Human infants are able to acquire quickly a language by “simple” exposure to speech. This remarkable capacity is rather surprising knowing that the auditory cortices are still developing until the end of adolescence. Many psychoacoustic studies have explored how the adult auditory system processes the acoustic components of speech, showing that slow variations in sound amplitude over time (AM) are of crucial importance for speech perception. In the present study, we investigated the processing of AM using electroencephalography (EEG) in 3- and 10-month-old awake infants, as well as in young adults. We measured the auditory brain activity following the modulation frequency of sinusoidally amplitude modulated tones at 8 and 40 Hz. Results showed that the Amplitude-Modulation Following Response (AMFR) was observable at 8 Hz at all ages, but that only adults showed reliable responses at 40 Hz. In light of the previous literature, we propose that the neural processing sources of faster AM rates may be located preponderantly in subcortical regions at younger ages, while, in adults, both cortical and subcortical sources are activated. Such neuro-developmental trajectories might underlie the processing of fine acoustic cues that are necessary for speech and language development.

Previous infant entrainment research has shown neural entrainment to a wide range of stimuli and amplitude modulated frequencies. However, it is unknown if infants neurally entrain more strongly to some frequencies more than others, and to which low amplitude modulated frequency infants show the strongest entrainment. The current study seeks to address this by testing the neural entrainment of N=23 4-6-month-old infants and N=22 control group adult caregivers while they listened to a range of sinusoidally amplitude modulated beep stimuli at rest (no sound), 2, 4, 6, 8, 10 and 12 Hz. Analysis examined differences across power and phase, regions of interest predetermined by previous literature and by segmented time windows. Results showed that the strongest entrainment was at 2Hz for both adult and infant participants; that there was no significant difference in power and phase, entrainment was occipital temporal and slightly left fronto-central in adults and right fronto-central and left occipito-temporal in infants, leading to some regions of interest used in previous studies being significant in infants and all regions of interest being significant in adults. Segmenting by time window did not show any significant increase or decrease in entrainment over time, but longer time windows showed a stronger entrainment response. In conclusion, it is important to choose appropriate stimulation frequencies when investigating entrainment between stimulation frequencies or across ages; whole head recording is recommended to see the full extent of activation; there is no preference on power vs phase analyses; and longer recordings show stronger effects.

.The capacity to pay attention underpins all subsequent cognitive development. However, we understand little about how attention control is instantiated in the developing brain in complex, real-world settings. We recorded naturalistic attention patterns, together with  autonomic arousal and brain activity, in 5- and 10-month-old infants during free play. We examined whether changes in autonomic arousal and brain activity associate with changes  in moment-by-moment attentional engagement, and whether they anticipate attention changes, or follow on from them. Early in infancy, slow-varying fluctuations in autonomic arousal forward-predicted attentional behaviours. Later in infancy, fluctuations in fronto-central theta power associated with changes in infants’ attentiveness and predicted the length of infants’ attention durations; however, changes in cortical power followed, rather than preceded, infants’ attention shifts. Together, our results suggest that attention  transitions from subcortical to cortical control; but that, even by later infancy, attention  control is still reactive, driven by brain changes that take place after the onset of a new attention episode.