Brain and Behavior - University of Texas at Arlington - Chapter Eleven

Emotion

Commonly represents as a response when reacting to environmental stimuli. It may behave mentally and physically.

Cognitive Process of an Emotional Reaction

1st - Cognition - Example: When faced with a dangerous or threatening situation, animals and humans then recognize and evaluate the situation (appraisal; “this is a dangerous situation”)

2nd - Subjective Feeling - Example: “I feel frightened”

3rd - Physically Autonomic and Somatic Arousal - Example: The body is activated to prepare for appropriate reactions.

4th - Action - Example: Attacking or defending in response to environmental stimuli; generating appropriate actions in response to being attacked such as “run away” or “attack”

Emotional Reaction: Physiological Arousal

Physically, emotional situations arouse somatic body activities, autonomic body activities including sympathetic (fight or flight) and parasympathetic (rest and digest) activities (also includes elevated alertness and sped up neuromuscular activity).

Autonomic Failure

An uncommon condition in which output from the ANS to the body fails (leads to the heart and other organs to no longer be regulated by the ANS). People with this disorder have no change in their ANS responses to psychological or physical stress, and experience the same emotions as anyone else, but the emotions are less intense.

Damaged Spinal Cord: ANS Effects

Cannot physically react to psychological or physical stress. Most report that they feel the same emotions before and after the damage.

Damaged PFC and SSC: ANS Effects

People with damage to somatosensory cortex report autonomic responses to emotional music but report little subjective experience. People with damage to the prefrontal cortex have weak autonomic responses but normal subjective responses.

Moebius Syndrome

Rare neurological disorder characterized by facial paralysis. People with this disorder usually report same emotional range as others not affected by disorder.

Do emotions require feedback from muscle movements?

Not necessarily, though these physical responses do contribute to emotions.

Facial-Feedback Hypothesis

Proposes that facial expressions affect emotions, for example, smiling makes you happier and frowning makes you unhappier. The effect of modifying facial expressions to effect mood is small, especially if the feedback is short-term.

Effects of Botox (Botulinum Toxin) on Facial-Feedback

Reduces muscle contractions to reduce wrinkles. This causes slower time in reading unhappy sentences, weaker than usual emotional responses after watching short videos, and depression relief due to relaxing of frown muscles.

Brain: Emotion

Traditionally, the limbic system has been regarded as critical for emotion. Particularly the amygdala. Additionally, the frontal and temporal lobes respond while people look at emotional pictures or listen to emotional stories that incite happiness, sadness, disgust, fear, or anger. Emotions tend not to be associated with one part of the brain and typically activate several parts of the brain.

Right Hemisphere Junction

Recently, researchers have found non-specific, but strong responses in the right hemisphere temporo-parietal junction while people watched an emotionally charged movie. Neurons in this area represent emotion as three gradients, i.e., pleasant vs unpleasant (polarity), intensity, and complexity.

Disgust

Associated with the response of a particular brain area (the insular cortex) unlike other emotions. Different parts of the insular cortex react to different types of disgust. Insular cortex is also the primary taste cortex.

Behavioral Activation System

Associated with activity in the frontal and temporal areas of the left hemisphere. It is marked by low to moderate autonomic arousal and activation can clearly characterize either happiness or anger.

Behavioral Inhibition System

Associated with activity in the frontal and temporal areas of the right hemisphere. Increases inhibiting impulses and makes a person prone to unhappy or “mixed” emotions.

PFC and Personality.

People with greater activity in the left prefrontal cortex tend to be happier, more outgoing, friendlier, and more fun-loving. People with greater activity in the right prefrontal cortex tend to be socially withdrawn, cautious, less satisfied with life, and prone to lower mood levels.

Adaptive Advantages of Emotions

1. Fear alerts us to danger

2. Disgust helps us avoid illness-inducing substances

3. Emotions may mediate moral decisions

PFC and Decisions

In general, the PFC is responsible for decision making and damage to it would lead to difficulty in decision making due to impaired emotions (slowing or stopping of processing emotional information). People with PFC damage make more impulsive and utilitarian choices.

Ventromedial PFC

The ventromedial PFC becomes active while comparing between the utilitarian and emotional aspects of a moral decision. Also responsible for empathy, as damage to it will leave people unable to empathize with others.

Attack and Escape Behaviors

In animals: Fight and Flight. In humans: fear, anger, and violent behaviors. Triggered by unpleasant stimuli, like pain or threat.

