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PNAS:纹状体对奖赏反应的机制或可解释青少年好冒险

2012/02/01 来源:新华网
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美国匹兹堡大学研究人员发现,成年和青少年小鼠大脑对食物奖赏的反应不同,鉴于人脑与鼠脑结构相似,这或能解释青少年为何喜怒无常、好冒险、易上瘾或罹患精神疾病。

PNAS:美从鼠脑结构解释青少年为何好冒险

美国匹兹堡大学研究人员发现,成年和青少年小鼠大脑对食物奖赏的反应不同,鉴于人脑与鼠脑结构相似,这或能解释青少年为何喜怒无常、好冒险、易上瘾或罹患精神疾病。研究结果刊载于PNAS

研究人员首先教小鼠一个简单把戏,当响起某种声音时,小鼠知道,如果把鼻子伸入洞内,将得到一粒食物。研究人员在小鼠大脑内植入电极,监控它们执行任务时大脑伏隔核以及背侧纹状体两个区域神经元活动情况。

伏隔核是大脑快乐区域之一,譬如当进食时,这一区域的神经元会释放“奖赏”化学物质,产生快乐感觉。毒品也能激活这一区域,发出“奖赏”信号。背侧纹状体主要掌管习惯养成、决策和积极学习。

美国科学促进会主办的EurekAlert网站援引研究负责人、神经学教授比塔·穆加达姆的话报道,获得食物时,处于青少年时期的小鼠和成年小鼠伏隔核区域反应非常类似,不过大脑背侧纹状体反应大不相同,青少年小鼠活跃,而成年小鼠不活跃。

穆加达姆说,对青少年小鼠而言,“奖赏能够直接接入对学习和习惯养成决定性的大脑区域”,这意味着,奖赏可能对它们的决策、行动计划和习惯养成具有强烈影响。

研究人员认为,这项实验对象虽然是小鼠,不过处于青少年时期的动物与人一样,爱好冒险,容易冲动,因此这一结果可能也适用于人。

 “青少年处于某种境遇时可能做一些愚蠢的事,并非因为他们愚蠢,而是因为他们的大脑工作机制不同,”穆加达姆说,“不知何故,他们对这一境遇的感知和反应(与成年人)不同。”

穆加达姆说:“这种差异令青少年的大脑对周围发生的事情、对有望得到的‘奖赏’更没有抵制力,更容易成瘾。环境中的事物对青少年下一步行动的影响力强于成年人。”

研究人员并不清楚大脑如何从青少年状态变成成年状态,但这种转变过程中的问题可能引发疾病。

穆加达姆说:“我们中多数人完好地转变为成年人,但一些人在转变过程中可能发生不正常,转变不够或过度转变,就可能生病。”

她说,青少年时期是多数精神疾病初现症状的时期,因此,对预防精神分裂症、双重人格和饮食紊乱等疾病具有重要意义,“更好地了解青少年的大脑如何处理奖赏和作决定对设计预防措施相当重要”。


Striatum processes reward differently in adolescents versus adults

David A. Sturman and Bita Moghaddam

Adolescents often respond differently than adults to the same salient motivating contexts, such as peer interactions and pleasurable stimuli. Delineating the neural processing differences of adolescents is critical to understanding this phenomenon, as well as the bases of serious behavioral and psychiatric vulnerabilities, such as drug abuse, mood disorders, and schizophrenia. We believe that age-related changes in the ways salient stimuli are processed in key brain regions could underlie the unique predilections and vulnerabilities of adolescence. Because motivated behavior is the central issue, it is critical that age-related comparisons of brain activity be undertaken during motivational contexts. We compared single-unit activity and local field potentials in the nucleus accumbens (NAc) and dorsal striatum (DS) of adolescent and adult rats during a reward-motivated instrumental task. These regions are involved in motivated learning, reward processing, and action selection. We report adolescent neural processing differences in the DS, a region generally associated more with learning than reward processing in adults. Specifically, adolescents, but not adults, had a large proportion of neurons in the DS that activated in anticipation of reward. More similar response patterns were observed in NAc of the two age groups. DS single-unit activity differences were found despite similar local field potential oscillations. This study demonstrates that in adolescents, a region critically involved in learning and habit formation is highly responsive to reward. It thus suggests a mechanism for how rewards might shape adolescent behavior differently, and for their increased vulnerabilities to affective disorders.

文献链接http://www.pnas.org/content/early/2012/01/09/1114137109.abstract

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