The hippocampus is a small structure in the brain that is surrounded by the temporal cortex. It is thought to play a major role in learning and memory. Many experiments have been done to study the impact of lesions to the hippocampus to determine how it affects learning in rats. Observational studies have been done that look at human patients with damage to the hippocampus to see how they function and how this damage affects their lives. In these human observational studies, the most obvious detriment is their failure to form new memories – especially those that are spatial oriented.
In the paper, “Memory for Places Learned Long Ago is Intact After Hippocampal Damage”, Edmund Teng and Larry Squire looked specifically at one of their patients, called patient E. P. E. P developed amnesia after suffering from an episode of herpes simplex encephalitis in 1992.
Due to the nature of this disease, he suffered major bilateral damage to all parts of his memory system, including the hippocampus. His damage to this system is so severe that he doesn’t recognize the testers that he encounters repeatedly and scores at chance (50%) on many recognition memory tasks. Since contracting the disease, he has trouble recalling memories of facts and events that have happened to him over the 40 years before his illness. However, one of the more interesting facts about E.
P. is that he does very well on spatial navigating tasks that involve areas that he had lived in for many years prior to his hippocampal decay. E. P. could navigate considerably well through his old neighborhood of Castro Valley; in fact just as well if not better than the control subjects who were very similar to E.
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P. E. P. was tested by comparing him with healthy subjects who shared similar background history with E. P. All the subjects were of the same age, had attended the same high school as E.
P. , had received approximately the same amount of schooling, had moved away from the Castro Valley area at about the same time and had not returned for any significant amount of time since. E. P. tested twice, both before and after the control subjects. Pre-test interviews with E.
P. and the control subjects established about twenty familiar locations. These locations were used to give ‘familiar navigation’ tasks which required the subjects to use both common routes and alternates routes when familiar streets and thoroughfares were “blocked” and not allowed to be used. Subjects were also given ‘pointing to landmark’ tasks where they had to point in the direction of specific landmarks once they had been given a starting point and a series of directions to follow to get to the final destination.
E. P. performed just as well if not better than the controls except on this last task. On this task, he verbally gave the correct direction twice but then physically pointed in the wrong direction. When these two test trials are removed his score is consistent with the controls.
These findings led both Teng and Squire to conclude that the hippocampus is important for encoding spatial maps but not necessarily for retrieval. This is also enforced by E. P.’s lack of ability to navigate successfully through San Diego County, where he had moved to in 1993 after he developed amnesia. These results, along with other brain studies performed on rats, indicate that the hippocampus and other medial temporal lobe structures are important for spatial cognition and learning. Both E. P.
and rats with lesions to the hippocampus and other area of the medial temporal lobe demonstrate a profound deficit in their ability to form new spatial memories. The fact that E. P. can still make use of old spatial maps indicates that perhaps the hippocampus is not needed for maintenance or retrieval of these maps after they have already been encoded into the brain.
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Quality control focuses on detection of errors performance changes of gamma camera systems which may adversely affect nuclear medicine interpretation (Technical Standards Subcommittee, 1999:1). Based on already prescribed baseline conditions, routine checks are conducted to ensure that the camera operated within the allowable limits. There are quite a number of factors which may contribute to ...
In fact, in other studies where patients lose their ability to navigate successfully into already encoded spatial locations, they have had extreme damage to their posterior cortical regions. These findings are very different from previous beliefs in which large amounts of data from rodent studies supported the belief that the hippocampus and the medial temporal lobe are essential for the formation of long-term spatial and non-spatial memories as well as their retrieval.
