Cognitive Neuroscience Emotion I. Expression and Recognition of Emotion The communication of emotion is very important for human interactions. We display emotions by our actions, and perceive it in others by the interpretation of those actions. The scientific study of human emotional expression and recognition depends on the use of human subjects. Our understanding of human emotion comes from: a) behavioral studies in normal subjects b) behavioral studies of patients with brain lesions c) imaging studies (PET & fMRI) of normals & brain-lesioned patients What are the behavioral components by which we express and recognize human emotion? a) Facial expression b) Hand gesture c) Tone of voice d) Word choice To study human emotion, subjects are asked to recognize emotional content in words or faces. They are asked to make judgments about emotional content in sentences and scenes. A. Facial Expression The ability to perform and perceive facial expressions is a very important part of human emotional communication. Charles Darwin suggested that facial expressions are innate behavioral responses. Support comes from the similarity of these expressions in cultures throughout the world. They are not culturally learned. 1 Also, blind children display normal facial expressions à again suggesting that they are not learned by observation. Although facial expressions of emotion appear to be stereotyped behaviors, they can be modified by social context. Sometimes cultures impose restrictions on the expression of emotion. A display rule is a cultural norm that modifies the expression of emotion in different societal situations. B. Neural Basis of Recognition 1. Studies of Hemispheric Difference Some studies indicate that areas in the right hemisphere of the brain are selectively involved in emotional comprehension. a. Perceptual Studies in Normals Tachistoscopic presentation of visual stimuli to one hemifield and dichotic listening are used to compare the effects of presentation of material to the left and right hemispheres. The contralateral hemisphere to the side of presentation receives more specific information than the ipsilateral side. Subjects are found to respond more quickly and with greater accuracy (i.e. fewer errors) in detecting emotional cues when stimuli are presented to the right hemisphere than the left hemisphere. b. Cortical Lesion Studies i. Patients with right hemisphere cortical lesions are impaired in recognizing the emotions expressed by facial expression and hand gesture. Ability to recognize facial expression is independent of ability to recognize faces. Adolphs study: right hemisphere lesions à selective recognition impairment for negative emotions. 2 ii. Patients with lesions in right temporal-parietal junction (rTPJ) cortex are impaired in judging emotion expressed by tone of voice. c. Imaging Studies PET recording of rCBF while subjects assessed emotional content of verbal input shows that the judgment of emotion from voice tone selectively activates right prefrontal cortex. 2. Other Brain Structures a. Amygdala The amygdala is active when people perceive and recall emotional content. It is also involved in emotional recognition: i. people with bilateral amygdala lesions are impaired in the ability to recognize facial expression of emotion. Impairment is particularly severe for recognition of negative emotions such as fear. ii. these people are also impaired in ability to assess threat from facial expression, as compared to normals. iii. normal subjects have elevated activity in the amygdala when viewing facial expressions of fear. b. Basal Ganglia The basal ganglia appear to be specifically related to the ability to recognize facial expressions of a particular emotion, disgust. i. Impairment in the ability to recognize facial expressions of disgust found in patients with degeneration (Huntingon’s disease) or malfunction (obsessive-compulsive disorder) of basal ganglia. ii. Increased activity in basal ganglia in neuroimaging of subjects viewing facial expression of disgust. 3 C. Neural Basis of Expression 1. Cortical Control of Facial Expression As noted earlier, the facial expression of emotion is largely innate and stereotyped. Evidence suggests that these expressions involve different systems than those involved in voluntary control of facial muscles: a. Duchenne’s muscle (orbicularis oculi) contracts during a genuine smile, but not a contrived smile. b. Volitional facial paresis: partial paralysis of the facial musculature under voluntary control, but activity of same muscles is normal in expression of genuine emotions. Damage to primary motor cortex or its efferent pathways. c. Emotional facial paresis: voluntary control of facial musculature is normal, but facial expression of emotion is impaired. Damage to insular cortex or its efferent pathways. 2. Hemispheric Differences As with recognition, facial expression of emotion has a stronger right hemisphere component. a. Chimerical face studies: stronger emotional content expressed by left half of face than right. b. Wada test studies: reduced emotional expression (i.e. less intense emotions described) when right hemisphere put to sleep as compared to baseline. c. Stroke patients: right-hemisphere lesions impair ability to accurately express emotion (facially & by tone of voice). Also, patients with right-hemisphere damage show less concern for disabilities than those with left-hemisphere damage. 4 II. Theories of Emotion Generation A. James-Lange Theory William James and Carl Lange each proposed similar theories to explain emotional experience. It involves a three-step process: 1. Emotion-producing situations initially produce somatic physiological responses, e.g. autonomic physiological changes, behavioral responses. 2. The brain receives sensory input from the viscera and muscles resulting from the peripheral activations. 3. Interpretation of this secondary sensory input leads to the feeling (experience) of emotion in higher brain regions, including the cerebral cortex. James-Lange theory thus implies that people cannot feel an emotion without first having a bodily (somatic) response. B. Cannon-Bard Theory Cannon and Bard were Harvard physiologists who opposed the James- Lange theory on 5 major grounds: 1) total separation of viscera from the CNS does not eliminate emotional behavior. 2) the same visceral responses occur in very different emotional states – the sympathetic n.s. functions as a single unit, and somatic physiological responses to emotion-producing situations are thus not distinct enough to distinguish among different emotions. 3) the viscera are relatively insensitive to external stimulation. 4) somatic physiological processes are too slow to be the origin of different emotions. 5) artificial production of emotion-related visceral changes does not actually cause emotional experience. 5 Cannon and Bard thus objected to the James-Lange theory because of its postulate that the brain’s emotional response is secondary to the peripheral response. Instead, they proposed that emotion involves simultaneous but independent activity of the peripheral nervous system and the brain. According to Cannon-Bard theory, the sympathetic n.s. coordinates the body’s reaction to the situation, and the brain simultaneously generates emotional feeling. Accordingly, emotional feeling does not need to follow visceral input to the brain, and should be intact when that visceral input is removed. C. Appraisal Theory In the various forms of appraisal theory, emotional processing depends on the interaction between the properties of a stimulus and the interpretation of those properties. For example, emotion may be a response to the evaluation by the brain of the benefits and harms represented by an external object. Thus, a cognitive appraisal, not necessarily conscious, precedes the somatic physiological response and feeling. D. Singer-Schachter Theory This theory (sometimes called James-Lange-Schachter theory) is a blend of James-Lange and appraisal theories. Singer & Schachter proposed that cognitive appraisal of emotion follows visceral input to the brain, and that this appraisal is required before an emotion is experienced. Evidence that visceral input to the brain is necessary for the experience of emotion comes from the study of paraplegic (spinal-cord-injury) patients (although this evidence is now considered controversial). It is claimed that these patients continue to express (learned) emotional responses, but with reduced emotional feeling. The subjective intensity of emotion experienced by these patients is reported to correspond to the level of the lesion: i.e., the higher the transection, the less emotion is experienced. This finding is explained by the hypothesis that the lower the transection, the greater the loss of visceral input to the brain, and hence the lower the emotional feeling. 6 Schachter and Singer administered adrenaline to volunteers, creating an ambiguous sense of arousal. These subjects would interpret the visceral changes produced by the drug according to the context in which they were put – e.g., they would say that they were experiencing feelings of fear if put in a context of fear, or say that their feelings were drug induced if told that they had received adrenaline. E. Constructivist Theory There are various forms of constructivist theory. They all suggest that emotion emerges from cognition, as guided by culture and language. The constructivist theory of Barrett holds that emotions are concepts that are constructed by humans as we