Cerebral lateralisation and rate of maturation.

Multifactorial inheritance applied to brain development implies a large continuum of normal variation with deviation from the norm at the extremes of maturational rate. The greater population of neurons, greater arborization of neural networks and excessive synaptic density in early maturation imply that adaptability (plasticity) is a main advantage, as opposed to a deficit in adaptability associated with the reduced number of neurons, reduced connectivity and reduced synaptic density in late slow maturation. It is hypothesised that Planum Temporale (PT) asymmetry and hand-preference predict the rate of CNS maturation as does the cognitive profile on the Wechsler Adult Intelligence Scale (WAIS): PT leftward asymmetry, right-handedness and a left-hemisphere cognitive advantage signifies early fast maturation: PT rightward asymmetry, left-handedness and a right-hemisphere cognitive advantage signify late maturation, while PT symmetry and ambilaterality represent rates of maturation in between. The slower development of males implies a male predominance in disorders affecting late maturers: Developmental Dyslexia (DD) with a predominance of rightward PT asymmetry/symmetry, left-handedness and multiple functional deficits, as well as excessive regressive events confirmed on PT/MRI. Schizophrenia, hypothesised to be a disorder in late maturers, is distinguished by rightward asymmetry/symmetry. Left-handedness and DD are common as is prior delayed development supporting excessive regressive events as do the findings on PT/MRI. To reduce the risk of DD and schizophrenia requires a reduction in late maturation through the enhancement of maturational rate by optimal nutrition before and during pregnancy and later.