Chapter 18: Brain Mechanisms and Emotions

Emotions

• Affective neuroscience - the investigation of the neural basis of emotion and mood

  • Affective disorders a.k.a. mood disorders)

  • Emotional experience (feelings) does =/ emotional expression

• Early Theories of Emotion

  • Humourism is the view that the body is filled with 4 fluids, which in emotion resulted in different emotions

    • Blood - passion, yellow bile - anger, black bile - depression, phlegm - dullness

  • Darwin observed that people in different cultures experience the same emotions and that animals appear to express some of the same emotions as humans

  • The James-Lange Theory of Emotion proposed that we experience emotion in response to physiological changes in our body

    • Ex: you feel scared because you become aware of your heart racing and muscles tensing

    • This doesn’t mean that emotion cannot be felt in the absence of obvious physiological signs, but for strong emotions, the bodily changes cause the emotion

    • Interoceptive Awareness - to some extent we can be aware of our body’s autonomic function

  • The Cannon-Bard Theory of Emotion proposed that emotional experience (feelings) can occur independently of emotional expression; subcortical brain activity triggers feeling and autonomic response

    • In surgeries where spinal cords were transected, eliminating sensation did not eliminate emotion

    • Theorized that the character of the emotion is determined by the pattern of activation of the thalamus irrespective of the physiological response to sensory input

      • Ex: you don’t have to cry to be sad

  • The Schachter Theory of Emotion proposes that the body responds to a stimulus before feeling; appraisal (thinking of the situation) causes a conscious feeling

  • Capilano Canyon Suspension Bridge Experiment - male participants were more likely to call the female researcher after crossing the scary bridge than taking the boring path

    • Racing heart rate switched from thinking of the scary bridge to the arousal from the female researcher on the other side

  • Unconscious emotions occur when sensory input causes emotional effects on the brain without us being aware of the stimuli

    • Ex: Aversive effect from shock when shown angry faces, even with masking stimulus

      • Measures of both autonomic response and amygdala activity correlate with presentation of angry faces that conditioned to be unpleasant despite the faces not being perceived

• The Limbic System

  • Broca’s Limbic Lobe is a cortical area that forms a ring or border around the brain stem

    • Includes the cortex of the cingulate gyrus, medial surface of the temporal lobe, and the hippocampus

      • Broca did not associate this lobe with emotion

  • The Papez Circuit suggests that there is an emotion system lying on the medial wall of the brain that links the cortex with the hypothalamus

    • Following damage to certain cortical areas, there are sometimes profound changes in emotional expression (personality) with little change in perception or intelligence (ex: Phineas Gage and prefrontal cortex damage)

      • Gage may have recovered from some of his injuries related to behavioral problems

    • Papez proposed that activity evoked in other neocortical areas by projections from the cingulate cortex adds “emotional coloring” to our experiences

    • The Circuit: emotional stimulus → thalamus → sensory cortex → cingulate cortex (feeling) → (fornix) → hypothalamus (bodily response)→ anterior thalamus → cingulate cortex

      • Compatible with Cannon-Bard theories of emotion

    • Often referred to as the limbic system by Paul Maclean

      • He added the amygdala as a important part of the limbic system

  • Given the diversity of emotions we experience and the different brain activity associated with each, there is no compelling reason to think that only one system, rather than several, is involved

    • Additionally, with the inclusion of structures, such as the hippocampus, compels researchers to label the system as more of a memory system, than an emotion system

• Emotion Theories and Neural Representations

  • Early theories of emotion and subsequent descriptions of the limbic system were built on a combination of introspection and inference based primarily on instances of brain injury and brain disease

    • Does not reveal normal function

  • In basic theories of emotion, certain emotions are unique, indivisible experiences that are innate and universal across cultures

    • Basic emotions: anger, disgust, fear, happiness, sadness, and surprise

    • Experiments have been conducted using fMRI or PET brain recordings to show brain activity associated with each basic emotion

      • Cross over between fear and sadness

  • In dimensional theories of emotion, emotions can be broken down into smaller fundamental elements combined in different ways and differing amounts

    • Proposed affective dimensions: valence (pleasant-unpleasant) and arousal (weak emotion-strong emotion)

      • Does not distinguish between emotions like fear and anger that are high arousal and negative valence

    • In psychological constructionist theories of emotion, an emotional state is constructed from physiological processes that do not concern only emotion

      • Ex: language, attention, internal sensations, and external sensations

  • Emotions are important for decision making

    • Damage to the ventromedial prefrontal cortex makes it difficult to make decision

• Fear and the Amygdala

  • Kluver-Bucy syndrome - changes after temporal lobectomy include:

    • In monkeys:

      • increased oral fixations

      • poor food recognition amongst other objects

      • increased interest in sex

      • decreases in fear, aggression, and anxiety

    • In humans (lesions in amygdala or temporal lobe:

