The Animal Model

These findings provided an understanding about the hippocampus as a whole, but structurally there was much more to learn. Because of H.M. and considerable research on amnesic patients, we know now that the hippocampus is critical in transferring new memories into stored ones. How does this system work? Researchers needed to first find a model to test that was comparable to humans. Rats have similar nervous systems to humans, but unlike humans they are not able to verbally recall (declarative) what they have learned. They do use spatial cues to find their way in the environment (spatial learning). Spatial learning is mediated by the hippocampus, and thus used as a model for declarative learning in animals. The Morris water maze tests spatial memory by placing rats in a pool of opaque water. The rats have to find a submerged platform only by using cues (a large black star on the wall or an inflated beach ball) which are placed around the pool. Rats must first make a choice about what they did before (how they found the platform) and then use visual cues. Because the time spent finding the platform decreases with each new trial, it is believed that they have learned to find the platform by using the visual cues. Research on spatial information processing in the hippocampus shows that there are cells, known as place cells, that code for specific cues in the environment. Animal studies have shown that the dorsal hippocampus is specifically required for spatial learning, and the equivalent (posterior) part of the human hippocampus shows increased metabolic activity when navigational information is being recalled. Some species actually show an increased hippocampal volume during periods when they need to bury and retrieve cached food. Is there an equivalent change in humans? A professional requirement for London taxi drivers is a detailed knowledge of the tortuous streets of that large city. Interestingly, these taxi drivers have an increase in volume of the posterior hippocampus relative to a matched control population. Moreover, the longer they have been taxi drivers, the more pronounced is this change.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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