The science of human diversity : a history of the Pioneer Fund by Lynn Richard 1930-

Author:Lynn, Richard, 1930-
Language: eng
Format: epub
Tags: Pioneer Fund (Foundation) -- History, Eugenics -- Research -- United States -- History, Intelligence levels, Race, Heredity, Human
ISBN: 076182040X
Publisher: Lanham, MD : University Press of America
Published: 2001-04-15T00:00:00+00:00

Nerve Conduction Velocity and Intelligence

Reed's work on nerve conduction velocity in mice set him thinking about the possibility that nerve conduction velocity might be part of the neurophysiological basis of intelligence in humans. The idea was that fast neural conduction would be a component of a neurally efficient brain and that this would be expressed in superior intelligence test performance. In 1987-1988 he took a sabbatical year's leave and went to Berkeley to work on this idea with Arthur Jensen. Much of Reed's work on nerve conduction velocity and its relation to intelligence has been carried out in collaboration with Jensen and has been supported by the Pioneer Fund.

The methodology of Reed's work on nerve conduction velocity has been to administer electrical stimulation to the wrist and pick up the registration of this in the brain. The initial electrical stimulation is transmitted along the neural pathways until it reaches the brain, where it is recorded. The time taken for this transmission is the nerve conduction velocity. Reed has carried out similar experiments with visual stimuli. These provide measures of nerve conduction velocity through the brain, whereas the experiments involving stimulation of the wrist provide measures of nerve conduction velocity principally through the arm. In addition to these measures, Reed has obtained measures of his subjects' reaction times and intelligence, using a standard intelligence test.

In the first of these studies4 carried out on 200 students it was found that nerve conduction velocity in the arm did not correlate with intelligence test performance. However, nerve conduction velocity in the brain did show a positive correlation with intelligence test results of 0.26 (adjusted to 0.37 when corrected for restriction of range) between nerve conduction velocity in the brain and intelligence on a sample of 147 students.5 It was also found that mentally retarded individuals had exceptionally slow brain nerve conduction velocities. There was no correlation between reaction times and nerve conduction velocity in this study. This suggests that reaction times and nerve conduction velocity are two independent determinants of intelligence test performance.6

Further studies measuring nerve conduction velocity from the wrist to the cerebral cortex at stages along the neural pathway confirmed that the speed of transmission up the arm and into the thalamus in the midbrain were uncorrelated with intelligence, but a positive correlation with intelligence was present with speed of transmission from the thalamus to the cerebral cortex.7 Thus the conclusion of this set of experiments was that it is only nerve conduction velocity in the brain that is associated with intelligence, not nerve conduction velocity in other parts of the nervous system. In a dispute with fellow Pioneer grantee J. P. Rushton over whether brain size is an important determinant of intelligence and of race differences in modern humans, Reed maintains that size is of relatively little significance and that the speed and accuracy of neural transmission is probably the more important neurophysiological determinant of intelligence.8

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