Amygdala: Encyclopedia - Amygdala

Amygdala

Located deep in the brain's medial temporal lobe, the almond-shaped amygdala (in Latin, corpus amygdaloideum) is believed to play a key role in the emotions. It forms part of the limbic system. In humans and other animals, this subcortical brain structure is linked to both fear responses and pleasure. Its size is positively correlated with aggressive behavior across species. In humans it is the most sexually dimorphic brain structure, and shrinks by more than 30% in males upon castration. Conditions such as anxiety, autism, depression, post-traumatic stress disorder, and phobias are suspected of being linked to abnormal functioning of the amygdala owing to damage, developmental problems, or neurotransmitter imbalance.

Amygdala - Anatomical subdivisions

The amygdala is actually several separately functioning nuclei that anatomists group together by the proximity of the nuclei to one another. Key among these nuclei are the basolateral complex, the centromedial nucleus, and the cortical nucleus.

Amygdala - Connections

The basolateral complex receives input from the sensory systems and is necessary for fear conditioning in rats. The centromedial nucleus is the main output for the basolateral complex and is involved in emotional arousal in rats and cats. The amygdala sends outputs to the hypothalamus for activation of the sympathetic nervous system, the reticular nucleus for increased reflexes, the nuclei of the trigeminal nerve and facial nerve for facial expressions of fear, and the ventral tegmental area, locus ceruleus, and laterodorsal tegmental nucleus for activation of dopamine, norepinephrine and epinephrine. The cortical nucleus is involved in olfaction and pheromone processing. It receives input from the olfactory bulb and olfactory cortex.

Amygdala - Fear conditioning

Fear conditioning, which trains animals to associate fear with other (previously neutral) stimuli, alters the information stored in the amygdala, as shown by experiments from Joseph LeDoux's lab and others, using rats as experimental subjects. In this regard the amygdala serves as a simple Pavlovian learning machine that associates aversive events with neutral events, helping animals react to their world.

If the amygdala of a rat is injected with a drug that blocks protein synthesis shortly after fear conditioning, the rat does not acquire long-term memory of the fear.

In language learning, some hypothesize that second-language learning for adults may not make ready use of the amygdala in procedural memory usage and so emotional links to words are slower to form.

See also

• Removal of the amygdala[1] from monkeys results in Kluver-Bucy syndrome.

Stathmin gene and Amygdala: Recent research works by Dr. Gleb Sumyatsky and Prof. Eric Kandel have led to the identification of the Stathmin gene. This gene is highly enriched in the Amygdala and is believed to be involved in controlling both innate and learned fear in mice. They "knocked out" the stathmin gene in the amygdala using gene knockout technology and found that mice that lacked stathmin gene lacked any kind of fear. For instance, such mice did not freeze on sighting a cat.

Adapted from the Wikipedia article "Amygdala", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki