17 General introduction Social challenge hypothesis Social events are usually associated with a temporary surge in testosterone levels. The social challenge hypothesis (Wingfield et al., 1990), originally based on testosterone and aggression associations in monogamous birds (Wingfield, Lynn, & Soma, 2001) and later also established in primates (Muller & Wrangham, 2004) and humans (Bateup, Booth, Shirtcliff, & Granger, 2002; Neave & Wolfson, 2003), is the most predominant theory of testosterone reactivity. It states that testosterone levels rise in preparation to a challenging encounter in which social status might be threatened, such as giving a speech in front of a public, and thereby initiating approach motivation and reducing fear (Archer, 2006; Bos, Panksepp, et al., 2012). Following this hypothesis, a rise in testosterone levels in preparation to public speaking, may stimulate Rose to fully approach this challenging situation, rather than using safety behaviors or avoiding it completely. Consistent with this hypothesis, in both animal and human studies, low levels of endogenous testosterone have been linked to socially submissive, anxious, and avoidant behaviors (Archer, 2006; Josephs, Sellers, Newman, & Mehta, 2006; Sapolsky, 1991), whereas high basal testosterone levels are related to social dominance and approach behavior (Maner, Miller, Schmidt, & Eckel, 2008; Mazur & Booth, 1998). Importantly, reduced levels of endogenous testosterone have been found in those suffering from SAD (Giltay et al., 2012) and other social avoidance-related disorders such as depression (Almeida, Yeap, Hankey, Jamrozik, & Flicker, 2008; Giltay et al., 2012). The threat-approach facilitating properties of testosterone have been linked to its effects on the amygdala (and its connectivity with the prefrontal cortex, PFC) and striatum: biasing the amygdala toward reward anticipation and threat approach (see figure 1.2B, Hermans et al., 2010; Volman, Toni, Verhagen, & Roelofs, 2011; Radke et al., 2015). Testosterone as a possible enhancer of exposure therapy in SAD Experimental studies using testosterone administration The social motivational enhancing effects of testosterone have been established not only by correlational but also by more causal testosterone administration studies. For example, administration of a single dose testosterone (0.5 mg sublingual vs placebo) to healthy (female) participants prior to exposure to a threat cue, has been shown to reduce fear, to enhance reward sensitivity and to promote social approach motivation (Bos, van Honk, Ramsey, Stein, & Hermans, 2012; Enter et al., 2014; Terburg et al., 2016). Critically, administration of a single dose of testosterone (0.5 mg sublingually versus placebo), specifically in females with SAD, prior to an eye-tracking experiment, result1
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