德国波恩大学的神经学家25日发表公报说，他们研究揭开了这一现象的生理机制。出乎意料的事物能激活大脑的奖赏中枢，后者与大脑记忆中枢以电压信号互相回应，令信息存入长期记忆区域。
研究人员举例说：“如果所有事都如常发生（例如某个早晨你买了一杯咖啡后去上班），那么其间的很多细节也许你不太可能记住；而如果发生了一些意外之事（如你将咖啡泼在裤子上），情况就不同了，你可能很久以后还能清楚记得。”
为解释这一现象，波恩大学研究人员参与的一个国际研究小组首先假设大脑奖赏中枢的伏隔核与记忆中枢的海马体之间存在相互作用，并对这两个区域进行观察。他们选择了正在接受治疗的8名癫痫症患者和6名抑郁症患者作为受检对象。两组患者的海马体和伏隔核中置有电极，能够方便对其进行测量。
研究人员选择了红色背景的人脸和绿色背景的房屋这两种反差明显的图片，并让一种图片的出现频率比另一种多得多，因此后者对于受检者来说就是“意料之外”的。
研究人员在实验中监测了受检者的海马体和伏隔核，发现当他们观看图片时，海马体会释放一个持续187毫秒的电压信号刺激伏隔核，后者受激后会释放出一个475毫秒的电压信号，最后海马体又会以一个482毫秒的信号予以回应。与此同时，当受检者看到“意料之外”的图片时这些脑部信号都更强烈，其对这些图片的记忆要比其他图片强1.5倍。此研究成果发表在最新一期的美国专业杂志《神经元》上。（生物谷Bioon.com）
生物谷推荐原始出处：
Neuron, Volume 65, Issue 4, 541-549, 25 February 2010 | Copyright ? 2010 Elsevier Inc. All rights reserved. | 10.1016/j.neuron.2010.02.006
Intracranial EEG Correlates of Expectancy and Memory Formation in the Human Hippocampus and Nucleus Accumbens
Nikolai Axmacher, Michael X. Cohen, Juergen Fell, Sven Haupt, Matthias Dümpelmann, Christian E. Elger, Thomas E. Schlaepfer, Doris Lenartz, Volker Sturm, Charan Ranganath
Department of Epileptology, University of Bonn, 53105 Bonn, Germany Department of Psychiatry and Psychotherapy, University of Bonn, 53105 Bonn, Germany Life and Brain Center of Academic Research, 53105 Bonn, Germany Center for Neuroscience, University of California, Davis, Davis, CA 95616, USA Department of Psychology, University of California, Davis, Davis, CA 95616, USA Epilepsy Center, University Hospital Freiburg, 79106 Freiburg, Germany Department of Stereotactical Neurosurgery, University of Cologne, 50937 K?ln, Germany Department of Psychology, University of Amsterdam, 1018 WB, Amsterdam, The Netherlands Department of Physiology, University of Arizona, Tucson, AZ 85724, USA Department of Psychiatry, The Johns Hopkins University, Baltimore, MD 21287-7413, USA Department of Mental Health, The Johns Hopkins University, Baltimore, MD 21287-7413, USA Corresponding author
The human brain is adept at anticipating upcoming events, but in a rapidly changing world, it is essential to detect and encode events that violate these expectancies. Unexpected events are more likely to be remembered than predictable events, but the underlying neural mechanisms for these effects remain unclear. We report intracranial EEG recordings from the hippocampus of epilepsy patients, and from the nucleus accumbens of depression patients. We found that unexpected stimuli enhance an early (187 ms) and a late (482 ms) hippocampal potential, and that the late potential is associated with successful memory encoding for these stimuli. Recordings from the nucleus accumbens revealed a late potential (peak at 475 ms), which increases in magnitude during unexpected items, but no subsequent memory effect and no early component. These results are consistent with the hypothesis that activity in a loop involving the hippocampus and the nucleus accumbens promotes encoding of unexpected events.
