Using electroencephalography (EEG) to measure maturation of auditory cortex in infants: Processing pitch, duration and sound location

The auditory system serves three main functions: identifying and locating objects, perceiving music, and understanding language. All of these rely on efficient processing of basic sound features. Electroencephalography (EEG) can be used to measure, for example, how auditory cortex processes pitch, fine temporal differences and sound location in infants. In particular, the brain’s response to a sound event (the event-related potential or ERP) changes across age in morphology (i.e., what positive and negative peaks are present at which recording sites on the scalp) and in the amplitude and latency of the peaks present.1 ERPs can also be analyzed developmentally in the frequency domain in terms of changes across age in phase-locked and non-phase-locked activity in different frequency bands such as alpha, beta and gamma.2,3 Many factors likely contribute to these changes. Processes such as waves of myelination, synaptic proliferation, synaptic pruning, and the presence and amounts of various neurotransmittors are largely under genetic control.4,5 These processes enable the development of more efficient circuits for processing auditory features. At the same time, the details of the networks formed are largely affected by experiential factors, such that synaptic connections receiving concurrent input are strengthened while others are weakened or eliminated. Thus, specific experience with sounds with pitch, with sound containing fine timing differences, and with sound from different spatial locations all affect auditory development. At a higher level, the specific musical system and language to which the infant or child is exposed also contribute substantially to auditory maturation, enabling efficient processing of certain musical pitch systems, rhythmic structures and phonemic categories.6 Here we outline the dramatic changes seen in ERPs during development and indicate how these changes could be used as diagnostic indicators of early abnormal auditory development.