 1953 in an attempt to cure his epilepsy. After the surgery, H.M. could still create procedural memories and short-term memories, but not declarative memories. This showed the distinction between the two main systems, especially within the hippocampus. Only explicit memory can be retrieved through the hippocampus.