Two Independent Response Mechanisms to Auditory Stimuli Measured with Functional Near-Infrared Spectroscopy in Sleeping Infants.
Onn Wah Lee, Darren Mao, Julia Wunderlich and 4 others
PMID 39053892WHAT IT FOUND
Sleeping infants show two distinct brain responses to sound.
A standard auditory response peaks early, while a separate arousal response causes a delayed drop in oxygenated blood that fades quickly with repetition. This means fNIRS tests in sleep must account for both mechanisms, not just the first.
Key findings
01Independent component analysis revealed two simultaneous responses: a positive auditory response peaking 5–7 seconds after stimulus onset and a negative arousal-related response peaking 15–17 seconds after onset.
02The negative response adapted rapidly, being largest in the first five trials and dropping to near zero by trials 6–10, unlike the positive response which habituated more slowly.
03Standard inference frameworks assuming a single canonical response are violated in sleeping infants because the negative trough is independent of the positive peak and does not fit recovery models.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study included only 16 infants, which limits the generalizability of the findings. Nine of the 25 recruited infants were excluded, primarily due to failure to sleep or technical issues, which may introduce selection bias. The study was conducted on naturally sleeping infants, so the findings may not apply to infants who are awake or sedated. The specific mechanism of the negative response is hypothesized to be arousal-related but was not directly measured with EEG in this study.
Declared interests
The authors declare no external financial support other than stated grants. However, five authors have a pending patent with IP Australia relevant to a spinoff company, NIRGenie Pty Ltd, established after the research. None of the authors are currently employed by NIRGenie.
The easy way to misread this
Do not assume the negative trough in fNIRS data is simply a recovery phase of the auditory response. It is a distinct, rapidly adapting signal likely related to arousal, and treating it as part of the auditory response can lead to incorrect conclusions about hearing function.