Provocation

An attack behavior spurred by an accumulation of unpleasant stimuli which prompts the effected organism to attack for a period of time after being exposed to the unpleasant stimuli

Amygdala: Provocation

During the provocation period, activity is built up in the amygdala. This increases probability and reactivity of attacking.

Environmental Factors: Violence

These factors increase violent tendencies. They include:

• being maltreated as a child

• witnessing abuse of parent(s)

• living in a violent neighborhood

• exposure to lead

Heredity: Violence

1. Monozygotic twins are more likely to resemble each other in adult crimes and aggressive behaviors than dizygotic twins

2. adoptive children resemble their biological parents more in terms of behavior and personality

3. no known genes that have 100% accuracy of predicting aggressive behavior

4. Scientists have found that violence is particularly enhanced associated with interactions between a genetic predisposition and an early troubled environment

MAO_A Levels and Aggression

MAO (monoamine oxidase, a metabolizing enzyme) breaks down monoamine transmitters such as dopamine, norepinephrine, and serotonin, preventing excess accumulation. Low MAO activity due to genetic difference is believed to genetically predispose someone to antisocial behavior. MAO deficiency leads to a build of monamines which alters early brain development. There is very little difference in aggressive or antisocial behavior between people with differing MAO levels with no bad environmental effects.

MAO_A Differences and Environmental Effects

1. Rate of antisocial behavior is low among those who were treated well in childhood regardless of MAO levels

2. Some maltreatment led to increased antisocial behavior but still with no significant difference between MAO levels

3. Severe maltreatment led to significantly higher antisocial behavior among those with low MAO activity

It remains unclear why low MAO activity, which results in high baseline serotonin (which when at a moderate level helps mood control), is linked to aggression or why the effect of this gene depends on the environment.

Testosterone and Aggression

Aggressive behaviors and increased strive for social dominance is influenced by testosterone. High testosterone was commonly found in men who committed violent crimes as opposed to those committed nonviolent crimes, however, the difference was small and did not apply to all kinds of violence. Violence is mostly determined by cortisol, which means that while testosterone does make a difference, its usually a small one. Aggression tends to be highest when cortisol levels are low and testosterone levels are high. Testosterone makes people less accurate in recognizing angry expressions. Higher testosterone also makes people more likely to argue instead of collaborate. Testosterone increases emotional arousal but decreases ability regulate emotion deliberately.

Serotonin Turnover

Defined as the amount of serotonin that is released/metabolized and resynthesized by presynaptic neurons. The rate can be inferred from the concentration 5-hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite, found in the cerbrospinal fluid, blood, and urine. High levels of 5-HIAA implies much serotonin release and use that increases turnover.

1. A study in male rodents found that social isolation decreased serotonin turnover and increased aggressive behaviors

2. In a study of 2-year old monkeys, researchers found that monkeys with the lowest serotonin turnover had the highest amount of aggressive behaviors and died before age 6.

3. Studies have found that lower than normal serotonin turnover is present in people who were convicted of violent crimes and those who committed or attempted suicide by violent means.

Serotonin: Genetics

Genes control production of the synthesizing enzyme, tryptophan hydroxylase, which converst tryptophan into serotonin. A less active form of this enzyme leads to less serotonin. Less serotonin correlates with frequent anger and aggression.

Serotonin and Aggression

While low serotonin is correlated with aggression it also correlates with depression. High levels of serotonin also inhibit impulsive decisions, which correlate with aggression and violence, yet serotonin is sometimes released during aggressive actions. The most likely and acceptable idea is that aggressive people generally have low initial serotonin activity, which prior to aggravation, magnifies a response when serotonin is released at the start of an aggressive encounter.

Amygdala: Anxiety

The amygdala is the key to regulating anxiety. Both experience and genetics can modify the amygdala’s activity, thus changing the reactivity of fear and anxiety. Developmentally, most infants with an inhibited temperament develop into shy, fearful children and then into shy adults who show an enhanced amygdala response to any unfamiliar face. In soldiers, higher amygdala activity is correlated with higher reports of unpleasant stimuli and emotions experienced. These soldiers have the greatest amygdala activity when reacting to unpleasant faces or photos due to huge amounts of combat stress that increased fear reactivity.

Startle Reflex

A type of fear response which is built-in, with even newborns demonstrating it. An extremely fast response to sudden noise which stimulates an area of the pons that commands the tensing of the neck and other muscles. Information reaches the pons 3-8ms after, the startle response occurs within 200 ms. The amygdala regulates the strength of the reflex. When the amygdala gets information about pain, axons carrying high firing action potentials project back to the pons to evoke a stronger reaction. Stress can lead to stronger startle reflex because of the amygdala. Damage to the amygdala results does not eliminate the reflex but does stop external factors from effecting reactivity of the reflex.

