Development of sensory gamma oscillations and cross-frequency coupling from childhood to early adulthood.

Given the importance of gamma oscillations in normal and disturbed cognition, there has been growing interest in their developmental trajectory. In the current study, age-related changes in sensory cortical gamma were studied using the auditory steady-state response (ASSR), indexing cortical activity entrained to a periodic auditory stimulus. A large sample (n = 188) aged 8-22 years had electroencephalography recording of ASSR during 20-, 30-, and 40-Hz click trains, analyzed for evoked amplitude, phase-locking factor (PLF) and cross-frequency coupling (CFC) with lower frequency oscillations. Both 40-Hz evoked power and PLF increased monotonically from 8 through 16 years, and subsequently decreased toward ages 20-22 years. CFC followed a similar pattern, with strongest age-related modulation of 40-Hz amplitude by the phase of delta oscillations. In contrast, the evoked power, PLF and CFC for the 20- and 30-Hz stimulation were distinct from the 40-Hz condition, with flat or decreasing profiles from childhood to early adulthood. The inverted U-shaped developmental trajectory of gamma oscillations may be consistent with interacting maturational processes-such as increasing fast GABA inhibition that enhances gamma activity and synaptic pruning that decreases gamma activity-that may continue from childhood through to adulthood.