Human Memory: How are memories stored and retrieved in the human brain?

  At the most basic level, memories are stored as microscopic chemical changes at the connection points between neurons in the brain.

  The brain has possibly 100 billion neurons, each of which connects to up to 10,000 (typically) other neurons. By some estimates, there are over 100 trillion total connection points or "synapses" in the human brain.

  As information flows through the neural circuits and networks of the brain, the activity of the neurons causes the connection points to become stronger or weaker in response. The strengthening and weakening of the synapses(synaptic plasticity) is how the brain stores information. This mechanism behind this is called "long-term potentiation" or "LTP" 

  From here, the story becomes much more complex. The hippocampus is a region of the brain that is specialized to codifying and structuring memories, particularly autobiographical and episodic memories (memories about people, places, and events). However some scientists believe that memories are only held in the hippocampus temporarily, and are later re-coded and dispersed throughout the rest of the brain using a process called "memory consolidation," which may happen during sleep. The precise way that long-term memories are structured and represented across billions of synapses is the subject of intense ongoing research and remains one of the great mysteries of neuroscience.

Location of the hippocampus, specialized for episodic memories:

Long-term memories and behavioral skills are stored broadly throughout the brain using a "distributed representation" which is both highly redundant and highly efficient. 

Factual knowledge and behavioral skill memories are stored in different systems. 

Short-term memory appears to work completely differently. A phone number can be remembered instantly, but forgotten just as fast. Repetition of experience, such as reciting a phone number, is one of many ways that memories migrate from short-term memory to longer-term systems. The most popular view on short-term memory is that it results from signaling patterns circulating in "recurrent feedback loops" within neural circuits on the scale of a 1 millimeter or so of brain tissue, but this too is the subject of ongoing research.

Memory is one of the most fascinating subfields of neuroscience, and the study of memory is still in its infancy. An important question is how are memories coded by neurons. The models that exist today are still very primitive.

Original -- http://www.quora.com/Human-Memory/How-are-memories-stored-and-retrieved-in-the-human-brain?redirected_qid=408138