The role of serotonin in emotional processing

到目前为止，我们的工作已经调查了在情绪处理任务中，使用急性色氨酸耗竭改变人类5-羟色胺能系统对行为表现的影响。此外，我们已经开始确定急性色氨酸缺乏对情绪处理的影响如何随着5-羟色胺转运体基因的变化而变化。 有证据表明，使用药理学挑战来操纵5-羟色胺会影响情绪处理的不同领域，而药理学挑战对情绪处理的影响因5-羟色胺相关的基因(例如，5-羟色胺转运体的多态)而不同。 我们发现，基因和急性色氨酸缺乏都调节了情绪处理的可分离成分。此外，我们还发现，通过色氨酸耗竭改变5-羟色胺传递的效果通常与基因型有关。例如，尽管色氨酸缺乏本身并没有扰乱恐惧表达的识别，但它确实损害了携带5-羟色胺转运体基因短等位基因的人的恐惧识别。这表明，仅靠5-羟色胺能传递的基因或变化可能不足以影响社交线索的处理，但当面临药理学挑战或5-羟色胺系统改变时，基因可能会影响情绪处理的这一领域。 在情绪和焦虑症的背景下，另一种重要的情绪处理形式是强化处理。奖惩加工直接指导行为和决策，非典型强化加工发生在多种精神疾病中。当我们开始研究时，有证据表明，改变5-羟色胺系统降低了对奖励的反应性，增加了对惩罚的敏感性。因此，我们试图进一步研究这些声明，以确定5-羟色胺在强化过程中的作用。在一系列研究中，我们发现，通过急性色氨酸耗竭改变5-羟色胺系统会改变增强过程，而且在某些情况下，这种影响是基因决定的。 在一项使用工具性学习任务的研究中，我们发现色氨酸缺乏会损害奖赏过程。有趣的是，长版本5-羟色胺转运体基因纯合子的个体与携带短版本基因的个体对惩罚的反应不同。与矮小携带者相比，高个子纯合子避开不良(惩罚)刺激的速度更慢。 我们还观察了色氨酸缺乏对反应逆转的影响，反应逆转衡量的是当之前奖励的行为变成惩罚行为时改变反应的能力。我们发现，与色氨酸耗竭的短载体相比，色氨酸耗竭的长载体在使用负反馈指导适当反应方面不如色氨酸枯竭的短载体有效。与色氨酸耗竭的S携带者和接受安慰剂的长期携带者相比，长期携带者在面临色氨酸耗竭期间的概率惩罚时，也不太可能保持正确的反应。 为了进一步探索5-羟色胺在奖惩敏感性中的作用，我们调查了色氨酸耗竭对决策任务的影响，该任务要求个体在两个与不同奖惩金额相关的对象中进行选择。我们发现，ATD改变了对惩罚相关信息的敏感性，并且对惩罚的敏感性随着转运体基因的不同而不同。 在过去的12个月里，我们通过研究色氨酸缺乏对参与表情处理、情绪注意和反转学习的神经区域的选择性影响，扩展了我们之前的工作。虽然来自情绪注意和反转学习范式的数据目前正在处理中，但我们已经观察到色氨酸枯竭在降低杏仁核对情绪表达的反应性(以及相关区域的反应性)方面的效果。

Our work thus far has investigated the effects of altering serotonergic systems in humans using acute tryptophan depletion on behavioral performance during emotional processing tasks. Additionally, we have begun to determine how acute tryptophan depletions effects on emotional processing vary as a function of serotonin transporter genotype. Evidence suggests that manipulating serotonin using pharmacological challenges impacts different domains of emotional processing, and the effect of pharmacological challenges on emotional processing varies as a function of serotonin-related genotype (e.g., polymorphisms in the serotonin transporter). We found that both genotype and acute tryptophan depletion modulated dissociable components of emotional processing. Furthermore we found that the effects of altering serotonin transmission via tryptophan depletion were often genotype-dependent. For example, although tryptophan depletion in and of itself did not disrupt fear expression recognition, it did impair fear recognition in individuals who carried the short allele of the serotonin transporter gene. This indicates that genotype or changes in serotonergic transmission alone may not necessarily be sufficient to affect processing of social cues, but genotype may influence this domain of emotional processing when faced with a pharmacological challenge or when serotonin systems are altered. Another form of emotional processing that is important in the context of mood and anxiety disorders is reinforcement processing. Processing reward and punishment directly guides behaviors and decision making, and atypical reinforcement processing occurs in a variety of psychiatric conditions. When we began our studies, there was evidence suggesting that altering serotonin systems reduces responsivity to reward and increases sensitivity to punishment. Thus, we attempted to investigate these claims further to determine the role of serotonin in reinforcement processing. In a series of studies, we found that altering serotonin systems via acute tryptophan depletion altered reinforcement processing, and that this effect was, in some cases, genotype dependent. In one study, using an instrumental learning task, we found that tryptophan depletion impaired reward processing. Interestingly, individuals who were homozygous for the long version of the serotonin transporter gene responded differently to punishment than did carriers of the short version. Long homozygotes were slower to avoid the bad (punishment) stimuli than were short carriers. We also looked at the effects of tryptophan depletion on response reversal, which measures the ability to change ones response when a previously rewarded behavior becomes a punished behavior. We found that tryptophan-depleted long carriers were not as efficient at using negative feedback to guide appropriate responding compared to tryptophan-depleted short carriers. Long carriers were also less likely to maintain correct responding in the face of probabilistic punishment during tryptophan depletion than tryptophan-depleted s carriers and long carriers who received the placebo. To further explore the role of serotonin in sensitivity to reward and punishment, we investigated the effects of tryptophan depletion on a decision making task, which requires individuals to choose between two objects associated with different amounts of reward or punishment. We found that ATD altered sensitivity to punishment-related information and that sensitivity to punishment varied as a function of transporter genotype. Over the past 12 months, we have extended our previous work by examining the selective effects of tryptophan depletion on neural regions engaged in expression processing, emotional attention and reversal learning. While the data from the emotional attention and reversal learning paradigms is currently being processed, we have observed the effects of tryptophan depletion on reducing amygdala responsiveness (and the responsiveness of associated regions) to emotional expressions.