Hemispheric Asymmetry of Endogenous Neural Oscillations in Young Children: Implications for Hearing Speech In Noise

Abstract

Speech signals contain information in hierarchical time scales, ranging from short-duration (e.g., phonemes) to long-duration cues (e.g., syllables, prosody). A theoretical framework to understand how the brain processes this hierarchy suggests that hemispheric lateralization enables specialized tracking of acoustic cues at different time scales, with the left and right hemispheres sampling at short (25 ms; 40 Hz) and long (200 ms; 5 Hz) periods, respectively. In adults, both speech-evoked and endogenous cortical rhythms are asymmetrical: low-frequency rhythms predominate in right auditory cortex, and high-frequency rhythms in left auditory cortex. It is unknown, however, whether endogenous resting state oscillations are similarly lateralized in children. We investigated cortical oscillations in children (3–5 years; N = 65) at rest and tested our hypotheses that this temporal asymmetry is evident early in life and facilitates recognition of speech in noise. We found a systematic pattern of increasing leftward asymmetry for higher frequency oscillations; this pattern was more pronounced in children who better perceived words in noise. The observed connection between left-biased cortical oscillations in phoneme-relevant frequencies and speech-in-noise perception suggests hemispheric specialization of endogenous oscillatory activity may support speech processing in challenging listening environments, and that this infrastructure is present during early childhood.

Hemispheric asymmetries in rapid temporal processing at age 7 predict subsequent phonemic decoding 2 years later: A longitudinal event-related potential (ERP) study

“…The presence of a distinct Tb response to the 25 ms ISI tonepairs, in particular, suggests that there are neuronal ensembles in the left hemisphere capable of responding to stimuli presented as quickly as 25 ms. These results provide evidence of left hemisphere specialisation for rapid temporal processing in children aged 7 and 9 years, and are consistent with previous findings of Thompson et al (2016) who observed leftward lateralisation of high-frequency (20-50Hz) endogenous cortical oscillations at the younger ages of 3-5 years.…”

“…Nevertheless, our results clearly demonstrate that hemispheric preferences for fast and slow modulations are present in children at age 7 and 9. In the context of previous findings byThompson et al (2016) and Vanvooren et al (2014), our results suggest that temporal processing asymmetries may become more consistent from at least 7 years. Earlier inconsistencies across studies of younger children may reflect reduced prominence of functional asymmetries, and therefore, difficulty identifying such asymmetries consistently.…”

“…Rightward lateralisation of temporal processing for slow modulations has been observed in infants (Telkemeyer et al, 2009) and children aged 5 years-old (Vanvooren et al, 2014). However, Thompson et al (2016) found no lateralisation of low-frequency endogenous oscillations in children aged 3-5 years old. Thompson et al (2016) suggested that the bilateral representation of low-frequency oscillations (3-7 Hz) in 3-5-year-old children might be due to the further maturation of the relevant neuronal populations in the right hemisphere in mid-to-late childhood.…”

“…Of the previous studies that have examined temporal processing asymmetries, most have focused on younger children (≤ 5 years of age), and have been relatively inconsistent. Thompson et al (2016) observed leftward lateralisation of high-frequency endogenous oscillations (20-Hz) in children aged to 5 years-old, while Vanvooren and colleagues (2014) observed no lateralisation for processing of Hz modulations in children of the same age. Rightward lateralisation of temporal processing for slow modulations has been observed in infants (Telkemeyer et al, 2009) and children aged 5 years-old (Vanvooren et al, 2014).…”

Incorporation of feedback during beat synchronization is an index of neural maturation and reading skills

“…Additionally, gamma activity may reflect the extent to which processing in distinct brain regions are coordinated Engel, König, Kreiter, & Singer, 1991). The areas that support language and reading are distributed throughout the brain; therefore an age-related decrease in gamma power, as observed from scalp electrodes, could also reflect greater localization, specialization, and efficiency of cortical processing with maturation (Benasich et al, 2008;Thompson et al, 2016;Tierney et al, 2014).…”