Maturation of auditory cortex neural responses during infancy and toddlerhood

Abstract

The infant auditory system rapidly matures across the first years of life, with a primary goal of obtaining ever-more-accurate real-time representations of the external world. Our understanding of how left and right auditory cortex neural processes develop during infancy, however, is meager, with few studies having the statistical power to detect potential hemisphere and sex differences in primary/secondary auditory cortex maturation. Using infant magnetoencephalography (MEG) and a cross-sectional study design, left and right auditory cortex P2m responses to pure tones were examined in 114 typically developing infants and toddlers (66 males, 2 to 24 months). Non-linear maturation of P2m latency was observed, with P2m latencies decreasing rapidly as a function of age during the first year of life, followed by slower changes between 12 and 24 months. Whereas in younger infants auditory tones were encoded more slowly in the left than right hemisphere, similar left and right P2m latencies were observed by ∼21 months of age due to faster maturation rate in the left than right hemisphere. No sex differences in the maturation of the P2m responses were observed. Finally, an earlier left than right hemisphere P2m latency predicted better language performance in older infants (12 to 24 months). Findings indicate the need to consider hemisphere when examining the maturation of auditory cortex neural activity in infants and toddlers and show that the pattern of left-right hemisphere P2m maturation is associated with language performance.

Keywords: Auditory; Hemisphere lateralization; Infant; Language; MEG; P2m.

Fig. 1.

(a) Butterfly plot shown for a representative 7-month-old infant’s auditory sensor evoked response. The magnetic field topography of the sink (blue) and the source (red) of the P2m response is circled in yellow. (b) Whole-brain MNE solutions were computed using the averaged sensor-level auditory evoked response. Left and right P2m regions of interest (ROI; size ≥ 50 cortical surface vertices) were created at the time of the peak P2m sensor activity. (c) Source timecourses, shown for a representative 7-month-old infant, were extracted from the left and right ROI. From the source waveform, left and right P2m peak latency and average amplitude (+/− 30 ms centered on the P2m peak) were obtained using in-house software and manually confirmed blind to hemisphere, sex, and age.

Fig. 2.

Left (blue) and right (red) P2m auditory source waveforms from 8 representative infants. Stimulus onset at 0 ms. Arrows indicate the P2m peak latency. The source waveform plots show a change in P2m latency as a function of age, although with occasional departures in this pattern for individual children.

Fig. 3.

(a) Whereas P2m latencies were later in the left than right hemisphere in younger infants, left and right P2m latencies were similar in older infants. (b) Predicted mean left and right P2m latencies for different ages.

Fig. 4.

Associations between age and auditory P2m latency lateralization index (LI) in females (blue) and males (red) (N = 110 with a P2m latency in the left and the right hemisphere).

Fig. 5.

Associations between P2m Lateralization Index (LI) and age- and sex-adjusted residualized composite language score.