Correlations between nonverbal intelligence and peripheral nerve conduction velocity in right-handed subjects: sex-related differences.

The speed hypothesis of intelligence was tested in relation to median nerve conduction velocity (NCV) in right-handed subjects. In total, NCV did not significantly correlate with IQ (Cattell's Culture Fair Intelligence test). The motor and sensory median NCVs correlated with IQ positively linearly in men and negatively linearly in women. These results supported the general, unqualified speed hypothesis of intelligence only for men. It was concluded that the conduction speed of the input-output channels of brain as an information processing unit may differentially contribute to nonverbal intelligence, depending upon sex. The male hormone, testosterone, was suggested to be the main factor responsible for sex-related differences in the IQ-NCV relationships.