Insights from Modern Imaging Studies of the Brain

Insights From Modern Imaging Studies of the Brain

Modern imaging techniques like functional Magnetic Resonance Imaging ( f MRI) enable scientists to study the human brain in real time. Areas of the brain that are active would “light up” when the subject perform a function or activity, giving us an idea the parts of the brain involved. Likewise, when the part of the brain that should light up when doing a certain activity but does not in a particular person doing that same activity, that also tells us something of the abnormality in that person’s brain. This particular observation is highly relevant in such conditions as autism.

            The basic principle of f MRI is based on changes in local blood flow in the brain that correlates with increased nerve cell activities. This increased flow alters the ratio of the oxygenated (unused) hemoglobin pigment versus the deoxygenated (used), which is picked up by the f MRI.

            There are fascinating studies on babies and also adults across cultures that help us better understand the workings of the human brain.

            The brain is unique in that it is far from fully developed at birth. It has considerable post-birth growth, making the birth process pivotal as interferences during it impacts the brain’s subsequent development. There are many examples of the tragic consequences on brain development from birth complications. Both nature and nurture influence post-birth growth.

            Pre-birth, genetic factors predominate, as with chromosomal abnormalities. Environmental factors like lack of essential vitamins (folic acid) and nutrients or the presence of toxins (lead, infection) could also be consequential.

            A baby’s brain has the same number of neurons as the adult’s. These neurons continue making their connections with each other (synapses) after birth, a process called synaptic growth. This is influenced by both nature (primarily genetic) and nurture (the baby’s physical and emotional experiences). Such activities like hearing, seeing, touching, smelling, and tasting stimulate the growth of these neural connections.

            When a pathway is used frequently, the brain recognizes its importance and covers the nerve cell branches with a fatty myelin sheath to insulate it so the impulses would travel faster and not stray, as well as to protect the nerve fiber. This myelination process is most dynamic up until adolescence but continues on though much more slowly into adulthood.

            Concomitant with synaptic growth is another process both complementary and in the opposite direction, that of synaptic pruning. Those connections not used will atrophy, as illustrated by the experiments on suturing shut the eyes of kittens cited earlier.

            There are three theories on brain development. First, the maturational perspective, postulates that brain development depends on the natural maturation process of its various parts and largely determined by nature. The environmental role would be restricted to only interference or acceleration of that maturation process. The child for example, would not learn to control its sphincters until the appropriate parts of the brain controlling those functions are mature (at about three or four years); likewise, learning to talk or walk (at about two).

            Second is the interactive specialization theory. Brain development (especially postnatal) involves organizing interactions between the different parts of the brain where the development (or lack) of one part affects the others. Meaning, primarily a process of integration. The studies on children blinded at birth with cataracts and later given sight-restoring surgery support this contention. The child does not “see” right after the surgery but has to learn it.

            The third is the skill-learning hypothesis. Imaging studies indicate that when children learn new skills, like walking, the frontal cortex (“higher” part) of the brain is activated. As they become facile, the active part shifts more posterior. The inference is that the frontal cortex is concerned with learning, but once that skill has become automatic (as with walking), brain activity shifts to the back, the non-thinking part.

            When we learn a new skill like playing a musical instrument, the front part of our brain would be active. Later when we have mastered it, the brain activity would shift to a more posterior part of the brain, from the learning to the routine center as it were.

            This theory is also supported by the findings that children who receive little social stimulation or opportunities to explore their world have 20 to 30 percent smaller brains than children of comparable age. Similarly, children exposed to prolonged stress, as with abuse or trauma, will have altered brain function as a consequence of that constant high level of the stress hormone, cortisol. They have difficulty developing warm and secure relationships. We saw this with Harlow’s baby monkeys.

            In essence the earlier nature-nurture dichotomy and the consequent heated controversies were misplaced. Instead we have a complex interplay of the two, one influencing and in turn being influenced by the other. It is a dynamic as well as adaptive process.

            An exciting development in modern genetics is epigenetics. Briefly explained, it is the inheritance of traits that are not due to changes in one’s underlying genes but induced by alterations in our environment. In traditional biology, only genetic changes are inherited; that still holds true. However, changes in the environment (like stress, starvation, exposure to drugs and chemicals) could alter how those genes would be expressed (phenotype), and then those changes would be passed on to the next generation. The gene itself is unchanged, only its expression.

            As a concept, it is an old one, predating Darwin, as with Lamark using it to explain the long neck of giraffes. The modern concept, with its understanding at the molecular level and integrating it with existing knowledge of DNAs, is very recent.

            Genes carry only the codes for proteins, and only that. Proteins are complex molecules, and how they function is influenced by its final shape or conformation even though the molecule itself is unchanged. Gene expression also depends on its conformations, and that in turn is influenced by its microenvironment.

            Consider the “simple” water molecule, one oxygen and two hydrogen atoms. Imagine a gene coding for it. At room temperature that chemical as water could be used to erode a slope; at higher temperatures as steam, to power turbines to produce electricity; at low temperatures as in the Arctic, it could crush the ships’ steel hulls. Same code for the same molecule, but with different environment you get vastly different consequences.

            Something similar with the workings of our genes. Depending on their conformations (shapes), different parts have different polarities, some more positive, others negative. Chemicals like the stress hormone cortisol has varying own polarities on its molecules. They would be attracted to the opposite polar parts of the genes, thus altering their shapes ever so subtly to the extent that the genes could not be expressed. This change in conformation would then be transferred to the next generation such that even though it has the genes, they are not expressed, which is the same thing as not having the genes.

            Experiments with rats showed that when the mother licked its babies frequently, they grew up to be contented and relaxed. Those babies in turn would have babies that were also contented and relaxed, and would lick their own babies frequently, thus perpetuating the transmission. Meanwhile those mothers that did not lick or prevented from licking their babies would have stressed babies. They in turn would not lick their young and produce yet another generation of stressed babies, and the cycle continues. The genes themselves have not changed rather the behaviors of the mother would be transmitted through the mechanism of epigenes to the next generation, influencing whether those genes would be expressed.

            Child rearing practices (and that would include what and how we feed as well as nurture our babies) vary with culture. Those practices, as with the licking of rat babies, affect our epigenome, and we pass that on to the next generation.

            Stated simply, we pass on through our biological mechanisms not only our genes (our nature) but also our cultural practices (nurture) through our epigenomes.

            The next major period of change is during adolescence. Again, the environment is crucial. This impact is consequential and defining enough to merit the designation of the “adolescent brain.” Nothing has changed with respect to the “nature” component, only the environment. One is internal, the surge of new hormones (primarily sex hormones) and the other, external, the cultural rites of passage. The effect on the brain at puberty however is not as critical though no less profound as with during the first few years.

            The different parts of the brain develop at different rates. The subcortical limbic system that controls emotions develops much faster than the cortical part, the “rational” center. Stated in Freudian language, the id maturing before the superego. Thus, teenagers are predisposed to impulsive and dangerous behaviors. Insights from studies of the adolescent brain have tremendous impact on the criminal justice system, questioning the basic premise of culpability and liability with these teenagers.

            In California, when a child is involved in an accident it is never at fault; it is always the adult’s. Likewise, the criminal records of juveniles are sealed or destroyed once they reach a certain age, based on the same principle.

Adapted from the author’s book, Liberating The Malay Mind, published by ZI Publications, Petaling Jaya, 2013. The second edition was released in January 2016.