Stress, memory and the amygdala

A recent study just published at the www.nature website, entitled, "Stress, memory and the amygdala", has maybe shown for the first time why some people suffer from chronic anxiety after experiencing a very emotional event in their lives.

According to the researchers of this study, "Benno Roozendaal1, Bruce S. McEwen & Sumantra Chattarj,

"Emotionally significant experiences tend to be well remembered, and the amygdala has a pivotal role in this process. But the efficient encoding of emotional memories can become maladaptive — severe stress often turns them into a source of chronic anxiety."

For those readers who have never heard of the "amygdala":,

"the amygdala, so named because it resembles an almond,
is a set of nuclei in the brain located closely to each other and therefore grouped under the same name."

"The amygdala is part of the limbic system, responsible for regulating the emotions. The amygdala is most commonly associated with the emotions of fear and anxiety, and its size is positively correlated to the level of aggression in a given species. It is also associated with the emotion of pleasure, though mainly in a negative sense, i.e., the pleasure sometimes inherent in aggression."

"There are two amygdalas, symmetrically arranged near the center of the brain, just above the hypothalamus. They are each about one inch in length. The amygdala has received much attention in recent decades, and has been the focus of many research projects."

"The amygdala plays a key part in what has been called the "general-purpose defense response control network" and reacts in response to unpleasant sights, sensations, or smells. Anger, avoidance, and defensiveness are emotions activated largely by the amygdala. Its evolutionary origins lie with the early fishes, and it has direct connections to one of the oldest sensory areas, the olfactory bulb. The amygdala is responsible for activating ancestral signs of distress such as "tense-mouth" and defensive postures such as crouching."

"Like many parts of the limbic system, the functioning of the amygdala is not purely associated with any one emotion. Poor amygdalic functioning has been associated with anxiety, autism, depression, narcolepsy, post-traumatic stress disorder, phobias, and schizophrenia. Lesion studies with monkeys have shown that when the amygdala is impaired before six months of age, individuals have difficulty adapting to social life. This is because the amygdala is necessary not just for experiencing emotions like fear, but also for modeling and quickly recognizing the presence of these emotions in others. Thus a damaged amygdala has become associated with the condition of autism, or social-blindness."

"In humans the amygdala is the brain structure that varies most widely between the sexes."

Source:http://www.wisegeek.com/what-is-the-amygdala.htm

Here is an image which shows where the 2 amygdala are located in the human brain:(Note only one of the amygdala is labelled in this image below)



Source of image: http://www.flyfishingdevon.co.uk/salmon/year2/aggression/amygdala-hippocampus.jpg

Back now to the research from Roozendaal1, Bruce S. McEwen and Sumantra Chattarji. These researchers conclude the following in their study "Stress, memory and the amygdala",

"Emotionally arousing experiences tend to form strong memories and the amygdala has a pivotal role in this process.
Stress hormones and stress-activated neurotransmitter systems in the basolateral amygdala are crucially important in the consolidation of emotional memories.
A growing body of evidences points to a central role for noradrenaline in mediating the enhancing effects of adrenal stress hormones, such as adrenaline and glucocorticoids, on the consolidation of emotional memories.
Basolateral amygdala activity affects memory consolidation and neural plasticity in other brain regions (for example, the hippocampus and various neocortical regions).
The basolateral amygdala, and its interactions with the hippocampus and prefrontal cortex, also plays a part in the stress-induced impairment of memory retrieval and working memory.
The same that facilitate the robust encoding of emotionally salient memories can become maladaptive under conditions of traumatic and chronic stress.
Chronic stress triggers patterns of structural plasticity in the basolateral amygdala, which are strikingly different from those seen in the hippocampus and prefrontal cortex. Chronic immobilization stress leads to dendritic growth and spinogenesis in principal neurons of the basolateral amygdala.
Stress-induced neuronal remodelling in animal models reveals unique features of structural plasticity in the amygdala that could be of relevance to studies of humans with mood disorders and post-traumatic stress disorder."

(source: "http://www.nature.com/nrn/journal/v10/n6/execsumm/nrn2651.html)


As someone who suffers from anxiety, and who has done quite a bit of reading about the causes of anxiety, I know that the amygdala in my brain is responsible for anxiety, now I know, due to the findings of this above-mentioned-study, that is is probably due to the fact that I get emotionally involved in most everything I do in life,that for some reason the stress-activated neurotransmitters in my brain are "too" active, and that for some reason amygdala mechanisms are maladaptive in my brain. Fortunately, scientists and chemists have been able to develop pharmaceutial products to help people like me who are chronically anxious.