Fm. Benes et al., MYELINATION OF A KEY RELAY ZONE IN THE HIPPOCAMPAL-FORMATION OCCURS IN THE HUMAN BRAIN DURING CHILDHOOD, ADOLESCENCE, AND ADULTHOOD, Archives of general psychiatry, 51(6), 1994, pp. 477-484
Background: A previous study demonstrated that myelination of the supe
rior medullary lamina along the surface of the parahippocampal gyrus i
s occurring in human brain during adolescence. To further investigate
whether postnatal increases of myelination may continue during the sec
ond decade and possibly even longer, the extent of myelination in this
region has been analyzed in 164 psychiatrically normal individuals ag
ed newborn to 76 years. Methods: Cross sections of the hippocampal for
mation with adjoining hippocampal gyrus were analyzed on a blinded bas
is using either a global rating scale or measurements of the area of m
yelin staining. Results: A curvilinear increase in the extent of myeli
nation between the first and sixth decades of life (r=.71 and r=.67, r
espectively) was observed. When the area of myelination was expressed
relative to brain weight, there was a twofold increase between the fir
st and second decades and an additional increase of 60% between the fo
urth and sixth decades. Female subjects showed a significantly greater
degree of myelin staining than did male subjects during the interval
of ages 6 to 29 years; however, after the third decade, there were no
gender differences in the area of myelin staining. Conclusions: The in
creased staining of myelin during the first and second decades princip
ally occurred in the subicular region and adjacent portions of the pre
subiculum. During the fourth through sixth decades, however, it extend
ed to progressively more lateral locations along the surface of the pr
esubiculum. The precise origin(s) of the axons showing progressive mye
lination is unknown; however, the axons in the subiculum may include s
ome perforant path fibers, while those found in the presubiculum may i
nclude cingulum bundle projections. Overall, our data are consistent w
ith the idea that both early and late postnatal increases of myelinati
on occur in a key corticolimbic relay area of the human brain and unde
rscore the importance of applying a neurodevelopmental perspective to
the study of psychopathology during childhood, adolescence, and even a
dulthood.