Differences in female and male development of the human cerebral cortex from birth to age 16
Hanlon, Harriet Wehner
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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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