Memory and emotion influence each other. On the one hand, emotion is a behavioral output and as such serves to express memories; the consequences of memory, when we remember something, often involve emotional expression (eg, with the inflection of language, the sweat of the hands). On the other hand, events that occurred around emotional experiences are often remembered better or in a very vivid way..
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The amygdala or amygdaloid complex is located inside the temporal lobe, just anterior to the hippocampus.
If we looked inside the human brain, we would see the amygdala deep in the temporal lobe, in an anterior position in the hippocampus.
The amygdala receives multimodal information (visceral, specific thalamic inputs with sensory information, information from association areas of the cortex). The intrinsic connectivity of the amygdala combines these inputs and orchestrates a wide range of influences on behavior. For example, it projects to the thalamic and cortical areas from which it receives information, sends influences to other systems related to other forms of memory (striatum, hippocampus), and also has outputs to the autonomic, endocrine and motor systems, which generate the responses. bodily emotional expression.
The amygdala is centrally positioned between cortical information processing, limbic system circuitry, and hypothalamic outputs that mediate brainstem-mediated response mechanisms..
These connections and recent research with injuries and registries indicate that the amygdala appears to be a key structure for learning and emotional memory; also seems important for memory modulation.
The experience can change the way we feel about what is being processed. The way we evaluate information (eg, if we add positive or negative feelings to a stimulus, our preferences and aversions) is the product, unconscious, of learning.
We feel in a certain way a type of food, a place, or a supposedly neutral stimulus, such as a tone, due to the experiences that have been associated with certain foods, places, tones.
A demonstration of unconscious learning about likes and dislikes is found in the study of the effect of "mere exposure." In one experiment, photos of geometric shapes were presented with a very fast exposure time (1 millisecond per shape). In a subsequent memory test, the subjects did not recognize any of the figures they had seen as familiar. Instead, they showed preferences for the shapes they had seen when compared to totally new ones. Thus, the subjects had developed positive judgments about the material they had seen, although they were not aware of having seen it before..
It seems that learning involving emotions can be done independently of conscious cognition.
The biology of emotional learning has been studied in a classical conditioning task called "conditioned fear." In this study, the rat or mouse is placed in a box that has a floor that can be electrified by providing a slight shock (unconditioned stimulus, EI) to the animal's legs. After a couple of minutes there is a tone (conditioned stimulus, CS) followed by shock. After one or two times of matching the CE and the US, the animal responds to the tone, presented in any environment, as if it were afraid of it or faced with a threat or danger: it stays still, its hair is lifted, its heart rate ...
The learned fear response is eliminated with bilateral amygdala injury.
The circuit that seems important for learning conditioned fear is based on the fact that information from CD and US converge in the amygdala. The amygdala sends information to different structures making the expression of fear possible.
Tone information appears to reach the amygdala (the basolateral nucleus) from sensory areas of the thalamus that process the stimulus first and from the peryrinic and insular cortex. The central nucleus of the amygdala is critical for communicating the fear state to the large number of systems that work together to express the body's response to fear..
There are neuronal activity log studies that show changes in the neural activity of the central nucleus of the amygdala parallel to the emergence of CR. Other experiments demonstrate plasticity in the receptor fields of neurons in the thalamus, auditory cortex and basolateral amygdala.
Another task used to study the neural bases of emotional learning is the potentiation of the startle response. Many species, including humans, are more frightened by a loud noise if they were previously in a state of fear or arousal. The task consists of matching a stimulus in principle neutral (eg, a light) with a shock. Then another stimulus (loud noise) occurs alone or in the presence of light. The startle reflex (a jump) is greater when noise occurs together with light than when it occurs alone.
The amygdala is not necessary for the startle response, but it is necessary for the enhancement of the response through fear; the amygdala thus has a modulatory influence on the startle reflex circuit.
The amygdala is not only necessary for learned fear or to enhance the fright response, but it is also involved in the basic ability to express fear.
With a lesion of the amygdala, a syndrome occurs that is characterized by a decrease in the response to affective stimuli; animals become calmer and show no signs of fear.
Stimulation of the amygdala can produce a complex pattern of behavior and changes in autonomic responses that resemble fear.
The amygdala also plays an important role in fear learning in humans.
When a neutral tone (CS) is associated with a loud noise (EI), after several pairings, subjects show signs of emotional arousal when the tone is present. One of the signs of activation is changes in sweating, such as increased skin conductance.
Patients with tonsil injury do not develop an emotional reaction to CD, although they may explain that a tone (CD) was normally followed by a loud noise (IE).
In patients with lesions of the entire medial temporal lobe including the amygdala, they are able to withstand harsh or unpleasant conditions without complaint, not even generating a galvanic response from normal skin. They are also unable to identify any stimulus as painful, although their perception does not have to be altered..
Selective lesions of the amygdala also produce deficits in the recognition of facial expressions of emotions, without affecting language, perception or memory of faces.
There is electrophysiological data in monkeys and humans showing that neurons in the amygdala respond to faces. In addition, a recent study with MRI (functional magnetic resonance imaging) showed that the amygdala is activated preferentially in response to the vision of faces that express fear than to the vision of neutral faces..
In other neuroimaging studies, changes in amygdala activity have been detected when subjects viewed fear-producing scenes or when psychiatric patients recalled traumatic events from the past.
All of these human and animal data indicate the following:
The amygdala is an "execution system" for analyzing affective information and for the expression of emotional response.
There is much evidence that memories associated with strong emotions are more vivid, accurate, and stable than memories of more ordinary or neutral events. This makes adaptive sense since in this way organisms better remember important events..
An example of those detailed and intense memories that were once stored and that can last a lifetime are events that were surprising and emotionally charged. An example can be the memory we have of what we were doing, where we were and who we were with when we found out that the two passenger planes had collided with the twin towers of New York.
There are specific neural mechanisms that modulate (facilitate or impair) the strength of the memories that have just been formed. It is thought that the amygdala could be a key structure in memory modulation in two ways:
Stress hormones (catecholamines, glucocorticoids, opioids) act as endogenous modulators for the memory of the events that caused their release.
The amygdala is the brain region most clearly involved in the memory-modulating effects of drugs and hormones. Direct stimulation of the amygdala can modulate memory, and the effects of stimulation of the amygdala on memory depend on the integrity of the adrenal glands..
Memory modulating mechanisms are based, at least in part, on the effects of emotional activation on memory, through the amygdala.
In laboratory animals, mildly stimulating experiences have been shown to release a variety of hormones into the blood and brain. When these same hormones are injected into animals shortly after they have been trained in a learning task, the animals retain the training better..
Stress hormones act through the amygdala, as lesions of the amygdala or stria terminalis (its most important input-output pathway) block memory modulation of many drugs and hormones.
When the amygdala is activated it can cause the cerebral cortex to activate and facilitate the processing of the present stimuli; also the anatomical connections between the amygdala and the hippocampus could influence declarative memory directly.
There are experiments that demonstrate the role of the amygdala in memory facilitation in humans. Volunteer subjects watched slides while listening to a story. The story and the slides explained that a boy was hit by a car and was taken to the hospital for an emergency operation..
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