Skilled motor learning does not enhance long-term depression in the motor cortex in vivo

J Neurophysiol. 2005 Mar;93(3):1486-97. doi: 10.1152/jn.00958.2004. Epub 2004 Nov 3.


Learning of motor skills may occur as a consequence of changes in the efficacy of synaptic connections in the primary motor cortex. We investigated if learning in a reaching task affects the excitability, short-term plasticity, and long-term plasticity of horizontal connections in layers II-III of the motor cortex. Because training in this task requires animals to be food-deprived, we compared the trained animals with similarly food-deprived untrained animals and normal controls. The results show that the excitability, short-term plasticity, and long-term plasticity of the studied horizontal connections were unaffected by motor learning. However, stress-related effects produced by food deprivation and handling significantly enhanced the expression of long-term depression in these pathways. These results are compatible with the hypothesis that the acquisition of a complex motor skill produces bi-directional changes in synaptic strength that are distributed throughout the complex neural networks of motor cortex, which remains synaptically balanced during learning. The results are incompatible with the idea that learning causes large unidirectional changes in the population response of these neural networks, which may occur instead during certain behavioral states, such as stress.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 6-Cyano-7-nitroquinoxaline-2,3-dione / pharmacology
  • Animals
  • Behavior, Animal
  • Electric Stimulation / methods
  • Evoked Potentials, Motor / physiology
  • Excitatory Amino Acid Antagonists / pharmacology
  • Food Deprivation
  • Functional Laterality / physiology
  • Learning / drug effects
  • Learning / physiology*
  • Long-Term Synaptic Depression / drug effects
  • Long-Term Synaptic Depression / physiology*
  • Long-Term Synaptic Depression / radiation effects
  • Male
  • Microdialysis / methods
  • Motor Cortex / drug effects
  • Motor Cortex / physiology*
  • Motor Cortex / radiation effects
  • Motor Skills / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Spectrum Analysis / methods
  • Time Factors


  • Excitatory Amino Acid Antagonists
  • 6-Cyano-7-nitroquinoxaline-2,3-dione