Intelligence, Neural Basis

Neuroimaging Studies

Both clinical lesion studies in humans and experimental lesion studies in animals indicate that intelligence is represented throughout the brain in specific networks rather than in a single specific part of the brain like the frontal lobes. Neuroimaging studies in humans over the past 20 years have begun to identify these networks in some detail. Several functional imaging studies using techniques like positron emission tomography, functional magnetic resonance imaging, and the electroencephalogram, show that high scores on tests of general intelligence are related to decreased brain activity in some circumstances. This suggests that the efficiency of information flow throughout specific networks may be a key variable. Structural magnetic resonance imaging studies indicate that higher general intelligence scores are related to increased gray and white matter in specific brain areas and to regional cortical thickness, as well as to whole brain size. A comprehensive review of neuroimaging studies proposed that a parietal-frontal network underlies individual differences in general intelligence, and recent evidence supports this view. These studies raise the possibility of replacing traditional psychometric testing with “neuro-metrics,” meaning that intelligence can be defined and assessed by the size or shape of brain structures, or even by measuring the speed of information flow throughout salient networks with advanced techniques like magnetoencephalography.

Research results in the emerging field of “neuro-intelligence” already provide strong validation for psychometric tests of intelligence by showing scores are related to brain properties. Many issues, however, remain unresolved. Several neuroimaging studies, for example, indicate that the networks related to intelligence, and the way they develop through childhood, differ for males and females, even when matched on intelligence. This suggests at least two different brain architectures can lead to the same cognitive performance. There also may be separate brain networks for specific mental abilities like musical talent, artistic rendering, or mathematical calculation that have limited overlap with networks for general intelligence, as suggested by rare cases of autistic savants. Another important open question is whether differences in intelligence among people may be related to differences in how individual neurons function. For example, some people may have more efficient mitochondria (the part of the cell that produces energy) per neuron than other people. Characteristics of synapses and neurotransmitter systems differ among individuals as well. It would be odd if such brain differences had no effect on cognitive abilities or intelligence.

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