On a cellular level, memories involve interconnected nerve cells that develop strong connections via a process called long-term potentiation (Morris 2003). Memories are made using several structures in the brain including the amygdala (which processes emotions), limbic cortex (which coordinates sensory input with emotions), and thalamus (which regulates sensory information and alertness) (Rajmohan 2007; Petrovich 2011). However, the hippocampus, located near the middle of the brain, is one of the most important structures for memory (Staniloiu 2012). The hippocampus is thought to serve as a temporary storage space for memories until they can be transferred to other parts of the brain for permanent storage (Nadel 1997; Gräff 2012). Damage to any of these structures can cause amnesia (Deng 2010).
Memory is divided into different categories based upon timeframe:
‘Short-term’ memory allows remembrance of a small amount of information for anywhere from several seconds to a few minutes (Staniloiu 2012).
‘Long-term’ memory facilitates storage and retrieval of memories over a much longer timeframe (Dudai 2002). Long-term memory has been categorized as:
- Non-declarative or procedural memory, which refers to unconscious memories such as knowing how to ride a bicycle (Ullman 2004).
- Declarative memory, which refers to memories that can be consciously recalled such as the name of the Capital of the United States. Declarative memory has been categorized based on the type of information that is stored and recalled.
- Semantic memory involves recalling pieces of information, such as the name of the president or a person’s birthday.
- Episodic-autobiographical memory allows a person to recall certain events they experienced and to mentally re-experience them (Ullman 2004; Renoult 2012; Staniloiu 2012).
The bridge between short- and long-term memory is termed ‘working memory’; it allows for retention of new information with simultaneous retrieval of older memories (Baddeley 1992; Staniliou 2012).