Conditioned Fear

In rats, the startle reflex is evoked by an electric shock and paired with a noise stimulus. The repeated shocks lead to prolonged fear aka anxiety that the shock will come again, and the noise stimulus becomes a conditioned fear signal. Conditioned fear is a learning process. Neurons in the amygdala receive input about fear-related stimuli such as from pain, vision, or hearing. Once established, its no longer a fear and instead becomes anxiety or an anxiety disorder. In the case of amygdala damage, it interferes with learning processes of fear which develop into conditioned fear, the extinction of learned fear (interfering with this can cause the fear to persist even after the danger had gone away), and interpreting/understanding stimuli with emotional consequences.

Amygdala and Higher Brain Centers: Fear

Amygdala sends signals to the hypothalamus which sends control to the ANS to regulate fear responses. Amygdala sends signals to the PFC which then regulates approach and avoidance responses. These higher center control the strength of conditioned fear.

Fear Learning

Mediated by a complex of amygdala that. includes the bed nucleus of the stria terminalis (BNST). This long-term, generalized emotional arousal depends on the BNST. The stria terminalis is a set of axons that connect the BNST to the amygdala. The learning process of conditioned fear is regulated by the amygdala includes learning what to fear and how to develop a long-term memory of fear. Conditioned learning is a typical type of long-term fear learning (being shocked in a cage may make rats wary of other cages, being attacked in an outside place may make someone scared of all outside places, etc.).

Kluver-Bucy Syndrome

Monkeys with damage to or removal of the amygdala become tame and placid. These monkeys decrease fear and are more likely to approach an object they normally avoid.

Amygdala and Facial Expressions

When you look at someone with a fearful expression, directed at you or not, or photos that evoke fear, your amygdala responds strongly. The same is true for ambiguously fearful faces, though to a lesser extent. When you look at someone with an angry expression, if its directed at you your amygdala doesn’t react much, but if the anger is directed somewhere else then your amygdala responds about the same or even stronger than a direct fear expression. This is because the amygdala is important for emotional processing and reflexively has a stronger response to ambiguous or puzzling facial expressions because you’re working harder to “decode” the expression.

PFC and Fear Reactivity

The PFC has top-down influence over fear reactivity with the PFC allowing re-appraisal of a situation to seem less threatening. People with higher activation of the PFC with “top-down control” were less likely to develop PTSD after a traumatic experience.

Amygdala Damage

People with this kind of damage can classify emotional pictures as pleasant or unpleasant, however, they don’t feel unpleasant feelings when looking at the unpleasant picture but still experience the cognitive aspect of unpleasant emotions. This means emotional processing is impaired but recognition of cognitive emotional aspects remain.

Urbach-Wiethe Disease

Reported in 1929, a rare disease that causes gradual atrophy of the amygdala. A woman with this disease showed fearlessness and low vigilant behaviors. She viewed scary movies and only felt excitement and became curious without fear or awareness of danger while handling venomous snakes. She was held at knifepoint and only remembers being angry and did not show discomfort at an unknown man approaching her to the point their noses touched. Her natural inclination to make eye contact (amygdala is responsible for this) to asses facial expressions was absent which made it difficult to identify disgust and fear. Eye whites are important for identifying fear which is why its hard to identify a fearful expression without making eye contact.

Amygdala Function: Final Consensus

All these experiments suggest: The amygdala is more likely responsible for detecting emotional information and then responding emotionally in the form of reactivity changes.
This is done by orchestrating other limbic brain areas to mediate different components of fear or conditioned fear.

Anxiety Disorders

Characterized by frequent episodes of intense, excessive, and persistent worry and fear about everyday situations. These episodes happen suddenly and can reach an intense peak of anxiety, fear, or terror in minutes. They include panic disorder, generalized anxiety disorder, phobias avoidance, OCD, and PTSD.

Post-Traumatic Stress Disorder

A severe and chronic emotional disorder that occurs in those who have experienced extremely traumatic events, usually involving injury or harm to themself or others. Symptoms include traumatic flashbacks, nightmares about the traumatic event, avoidance of reminders of the traumatic event, and an enhanced startle reflex. Most people with PTSD have a smaller than average hippocampus. Severe damage to the amygdala prevents the development of PTSD while slight damage or unnoticeable damage still allows PTSD to develop. This means the amygdala, which is important for emotional processing, is essential for the extreme emotional impact that contributes to PTSD.

