Rapid spine stabilization and synaptic enhancement at the onset of behavioural learning

摘要

以前的研究表明，脑部结构变化和感官体验之rn间有一个关联，但类似变化是否也伴随着学rn习却并不确定。对正在学习成鸟鸣叫模式的rn斑胸草雀幼鸟的声音控制核HVC(higller vocalrncentre)中的单个神经元所做的高分辨率双光rn子活体成像表明，学习的确涉及这样的变化。rn在学习它们第一首歌的24小时内，斑胸草雀幼rn鸟HVC中在正常情况下处于动态的树状脊会变rn得更大、更稳定，突触活动得到增强。%Behavioural learning depends on the brain's capacity to respond to instructive experience and is often enhanced during a juvenile sensitive period. How instructive experience acts on the juvenile brain to trigger behavioural learning remains unknown. In vitro studies show that forms of synaptic strengthening thought to underlie learning are accompanied by an increase in the stability, number and size of dendritic spines, which are the major sites of excitatory synaptic transmission in the vertebrate brain. In vivo imaging studies in sensory cortical regions reveal that these structural features can be affected by disrupting sensory experience and that spine turnover increases during sensitive periods for sensory map formation. These observations support two hypotheses: first, the increased capacity for behavioural learning during a sensitive period is associated with enhanced spine dynamics on sensorimotor neurons important for the learned behaviour; second, instructive experience rapidly stabilizes and strengthens these dynamic spines. Here we report a test of these hypotheses using two-photon in vivo imaging to measure spine dynamics in zebra finches, which learn to sing by imitating a tutor song during a juvenile sensitive period. Spine dynamics were measured in the forebrain nucleus HVC, the proximal site where auditory information merges with an explicit song motor representation, immediately before and after juvenile finches first experienced tutor song20. Higher levels of spine turnover before tutoring correlated with a greater capacity for subsequent song imitation. In juveniles with high levels of spine turnover, hearing a tutor song led to the rapid (～24-h) stabilization, accumulation and enlargement of dendritic spines in HVC. Moreover, in vivo intracellular recordings made immediately before and after the first day of tutoring revealed robust enhancement of synaptic activity in HVC. These findings suggest that behavioural learning results when instructive experience is able to rapidly stabilize and strengthen synapses on sensorimotor neurons important for the control of the learned behaviour.