闰土的大脑

原址:http://home.52brain.com/home-space-uid-3811-do-blog-id-630.html

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记得在鲁迅先生的《故乡》一文中,描述了前后对比非常明显的两个闰土:

少年闰土的心里有无穷无尽的希奇的事,都是我往常的朋友所不知道的:

“……我们沙地上,下了雪,我扫出一块空地来,用短棒支起一个大竹匾,撒下秕谷,看鸟雀来吃时,我远远地将缚在棒上的绳子只一拉,那鸟雀就罩在竹匾下了。什么都有:稻鸡,角鸡,鹁鸪,蓝背……”

“要管的是獾猪,刺猥,猹。月亮地下,你听,啦啦的响了,猹在咬瓜了。你便捏了胡叉,轻轻地走去……走到了,看见猹了,你便刺。这畜生很伶俐,倒向你奔来,反从胯下窜了。他的皮毛是油一般的滑……”

而中年闰土像一个木偶人:

“他站住了,脸上现出欢喜和凄凉的神情;动着嘴唇,却没有作声。”

“他只是摇头;脸上虽然刻着许多皱纹,却全然不动,仿佛石像一般。他大约只是觉得苦,却又形容不出,沉默了片时,便拿起烟管来默默的吸烟了。”

原因其实也很明显:多子,饥荒,苛税,兵,匪,官,绅。用我们的话来说,就是贫困、压力山大。

贫困和压力如何让一个聪明活泼,情境记忆力强(当然不能排除是鲁迅先生的情境记忆好而把少年闰土描述成这个样子,这里我们假定鲁迅先生描述就是闰土本人)的少年,变成一个木讷甚至麻木的中年?

这一切表现者和大脑有关,而最近两篇几乎同时出现的两篇论文似乎可以为我们说明一些问题。

少年闰土的大脑

Hanson等(Hanson,
Chandra, Wolfe, & Pollak, 2011
)发表在PloS
One上的这个研究检验了经济收入与一个特殊大脑结构——海马——的关系。

文章的摘要如是说:

“贫困是一种可能影响生物-行为加工过程的经历,因为在贫困环境中长大的儿童经常会面临很大的压力,同时经历的环境刺激不够。本研究探索社会经济状况与海马(一个参与学习和记忆并且受到压力影响的脑区)的关系。我们使用基于体素的形态测量学分析方法,对不同社会经济状况(n=317)参与者的大脑结构图的兴趣区进行分析。来自低收入背景儿童的海马灰质密度(一种对体积的测量)更低。我们从不同社会经济状况的教育和健康不平等角度来讨论了本结果。

Poverty is a type of pervasive experience that is likely to
influence biobehavioral processes because children developing in
such environments often encounter high levels of stress and reduced
environmental stimulation. This study explores the association
between socioeconomic status and the hippocampus, a brain region
involved in learning and memory that is known to be affected by
stress. We employ a voxel-based morphometry analytic framework with
region of interest drawing for structural brain images acquired
from participants across the socioeconomic spectrum (n = 317).
Children from lower income backgrounds had lower hippocampal gray
matter density, a measure of volume. This finding is discussed in
terms of disparities in education and health that are observed
across the socioeconomic spectrum.

clip_image002

图1 海马灰质总体密度(包括左右两侧)与收入关系的散点图。

在对结果的讨论中,作者们写道:

“这些结果说明海马的差异可能部分解释了在长时记忆、学习、神经内分泌功能和控制情绪行为上的差异。而本研究的这些结果与其他研究不同社会经济状况的神经心理差异的结论一致。

these findings suggest that differences in the hippocampus,
perhaps due to stress tied to growing up in poverty, might
partially explain differences in long-tern memory, learning,
control of neuroendocrine functions, and modulation of emotional
behavior. These results are consistent with research on
neuropsychological differences across the SES gradient.”

在讨论中,作者们还提到这么一句:

“先前研究表明海马与环境刺激的质量和压力相关。

The hippocampus has previously been found to be associated
with quality of environmental input and stress.

