Cases of amnesia due to head injury provide clues about the anatomy of memory. Retrograde amnesia occurs when a person loses memories for events that occurred prior to the injury, while anterograde amnesia occurs when a person loses memories for events that occur after the injury. The well known case of H.M., who experienced anterograde amnesia, as well as subsequent research, points toward the entire hippocampal region, as well as the parahippocampal region, as a critical structure in many types of long-term memory. Many theorists believe that the hippocampal region plays a key role in the consolidation of memories – the hypothetical process involving the gradual conversion of information into durable memory codes stored in long-term memory. This process is complex, and many brain structures have been shown to be important in memory.
	From a neural perspective, memories appear to depend on localized neural circuits in the brain. These are reusable pathways in the brain that may be specific for specific memories. Various other lines of research have implicated biochemical processes in the operation of memory. Studies show that alterations in neurotransmitter secretions at specific synapse sites, hormonal fluctuations, and protein synthesis in the brain are all related to memory.
	In summary, anatomical, neural, and biochemical processes all appear to play a role in memory.