Dynamic modulation of frontal theta power predicts cognitive ability in infancy

•This longitudinal infant study found that frontal theta power increased over the course of video viewing in 6-month-olds.•Individual differences in frontal theta power change at 6-months-old significantly predicted non-verbal cognitive ability.•Individual differences in frontal theta power change at 6 months was not associated with executive function at 9 months.•Frontal theta change at 6 months may be an early indicator of later cognitive abilities.