Theta-gamma cross-frequency coupling relates to the level of human intelligence

In order to examine whether theta-gamma cross-frequency relates to intelligence, two EEG experiments were conducted on healthy participants. In the first experiment, theta-gamma functional coupling was determined based on resting (eyes closed) EEG data of 100 participants. Twenty participants with either low or high theta-gamma correlation coefficients were asked to participate in the second experiment in which they were presented with a test of fluid intelligence. The results showed that: (1) resting-state theta-gamma cross-frequency coupling in bilateral frontal and parieto-occipital areas negatively correlated with IQ scores and (2) theta-gamma cross-frequency coupling in frontal areas correlated with performance on the test of fluid intelligence. Individuals with low theta-gamma coupling during rest showed an increase in theta-gamma functional coupling in frontal areas as task difficulty increased, which was associated with better performance on the test. These findings demonstrate for the first time that theta-gamma cross-frequency coupling in frontal areas, and partly also in parietal areas (Experiment 1), relates to the level of intelligence.