Nature And Nurture On Neural And Cognitive Development

Throughout history, an ongoing debate has taken place regarding whether the development of certain aspects of an individual’s life are affected more through nature or nurture. Those that argue for nature believe that genes influence an individual’s development. Those that believe in nurture’s influence claim that an individual’s experience has more of an effect upon an adolescent’s temperament. Recently, researchers have uncovered evidence that it is not only nature or nurture that influences development, but a complex combination of both. This manuscript will attempt to cover some of the factors that influence an adolescent’s neural, cognitive, and emotional development. The degree to which nature and nurture influence these particular aspects of an individual’s life will also be discussed. Lastly, this manuscript will briefly explore the possibility of genetics and environment off setting deficiencies in the one another.

Discussion

Neural Development

One aspect of human development that has been focused upon in research is that of neural development. During early prenatal neural development, the brain takes its initial shape as well as forms neurons which create a foundation for future neural development. To guide this development, neurons are directed either chemically or by other cells which act as signposts. This guiding allows neurons to form the distinct sections of the brain which include the hindbrain, the midbrain, and the forebrain. It is during this formation neuron specialization takes place in that like-minded cells bunch together to process certain forms of information like auditory and visual. It is still controversial amongst researchers how this specialization occurs with some researchers believing that neurons possess a protomap (Rakic, 1988) while others believe that the functions of neurons are decided by the environmental inputs received (O’Leary, 1989). While most evidence found points to the latter result, there is still much research that needs to be performed (Broderick & Blewitt, 2010).

During later prenatal brain development, researchers have found that the sensory organs of the fetus have developed enough to receive and interpret information from outside of the mother’s womb. One study performed found that fetuses showed recognition to a point when a familiar nursery rhyme was played for the mother carrying the fetus (Decasper, Lecaneut, Busnel, Granier-Deferre, & Maugeais, 1994). In another study, researchers sewed one eye shut of several kittens at birth. Several weeks later, the researchers opened the closed eyes and found the kitten had been rendered irreversibly blind in that particular eye (Wiesel & Hubel, 1965). This research provided evidence that environmental neural stimulation was important for the neurons to initiate the connections that are needed for sight which, one may assume, would be the same for hearing as well (Broderick & Blewitt, 2010).

After birth, researchers have found that most neural development is associated with the creation of synapses rather than the production of more neurons as well as a pruning of arbitrary neurons. This production and pruning of synapses and neurons is a result of both the introduction of chemical substances to the neurons which promote synaptic growth and the sensory information introduced to the neurons as a result of infant actions and environmental factors. As this sensory information is introduced, synapses are formed to accommodate this new information. Greenough and Black (1992) discussed how during this period, two types of synapses are created which are experience-expectant and experience-dependant. Experience-expectant synapses are synapses that are overproduced because they are synapses that have occurred regularly within the evolution of the species. It is when these synapses are not stimulated that problems such as what was discussed above with the kittens occur. The formation of experience-dependant synapses, as the name would suggest, is dependant upon the amount of stimulation available from the experiences of the infant. Researchers have found that stimulating and complex environments have positive effects upon the growth of experience-dependant synapses in rat pups and other mammals (Kolb, Gibb, & Robinson, 2003). The branching points that are left after this process are a direct result of genetics, conditions of the prenatal period, nutrition, and the infant’s experiences and environmental experiences after birth.

Cognitive Development

The next developmental area on which this manuscript shall focus is that of cognitive development. During infancy, one area researchers have focused upon is an infant’s ability to remember and recall. Researchers have found that infants as young as three-days-old suck harder on pacifiers when they hear their mother’s voice as opposed to that of a stranger indicating a sense of recognition on the infant’s part (DeCasper & Fifer, 1980). This recognition has been shown to improve throughout infancy. A newborn’s recognition period has been found to fade after a few minutes or seconds (DeCasper & Spence, 1986) while, in other studies, three-month-olds have been shown to give recognition after several months (Bahrick & Pickens, 1995). Likewise, recall has been shown to increase dramatically once it begins. Studies have shown that infants display recall of simple actions as early as nine months (Meltzhoff, 1988). Further studies have shown that 11-month-olds may recall simple actions for as long as three months and 20-month-olds may recall more complex actions for as long as a year later (Bauer, 2006).

Research has also been preformed on cognitive development during an individual’s preschool years. One area of study included the child’s understanding of numbers. For example, Antell and Keating (1983) allowed a five-month-old to watch as they placed a doll behind a screen and also as they added one additional doll. The infants displayed surprise if there was one doll present when the screen was removed while those that saw two were not. This would indicate that newborns have some knowledge of addition and subtraction. Another study by Gelman and Gallistel (1978) taught children to pick a plate with a larger number of items between two plates each with a differing quantity of items. After the researchers changed the way the items were arranged on the plate, the children expressed surprise at the change but were still able to correctly choose the plate with the larger number of items. A more recent study by Sigler and Ramani (2008) found that children who were introduced to number-based board games displayed a greater ability to correctly estimate a number on a number line than those who played games that did not include numbers. These studies give evidence for both the nature and nurture sides of the debate.

