The hippocampus is a structure in the temporal lobe of the brain. It was the first place where long term potentiation was found. Long term potentiation is believed to affect the brain's plasticity. That plasticity is what might allow for the structural change that occurs when we remember something. (http://nba19.uth.tmc.edu/nrc/newsltr/winter95/nrcnews2.html) In further studies where lesions were made, the memory of the subjects was found to be affected.One such example would be a study where the researchers leasioned the hippocampus and various other areas in rat's brains and had the rats run a maze. It was found that after the lesions if the experimenter had changed the location stimuli, the rats with hippocampal lesions could not negotiate the maze anymore. While rats with different lesions did not suffer the same deficit.(http://www.idealibrary.com)
It has been found that the hippocampus might be an intermediary between the neo-cortex's representations and the filing away of information into long term memory. This would go along with the idea of various components of the nervous system communicating with each other to create inputs and outputs. In one study, rats were presented with food only if a tone and a light were presented together. Rats which had received a lesion to the hippocampus had a hard time learning the conditioned response to obtain the food. This finding might lead one to the idea that the lesion affected the animal's ability to remember or retrieve the information that would tell it to perform the response and get food. Animals when trained to a fearful stimulus in a specific context will become conditioned to the context, they will begin to fear the context in which the fearful stimulus is given. Animals with hippocampal lesions do not gain this context conditioning. Or rather, they do not gain a fear of the context of the situation where fearful shocks are given. (http://www.cogsci.soton.ac.uk/bbs/Archive/bbs.eichenbaum.html) This prompted some researchers to think that the hippocampus may have something to do with our ability to remember context, or context cues that surround us in the real world.
Another study done found that the hippocampus was significant in its chemical interactions. It was found that if the animal was not allowed 3 hours of chemical functioning in the hippocampus, it could not remember inhibitory avoidance behavior. The belief behind this is that the hippocampus chemical functioning is what might help to consolidate memories in the animal. This would also support the idea that the hippocampus is an intermediary step between a short-term representation and a long-term storage piece. (http://www.idealibrary.com:80)
The disease Alzheimer's appears to affect the memory functioning of people. It causes people to not be able to remember where they are, who they are, or even who others dear to them are. Much research has gone in to this disease in the hope of finding some way to predict it, and begin early treatment. One study has found that the hippocampus atrophy is indicative of Alzheimer's and other dementias in patients. By using magnetic resonance imaging, the disease can be excluded as a potential explanation for memory loss behavior. The reason for this significance is the fact that normal aging does not appear to cause the same amount of atrophy in the temporal lobe and specifically in the hippocampus. In the study, it was found that patients with Alzheimer's and other dementias were found to have a great amount of atrophy. For Alzheimer's no correlation was found between the length of time they had the disease and the amount of atrophy. (http://www.uku.fi/laitokset/neuro/37the.htm)
There is some research that the hippocampus has a lot to do with spatial mapping of stimuli. In fact the first study cited here states that spatial mapping of some kind was affected by lesions to the hippocampus.(http://w3.arizona.edu/%7Epsych/facsfls/nlri.htm) If that is the case it might explain something about the disease Alzheimer's. Since there is atrophy of the hippocampus in Alzheimer's, as well as other areas, and the individual who is affected does at times have trouble remember where they are in a very real and physical sense, it might be concluded that the atrophy of the hippocampal section might have something do with that not being able to remember where one is.
In researching the idea of memory on the net, the hippocampus kept reappearing as a place of research into the memory of humans and animals. It had been found that lesions to that area of the brain affected an animal's ability to remember context and context cues, the animals ability to learn responses, and the animal's ability to negotiate mazes. The hippocampus from that research has been concluded to have something to do with our memory of spatial relations, how the external world works together so that we can move within it. In Alzheimer's, people have trouble learning new routes and moving within the world as a whole. They also suffer from pronounced atrophy in the hippocampal section of their brain. By using MRI analysis, we might be able to effectively diagnose whether a person is merely forgetful, or might have something much more dangerous. If the brain is composed of different areas talking to each other, then each area needs to provide the other areas with useful information. Since the hippocampus appears to have control of such a specific aspect of memory, it might be one of the areas that talks to other areas, it might be a smaller box within the big box.
The Brain Mechanisms of Memory.
Mechanisms Regulating Synaptic Plasticity in Brain. Paul T. Kelly.
The Flexible Use of Multiple Cue Relationships in Spatial Navigation: A Comparison of Water Maze Performance Following Hippocampal, Medial Septal, Prefrontal Cortex, or Posterior Parietal Cortex Lesions. David M. Compton, H. Randall Griffith, William F. McDaniel, Robert A. Foster, Brenda K. Davis.
Two Component Functions of the Hippocampal Memory System. Howard Eichenbaum.
Memory Formation: The Sequence of Biochemical Events in the Hippocampus and Its Connection to Activity in Other Brain Structures. Ivan Izquierdo, Jorge H. Medina.
MRI of Hippocampus In Incipient Alzheimer's Disease. Mikko Laakso.
Spatial Cognition, Memory, Hippocampus. Lynn Nadel.
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This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.