Hockenbury Discovering Psychology 5th txtbk

Emotion349Levenson (1992, 2003) believes that these differing patterns of sympatheticnervous system activation are universal, reflecting biological responses to the basicemotions that are hard-wired by evolution into all humans. Supporting this contention,Levenson found that male and female subjects, as well as young and elderlysubjects, experience the same patterns of autonomic nervous system activity for differentbasic emotions. These distinctive patterns of emotional physiological arousalwere also found in members of a remote culture in western Sumatra, an island inIndonesia (Levenson & others, 1992). Broader surveys of different cultures havealso demonstrated that the basic emotions are associated with distinct patterns ofautonomic nervous system activity (Levenson, 2003; Scherer & Wallbott, 1994).The Emotional BrainFear and the AmygdalaSophisticated brain-imaging techniques have led to an explosion of new knowledgeabout the brain’s role in emotion. Of all the emotions, the brain processes involvedin fear have been most thoroughly studied. Many brain areas are implicated in emotionalresponses, but the brain structure called the amygdala has long been knownto be especially important. As described in Chapter 2, the amygdala is an almondshapedcluster of neurons located deep in the temporal lobe on each side of thebrain. The amygdala is part of the limbic system, a group of brain structures involvedin emotion, memory, and basic motivational drives, such as hunger, thirst, and sex.Neural pathways connect the amygdala with other brain structures.Several studies have shown that the amygdala is a key brain structure in the emotionalresponse of fear in humans (Davis & Whalen, 2001). For example, brainimagingtechniques have demonstrated that the amygdala activates when you viewthreatening or fearful faces, or hear people make nonverbal sounds expressing fear(Morris & others, 1999; Öhman & others, 2007). Even when people simply anticipatea threatening stimulus, the amygdala activates as part of the fear circuit in thebrain (Phelps & others, 2001).In rats, amygdala damage disrupts the neural circuits involved in the fear response.For example, rats with a damaged amygdala can’t be classically conditioned to acquirea fear response (LeDoux, 2007). In humans, damage to the amygdala also disrupts elementsof the fear response. For example, people with amygdala damage lose the abilityto distinguish between friendly and threatening faces (Adolphs & others, 1998).amygdala(uh-MIG-dull-uh) Almond-shaped cluster ofneurons in the brain’s temporal lobe, involvedin memory and emotional responses,especially fear.©Dan Piaro. Reprinted with special permission of King Features SyndicateActivating the Amygdala: Direct and Indirect Neural Pathways Let’s use an exampleto show how the amygdala participates in the brain’s fear circuit. Imagine that yoursister’s 8-year-old son sneaks up behind you at a family picnic and pokes you in the backwith a long stick. As you quickly wheel around, he shouts, “Look what I found in thewoods!” Dangling from the stick is a wriggling, slimy-looking, three-foot-long snake.He tosses the snake into your face, and you let out a yell and jump two feet into the air.As he bursts into hysterical laughter, you quickly realize that the real-looking snake ismade of rubber, your nephew is a twit, and your sister is laughing as hard as her son.Even if you don’t know any obnoxious 8-year-old boys, you’ve probably experienceda sudden fright where you instantly reacted to a threatening stimulus, like asnake, a spider, or an oncoming car. Typically, you respond instinctively, withouttaking time to consciously or deliberately evaluate the situation.So how can we respond to potentially dangerous stimuli before we’ve had timeto think about them? Let’s stay with our example. When you saw the danglingsnake, the visual stimulus was first routed to the thalamus (see Figure 8.10 on thenext page). As we explained in Chapter 2, all incoming sensory information, withthe exception of olfactory sensations, is processed in the thalamus before being relayedto sensory centers in the cerebral cortex.However, the neuroscientist Joseph LeDoux (1996, 2000) discovered that there aretwo neural pathways for sensory information that project from the thalamus. One leadsto the cortex, as previously described, but the other leads directly to the amygdala, bypassingthe cortex. When we are faced with a potential threat, sensory informationabout the threatening stimulus is routed simultaneously along both pathways.