Emotional Development

The last developmental area focused upon within this manuscript is that of emotional development. Currently, researchers disagree upon the initial development of emotions. One argument is that an infant is born with a set of basic emotions directly related to the neural processes that are related to the emotional expression of the infant (Izard, 2004). For example, if an infant looks angry, then it is angry. In contradiction to this theory, Sroufe (1996) believes that emotions start as undifferentiated responses that develop into differentiated responses which then develop into an emotional repertoire. Sroufe argues that emotions start this way because infants lack the cognitive processes with which to assign emotional experiences. Both theories give indication of genetic origins of an individual’s emotions.

As emotional development continues, researchers have found that infants learn how to moderate their emotions for different situations. For example, during one study by Jahromi, Putnam, and Stifter (2004) on infant’s emotional responses to inoculations, the researchers observed as mothers of two-month-olds soothed their infants. The researchers found that as the infants grew older the intensity and duration of the infants crying decreased which indicates an increasing emotional control as infants grow older. The researchers believed that the change in the emotional control came about to a degree from the mother’s interaction with the infant.

Another study, by Tronick, Als, and Brazelton (1980), observed the exchange as mothers either responded positively or negatively towards their infant’s emotions. During the exchanges the mother was instructed to respond positively to the infant’s emotions which garnered a positive emotional reaction from the infant. The mother was then instructed to stop responding to the infant that garnered what researchers referred to as other-directed coping behaviors which are facial expressions and vocalizations designed to try and get the mother to resume their previous actions. As the mother continued this action the baby became frustrated and took part in what the researchers referred to as self-coping behaviors such as thumb sucking and rocking. This research provides evidence that an infant’s adult caregiver provides critical support during an infant’s development of emotional self regulation (Broderick & Blewitt, 2010).

Gene Expression

When discussing human development, the question of why certain genes express themselves while others do not is, many times, brought to the forefront. Each gene is made up of alleles that a child receives from both their mother and their father. Alleles may be dominant or recessive. If an infant receives two dominant or two recessive alleles, the infant will display those characteristics. Sometimes, in the case of two dominant alleles, alleles express codominance such as in the case of a dominant Type A blood allele and dominant Type B blood allele the infant will express Type AB blood. If an infant receives one dominant and one recessive gene, the infant will display the characteristics of the dominant allele. For example, if a child receives a recessive allele for red hair from both parents, then the infant will develop red hair. If the same child had received a dominant allele for brown hair from one of the parents, the child would have developed with brown hair. This phenomenon may also be used to explain why certain genetic disorders express themselves when they do such as the defective recessive allele for sickle-cell anemia or the defective dominant allele for progeria (Broderick & Blewitt, 2010).

Nature and Nurture Off Setting

One would assume that, based upon the recent evidence that development is affected by both nature and nurture, that, in certain situations, one may be used to off set a deficiency in the other. The results provided in the following studies offer evidence supporting the phenomenon of epigenesis which is the control of genetic expression through correlation of both environmental and genetic factors (Broderick & Blewitt, 2010). One study by Caspi, McClay, Moffitt, Mill, Martin, Craig, et. al. (2002) conducted to find out how different MAOA alleles, which release the enzymes controlling production of neurotransmitters such as serotonin, norepinephrine, and dopamine, affect children’s susceptibility to the negative effects of abusive environments in the early years of life. The researchers found that in individuals that had experienced early child abuse, there was a link between the low MAOA allele and aggression. Likewise, in individuals that had not experienced abuse as a child, there was no correlation between the production of MAOA and aggression. Reiss and Neiderhiser (2000) discussed how some irritable children appear to inherit some qualities such as irritability from their parents which evokes a hostile environment from those around them only reinforcing their irritable tendencies. They further discussed how these tendencies may be off set by environmental circumstances that do not sustain their irritable behavior. Results such as those provided by this research along with many others shed light upon one of the many possibilities unlocked by the further research of the nature and nurture controversy.

Conclusion

The nature versus nurture controversy has been strongly debated within the discipline of developmental psychology for many years. This manuscript cited many studies which have given evidence to the degree of influence both nature and nurture has on the neural, cognitive, and emotional development of an individual. From the results of these studies, it is easy to see that development is impacted by both nature and nurture in their own unique ways. Studies have even shown that it may be possible to off set certain deficiencies in genetics with environmental aspects or vice versa. The results of these studies provide important insight into the behavior of an individual, how they may have developed that way, and how that particular form of development may be reversed or avoided in others. There is no doubt that as the depth of research into the nature versus nurture controversy grows those within the psychological community, as well as numerous other disciplines, will be able to assist a larger number of individuals with developmental problems with increasing levels of accuracy.