Updated: Jun 6, 2021
[Photo Credit: Queensland Brain Institute]
This diagram of the human brain shows where explicit and implicit memories are stored.
Memories are the process of encoding, storing, and retrieving experiences and knowledge. It makes us who we are: without it, we would just be a body, unable to communicate or identify danger. Memory is the reactivation of a specific group of neurons, formed from persistent changes in the strength of connections between neurons, which is also known as synaptic plasticity. The hippocampus and neocortex take part in a carefully choreographed dialogue in which the hippocampus replays recent events. This replay only happens during sleep, so the lack of sleep doesn’t allow your brain to consolidate memories.
Types of Memories
There are various types of memories. Explicit memories and implicit memories are two types of long term memories. Explicit memories are episodic and those we can consciously recall. Or, they are semantic because they relate to facts or general knowledge. Explicit memories are affected by neurodegenerative diseases such as Alzheimer's disease. Explicit memories happen in three different parts of the brain. The hippocampus is where episodic memories are formed and indexed for later access. Next, the neocortex is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning and language. Lastly, the amygdala makes memories stronger because it attaches emotional significance to memories. Implicit memories are motor memories. It takes place in the basal ganglia and cerebellum. The basal ganglia is involved in processes such as emotion, reward processing, habit formation, movement and learning. The cerebellum is a fine motor control.
Short term memory allows the brain to remember a small amount of information for a short period of time. This includes the working memory, which is used to hold information in our head while we engage in other cognitive processes. It is stored in the prefrontal cortex, which controls planning, decision making, and working memory.
Memory Recollection and Forgetting
The idea of memory indexing and recollection is still a theory. The hippocampus serves as a memory index. The analogy is to a digital database or filing cabinet: something triggers a search of the database, and we retrieve and recall the memory. The hippocampus then directs neuronal traffic back to the appropriate circuits of the neocortex, reactivating the memory. Memories we forget happen when the brain does not reinforce a memory long enough to store it. There are two main theories. The decaying theory infers that if a certain memory isn’t repeated, it will eventually deteriorate. The interference theory infers that new information received by the brain replaces old information. Forgetting memories explains infantile amnesia, which is why you can’t remember anything about being a toddler. Memories transform us from helpless newborns into capable adults, making us who we are today.
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