Throughout history, multiple authors have tried to approach the term high capacity, however, its definition has never been precise. Nowadays, there is still no agreement on a definition of intelligence. We owe the beginnings of its scientific conception to Alfred Binet and Theodore Simon in 1905 with the creation of the first intelligence scale together with William Stern's proposal of the term IQ. At first, we talked about Mental Age, (Binet) being the average capacity that an individual and in particular a child is supposed to have. He used a statistical criterion to measure intelligence and called it Intelligence Quotient (IQ), which is calculated by dividing mental age by chronological age and multiplying by one hundred.
However, a problem persists when establishing the cut-off point from which a person is considered highly capable. But most authors converge in identifying an IQ of 130 as a threshold, which groups 2.2% of the population.
High capacities’ children have certain brain characteristics from both a structural and functional point of view that are related to their high intellectual capacities.
These characteristics are on the one hand inherited and on the other, they are modulated by environmental factors. Different studies with monozygotic twins who were separated early and educated in different environments show that intelligence scores are related to heredity, with a correlation that reaches between 0.47 and more than 0.80, being quite significant.
On the other hand, chromosomes 2 (region 2q) and 6 (region 6q) have been associated with high IQ. Among the genes studied, Neuritin 1 stands out, involved in the development of the nervous system and its long-term plasticity.
Regarding structural brain differences, a positive relationship between brain size and IQ has traditionally been observed. In this way, people with high intellectual abilities have a greater amount of gray and white matter, mainly in the frontal cortices (responsible for planning, coordination, control and execution of behaviours) and parietal cortices (processing sensory information from various sources, parts of the body, the knowledge of numbers and their relationships and in the manipulation of objects). This reflects the presence of more complex circuits and greater dendritic arborization, number of synapses, and number of myelinated axons.
Among the differences in the gray matter, a greater volume in the cortical gray matter has been especially described, not only in the frontoparietal areas, but also in the temporal lobe (related to memory), specifically in the hippocampus. In recent studies, it has been found that the greater volume of gray matter may be due to the fact that more intelligent individuals seek more challenging activities, exercising the brain structures and thus acquiring more volume of gray matter.
In relation to the white matter, a relationship has been found between performance in intelligence tasks and the size of the knee and splenius of the corpus callosum, as well as the superior longitudinal fasciculus and the cingulate tract. This area of the brain contains numerous synaptic connections and a great deal of myelination of neuronal axons.
The corpus callosum is the largest bundle of nerve fibres (central commissure) in the human brain. Its function is to serve as a communication channel between one cerebral hemisphere and another, so that both sides of the brain work together and complement each other.
On the other hand, the volume growth of the cerebral cortex is different in children with high intelligence. The cerebral cortex of children thickens as they grow older and thins during adolescence. However, the cortex of children with an IQ between 121 and 149 has been observed to grow more slowly than those of children with normal intelligence, reaching its maximum thickness at age 11, rather than age 6.
Researchers believe that the brain of the high capacities’ is more malleable or modifiable.
Regarding differences in brain function, studies with positron emission tomography and functional magnetic resonance imaging tend to show converging data. Consequently, the hypothesis of neural efficiency (1988) stands out, which would tell us that if we give the same task to two people with different levels of intelligence, the brains of the more intelligent individuals would be able to solve that same task more efficiently, fast and efficient, thanks to its higher cognitive faculties, and without the need to activate as many cortical areas as a less intelligent individual, consuming less energy during execution.
When the task’s complicated, it seems that high capacities’ people are more prepared to increase cortical effort than people with less abilities. The difficulty of the task is modulated by its learning. In fact, training in a task produces a reduction in brain activity, making more efficient use of the system, due to an improvement in the connections that support the cognitive functions necessary to solve it.
In the case of the high capacities’, this decrease in brain activity after training is more pronounced, mainly in the prefrontal cortex. The higher the IQ, the more efficiency you gain through practice. Studies with electroencephalography and evoked potentials suggest that high capacities’ people show higher processing speed with shorter reaction times, which seems to reflect better connectivity.