ABSTRACT
The times of emergence of select psychological features during the first 8 years, summarized in Table 7.1, are partially dependent on specific changes in brain anatomy, physiology, and biochemistry. The disappearance of the newborn’s reflexes is due, in part, to increased synaptic contact between the supplementary motor cortex and the brainstem; the improved recognition memory at 12 weeks requires hippocampal growth; the enhanced working memory at 7 to 12 months profits from maturation of the prefrontal cortex; the appearance of speech is enabled by the dendritic growth in Wernicke’s, Broca’s, and the orofacial motor areas; and the appearance of inference, a moral sense, and self-awareness, should be aided by the enhanced connectivity of the two hemispheres. The psychological properties that appear after age 3, especially the increased reliance on semantic categories and integration of present with past, should be facilitated by the attainment of maximum synaptic density in the prefrontal cortex, refinement of circuitry, changes in neurotransmitter function, increased coherence, and the shift in predominant blood flow from the right to the left hemisphere.
