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354 REVERSIBLE DISORDERS OF BRAIN DEVELOPMENT(Fredrickson, 2001). Additionally, it has been proposed that positive emotionsdecrease autonomic arousal (Folkman & Moskowitz, 2000; Isen et al., 1987),protecting the individual against the development of stress-related disorders andfacilitating the maintenance of allostasis.The field is beginning to elucidate the underlying neurobiology of optimism, apsychological attribute that is at least partially inherited. The neural circuitry ofbrain reward systems is complex and involves several regions, including mesolimbicdopamine pathways, the PFC, and the amygdala. Mesolimbic dopaminepathways play a critical role in reward, motivation, and pleasure (Charney, 2004).Dopaminergic neurons in the ventral tegmental area innervate the nucleus accumbens,where increased dopamine activity has been associated with reward andreward expectations. It has been suggested that people who remain optimistic andhopeful in the context of trauma and other extremely stressful life events may havea dopaminergic reward system that is either hypersensitive to rewarding stimulior resistant to dysregulation in the face of chronic stress (Charney, 2004). Forexample, research on U.S. Special Forces soldiers demonstrated enhanced activationof brain regions that govern emotion and reward processing in rewardrelatedsituations, such as the anterior cingulate cortex, right caudate, and rightmidbrain, as compared to healthy civilians (Vythilingham et al., 2005).The appreciation and use of humor characterizes many resilient individuals.Humor has been identified as a mature defense mechanism (Vaillant, 1977) andas a coping strategy that may decrease the probability of developing stress-induceddepression (Deaner & McConatha, 1993; Thorson & Powell, 1994). In studies ofresilient Vietnam veterans (Hendin & Haas, 1984), surgical patients (Carveret al., 1993), cancer patients (Culver et al., 2002), and at-risk children (Werner &Smith 1992; Wolin & Wolin, 1993), the ability to use humor to deal with adversityhas been cited as a healthy coping mechanism. Humor is thought to diminishthe threatening nature and negative emotional impact of stressful situations viacognitive reappraisal or reframing (Folkman, 1997), fostering a more positiveperspective on challenging circumstances. Humor also relieves tension and discomfort(Vaillant, 1992) and attracts social support (Silver et al., 1990). For instance,Manne et al. (2003) found that humor was associated with reductions inmaternal depressive symptoms in a study of mothers of children undergoing bonemarrow transplantation. Additionally, Thorson and Powell (1994) and Deaner andMcConatha (1993) found a negative relationship between sense of humor anddepression.Humor is thought to activate a network of subcortical regions that are criticallyinvolved in the dopaminergic reward system (Mobbs et al., 2003; Moran et al.,2004). In a functional magnetic resonance imaging study of healthy volunteers,Mobbs et al. (2003) found that funny cartoons, in contrast to nonfunny cartoons,activated the amygdala, ventral striatum/nucleus accumbens, ventral tegmentalarea, anterior thalamus, and subadjacent hypothalamus. A time-series analysis