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Abstract
Time series of mean EEG coherence were used to track changes in synaptic potentials in a large sample of normal girls and boys, mapping the human cerebral neural networks emerging at 56 paired brain sites between birth and age 24 years. Development of neural networks proceeds in a sequence of synchronous and asynchronous growth periods suggesting that ontogenetic inputs establish the distinct stages of the life cycle. Networks have gender-specific signatures; each sex has local networks organized into complementary regional clusters. Accelerated regional networks emerge shortly after birth, while delayed networks emerge during the latency period. Accelerated networks have synchrony in growth and pruning in all local neural networks during childhood, asynchrony during latency and synchrony during adolescence. These gray matter expansions and contractions are for brain functions and skills primarily attributed to male hunters and female gatherers. Delayed regional networks have synchrony in local neural network growth and pruning during latency, asynchrony during childhood and adolescence and synchrony during young adulthood. Brain regions in these late developing networks sample the environment for a long period of time before plasticity is reduced. They are assumed to support more complex verbal and nonverbal reasoning tasks. Bifurcations or cusps ripple across all spatial gradients during latency marking the transfer of exuberant synchronized growth and pruning from the hunter/gatherer neural networks to the complex-reasoning neural networks. Each of the sexes' 56 neural networks has one or two discontinuities that can be cusp-fitted. The majority of networks align with only one regional cluster. Nonlinear analyses show that the sexes' neural networks develop as a sequence of low-dimensional strange attractors with age a surrogate for the underlying ontogenetic process. This study confirms that brain regions do not develop concurrently and that each sex has different critical periods for assimilating the culture in hunter/gatherer and complex-reasoning networks. The low fractal dimensions of the neural networks suggest genes rigidly program each stage of the life cycle for environmental input.
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Introduction
Longitudinal and longisectional brain-mapping studies since 1999 add to existing evidence that the human cerebral cortex does not have concurrent development of neural networks from birth to late adolescence. Magnetic resonance image (MRI) studies by researchers at UCLA, McGill University and the National Institute of...