Worbe Yulia, Savulich George, de Wit Sanne, Fernandez-Egea Emilio, Robbins Trevor W
Behavioral and Clinical Neuroscience Institute (Drs Worbe, Fernandez-Egea, and Robbins), Department of Psychiatry (Drs Savulich and Fernandez-Egea), and Department of Psychology (Dr Robbins), University of Cambridge, Cambridge, United Kingdom; Department of Clinical Psychology, University of Amsterdam, Amsterdam, The Netherlands (Dr de Wit).
Int J Neuropsychopharmacol. 2015 Feb 5;18(10):pyv013. doi: 10.1093/ijnp/pyv013.
Optimal behavioral performance results from a balance between goal-directed and habitual systems of behavioral control, which are modulated by ascending monoaminergic projections. While the role of the dopaminergic system in behavioral control has been recently addressed, the extent to which changes in global serotonin neurotransmission could influence these 2 systems is still poorly understood.
We employed the dietary acute tryptophan depletion procedure to reduce serotonin neurotransmission in 18 healthy volunteers and 18 matched controls. We used a 3-stage instrumental learning paradigm that includes an initial instrumental learning stage, a subsequent outcome-devaluation test, and a slip-of-action stage, which directly tests the balance between hypothetical goal-directed and habitual systems. We also employed a separate response inhibition control test to assess the behavioral specificity of the results.
Acute tryptophan depletion produced a shift of behavioral performance towards habitual responding as indexed by performance on the slip-of-action test. Moreover, greater habitual responding in the acute tryptophan depletion group was predicted by a steeper decline in plasma tryptophan levels. In contrast, acute tryptophan depletion left intact the ability to use discriminative stimuli to guide instrumental choice as indexed by the instrumental learning stage and did not impair inhibitory response control.
The major implication of this study is that serotonin modulates the balance between goal-directed and stimulus-response habitual systems of behavioral control. Our findings thus imply that diminished serotonin neurotransmission shifts behavioral control towards habitual responding.
最佳行为表现源于目标导向和习惯性行为控制系统之间的平衡,这两个系统由上行单胺能投射调节。虽然多巴胺能系统在行为控制中的作用最近已得到研究,但血清素整体神经传递变化对这两个系统的影响程度仍知之甚少。
我们采用饮食性急性色氨酸耗竭程序,以降低18名健康志愿者和18名匹配对照者的血清素神经传递。我们使用了一个三阶段工具性学习范式,包括初始工具性学习阶段、随后的结果贬值测试和行动失误阶段,该阶段直接测试假设的目标导向和习惯性系统之间的平衡。我们还采用了一个单独的反应抑制控制测试来评估结果的行为特异性。
急性色氨酸耗竭导致行为表现向习惯性反应转变,这通过行动失误测试中的表现来衡量。此外,急性色氨酸耗竭组中更强的习惯性反应可由血浆色氨酸水平的更急剧下降预测。相比之下,急性色氨酸耗竭并未影响利用辨别性刺激来指导工具性选择的能力,这通过工具性学习阶段来衡量,并且也未损害抑制性反应控制。
本研究的主要意义在于血清素调节行为控制的目标导向和刺激 - 反应习惯性系统之间的平衡。因此,我们的研究结果表明血清素神经传递减少会使行为控制转向习惯性反应。