Hippocampus
From Psy3242
==Anatomy==
The hippocampus a brain structure comprised in the limbic system, with neurons packed into an S-shape. Located in the forebrain, the hippocampus is part of the medial temporal lobe. The hippocampus receives inputs from many areas of the brain for information processing, and is able to recall large amounts of information from small inputs. (Fun Fact: The origin of the word is Greek for seahorse, because of its seahorse shape. Hippos means horse and kampos means sea.)
Contents |
Functions
The hippocampus plays roles in memory, navigation, spatial orientation, and capable of neurogenesis. The exact functions of this brain area widely debated because of its multimodal characteristics.
- Episodic Memory
The hippocampus plays a role in the formation of new memories about experiences, allowing learning. For example, you know where you are in space in time. Then, you have an experience that is consolidated to make a memory. This experience is then stored in the hippocampus. This brain structure is responsible for information processing and new learning.
- Spatial Coding/ Memory Creating a Cognitive Map
Research has found that specific neurons, located in the hippocampus, fire in particular locations in the environment. These cells are called place cells and form a cognitive map of our environment around us. We are able to recall familiar places based on the firing patterns of these cells, and make shortcuts.
- Plasticity
The hippocampus and olfactory bulbs are the only systems in the brain that are capable of producing new cells. This ability to produce more neurons in this area can help improve learning and memory.
Known Causes of Hippocampus Damage
- Alzheimer�s Disease
- Anoxia (oxygen starvation)
- Encephalitis
- Epilepsy
Complications Associated with Damage to the Hippocampus
- Amnesia
- Anterograde Amnesia: Particularly explicit memory problems, the inability to form new memories or learning.
- Retrograde Amnesia: Inability to access memories prior to the brain damage.
- Loss of memory from verbal, non verbal, visual, or auditory inputs.
- Alzheimer�s Disease
- Unknown emotional expression: A person with hippocampus damage will experience emotions, but will not understand why.
Studies/ Tests that Increase Knowledge about the Functions of the Hippocampus
- H.M.
H.M. was one of the most influential patients ever studied in neuropsychology in reference to the hippocampus. This subject was given a surgery to decrease the symptoms of his epilepsy, which required the removal of the hippocampus. Research on H.M. has lead to a strong understanding of the functions of the brain associated with memory formations.
- McGuire Cab Driver Study
In this study London Taxi drivers were assessed using a structural fMRI. Their findings determined what areas of the brain were active during recall of familiar places, also known as a cognitive map, and figuring out a route to take their customer. The results proved that taxi drivers have a larger right hippocampus, the area responsible for spatial navigation, than non taxi drivers. There was also a correlation between the size of the hippocampus and the amount of experience a taxi driver had. As the number of years that a person was a taxi driver increased, so did the size of their hippocampus.
- Morris Water Maze
This maze is a test designed to test spatial memory. The test subject, usually a rat, is placed in a small pool of water with a small platform hidden below the water. The researchers record the amount of time it takes the rat to find the platform and will train an animal to use this paradigm. After extensive practice, the rat will be able to swim to the platform, suggesting that there is a cognitive map that we use to navigate ourselves to a point of interest. The rat does not simply use luck to find the platform each time; it learns where it is located.
- Radial Arm Maze
This is another maze that tests spatial learning and memory in animals. It consists of a center circle with multiple hallways coming off the circle. At the end of the hallways, there is a reward, usually food. The animal is trained to go down each hallway once, and returning to the center chamber after each hallway. The animal must use spatial learning and memory to recall which hallways it has already been down and which hallways it still has yet to explore.
- LTP Induction
In an experiment by Lomo, the researchers were interested to see if you stimulate two neurons at once at a high frequency, if you can influence and increase the synaptic firing of that response. This is believed to be a very influential discovery in learning and memory functioning.
- Mirror Drawing Tasks
This is a visuomotor procedural learning task. The participant is asked to trace a shape while looking only into a mirror. This task is hard to do because the visual information is in a different form than you are used to, but your hand still wants to react the way it normally does, causing us to become confused, and making this task difficult. Like the water maze, with multiple trials, participants can learn how to do this task and decrease their error rate and time.
- Louis and Wilson Sleep Study
This study found that sleep can enhance memory retention because while sleeping, we replay the firing of place cells. Animals were placed in a doughnut shaped maze and doors were positioned at different locations with food on the opposite side of the door. The study looked at the activity of place cells and found that certain cells turn on only in particular places in the environment, creating a cognitive map pattern. The research shows that animals replay the pattern of firing of place cells at night, allowing them to relearn memory functions during sleep.
- O�Keefe and Nadal�s study on Place Cells
This study found that the hippocampus� main function in a rat was to form a cognitive map of the surrounding environment. The rats showed that there was increased firing rate when in reference to a particular area, called the cell�s place field. When exposed to a new area, we adapt new place fields and gradually, as we revisit the location, we develop particular patterns of firing that remain in reference to that particular place.
Interesting fact:
The hippocampus, located in the temporal lobe, is responsible for remembering music(memory),musical experiences and contexts.
Links
http://youtube.com/watch?v=YYJ4VTqhoy8&feature=related
References
- Ogden, Jenni A. (1996). Fractured Minds. Oxford: New York.
- Stirling, John. (2002). Introducing Neuropsychology. Psychology Press: New York.
