Neuroscience and intelligence

Neuroscience and intelligence refers to the various neurological factors that are partly responsible for the variation of intelligence within a species or between different species. A large amount of research in this area has been focused on the neural basis of human intelligence. Historic approaches to study the neuroscience of intelligence consisted of correlating external head parameters, for example head circumference, to intelligence. Post-mortem measures of brain weight and brain volume have also been used. More recent methodologies focus on examining correlates of intelligence within the living brain using techniques such as magnetic resonance imaging (MRI), functional MRI (fMRI), electroencephalography (EEG), positron emission tomography and other non-invasive measures of brain structure and activity.

Researchers have been able to identify correlates of intelligence within the brain and its functioning. These include overall brain volume, grey matter volume, white matter volume, white matter integrity, cortical thickness and neural efficiency. Although the evidence base for our understanding of the neural basis of human intelligence has increased greatly over the past 30 years, even more research is needed to fully understand it.

The neural basis of intelligence has also been examined in animals such as primates, cetaceans and rodents.

One of the main methods used to establish a relationship between intelligence and the brain is to use measures of Brain volume. The earliest attempts at estimating brain volume were done using measures of external head parameters, such as head circumference, however, such approximations proved to be inaccurate when estimating brain size. More recent methodologies that were employed to study this relationship are post-mortem measures of brain weight and volume. However, such measures also proved to be somewhat inconclusive, yielding diverging results depending on sex, which hemisphere was examined and on the type of intelligence measured.

The most widespread methodology in contemporary neuroscience to measure brain volume and size is MRI. MRI is a non-invasive technique used to study the brain structure and function (using fMRI) of living subjects. Overall, larger brain size and volume is associated with better cognitive functioning and higher intelligence. The correlations range from 0.0 to as high as 0.6, and are predominantly positive. The specific regions that show the most robust correlation between volume and intelligence are the frontal, temporal and parietal lobes of the brain. Therefore, it can be safely concluded that larger brains predict greater intelligence.

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