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The hippocampus is part of the limbic system and plays a part in memory and spatial navigation. It is located inside the medial temporal lobe of the brain.
The illustration shows the underside of the brain, with the frontal lobe at the top and the occipital lobe at the bottom.
The name hippocampus derives from its curved shape in coronal sections of the brain, which resembles a seahorse (Greek: hippos = horse, kampi = curve).
Recent research shows the hippocampus is important for stress and learning interactions. It is necessary for modifying learning in males and females after acute stressful experience. (Bangasser & Tracey J Shors, 2007).
It is one of a number of brain regions that differ significantly in size between men and women. This has led many people to think that such variations result in sex differences in function and behavior, such as memory and emotionality.
For example, part of the hippocampus at the center of the brain and other areas at the front of the brain contribute to short-term memory. They are larger in women. Does this mean they have better working memories?
Other areas, thought to be seats of mating and arousal, grow larger in males, leading to conclusions that men are more aggressive. However, this is not always the case since size alone does not drive function.
Tests show that female and male brains can take different actions to arrive at the same behavioral response. While brain activity differs between sexes, short-term memory performance is the same.
Cambridge, MA, USA. Researchers for the first time have created a way to see the effect of blocking and unblocking a single neural circuit in a living animal. This method allowed researchers to learn how bypassing a major memory-forming circuit in the brain affected learning and memory. The specific area, the hippocampus, has been impicated in a variety of neurological disorders. It is also suspected as involved in the early expression of Harry Benjamin Syndrome (HBS).
According to Susumu Tonegawa, "Our data strongly suggest that the hippocampal neural pathway called the tri-synaptic pathway, or TSP, plays a crucial role in quickly forming memories when encountering new events and episodes in day-to-day life." Tonegawa, of the Picower Institute for Learning and Memory, and his colleagues reported their findings in the journal Science.
Transgenic Inhibition of Synaptic Transmission Reveals Role of CA3 Output in Hippocampal Learning. Toshiaki Nakashiba, Jennie Z. Young, Thomas J. McHugh, Derek L. Buhl, Susumu Tonegawa. Science. DOI: 10.1126 / science.1151120. [ abstract below ]
Combining several advanced genetic engineering techniques, Tonegawa's laboratory invented a method called doxycycline-inhibited circuit exocytosis-knockdown, or DICE-K-an acronym that also reflects Tonegawa's admiration of ace Boston Red Sox pitcher Daisuke Matsuzaka. DICE-K allows researchers for the first time to induce and reverse a blockade of synaptic transmission in specific neural circuits in the hippocampus.
"The brain is the most complex machine ever assembled on this planet," Tonegawa said. "Our cognitive abilities and behaviors are based on tens of thousands of molecules that compose several billion neurons, as well as how those neurons are connected.
"One effective way to understand how this immensely complex cellular network works in a major form of cognition like memory is to intervene in the specific neural circuit suspected to be involved," he said.
The green-stained section of this mouse hippocampus represents where the new DICE-K technique blocked the neural-signal transmission in one of the hippocampal circuits of the brain.
Photo: Toshi Nakashiba, MIT.
Computing memories
The hippocampus, a seahorse-shaped brain region, plays a part in memory and spatial navigation. The hippocampus is made up of several regions — CA1, CA3 and the dentate gyrus — that are wired up with distinct pathways.
Imagine that the three hippocampal regions are computers, and neural pathways are the conduits through which the computers get data from all over the brain. The computers perform different tasks, so the types of data processing will depend on which conduits the data travels through.
The hippocampus has two major, parallel information-carrying routes: the tri-synaptic pathway (TSP) and the shorter monosynaptic pathway (MSP). The TSP includes data processing from all three hippocampal regions, whereas the MSP skips through most of them.
The MIT study sought to determine how the interactions between neural pathways and the hippocampal regions affect learning and memory tasks.
Using DICE-K, the researchers were surprised to find that mice in which the major TSP pathway was shut down could still learn to navigate a maze. The shorter MSP pathway was sufficient for the job.
However, the maze is a task that is slowly learned over many repeated trials. When the mice were tested with a different task in a new environment that required rapid learning and memory formation, the researchers found that the mice with TSP shut down could not perform the task. Thus, the TSP pathway is required for animals to quickly acquire memories in a new environment. "This kind of learning results in the most sophisticated form of memory that makes animals more intelligent and is known to decline with age," Tonegawa said.
He says "Our results indicate that the decline of these abilities, such as that which accompanies neurodegenerative diseases and normal aging in humans, is likely to be due, at least in part, to the malfunctioning of this circuit." Tonegawa, Picower Professor of Biology and Neuroscience at MIT.
In Alzheimer's disease, the hippocampus is one of the first regions to suffer damage; memory problems and disorientation are among the disease's first symptoms.
In addition to Susumu Tonegawa, a Howard Hughes Medical Institute investigator, authors include Picower Institute research scientist Toshiaki Nakashiba; postdoctoral associate Jennie Z. Young; research scientist Thomas J. McHugh; and HHMI staff affiliate Derek L. Buhl.
Transgenic Inhibition of Synaptic Transmission Reveals Role of CA3 Output in Hippocampal Learning. Toshiaki Nakashiba, Jennie Z. Young, Thomas J. McHugh, Derek L. Buhl, Susumu Tonegawa. Science. DOI: 10.1126 / science.1151120.
Abstract. The hippocampus is an area of the brain involved in learning and memory. It contains parallel excitatory pathways referred to as the trisynaptic pathway (which carries information from the entorhinal cortex dentate gyrus CA3 CA1 entorhinal cortex) and the monosynaptic pathway (which connects entorhinal cortex CA1 entorhinal cortex). We developed a generally applicable tetanus toxin-based method for transgenic mice that permits inducible and reversible inhibition of synaptic transmission and applied it to the trisynaptic pathway while preserving transmission in the monosynaptic pathway. We found that synaptic output from CA3 in the trisynaptic pathway is dispensable and the short monosynaptic pathway is sufficient for incremental spatial learning. In contrast, the full trisynaptic pathway containing CA3 is required for rapid, one-trial contextual learning, for pattern completionbased memory recall and for spatial tuning of CA1 cells.
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Robot Violinist. A robot plays Pomp and Circumstance on the violin. The robot used its mechanical fingers to push the strings and bowed with its other arm.
The 152 cm (five foot) performer can perform a variety of tasks with its hands and arms, each of which has 17 joints.
Using precise control and coordination to achieve human-like agility, the robot could also be used to assist with domestic duties or nursing and medical care.
Combining several advanced genetic engineering techniques, Tonegawa's laboratory invented a method called doxycycline-inhibited circuit exocytosis-knockdown, or DICE-K-an acronym that also reflects Tonegawa's admiration of ace Boston Red Sox pitcher Daisuke Matsuzaka. DICE-K allows researchers for the first time to induce and reverse a blockade of synaptic transmission in specific neural circuits in the hippocampus. 
The green-stained section of this mouse hippocampus represents where the new DICE-K technique blocked the neural-signal transmission in one of the hippocampal circuits of the brain. 
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