Limbic system
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The limbic system is a group of brain structures that are involved in various emotions such as aggression, fear, pleasure and also in the formation of memory. The limbic system affects the endocrine system and the autonomic nervous system. It consists of several subcortical structures located around the thalamus:
- hippocampus: involved in the formation of long-term memory
- amygdala: involved in aggression and fear
- cingulate gyrus (the circular shape of the cingulate gyrus resembles that of a "limb", hence the name)
- fornicate gyrus
- archicortex
- hypothalamus: controls the autonomic nervous system and regulates blood pressure, heart rate, hunger, thirst, sexual arousal and the sleep/wake cycle. Connected to the pituitary gland and thus regulates the endocrine system. (Not all authors regard the hypothalamus as part of limbic system.)
The limbic system is among the oldest parts of the brain in evolutionary terms: it can be found in fish, amphibians, reptiles and mammals.
The pleasure center is located in the limbic system. It is involved in sexual arousal and in the "high" derived from certain recreational drugs. Dopamine acts here. Rats with electrodes implanted into their limbic system will self-stimulate in preference over food and will eventually die of exhaustion.
The limbic system is tightly connected to the prefrontal cortex. It has been conjectured that this connection is related to the pleasure obtained from solving problems. To cure severe emotional disorders, this connection was sometimes surgically severed, a procedure of psychosurgery. Patients who underwent this procedure often became passive and lacked all motivation.