# Long-latency auditory evoked responses across species show increased amplitude during early life

## TL;DR

This study shows that both humans and rats have stronger late auditory brain responses in early life, suggesting a shared developmental pattern in brain maturation.

## Contribution

The study reveals a cross-species increase in long-latency auditory responses during early life, potentially indicating shared developmental mechanisms.

## Key findings

- Both humans and rats show increased amplitude in long-latency auditory responses during early life.
- The long-latency response in children is more consistent in timing compared to adults.
- The late response may reflect GABAergic circuit maturation and passive sensory processing.

## Abstract

Auditory evoked responses undergo notable changes during childhood, likely reflecting modifications in synaptic signaling in the auditory cortex. Particularly robust response, observed around 200 to 300 ms post stimulus (N/M250), has been consistently reported in children but is absent in adults. This long-latency response, evoked even in passive listening conditions, may indicate heightened sensory pathway responsiveness, facilitating experience-driven cortical plasticity. However, it remains unclear whether this delayed activation pattern is an intrinsic, species-general feature of brain development. We recorded cortical auditory evoked responses to monaural sine-wave tones/click sounds in 3 age groups (preadolescents, adolescents, and young adults) of human subjects and rats. Following short-lived early responses, both species exhibited a long-latency (150 to 450 ms) response in the auditory cortex. In both species, the relative amplitude of the long-latency response, compared to early responses, was increased in younger individuals. In human children, single-trial analysis demonstrated more consistent trial-by-trial timing of the response in this later time window than in the adult-typical 100-ms response in the earlier time window. Given its emergence in purely passive conditions, and across species, the robust current activity in late time window could represent a distinct synaptic event and may serve as a marker of the maturational stage, particularly in GABAergic cortical circuits.