This study compares the development of the human
cerebral cortex of 224 girls and 284 boys in a series of
cross-sectional analyses as measured by EEG coherence on
normal children's brains (longisectional design). Correlations
of these EEG readings taken from all brain regions
between a mean age of 6 months and 16 years yield measures
of synaptic communication. Time series of these measures
reflect the changing growth patterns across the 16 years.
Time series of mean EEG coherence are oscillating waves
that travel across left-right and front-back spatial gradients
in both hemispheres. Growth spurts in mean coherence
correlate with the genetic process of synapse overproduction
and pruning spurts correlate with synapse elimination.
Growth processes in neural connections evident in each
hemisphere were examined in detail. Principal components
analysis with varimax rotation identified in-phase patterns
of connectivity for 64 electrode-pair sites. Analyses of
effect-size differences in mean and variance ratios assisted
in determining the developmental patterns in each of the
brain regions studied.
The study finds gender differences in both neurological
structures and the timing of their development, with the
timing differences being most prominent. Each sex's postnatal
development concentrates on networks that showed less
cortical growth during early fetal development; i.e, females
favor the right hemisphere and males favor the left. Gender
differences are greatest in the left prefrontal medial and
lateral regions and the right posterior region, supporting
gender differences indicated by anatomical, neurological and
psychometric assessments. These regions support cognitive
tasks of language expression and articulation, spatial
visualization, judgment and goal setting.
Fine-grain analyses of 42 intrahemisphere electrode-pair
sites indicate the timing difference at some sites is a
phase shift less than a year; at other sites, the difference
is substantial, not easily described by a phase-shift
dimension. other gender differences related to rate of
development are specified.
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