Learning and memory are core parts of our cognition and experience as humans. Memory can generally be thought of as a mental storage device or characterized by its capacity. There are two types of long term memory: declarative, or explicit memory, and nondeclarative, or implicit memory. The difference between these two is that declarative/explicit memory requires active recall, like if you were taking a test and had to remember how an action potential propagates (semantic memory), or if you were recalling events when telling your friend a story (episodic memory). Nondeclarative/implicit memory refers to skills and habits, or anything that you can just recall without thinking about. Memory is also associated with the hippocampus, which is deep within the temporal lobe; the medial temporal lobe and structures like the hippocampus are involved with memories for facts and events; the striatum is involved with memories for skills and habits; the neocortex is involved with priming; the amygdala is involved with emotional memories; and the cerebellum with simple forms of associative learning. Lower brain regions and the spinal cord contain even simpler forms of learning.
Associative and nonassociative learning are the two types of learning. Associative learning includes classical and operant conditioning, as well as emotional and muscular responses, while nonassociative learning involves priming, reflexes, habituation, and habits. Classical conditioning, popularized by physiologist Ivan Pavlov, makes associations between involuntary responses to unconditioned and neutral stimuli. On the other hand, operant conditioning associates voluntary behaviors with stimuli, like a mouse pulling a lever to receive a food pellet. Memory formation follows four steps–acquisition, consolidation, storage, and retrieval. Alzheimer’s is a neurodegenerative disease that involves atrophy of the hippocampus, causing irreversible apoptosis. There are many ways that researchers are exploring to help combat this widespread disease, of those including TMS and drug based therapies.