Regional differences in synaptogenesis in human cerebral cortex.
Level 4 - case-series / case-control
Post-mortem comparative neuroanatomical case-series
PubMed 9336221 · doi:10.1002/(sici)1096-9861(19971020)387:2<167::aid-cne1>3.0.co;2-z
What was done
The authors compared the timing and progression of synapse formation and elimination in post-mortem human cerebral cortex tissue across two regions: the auditory cortex (Heschl's gyrus) and the prefrontal cortex (middle frontal gyrus). Developmental timing was evaluated from fetal stages (prior to 27 weeks conceptual age) through childhood and adolescence, alongside concurrent observations of dendritic growth, axonal growth, and subcortical white matter myelination, and compared to patterns in rhesus monkeys.
What was found
Synapse formation in both regions begins before 27 weeks conceptual age. Synaptic density increases faster in the auditory cortex, reaching a maximum near 3 months postnatal age, whereas maximum density in the middle frontal gyrus is reached after 15 months. Net synapse elimination ends by age 12 years in the auditory cortex, but extends to mid-adolescence in the prefrontal cortex. This heterochronous development in humans contrasts with concurrent development in rhesus monkeys, although both species exhibit similar synaptic overproduction, persistence into late childhood/adolescence, absolute synaptic densities, and layer-specific patterns.
Why it matters
This paper provides foundational evidence that human synaptic proliferation and pruning follow region-specific timelines, with prefrontal maturation extending substantially later into development than primary auditory cortex.
Limits
The abstract provides developmental milestone ages but no quantitative synaptic counts, standard deviations, or statistical test results. Sample size (n), donor demographics, post-mortem intervals, and causes of death are not reported in the abstract.