人类自从进化为人类后,不仅有所得亦有所失。我们的认知能力比其它动物的都高,我们可以有意识地去改变命运。但另一方面,我们高度进化的大脑更易发生严重故障,比如神经系统疾病和痴呆(dementia)。最近,一支神经科学研究小组发现这些“的”和“失”都发生于同一特定的神经回路(neural circuits)。
1999年,有文章报道人类大脑和大猩猩的大脑都含有特异的被拉长的神经细胞——纺锤体神经元(spindle neurons)。这些细胞也被称作Von Economo神经元(VENs),位于大脑皮层中与社会行为、意识和情感有关的两个部分。在其它灵长类动物中没有找到纺锤体神经元,近来有报道说在一些鲸中有出现(ScienceNOW, 27 November)。
加州大学神经生物学家William Seeley及其同事研究VENs对额颞痴呆(frontotemporal dementia,FTD)的影响。额颞痴呆患者有时出现不适当的冲动行为甚至入店抢劫等犯罪行为。研究人员对比7例FTD死亡患者的大脑(实验组)和7例非脑部原因死亡的患者的大脑(对照组),以及5名被确诊为阿尔茨海莫氏症(另一种痴呆,主要是影响记忆)的患者。研究人员发现包含VENs的两个大脑区域中的一个——前扣带皮层(anterior cingulate cortex)在FTD患者中出现了变化:与对照组相比,VENs的数量缩减了74%。相反,阿尔茨海莫氏症患者的前扣带皮层变化较小,统计学意义上可以忽略。研究结果刊登于12月22日《Annals of Neurology》。
Seeley及其同事认为,VENs在人类进化出社会行为中扮演重要角色,但同时也将人类推向神经变性疾病的危险边缘。亚特兰大Emory大学神经科学家Lary Walker不赞诚将复杂的社会行为归因于特定细胞的行为和部分脑区域。
英文原文:
'Social Dementia' Decimates Special Neurons
Being human has its pluses and minuses. Our cognitive powers are superior to that of other animals, and we can act consciously to alter our destinies. On the other hand, our highly evolved brains are prone to serious malfunctions such as mental illness and dementia. Now a team of neuroscientists has found that some of these blessings and curses might be linked to the same specialized neural circuits.
In 1999, researchers discovered that the brains of humans and great apes such as chimpanzees and gorillas contain special elongated nerve cells called spindle neurons. These cells, also known as Von Economo neurons (VENs), are localized in two parts of the cerebral cortex known to be associated with social behavior, consciousness, and emotion. They are not found in other primates, although very recently they were discovered in some whales (ScienceNOW, 27 November).
William Seeley, a neurologist at the University of California, San Francisco, and colleagues set out to see whether VENs play a role in a type of dementia that causes people to lose inhibition in social situations. People with frontotemporal dementia (FTD) engage in inappropriate and impulsive behavior and sometimes even carry out criminal acts such as shoplifting. The team looked at the brains of 7 deceased patients with FTD and compared them to 7 controls who had died of causes unrelated to the brain, as well as 5 patients diagnosed with Alzheimer's disease, a very different type of dementia that mainly affects memory. The researchers found that one of the two brain areas that contain VENs, the anterior cingulate cortex, looked very different in FTD patients: There was a 74% reduction in the number of VENs compared to controls. In contrast, Alzheimer's patients had only a small and statistically insignificant reduction, they report online today in Annals of Neurology.
Seeley and his colleagues conclude that VENs may play a key role in making humans the social creatures that we are, but that they also expose us to a higher risk of degenerative neural diseases. Lary Walker, a neuroscientist at Emory University in Atlanta, Georgia, says that the authors make a "reasonably compelling case that the VENs are selectively vulnerable in FTD". Nevertheless, Walker cautions against ascribing complex behaviors to the action of specific cells or regions in the brain.