Synaptic organization of cortico-cortical communication in primates

Maria Ashaber, László Zalányi, Emese Pálfi, István Stuber, Tamás Kovács, Anna W. Roe, Rob M. Friedman, László Négyessy

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


In cortical circuitry, synaptic communication across areas is based on two types of axon terminals, small and large, with modulatory and driving roles, respectively. In contrast, it is not known whether similar synaptic specializations exist for intra-areal projections. Using anterograde tracing and three-dimensional reconstruction by electron microscopy (3D-EM), we asked whether large boutons form synapses in the circuit of somatosensory cortical areas 3b and 1. In contrast to observations in macaque visual cortex, light microscopy showed both small and large boutons not only in inter-areal pathways, but also in long-distance intrinsic connections. 3D-EM showed that correlation of surface and volume provides a powerful tool for classifying cortical endings. Principal component analysis supported this observation and highlighted the significance of the size of mitochondria as a distinguishing feature of bouton type. The larger mitochondrion and higher degree of perforated postsynaptic density associated with large rather than to small boutons support the driver-like function of large boutons. In contrast to bouton size and complexity, the size of the postsynaptic density appeared invariant across the bouton types. Comparative studies in human supported that size is a major distinguishing factor of bouton type in the cerebral cortex. In conclusion, the driver-like function of the large endings could facilitate fast dissemination of tactile information within the intrinsic and inter-areal circuitry of areas 3b and 1.

Original languageEnglish (US)
Pages (from-to)4037-4056
Number of pages20
JournalEuropean Journal of Neuroscience
Issue number9
StatePublished - Nov 1 2020


  • Saimiri sciureus
  • axon terminal
  • electron microscopy
  • human
  • multivariate analyses
  • serial section reconstruction
  • tract tracing

ASJC Scopus subject areas

  • General Neuroscience


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