The Science of Emotions

How the Brain Shapes How You Feel

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The Science of Emotion. Image by Catherine MacBride / Getty Images

In a laboratory at Berkeley, California, a grey-haired man sits in front of a television screen. A series of movies is played for him: a bit of Charlie Chaplin comedy, a recording of abdominal surgery, a crying child.*

Meanwhile, in the opposite room, we are also watching a television screen. On this, however, is the face of the man next door, showing each reaction to the films. Remarkably, all of his reactions are the same.

He responds to each with a lighthearted laugh. A love scene, a comedy, or a murder scene are equally amusing. After each, he confidently states that he feels wonderful. The gentleman has behavioral variant frontotemporal dementia. His emotions no longer vary appropriately with the world around him.

Thinking About Emotion

You don't have to be a neuroscientist to understand the importance of emotions to our everyday life. Much of our everyday life is driven by emotions- we pursue what we think we will find rewarding and try to avoid what will make us unhappy. Still, compared with movement, sensory and cognitive abilities, emotion is relatively understudied in neurology, perhaps due in part to greater difficulties in reliable measurement.

Dr. Robert Levenson once defined emotions as "short-lived psychological-physiological phenomena that represent efficient modes of adaptation to changing environmental demands." Emotion orchestrates a variety of bodily and neurological responses including sensations in the viscera (or "gut"), expressions in the face and body, and altered attention and thought.

These responses are usually very helpful and immediate ways the mind and body coordinate for emergent situations.

The brain processes emotions in a series of steps. First, incoming information must be appraised and assigned an emotional value. This process is often very quick and may go beyond our conscious awareness.

Even so, our initial emotional reaction depends on a number of individual biases and contexts. We can then identify and feel the emotion. Depending on the social situation, we may then have to regulate that emotion's expression. For example, there are times where we may want to express rage or disgust, but have to keep calm regardless.

Emotional Neuroanatomy

The initial reflexive emotional response to something in our environment occurs very quickly and often eludes conscious control. These responses occur in an ancient part of our brain known as the limbic system. Unlike the more recently developed cortex, the limbic system has fewer layers of neurons to process information. The result is fast, but as our experience shows, it also does not always integrate all the relevant information.

The borders of the limbic system are inconsistently described in the literature and seem to expand or contract to best suit the interests of the writer. The functions of the limbic system also extend beyond emotion to include memory, olfaction and autonomic function.

The most important components of the limbic system for emotion include the amygdala, the hypothalamus, cingulate cortex, and the ventral tegmental area. These structures generally have in common a simpler type of cortical structure (fewer layers of neurons than six) and all are located closer to the center and base of the brain. While the importance of the limbic system in emotion has been emphasized, these structures are also influenced by other areas of the brain, particularly the prefrontal cortex.

Appraisal

There are several different systems in the brain that connect a stimulus with an emotional value. These systems are also highly connected with motivation, as our emotions often lead us to action. Emotional systems do not exist in isolation, but rather communicate with and influence each other.

The first system involved with appraisal is the dopaminergic reward system, involving the ventral tegmental area and nucleus accumbens. These structures sit at the center and bottom of the brain, at about the level of the eyes and as far back as the temples. This system responds to rewards, and motivates us to repeat something that feels "good."

The second system involves the circuits of the amygdalae. These are two clusters of nerves about the size of an almond that sit in each temporal lobe. These predominantly mediate responses of anger, fear, and aggression.

Other structures, such as the insula, are also involved with emotion. The insula (meaning cave) is a region of brain tucked behind the fold of the frontal and temporal lobe at the side of the brain. The anterior part helps mediate reactions of disgust.

Emotional Recognition

Once these structures associate a stimulus with a particular emotional value, a stereotyped reaction begins. For example, the amygdala is connected to the hypothalamus and can stimulate an increased heart rate and increased blood pressure, both of which are an important part of fear or anger. The insula is connected to visceral nervous tracts that can make the stomach feel nauseous. Our body can pick up on these symptoms and recognize an emotion.

In addition to noting changes in the body, centers of emotion project to areas of cortex that permit us to recognize an emotion is taking place. For example, the reward circuits project to the medial orbitofrontal cortex, which helps us determine future actions based on emotional information.

Regulation of Emotion

There are times in which an emotion must be regulated. For example, we shouldn't laugh at a funeral even if someone is wearing a ridiculous dress. As an emotion comes forward, we may have to regulate that emotion's expression. We may try to suppress the emotion by not permitting our face or body to naturally show what we feel. For example, if we see a tiger, we may still try to behave courageously. We may reappraise, meaning consciously reframing the context of the stimulus that first made us emotional. For example, we may remind ourselves that it is actually just a picture of a tiger rather than the real thing.

The orbitofrontal cortex activates in cases of emotional regulation, and damage to this region can cause impulsiveness and an inability to regulate initial emotions The most famous example is Phineas Gage, a railway foreman who suffered an accident that sent a large iron rod through this part of the brain. According to the reports of his physician, he was more emotional and impulsive shortly after the accident. Other studies have shown that patients are unable to reappraise an emotional value when conditions change. For example, in an experiment where such patients change from a gambling task, they are more likely to choose large rewards in the short term despite knowing that it is not in their long-term interests.

Generally, many people have suggested that the right side of our brain is more involved with processing of emotions such as fear, sadness and disgust. The left hemisphere has been suggested to be more involved with happiness and perhaps anger. These are likely oversimplifications, though several studies to support the basic concept.

Conclusion

Emotion is not just generated from one part of our brain, but relies on several interwoven networks involving the amygdala, ventral tegmental area, orbitofrontal cortex, and many more which all serve to appraise external stimuli, generate an initial emotional response, and then regulate that response if needed. A disruption in this system can lead to lack of emotion or too much, depending on the nature and location of the disturbance.

*Some details have been changed to protect confidentiality.

Sources:

Bechara A, Tranel D, Damasio H, Damasio AR (1996): Failure to respond autonomically to anticipated future outcomes following damage to prefrontal cortex. Cereb Cortex. 6:215-225.

Davidson RJ, Ekman P, Saron CD, Senulis JA, Friesen WV (1990): Approach-withdrawal and cerebral asymmetry: emotional expression and brain physiology. I. J Pers Soc Psychol. 58:330-341.

Levenson R (1994): Human emotion: A functional view. In: Ekman P, Davidson R, editors. The nature of emotion: Fundamental questions. New York: Oxford, pp 123-126.

Mesulam M-M (2000): Behavioral Neuroanatomy. In: Mesulam M-M, editor. Principles of Behavioral and Cognitive Neurology. New York: Oxford, pp 1-120.

Rosen HJ, Levenson RW (2009): The emotional brain: combining insights from patients and basic science. Neurocase. 15:173-181.

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