Wellcome Trust Centre for Neuroimaging, University College London, London WC1N 3BG, United Kingdom.
J Neurosci. 2011 Jun 22;31(25):9383-9. doi: 10.1523/JNEUROSCI.1524-11.2011.
Pavlovian fear conditioning is highly conserved across species, providing a powerful model of aversive learning. In rodents, fear memory is stored and reactivated under the influence of the amygdala. There is no evidence for an equivalent mechanism in primates, and an opposite mechanism is proposed whereby primate amygdala contributes only to an initial phase of aversive learning, subsequently ceding fear memory to extra-amygdalar regions. Here, we reexamine this question by exploiting human high-resolution functional magnetic resonance imaging in conjunction with multivariate methods. By assuming a sparse neural coding, we show it is possible, at an individual subject level, to discriminate responses to conditioned (CS+ and CS-) stimuli in both basolateral and centro-cortical amygdala nuclei. The strength of this discrimination increased over time and was tightly coupled to the behavioral expression of fear, consistent with an expression of a stable fear memory trace. These data highlight that the human basolateral and centro-cortical amygdala support initial learning as well more enduring fear memory storage. A sparse neuronal representation for fear, here revealed by multivariate pattern classification, resolves why an enduring memory trace has proven elusive in previous human studies.
巴甫洛夫式恐惧条件反射在物种间高度保守，为厌恶学习提供了强有力的模型。在啮齿动物中，恐惧记忆在杏仁核的影响下被存储和重新激活。在灵长类动物中没有证据表明存在等效机制，而是提出了相反的机制，即灵长类动物的杏仁核仅有助于厌恶学习的初始阶段，随后将恐惧记忆让位于杏仁核外区域。在这里，我们通过利用人类高分辨率功能磁共振成像结合多元方法重新研究了这个问题。通过假设稀疏的神经编码，我们证明在个体受试者水平上，可以区分基底外侧和中央皮质杏仁核核中条件（CS+和 CS-）刺激的反应。这种区分的强度随着时间的推移而增加，并且与恐惧的行为表现紧密相关，这与稳定的恐惧记忆痕迹的表达一致。这些数据强调，人类的基底外侧和中央皮质杏仁核支持初始学习以及更持久的恐惧记忆存储。通过多元模式分类揭示的恐惧稀疏神经元表示，解决了为什么在以前的人类研究中，持久的记忆痕迹一直难以捉摸的问题。
