Memory formation is a complex and not completely understood process that describes the brain’s ability to encode, consolidate, and retrieve information.
There are a lot of different types of memories handled by different parts of the brain. While it is well understood that the Hippocampus is almost entirely responsible for the creation and management of long term memories, it has been shown that other mediums of of memory can be retained.
The Amygdala is also a key player in the formation of emotional memories, which are often more vivid and long-lasting than other types of memories. The Cerebellum is involved in the formation of procedural memories, which are responsible for motor skills and habits.
Patient H.M.
One such case is that of Patient H.M.,1 who had his a large portion of his anterior hippocampi surgically removed. While the surgery did cure his Epilepsy, he lost the ability to form new long term memories - roughly 10 minutes after a conversation everything would be forgotten. Though new ones could not be performed, he retained his memories up until the surgery.
Interestingly however, Patient H.M. was still able to form some different kinds of long term memory. He was able to recall the layout of room in an institute, a place in which he only knew after his surgery. Not only that, but some of his motor control skill were able to develop, suggesting that “muscle memory” might also be independent of the Hippocampus.
Encoding
Memory Encoding differs depending on if it is a short term or long term memory. Short term memories are typically encoded in the Prefrontal Cortex and are often lost after a few minutes. Long term memories are encoded in the Hippocampus and are stored in the Cerebral Cortex.
The process of encoding is not fully understood, but it is thought to involve the strengthening of synaptic connections between neurons, a process known as synaptic plasticity. This is thought to be mediated by the release of neurotransmitters such as glutamate and dopamine, which play a key role in the formation of new synapses.
Consolidation
During sleep, the brain undergoes a process called memory consolidation, where newly formed memories are stabilized and integrated into existing memory networks. This process is thought to involve the reactivation of neural circuits that were active during the initial encoding of the memory.
I will write a more detailed section on this later, but it is thought that the Hippocampus plays a key role in this process, as it is involved in the transfer of information from short-term to long-term memory.
Retrieval
Memory retrieval is a process most commonly associated with the Cerebral Cortex. It is believed to involve the reactivation of neural circuits that were active during the initial encoding of the memory. This process can be influenced by various factors, including context, emotional state, and cues.