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 【DavidShi译文】神经生物学家已经知道新奇的环境能激发探索和学习，但不知道脑是否真正喜欢此类新奇刺激。脑中主要的“新奇中心”称作黑质/腹侧被盖区（SN/VTA），可能接受意外刺激、由此引起的情绪激发的刺激和需要产生行为反应的刺激。黑质/腹侧被盖区对学习过程施加主要影响，因为它和作为脑学习中心的海马与作为处理情感信息中心的杏仁核都发生功能性联系。

现在，尼克·彭则克和艾姆勒·杜哲在人身上的研究显示，黑质/腹侧被盖区确实以此类方式对新奇刺激作出反应，新奇刺激引发脑寻求报酬而进行探索。伦敦大学学院和德国马格德堡大学的研究人员在2006年8月3日的《神经元》杂志上报道了此项发现。

试验时，彭则克和杜哲运用了“怪球”（oddball）实验范式，从而来研究新奇图像如何激活志愿者脑中的黑质/腹侧被盖区。应用这一方法，研究人员将一系列相同的脸或户外景色的图像展现在受试者面前，同时用功能磁共振成像技术扫描了他们的脑部。研究人员将4类不同的脸或景色（即“怪球”）随机混合。一个“怪球”是一幅略显不同的中性图像，另一个中的不同图像需要研究人员按下一个按钮，再一个是情感图像，还有一个是全新的图像。功能磁共振成像技术应用了无害放射信号和磁场来检测脑区的血流，血流能反映这些脑区的活动情况。

 通过这样的实验设计，研究人员能够比较受试者对不同“怪球”作出的反应，从而将脑对纯新奇刺激的反应和其他来源引发的反应，如情绪激发，区别开来。

 在第二组“怪球”实验中，研究人员试图验证是否是黑质/腹侧被盖区对新奇程度进行了编码。他们检测了该脑区受不同熟悉程度或新奇程度的图形刺激后的反应。在另外的研究中，他们评估了受试者对熟悉图像的记忆是否比新奇图像或更加熟悉的图像要好一些。

研究人员发现，黑质/腹侧被盖区确实对新奇刺激有反应，反应的程度与新奇程度成正比。他们总结道，他们的数据为“功能性海马－黑质/腹侧被盖区环路”提供了证据，该环路受新奇信息的刺激，胜于受其他形式的刺激，如情感和对一个图像作出反应的需求。研究人员说，刺激越新奇，黑质/腹侧被盖区的反应越激烈，这一发现和脑功能的模型研究相一致，亦即“将新奇刺激当作寻求报酬时候的一种刺激奖励以探索环境，而不是成为报酬自身。”

彭则克和杜哲还发现，新奇刺激促进了受试者的学习。“这样，人类黑质/腹侧被盖区能编码完全刺激的新奇性，也可能有利于促进对新奇内容的学习。”

他们最后说道，他们的发现提升了这样一种可能性：海马中的选择性脑损伤能消除新奇刺激在这类病人中的积极作用，也是这类病人再认记忆衰退的一个来源。

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【英文原文】

Pure novelty spurs the brain

Neurobiologists have known that a novel environment sparks exploration and learning, but very little is known about whether the brain really prefers novelty as such. Rather, the major "novelty center" of the brain--called the substantia nigra/ventral tegmental area (SN/VTA)--might be activated by the unexpectedness of a stimulus, the emotional arousal it causes, or the need to respond behaviorally. The SN/VTA exerts a major influence on learning because it is functionally linked to both the hippocampus, which is the brain's learning center, and the amygdala, the center for processing emotional information.

 Now, researchers Nico Bunzeck and Emrah Düzel report studies with humans showing that the SN/VTA does respond to novelty as such and this novelty motivates the brain to explore, seeking a reward. The researchers of University College London and Otto von Guericke University reported their findings in the August 3, 2006, issue of Neuron, published by Cell Press.

In their experiments, Bunzeck and Düzel used what is known as an "oddball" experimental paradigm to study how novel images activate the SN/VTA of volunteer subjects' brains. In this method--as the subject's brains were scanned using functional magnetic resonance imaging--they were shown a series of images of the same face or outdoor scene. However, the researchers randomly intermixed in this series four types of different, or "oddball," faces or scenes. One oddball was simply a different neutral image, one was a different image that required the researchers to press a button, one was an emotional image, and one was a distinctly novel image. In fMRI, harmless radio signals and magnetic fields are used to measure blood flow in brain regions, which reflects activity in those regions.

With this experimental design, the researchers could compare the subjects' response to the different kinds of oddball images to distinguish the brain's reaction to pure novelty itself from the other possible sources of brain activation, such as emotional arousal.

 In a second set of oddball experiments, the researchers sought to determine whether the SN/VTA encodes the magnitude of novelty. In those experiments, the researchers measured activation of the region by images of different levels of familiarity or novelty. In yet other studies, the researchers assessed whether the subjects' memory of familiar images was better when presented along with novel images or very familiar images.

The researchers found that the SN/VTA does, indeed, respond to novelty, and these response scales according to how novel the image was. They concluded that their data provide evidence for "a functional hippocampal-SN/VTA loop" that is driven by novelty rather than other forms of stimulus salience such as emotional content or the need to respond to an image. The researchers said their finding that the SN/VTA is more activated by greater novelty is compatible with models of brain function "that see novelty as a motivating bonus to explore an environment in the search for reward rather than being a reward itself."

 Also, Bunzeck and Düzel found that novelty enhanced learning in the subjects. "Thus, the human SN/VTA can code absolute stimulus novelty and might contribute to enhanced learning in the context of novelty," they concluded.

 Finally, they said their findings raise the possibility that selective brain injury to the hippocampus could eliminate the positive effects of novelty in such patients and constitute one source of reduction in recognition memory in the patients.

 Source : Cell Press