2008-5-7 11:22:04

核磁共振揭示青春期大脑变化

2008年4月的爱思唯尔期刊《青春期健康杂志》（Journal of Adolescent Health）刊登了美国国立精神卫生研究所的一项最新研究。研究中采用核磁共振成像对青春期脑部的的变化做了描述，同时研究了脑部的变化如何影响这个时期青少年认知，情感和行为。

大脑是中枢神经系统的最高级部分，也是脑的主要部分。它分为左右两个半球，二者由神经纤维构成的胼胝体相连。被覆在大脑半球表面的灰质叫大脑皮层。研究人员利用核磁共振成像技术对人类大脑进行了扫描，研究显示大脑皮层的灰质数量在十几岁前会一直增长，随后会逐渐降低，直到晚年。

研究人员发现青春期大脑有三个主要变化。首先是信息综合处理和连贯性上，脑部的功能性和结构性增加变得更为一体化。形象的比喻就是此时脑部功能不是认识新的字母，而是将已认识的字母连成字，组成句，最后成段。接下来是大脑构造的巨大变化，大脑总体积在3至15岁基本无变化，某些区域的大脑物质会一年内增长近一倍，但由于此后的清除无用细胞和大脑持续重组，大量的组织又迅速消失。颞叶（语言处理和长时记忆）和顶叶（空间位置）在此时期也生长迅速。大脑中发育最晚的是前额皮层，这部分负责计划、确定重点、抑制冲动和权衡后果行为，在青春期仍然处于成长阶段。正因如此，这个时期青少年行为上表现出易冲动。

研究人员认为，青春期的很多行为都与大脑结构变化有着密切的关系。

生物谷推荐原始出处：

Journal of Adolescent Health，doi:10.1016/j.jadohealth.2008.01.007，Jay N. Giedd

The Teen Brain: Insights from Neuroimaging

Jay N. Giedd M.D.^,^a^,

Abstract

Few parents of a teenager are surprised to hear that the brain of a 16-year-old is different from the brain of an 8-year-old. Yet to pin down these differences in a rigorous scientific way has been elusive. Magnetic resonance imaging, with the capacity to provide exquisitely accurate quantifications of brain anatomy and physiology without the use of ionizing radiation, has launched a new era of adolescent neuroscience. Longitudinal studies of subjects from ages 3–30 years demonstrate a general pattern of childhood peaks of gray matter followed by adolescent declines, functional and structural increases in connectivity and integrative processing, and a changing balance between limbic/subcortical and frontal lobe functions, extending well into young adulthood. Although overinterpretation and premature application of neuroimaging findings for diagnostic purposes remains a risk, converging data from multiple imaging modalities is beginning to elucidate the implications of these brain changes on cognition, emotion, and behavior.