Fear: A Blessing and Curse

Abstract

F ear : a B lessing and C urse B S J Shruti Koti Imagine a lone adventurer standing at the edge of a cliff, miles away from civilization. He looks down at the unknown below and, taking a deep breath, jumps, attached to nothing but a single bungee cord. He feels the wind in his face, his clothes billowing up above him, and something else: a hollow pit in his stomach and the terrifying feeling that he may die at any moment. It sounds extreme, but what he is feeling is something we have all experienced, and it is completely natural: fear. To jump, the bungee jumper had to overcome his fear of heights, a fairly common fear as far as phobias go. However, grappling with fear is not always this easy. The reason we feel fear is not a mystery – evolutionarily, it puts you on guard and reduces your likelihood of getting attacked. Bats have evolved echolocation to detect and catch their prey; moths in turn have evolved echolocation and evasive flight maneuvers. Noctuid moths, which are eaten by bats, respond to bat echolocation in three ways: a startle response, sonar jamming, and acoustic aposematism (Yager, 2012).This is a prime example of how in a predator-prey relationship, there is an evolutionary arms race in which prey is usually better adapted for exaggerated caution. This basic fear response forms the biological foundation for human anxiety disorders. Early learning theory hypothesized that stimuli that became associated with fears were equipotent, i.e. every stimulus had an equal chance of becoming a feared stimulus (Carey, 1990). However, in practice, the limited range of common fears – heights, enclosed spaces, and certain types of animals (snakes, spiders) – led theorists to favor the concept of prepotency or preparedness, which states that we are biologically predisposed to certain fears, or “primed” to automatically select certain evolutionary stimuli. Fear is a complicated term because it can refer to both an emotion and a physical response to a stimulus. A stimulus is an object or event that promotes a fear response (increased heartbeat, freezing, etc.). Then fear conditioning is the behavioral process that leads organisms to predict and react to adverse events or stimuli – this refers to the natural fear acquisition process, too, not just processes occurring in laboratories. Conditioning occurs if the probability of the unconditioned stimulus (US) in the presence of the conditioned stimulus (CS) is different than it its absence. One of the most famous examples of classical (Pavlovian) conditioning was an experiment in which a little boy was conditioned to fear white rats. Initially, he showed no fear of a white rat, the neutral stimulus. Then the rat was continuously presented along with loud, unpleasant sounds – here the sounds were the unconditioned stimulus. By repeatedly pairing the rat with the unconditioned stimulus, the white rat (now the conditioned stimulus) came to evoke a fear response (the conditioned response) in the child (Jones, 1924). In general, a selective associative model shows four basic characteristics shaped by evolution: selectivity with regard to input, or threatening stimuli; automaticity, the triggering of a response in the absence of conscious awareness; encapsulation, the resistance to conscious cognitive influences; and specialized neural circuitry, the module controlled by a specific neural circuit that has been shaped by evolution (Hofmann, 2008). “...we are biologically predisposed to certain fears, or “primed” to automatically select certain evolutionary stimuli.” In expressing fear, exposure to acute stress triggers the “fight or flight” response, stimulating activity in the hypothalamic-pituitary-adrenal (HPA) axis, the locus coreruleus, noradrenergic systems, and the neurocircuitry of the fear system. The fear circuitry includes the amygdala and its subnuclei, the nucleus accumbens, the hippocampus, ventro- medial hypothalamus, periaqueductal gray, several brain stem nuclei, thalamic nuclei, insular cortex, and some prefrontal regions. Some regions, however, play a more prominent role in fear circuitry. The forebrain structures that have expanded the most in evolution are the prefrontal cortex and the amygdala. It has been shown that damage to the right and left amygdala disrupts fear conditioning: the right correlates with expression of learning, and the left hemisphere is involved in tasks that require cognitive interpretation of stimuli (Delgado et al, 2008). There are extensive connections between the amygdala and the visual system, consistent with behavioral, lesion, and neuroimaging data which show that the amygdala tunes visual brain areas for effective perception of fear-related stimuli (Ohman, 2009). Sensory information reaches the amygdala by two pathways. The first involves classical sensory 16 • B erkeley S cientific J ournal • E xtremes • F all 2014 • V olume 19 • I ssue 1