Abstract
The steroid hormones testosterone and cortisol can be considered hormones for environmental challenges; they are involved in adaptive neural and behavioral responses towards emotional stimuli. A key challenge of human psychoneuroendocrinology is to unravel the neural mechanisms by which testosterone and cortisol act on the brain to give rise to
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their effects on socio-emotional behaviors. Therefore, one of the main goals of the research reported in this thesis is to investigate neural mechanisms underlying the effects of cortisol on fear, reward and parenting behaviors. Another important challenge for human psychoneuroendocrinology is to investigate if the effects of hormones extend to behaviors that can be considered uniquely human. Hence, a second main goal is to investigate if testosterone influences higher order social functions, such as social cooperation and morality. Finally, hormones do not work in isolation: they interact with early life factors such as the prenatal hormonal milieu and early life stress such as childhood trauma. Another goal of this thesis is therefore to gather more insights in how theses early life factors interact with the effects of steroid hormones.
To these ends, this thesis includes a literature review and empirical studies employing single administration of cortisol and testosterone together with neuroimaging and behavioral paradigms. A marker of prenatal testosterone is used in the testosterone studies, based on animal studies showing that prenatal testosterone programs the effects of the hormone in adult life. Childhood trauma is taken into account in the cortisol studies, as previous animal and human studies have demonstrated that this is an important factor in shaping the cortisol system.
This thesis starts with a literature review that discusses evidence for the notion that testosterone and cortisol, together with serotonin, regulates reactive aggression. The evidence suggests that high testosterone and low cortisol levels together increases the occurrence of social aggression, and that low serotonin on top of this imbalance might specifically predispose towards impulsive aggression instead of instrumental aggression. This literature overview proposes this hypothesis as a guide for future research and provided the theoretical framework for the following studies.
The findings of the first empirical part of this thesis show that cortisol modulates the brain systems important for reward, fear and parenting. It is also observed that early life factors such as childhood trauma shape the effects of cortisol on neural processing of stimuli important for parenting.
The findings of the second empirical part of this thesis show that testosterone, in addition to affecting basal emotional processes such as fear and reward processing, also affects higher order social functions such as social cooperation and moral judgement. By using a proxy for prenatal testosterone exposure, it is shown that the effects of testosterone depend on prenatal hormone priming.
This thesis contributes to increasing the knowledge about how hormones shape our social and emotional behavior, and suggests that early life factors mediate hormone-behavior relationships later in life. As such, the findings in this thesis might have relevance for understanding the neurobiology of psychological disorders and might provide insights in treatments.
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