      • flattened affect (reduced emotional responses)

      • inappropriate sexual behaviors & oral fixation

      • poor object recognition (visually)

  • The amygdala is located in the pole of the temporal lobe, just below the cortex on the medial side

    • Human amygdala divided into: basolateral nuclei, corticomedial nuclei, and the central nucleus

      • The basolateral nuclei receive visual, auditory, gustatory, and tactile afferents

      • The corticomedial nuclei receive olfactory afferents

      • The central nucleus triggers behavioral, ANS, and hormonal responses

    • Each sensory system has a different projection pattern to the amygdala, with interconnections allowing the integration of info

      • The amygdala is connected to the hypothalamus via the ventral amygdalofugal pathway and the stria terminalis

  • Lesions of the amygdala have the effect of flattening emotion in a manner similar to the Kluver-Bucy syndrome

    • Commonly reported symptom of lesions involving the amygdala is an inability to recognize fear in facial expressions

      • S.M.’s amygdala lesion selectively decreased her ability to recognize fear in faces from visual input alone

        • In a follow-up study, it was revealed that she looked at people’s mouths not their eyes, when she could not recognize fear

    • Evidence suggests that the amygdala plays a key role in detecting fearful and threatening stimuli

  • Learned fear refers to the memories and emotional events that causes us to avoid certain behaviors

    • Experiments suggest that neurons in the amygdala can learn to respond to stimuli associated with pain, which evokes a fearful response (classical (Pavlova) fear conditioning)

      • The mouse freezes ( CS - controlled response) due to fear of electric shock (US - uncontrolled response) via the sound

      • Amygdala lesions eliminate the learned visceral responses, such as the changes in heart rate and blood pressure

      • The conditioned response in the amygdala arises from synaptic changes in the basolateral nuclei

• Anger and Aggression

  • Anger - emotional response; Aggression - violence or threat of violence

  • There are different forms of aggression in humans and animals

    • Aggression can be influenced by levels of androgens (more apparent in animals than humans)

    • Predatory aggression involves attacks against a member of a different species for the purpose of obtaining food

      • Not associated with high levels of activity in the sympathetic division

    • Affective aggression involves a show of aggression rather than aggression to kill for food

      • Associated with high levels of activity in the sympathetic division and vocalizations

    • Defensive, Rage, Predatory, Intermale, Maternal, Territorial

    • Monkeys after an amygdalectomy fell in rank among the colony

  • Psychosurgeries were performed in the early 20th century to treat psychiatric disorders, with amygdalectomies being one of the surgeries

    • Drug treatments are common practice now

  • One of the earliest structures linked to anger and aggressive behavior is the hypothalamus

    • In experiments where cats and dogs cerebral hemispheres (telencephalon) were removed, a sham rage occurred where an animal demonstrated all the behavioral manifestations of rage but in a situation that normally would not cause anger

      • Sham rage is observed if the anterior hypothalamus is destroyed along with the cortex but is not seen if the lesion is extended to include the posterior half of the hypothalamus

    • Hess’s hypothalamic stimulation of cats resulted in spiting, growling, and folding of its ears back

      • If the intensity was increased, the animal might make an attack, swatting with a paw or leaping onto an imaginary adversary

    • Flynn found that stimulation of the medial hypothalamus led to affective aggression, while stimulation of the lateral hypothalamus led to predatory aggression

  • The hypothalamus sends signals involving autonomic function to the brain stem via the medial forebrain bundle and the dorsal longitudinal fasciculus

    • Axons from the lateral hypothalamus make up part of the medial forebrain bundle, which projects to the VTA in the midbrain

      • Stimulation of the VTA can elicit behaviors characteristic of predatory aggression

    • Axons from the medial hypothalamus projects to the periaqueductal gray matter (PAG) of the midbrain by the dorsal longitudinal fasciculus

      • Stimulation of the PAG can produce affective aggression

      • The medial hypothalamus and amygdala are also important in aggression

    • The mesolimbic cortical system is also important in predatory aggression (quiet biting), as it motivates aggression (hunting in cats)

  • Reactive aggression (hot-headed aggression) vs. Instrumental aggression (premeditated murder) - similar to affective aggression vs. predatory aggression

  • Studies suggest that 5-HT plays an important role in regulating anger and aggression

    • MAO-A “Warrior” Gene - monoamine oxidase does not break down 5-HT, resulting in more aggressive behavior

    • The serotonin deficiency hypothesis states that aggression is inversely related to serotonergic activity

      • Evidence indicates that drugs that block the synthesis or release of serotonin increase aggressive behavior

      • 5-HT_1A and 5-HT_1B subtypes are involved in modulating anger and aggression

  • Testosterone stimulates vasopressin production, which promotes intermale aggression (in non-human animals)

    • Effects on other types of aggression are less clear