一般而言,环境刺激丰富对大脑的生长是有好处的。那么,鲁迅先生笔下的少年闰土正是处于一种环境刺激丰富的农村长大的,因为与在围墙下望着天空长大的孩子相比,闰土有更多的经历,可能有更好的大脑发育状况。但是随着闰土的成长,他的环境可能变化不大,当这些刺激不再新鲜有趣时,当他体会生存压力时,可能他的大脑进一步成长就受阻。然而,这些信息却无从得知。

中年闰土的大脑

在一篇即将发表在《Social Cognitive and Affective
Neuroscience》的论文中,Butterworth等(Butterworth, Cherbuin,
Sachdev, & Anstey,
2011
)以他们长期追踪研究的三批成年人为被试,研究经济困难与大脑结构的关系。文中摘要如下:

“本研究想了解在儿童期有过贫困经历或者当前正有经济困难的中年人与那些没有经历这种逆境的中年人是否存在可检测的大脑结构差异。我们对人格与总体健康(Personality
and Total
Health,PATH:一项大规模的纵向社会研究,测量来自澳大利亚东南部三批参与者的健康和幸福状况)研究中的参与者进行结构性磁共振成像扫描。本研究的分析数据来自431名中年人,调查之时年龄从44~48岁。使用Freesurfer图像分析软件对数据进行处理。本次调查中同时收集了社会-人口学环境、心理健康和认知功能的数据。结果显示,在控制了已知的萎缩风险因素后,报告有经济困难的成人比那些没有经济困难的成人在左右海马和杏仁核体积上均更小。相反,在经济困难与颅内体积、儿童期贫困经历与其他体积测量之间均无显著相关。经济困难可以看作是很大的压力源,本研究的结果支持了经济困难通过下丘脑-垂体的肾上腺轴功能和其他压力通道影响海马和杏仁核体积。

This study examined whether middle-aged adults exposed to
poverty in childhood or current financial hardship have detectable
brain differences from those who have not experienced such
adversity. Structural magnetic resonance imaging (MRI) was
conducted as one aspect of the Personality and Total Health (PATH)
through life study: a large longitudinal community survey measuring
the health and well-being of three cohorts from south-eastern
Australia. This analysis considers data from 431 middle-aged adults
in the aged 44–48 years at the time of the interview. Volumetric
segmentation was performed with the Freesurfer image analysis
suite. Data on socio-demographic circumstances, mental health and
cognitive performance were collected through the survey interview.
Results showed that, after controlling for well-established risk
factors for atrophy, adults who reported financial hardship had
smaller left and right hippocampal and amygdalar volumes than those
who did not report hardship. In contrast, there was no reliable
association between hardship and intra-cranial volume or between
childhood poverty and any of the volumetric measures. Financial
hardship may be considered a potent stressor and the observed
results are consistent with the view that hardship influences
hippocampal and amygdalar volumes through
hypothalamic–pituitary–adrenal axis function and other
stress-related pathways.”

The association between financial hardship and amygdala and hippocampal volumes

图2 使用Freesurfer
呈现出现来的海马(黄)与杏仁核(蓝)

这个研究结果显示的是目前的经济问题会影响到海马和杏仁核,却没有发现成人早期贫困的影响。作者在讨论中也指出此研究中没有发现儿童期贫困经历与体积测量关系可能是由于基于参与者自已回忆的报告缺乏精确性(The
lack of association between poverty in childhood and the volumetric
measures may reflect that this measure, based on retrospective
report of childhood circumstances, lacks precision.)。

从这个研究中,我们可以很好地推测,中年闰土所面临的巨大经济压力(多子,饥荒,苛税,兵,匪,官,绅),通过肾上腺轴影响到了其海马和杏仁核,导致其与当时的作者相比,显得“木”,没有情绪上的变化(杏仁核参与)。

闰土只是小说中人物。在当前的社会中,不少贫困地区孩子不仅没有了少年闰土时的有趣的经历,反而面临比少年闰土更大的压力(学习、生存),他们的海马结构是不是也受到影响?《独立宣言》中说:all
men are created equal。但是一旦我们出生于这个世界,就有不平等,大脑结构发育的不平等又是一个。

蚁族、月光族以及研究生博士生,他们虽然不至于像中年闰土那样面临了兵、匪、官等的苛税,但是变了样的压力照样有。老板、deadline、房子、车子和票子是不是也会“都苦得我们像一个木偶人的呢”?会不会让我们的海马、杏仁核变小呢?值得反思和警惕。

Butterworth, P., Cherbuin, N., Sachdev, P.,
& Anstey, K. J. (2011). The association between
financial hardship and amygdala and hippocampal volumes: results
from the PATH through life project. Social Cognitive and
Affective Neuroscience
. doi: 10.1093/scan/nsr027

Hanson, J. L., Chandra, A., Wolfe, B. L.,
& Pollak, S. D. (2011). Association between Income
and the Hippocampus. PLoS One, 6(5), e18712. doi:
10.1371/journal.pone.0018712

2 thoughts on “闰土的大脑

  1. Pingback: 关于社会经济地位对人的影响 | Know Thyself

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