Plasticity and variation in brain organization and behaviour

哺乳动物的大脑在一生中都会发生变化，但早期生活经历的影响对大脑的构造有着最深刻的影响。具体地说，新大脑皮层的连接和组织以及它所指导的行为的变化，给了哺乳动物(包括人类)巨大的灵活性，以适应新的环境。这种基于经验的可塑性已经通过增强或剥夺感觉运动经验来证明，感觉运动经验通常分别放大和缩小相应的身体部分表征。例如，修剪大鼠和小鼠的胡须会导致皮质胡须的代表缩小，而前肢的代表则会生长。训练啮齿类动物用前肢伸展，可以扩大爪子的代表性。在更大的表征中，可能的额外神经处理被认为是增强相应身体部分能力的基础。

Mammalian brains change throughout the course of a lifetime, but the impact of early life experience has the most profound effect on how the brain is constructed. Specifically, changes in connectivity and organization of the neocortex and the behavior it directs give mammals (humans included) enormous flexibility to adapt to novel environments. Such experience-based plasticity has been demonstrated by enhancing or depriving sensorimotor experience, which generally enlarges and shrinks corresponding body part representations, respectively. For example, trimming the whiskers of rats and mice causes the cortical whisker representation to shrink and that of the forelimb to grow. Training rodents to reach with their forelimbs enlarges the paw representation. The additional neural processing possible in larger representations is thought to underlie enhanced abilities of the corresponding body parts.