The limbic system wraps around the brain stem and is beneath the cerebral cortex. It is a major center for emotion formation and processing, learning, and memory. The limbic system contains many parts, including the cingulate gyrus, a band of cortex that runs from the front of the brain to the back, the parahippocampal gyrus, the dentate gyrus, and most notably, the hippocampus and amygdala. The hippocampus is involved in memory storage and formation. It is also involved in complex cognitive processing. The amygdala is associated with forming complex emotional responses, particularly involving aggression. The limbic structures are also connected with other major structures such as the cortex, hypothalamus, thalamus, and basal ganglia.
HD affects the communication of the limbic system with the frontal lobes by damaging the caudate nucleus, a relay station between them. As the connections degenerate, the activity-initiating frontal lobes are disconnected from the emotion-processing center of the brain, producing apathy.
The limbic system is the part of the brain involved in our behavioral and emotional responses, especially when it comes to behaviors we need for survival: feeding, reproduction and caring for our young, and fight or flight responses.
You can find the structures of the limbic system buried deep within the brain, underneath the cerebral cortex, and above the brainstem. The thalamus, hypothalamus (production of important hormones and regulation of thirst, hunger, mood, etc), and basal ganglia (reward processing, habit formation, movement, and learning) are also involved in the actions of the limbic system, but two of the major structures are the hippocampus and the amygdala.
Hippocampus
The hippocampus, like many other structures in the brain, comes as a pair, one in each hemisphere of the brain. It resembles the shape of a curvy seahorse (and is named after its scientific genus) and is essentially the memory center of our brains. Here, our episodic memories are formed and cataloged to be filed away in long-term storage across other parts of the cerebral cortex.
Connections made in the hippocampus also help us associate memories with various senses (the association between Christmas and the scent of gingerbread would be forged here). The hippocampus is also important for spatial orientation and our ability to navigate the world.
The hippocampus is one site in the brain where new neurons are made from adult stem cells. This process is called neurogenesis and is the basis of one type of brain plasticity. So it’s not surprising this is a key brain structure for learning new things.
Amygdala
The amygdala’s name refers to its almond-like shape. Located right next to the hippocampus, the left and right amygdalae play a central role in our emotional responses, including feelings like pleasure, fear, anxiety, and anger. The amygdala also attaches emotional content to our memories, and so plays an important role in determining how robustly those memories are stored. Memories that have strong emotional meaning tend to stick.
The amygdala doesn’t just modify the strength and emotional content of memories; it also plays a key role in forming new memories specifically related to fear. Fearful memories are able to be formed after only a few repetitions. This makes ‘fear learning’ a popular way to investigate the mechanisms of memory formation, consolidation, and recall.
QBI researchers are working on mapping the neural connections that underpin learning and memory formation in the amygdala. Suppressing or stimulating activity in the amygdala can influence the body’s automatic fear response, which kicks in when something unpleasant happens, such as a startling noise. Through this research, QBI scientists have identified receptors in the amygdala that could help to develop new types of anti-anxiety drugs.
Recently QBI researchers have confirmed that new neurons are made in the amygdala.
These are good links for information on the Limbic System:
https://webspace.ship.edu/cgboer/limbicsystem.html
http://en.wikipedia.org/wiki/Limbic_system
http://webspace.ship.edu/cgboer/limbicsystem.html
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