Invariant synapse density and neuronal connectivity scaling in primate neocortical evolution

Chet C. Sherwood, Sarah B. Miller, Molly Karl, Cheryl D. Stimpson, Kimberley A. Phillips, Bob Jacobs, Patrick R. Hof, Mary Ann Raghanti, Jeroen B. Smaers

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


Synapses are involved in the communication of information from one neuron to another. However, a systematic analysis of synapse density in the neocortex from a diversity of species is lacking, limiting what can be understood about the evolution of this fundamental aspect of brain structure. To address this, we quantified synapse density in supragranular layers II-III and infragranular layers V-VI from primary visual cortex and inferior temporal cortex in a sample of 25 species of primates, including humans. We found that synapse densities were relatively constant across these levels of the cortical visual processing hierarchy and did not significantly differ with brain mass, varying by only 1.9-fold across species. We also found that neuron densities decreased in relation to brain enlargement. Consequently, these data show that the number of synapses per neuron significantly rises as a function of brain expansion in these neocortical areas of primates. Humans displayed the highest number of synapses per neuron, but these values were generally within expectations based on brain size. The metabolic and biophysical constraints that regulate uniformity of synapse density, therefore, likely underlie a key principle of neuronal connectivity scaling in primate neocortical evolution.

Original languageEnglish
Pages (from-to)5604-5615
Number of pages12
JournalCerebral Cortex
Issue number10
StatePublished - 1 Oct 2020


  • Brain evolution
  • Neocortex
  • Primate
  • Synapse


Dive into the research topics of 'Invariant synapse density and neuronal connectivity scaling in primate neocortical evolution'. Together they form a unique fingerprint.

Cite this