Neural correlates of cognitive ability.

The challenge to neuroscientists working on intelligence is to discover what neural structures and mechanisms are at the basis of such a complex and variegated capability. Several psychologists agree on the view that behavioral flexibility is a good measure of intelligence, resulting in the appearance of novel solutions that are not part of the animal's normal behavior. This article tries to indicate how the supposed differences in intelligence between species can be related to brain properties and suggests that the best neural indicators may be the ones that convey more information processing capacity to the brain, i.e., high conduction velocity of fibers and small distances between neurons, associated with a high number of neurons and an adequate level of connectivity. The neural bases of human intelligence have been investigated by means of anatomical, neurophysiological, and neuropsychological methods. These investigations have led to two important findings that are briefly discussed: the parietofrontal integration theory of intelligence, which assumes that a distributed network of cortical areas having its main nodes in the frontal and parietal lobes constitutes a probable substrate for smart behavior, and the neural efficiency hypothesis, according to which intelligent people process information more efficiently, showing weaker neural activations in a smaller number of areas than less intelligent people.