Letter

Nature 463, 948-952 (18 February 2010) | doi:10.1038/nature08759; Received 11 June 2009; Accepted 2 December 2009

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

Todd F. Roberts1, Katherine A. Tschida1, Marguerita E. Klein1 & Richard Mooney1

  1. Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA

Correspondence to: Richard Mooney1 Correspondence and requests for materials should be addressed to R.M. (Email: mooney@neuro.duke.edu).

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 brain1, 2, 3, 4, 5, 6, 7. 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 formation8, 9, 10, 11, 12. 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 period13, 14. Spine dynamics were measured in the forebrain nucleus HVC, the proximal site where auditory information merges with an explicit song motor representation15, 16, 17, 18, 19, 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.

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