Conduction velocity in a brain nerve pathway of normal adults correlates with intelligence level

This is a detailed report of the first demonstration in normal individuals of a correlation between intelligence level (“IQ”) and nerve conduction velocity (NCV) in a brain nerve pathway. A total of 147 postsecondary students were tested for nonverbal IQ and latency of the P100 (a visually evoked potential recorded over the primary visual cortex); this latency was used to estimate an approximate NCV in the visual pathway (retina to visual cortex). The correlation between this NCV and IQ is + .26 ( p = .002); after correction for the restricted IQ range (but not for rest ceiling or attenuation), + .37. Three recent studies of mentally retarded patients, using similar stimulation and recording, also showed increased P100 latencies relative to controls. These results, plus those of other IQ studies using choice reaction time or long-latency evoked potentials, are all explainable by positive correlations between brain NCV and speed of information processing and between this speed and intelligence level.