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

Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Nature (Impact Factor: 42.35). 02/2010; 463(7283):948-52. DOI: 10.1038/nature08759
Source: PubMed

ABSTRACT 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 song. 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 ( approximately 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.

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    • "Within critical time periods, these excessive synapses are eliminated, whereas the remaining inputs are further strengthened to form the mature neural circuit (Shatz 1983; Sanes and Lichtman 1999). Synapse-elimination processes have also been observed during synaptic plasticity in the adult brain (Xu et al. 2009b; Yang et al. 2009; Roberts et al. 2010 "
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    • "For example, in vivo imaging of cortical motor neurons has demonstrated increased dendritic spine density concurrent with the acquisition of a learned motor behavior (Yang et al., 2009). Moreover, in zebra finches, the acquisition of singing behavior is accompanied by enlargement and stabilization of dendritic spines in forebrain neurons (Roberts et al., 2010). These in vivo imaging studies elegantly demonstrate that cortical circuit remodeling accompanies behavioral modification, and implicate circuit rewiring as a powerful mechanism for information storage in the cortex. "
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    • "The dendritic spines on pyramidal cells represent main postsynaptic elements of cortical excitatory synapses and are fundamental structures in memory, learning, and cognition [27]. In particular, long-term memory is mediated in part by the growth of new dendritic spines (or the enlargement of pre-existing spines) to reinforce a particular neural pathway [28]. "
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