page_title: Explicit memory
section_title: Hippocampus
hierarchical_section_title: Explicit memory / Neuropsychology / Normal brain function / Hippocampus
caption_attribution_description: English: Hippocampus. Images are from Anatomography maintained by Life Science Databases(LSDB). 日本語: 海馬。 画像はLife Science Databases(LSDB)のAnatomographyというサイトより。
context_page_description: Explicit memory is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and concepts. Explicit memory can be divided into two categories: episodic memory, which stores specific personal experiences, and semantic memory, which stores factual information. Explicit memory requires gradual learning, with multiple presentations of a stimulus and response.
  Procedural memory, a type of implicit memory, refers to unconscious memories such as skills. Procedural memory learns rule-like relations, whereas explicit memory learns relations that are arbitrary. Unlike explicit memory, procedural memory learns rapidly, even from a single stimulus, and it is influenced by other mental systems.
  Sometimes a distinction is made between explicit memory and declarative memory.
context_section_description: Although many psychologists believe that the entire brain is involved with memory, the hippocampus, and surrounding structures appear to be most important in declarative memory specifically. The ability to retain and recall episodic memories is highly dependent on the hippocampus, whereas the formation of new declarative memories relies on both the hippocampus and the parahippocampus. Other studies have found that the parahippocampal cortices were related to superior recognition memory.
  The Three Stage Model was developed by Eichenbaum, et. Al (2001), and proposes that the hippocampus does three things with episodic memory:
  Mediates the recording of episodic memories
  Identifies common features between episodes
  Links these common episodes in a memory space.
  To support this model, a version of Piaget's Transitive Inference Task was used to show that the hippocampus is in fact used as the memory space.
  When experiencing an event for the first time, a link is formed in the hippocampus allowing us to recall that event in the future. Separate links are also made for features related to that event. For example, when you meet someone new, a unique link is created for them. More links are then connected to that person's link so you can remember what colour their shirt was, what the weather was like when you met them, etc. Specific episodes are made easier to remember and recall by repeatedly exposing oneself to them (which strengthens the links in the memory space) allowing for faster retrieval when remembering.
  Hippocampal cells (neurons) are activated depending on what information one is exposed to at that moment. Some cells are specific to spatial information, certain stimuli (smells, etc.), or behaviours as has been shown in a Radial Maze Task. It is therefore the hippocampus that allows us to recognize certain situations, environments, etc. as being either distinct or similar to others. However, the Three Stage Model does not incorporate the importance of other cortical structures in memory.
  The anatomy of the hippocampus is largely conserved across mammals, and the role of these areas in declarative memory are conserved across species as well. The organization and neural pathways of the hippocampus are very similar in humans and other mammal species. In humans and other mammals, a cross-section of the hippocampus shows the dentate gyrus as well as the dense cell layers of the CA fields. The intrinsic connectivity of these areas are also conserved.
  Results from an experiment by Davachi, Mitchell, and Wagner (2003) and subsequent research (Davachi, 2006) shows that activation in the hippocampus during encoding is related to a subject's ability to recall prior events or later relational memories. These tests did not differentiate between individual test items later seen and those forgotten.
caption: Hippocampus as seen in red