Biphasic dendritic growth of associative neurons in the human prefrontal cortex is associated with rapid cognitive development during infancy and childhood.

Aim To analyze postnatal development and life-span
changes of apical dendrite side branches (oblique dendrites)
from associative layer IIIC magnopyramidal neurons
in the human dorsolateral prefrontal cortex and to compare
the findings with the previously established pattern
of basal dendrite development.
Methods We analyzed dendritic morphology from 352
rapid-Golgi impregnated neurons (10-18 neurons per subject)
in Brodmann area 9 from the post-mortem tissue of
25 subjects ranging in age from 1 week to 91 years. Data
were collected in the period between 1994 and 1996, and
the analysis was performed between September 2017 and
February 2018. Quantitative dendritic parameters were statistically
analyzed using one-way analysis of variance, Student Newman Keuls posthoc test for multiple comparisons and two-tailed t tests.
Results Oblique dendrites grew rapidly during the first
postnatal months, and the increase in the dendrite length
was accompanied by the outgrowth of new dendritic segments.
After a more than one-year-long “dormant” period
of only fine dendritic rearrangements (2.5-16 months),
oblique dendrites displayed a second period of marked
growth, continuing through the third postnatal year. Basal
and oblique dendrites displayed roughly the same growth
pattern, but had considerably different topological organization
in adulthood.
Conclusion Our analysis confirmed that a biphasic pattern
of postnatal dendritic development, together with a
second growth spurt at the age of 2-3 years, represents a
unique feature of the associative layer IIIC magnopyramidal
neurons in the human dorsolateral prefrontal cortex.
We propose that these structural changes relate to rapid
cognitive development during early childhood.