[2] The capacity of the brain to adapt its connections to environmental stimuli diminishes over time, and therefore it would follow that there is a critical period for intellectual development as well.
In order for a person to develop certain intellectual abilities, they need to be provided with the appropriate environmental stimuli during childhood, before the critical period for adapting their neuronal connections ends.
[16] In terms of what matters about school, it appears that simple quantity or years-in-school may be what underpins the linkage of education with performance on IQ tests.
This indicates that teaching incremental theory may improve performance on academic tasks, though further research is needed to investigate whether the same results can be found for general intelligence.
One such study gave participants a number of known nootropics in combination in the hopes of targeting numerous cellular mechanisms and increasing the effects on cognition that each would have if administered individually.
[2] In an experiment, four different habitats were set up to test how environmental enrichment or relative impoverishment affected rats' performance on various measures of intelligent behavior.
Sean Deoni, lead study author and associate professor of paediatrics (research) at Brown University said the shockingly low IQs were caused by limited stimulation at home and less interaction with the world.
[24] The first longitudinal study looking at the effects of under-nutrition, as measured by birth weight, and intelligence focused on males who were born during the Dutch famine.
However, many studies since have found a significant relationship and a meta-analysis by Shenkin and colleagues indicates that birth weight is associated with scores on intelligence tests in childhood.
[4] Malnutrition has been shown to affect organizational processes of the brain such as neurogenesis, synaptic pruning, cell migration and cellular differentiation.
This study also found that the extent to which the caudate volume size related selectively to verbal IQ was much greater in male participants, and not very significant in females.
[27] Breast feeding has long been purported to supply important nutrients to infants and has been correlated with increased cognitive gains later in childhood.
[36] Stress during early childhood may also affect the child's development and have negative consequences on neural systems underlying fluid intelligence.
A 2006 study found that IQ scores were related to the number of traumas and symptoms of post traumatic stress disorder (PTSD) in children and adults.
[37] Similarly, another study found that exposure to violence in the community and the subsequent distress, were related to a significant decrease in intelligence scores and reading abilities in children aged 6–7 years.
[39] However, this relationship may be non-linear with older mothers being at increased risk of giving birth to children with down syndrome which greatly affects cognitive abilities.
[4] In a long-term study done by Baghurst et al. 1992, children who grew up next to a lead-smelting plant had significantly lower intelligence test scores, negatively correlated with their blood-lead level exposure.
At high doses, fetal alcohol syndrome can develop, which causes intellectual disabilities, as well as other physical symptoms, such as head and face deformities, heart defects and slow growth.
[26] However, studies have shown that even at slightly less severe doses, prenatal exposure to alcohol can still affect the intelligence of the child in development, without having the full syndrome.
Through a study done by Streissguth, Barr, Sampson, Darby, and Martin in 1989, it was shown that moderate prenatal doses of alcohol, defined as the mother ingesting 1.5 oz.
[43] In another study, prenatal drug exposure was shown to have significantly negative effects on cognitive functioning, as measured at the age of five, compared again controls matched for socioeconomic status and inner-city environment.
The researchers concluded that prenatally drug-exposed children are at greater risk for learning difficulties and attention problems in school, and therefore should be the subject of interventions to support educational success.
[48] One study indicated that children whose mothers had smoked 10 or more cigarettes a day were between 3 and 5 months behind schoolmates in reading, maths and general ability.
[4][41] There are two reasons for low birth weight, either premature delivery or the infant's size is just lower than average for its gestational age; both contribute to intellectual deficits later in life.
This is utilizing the definition of genius that is not just a significantly higher than average IQ score, but also having some type of exceptional understanding or ability in a specific field.
Albert Einstein is often used as an example of genius; he did not demonstrate generalized exceptional intelligence as a child; however, there is evidence that he started exploring the ideas of physics and the universe at a young age.
The idea is if you expose a child to concepts of, for example theoretical physics, before their brain stops responding to the environment in a plastic way, then you get exceptional understanding of that field in adulthood, because there was a framework developed for it in early childhood.
The parents of gifted children tend to supply enriching environments with intellectually and culturally stimulating materials thus increasing the child's likelihood to engage in creative activities.
It seems as though exposure to these various positive or negative influences on intelligence levels needs to happen early on in the development of the brain, before the neuronal connections have ceased forming.
The authors suggest that this could in part be because musicians from a young age translate visually perceived musical notes into motor commands whilst listening to the auditory output.