Hippocampus and Stress

In a study of twins, a smaller hippocmapus only made a difference when one was exposed to an environment with several unpleasant stimuli (war). Another study in twins also found that those with PTSD had a smaller hippocampus than their twin, suggesting that PTSD atrophies the hippocampus to some extent.

Anxiolytics

Anxiety disorders are associated with decreased activity of GABA (an inhibitory neurotransmitter which calms the nervous system) and increased levels of orexin (maintains wakefulness and activity). Benzodiazepine , a commonly used class of anxiolytics, binds to a receptor site of a GABA receptor which causes the receptor to change shape, allowing GABA to attach easily and bind more tightly to it, allowing chloride to enter and inhibit neuronal activity in the amygdala, thus decreasing anxiety.

Concepts of Stress

In 1979, Hans Selye, the endocrinologist defined stress as the non-specific response of the body to any demand placed upon it. Manifests as fever, loss of appetite, inactivity, sleepiness, and overactive immune systems are non-specific responses to stress known as “illness”. When rats are exposed to external stressors they respond in similar ways including increased heart rate, breathing rate, and adrenal secretions.

General Adaptation Syndrome

Generalized responses to stress. Includes the following three stages:

• Alarm Stage: Characterized by increased activity of SNS

• Resistance Stage: Lasts longer, when the SNS declines to fight infections and heal wounds, the hypothalamus-adrenal-pituitary axis is activated. Adrenal cortex releases cortisol that allows the body to maintain prolonged alertness.

• Exhaustion Stage: Occurs after prolonged stress, the nervous system and immune system no longer have the energy to maintain heightened responses so the individual becomes tired, inactive, and vulnerable.

HPA Axis

Activated by stress beginning at the hypothalamus by secreting corticotropin-releasing factor (CRF) that sends messages to the anterior pituitary gland to secrete adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal cortex to secrete cortisol, which increases blood sugar levels and enhances metabolism.

1. Cortisol helps mobilize energies to help fight a difficult situation.

2. Good outcome of resistance stage: Dealing with brief or moderate stress improves attention and memory formation and improves performance on simple tasks.

3. Bad outcome of resistance stage: Responding to prolonged stress impairs performance that affects complex, flexible thinking, and produces enhanced activity of the immune system.

Immune System

Comprised of cells that protect the body against intruders, bacteria, and viruses.

Leukocytes

White blood cells which are produced in the bone marrow before migrating to the thymus gland, spleen, and peripheral lymph nodes. Patrol the blood and other bodily fluids looking for intruders.

B Cells

A type of leukocyte that matures in the bone marrow and can secrete antibodies. Y shaped proteins that attach to particular antigens like viruses.

Antigens

A surface protein that serves as an antibody-generator molecule and is recognized by B leukocytes. When leukocytes discover and recognize intruders as antigens, they secrete antibodies and attack them.

T Cells

Leukocytes that mature in the thymus. There are cytotoxic T cells, which directly attack intruder cells, and helper T cells, which stimulate other T cells or B cells to multiply more rapidly.

Natural Killer Cells

Attach directly to all intruders including cells infected with viruses and certain kinds of tumor cells.

Cytokines

Leukocytes and other cells secrete these in response to infections. They combat illness and communicate with the brain to inform of illness. Cytokines stimulate the vagus nerve which releases prostaglandins which are inflammatory substances that stimulate the hypothalamus to produce fever, sleepiness, and lack of energy. Sleep and inactivity are the body’s way of conserving energy to fight off illness and lack of appetite helps conserve energy and deprive the body of food for bacteria and viruses.

CNS and Immune System

The CNS may stimulate the HPA axis due to stress which increases leukocyte and cytokine production which feeds back into and influences the CNS. Excessive cytokines produced from stress might feed back into the CNS and cause fever-like symptoms due to the stress. Prolonged stress leads to prolonged cortisol production which weakens the immune system by drawing too much energy. Cortisol shifts energy away from immune system to increase blood sugar and metabolism, which may leave the individual vulnerable to illness after months of prolonged stress. Stress atrophies the hippocampus preventing the production of neurons and increases metabolic activity which makes the neurons sensitive to toxins or over-stimulation.

Enteric Nervous System

The ENS, located in the gut via the brain-gut axis, controls digestion and stretches from the esophagus to the rectum. Upsets your digestive system in response to the CNS and hormonal system’s responses to stress. Stress can also irritate bacteria in your gut which may cause IBS, visceral pain, or increases the risk of anxiety and depression.