9.7 The early environment of the developing brain.
The mother-tongue is learned by immersion in an environment of sounds and expressions. One's native language environment is important. Equally important is an even earlier period: before language stimulation becomes significant, the intra-uterine environment of the developing foetal brain has influenced its structural patterns. It does so by the chemical (hormonal) composition of the tissue fluid around the brain cells which affects their migration patterns. This can have a profound influence on later language functions.
Language breeds like a virus: when it circulates in a society it can reproduce itself in the neuronal system of an infant. Speech- and language skills grow in an infant's brain and take possession of it, but only if the brain is susceptible to the intruder. It is comparable to what happens in the lymphoid system: antibody-receptors (idiotopes) on the surface of lymph cells and immune globulines are part of the environment of the other lymphocytes. When external antigens have an impact the external stimuli give rise to a reshuffling of the network.
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We wanted to find out about the interaction between early immune- and cognitive development because we had repeatedly observed that in some children who suffered from a speech/language handicap no other explanation could be found than an early episode of atopic eczema. Moreover investigations by N.Geschwind e.a. have encouraged us to consider the role of the pregnant mothers' immune system as the earliest environment enveloping and influencing the language-generating systems of the child.
This is a very brief review of his theory. Individual differences in language acquisition and language processing can be ascribed in part to the distribution of functions over the two hemispheres of the brain. In most people the left hemisphere dominates with respect to verbal memory. Damage to the left half of the brain leaves a defect in language function; repair is slow and incomplete. In young children however such a defect can be completely restored in several months. It is possible that in the critical period of language acquisition the necessary receptive and expressive skills are still stored in both hemispheres. At a later stage people would get into the habit of using only the more efficient half (in right-handed people this is usually the left half). But young children would still have easy access to the information that is also stored in the right half of the brain. It is a remarkable fact that more rapid recovery from a language defect occurs in left-handed adults and people with left- handedness in the near family. Geschwind also had the impression that people who in childhood had been dyslectic had a more rapid recovery after accidents resulting in aphasia.
Another remarkable finding by several independent researchers is a high proportion of cardiovascular anomalies in families with dyslectic children. This was a reason to search for the presence of auto-antibodies in the blood of the mothers of children having these defects. It appeared that several auto-antibodies were present at levels that were higher than could be expected on the basis of probability. It is supposed that auto-antibodies occur more in atopic families: the existence of exceedingly sensitive people is the price that humanity has to pay for an immune system that is sufficiently vigilant. Geschwind supposes that the relation with dyslexia is explained by the circulating auto-antibodies in an expectant mother influencing the migration of neurons in the foetal life episode of her child. Thus the child's earliest environment, the womb, would exert an influence on the maturation of its brain. The resulting brain architecture and distribution of functions over both halves of the brain, being partly of genetic and partly of environmental origin, presents a challenge for future research.