125 Summary and General Discussion This discussion has parallels with the upcoming line of literature discussing the often overlooked role of avoidance in in fear-conditioning studies that provide an experimental model for the maintenance and treatment of anxiety disorders (Arnaudova et al., 2017; Krypotos, Beckers, Kindt, & Wagenmakers, 2015; LeDoux, Moscarello, Sears, & Campese, 2017; Pittig et al., 2018). Important within this line of research is the notion that avoidance is a complex construct fueled by several processes. As such, there is no one-size-fits- all solution in deciding which measure of avoidance is most suitable, and I would advise different type of measures (e.g., video ratings, eye-tracking, self-report questionnaires). Fourth, power analyses indicated that our number of participants was sufficient to detect effects of testosterone enhancement on changes in fear levels during exposure therapy and symptom severity, but it was not optimized for individual differences analyses regarding baseline testosterone and social avoidance. Future studies In chapter 2 we presented an agenda for future research that was too ambitious to cover within the scope of the present dissertation. However, we made a start with a few points related to SAD and based on those, I will complement the agenda with additional suggestions for future research. First, there is need to replicate the current findings as well as to extend them, ideally using a more extended protocol including multiple sessions of exposure treatment rather than two sessions, combined with additional doses of testosterone. An example could be the previously mentioned SCED design with a full treatment protocol (12 sessions) in which some sessions would be supplemented with testosterone or placebo. The use of an outcome measure close to the hypothesized mechanism of action (enhanced approach behavior), for example eye-tracking, could be used to gain more insight if testosterone indeed affects within session approach behavior. Repeated administration throughout the complete treatment is not recommended as it could lead to minor hair growth and acne (Islam, Bell, Green, Page, & Davis, 2019). Moreover, individuals may misattribute their exposure success to the use of testosterone, and thereby it could hamper treatment effects rather than boosting it. A more extended protocol is needed to better understand the effects of exogenous testosterone on fear activation and reduction within and across multiple exposure sessions. The current studies did not include a long follow-up period and therefore it would be interesting to follow participants for a longer period (for example six months) to gain insight in the long-term effects of testosterone enhancement on symptom reduction. Next, in all of the empirical chapters we used subjective fear levels as our main outcome measure. Although this is in line with many other proof-of-concept studies (Davis 6
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