Major feedforward thalamic input into layer 4c of primary visual cortex in primate

Virginia Garcia-Marin, Jenna G. Kelly, Michael J. Hawken

Research output: Contribution to journalArticlepeer-review


One of the underlying principles of how mammalian circuits are constructed is the relative influence of feedforward to recurrent synaptic drive. It has been dogma in sensory systems that the thalamic feedforward input is relatively weak and that there is a large amplification of the input signal by recurrent feedback. Here we show that in trichromatic primates there is a major feedforward input to layer 4C of primary visual cortex. Using a combination of 3D-electron-microscopy and 3D-confocal imaging of thalamic boutons we found that the average feedforward contribution was about 20% of the total excitatory input in the parvocellular (P) pathway, about 3 times the currently accepted values for primates. In the magnocellular (M) pathway it was around 15%, nearly twice the currently accepted values. New methods showed the total synaptic and cell densities were as much as 150% of currently accepted values. The new estimates of contributions of feedforward synaptic inputs into visual cortex call for a major revision of the design of the canonical cortical circuit.

Original languageEnglish (US)
Article numberbhx311
Pages (from-to)134-149
Number of pages16
JournalCerebral Cortex
Issue number1
StatePublished - Jan 1 2019


  • Cortical layers
  • Neun
  • Thalamic afferents
  • V1
  • Vglut2

ASJC Scopus subject areas

  • Cognitive Neuroscience
  • Cellular and Molecular Neuroscience


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