Anger receptors start early
The part of the brain we use to process angry voices is at work in babies as young as six months old, according to international researchers.
Not only is the same brain network active, the effect is strongest in infants whose mothers spend the most time controlling their behaviour.
It is well known that infants can distinguish the emotional content of their mothers’ voices long before they understand words, based on intonation, tone, rhythm, and other elements. In adults, that emotional content is processed in the frontal and temporal lobes.
Brain imaging studies in infants have been performed, but the noise of an MRI machine has made analysis of response to sounds challenging.
A research team at the University of Manchester in the UK has overcome that limitation by using functional near infrared spectroscopy, a silent, non-invasive method that measures blood flow to cortical areas, while infants sat in their mothers’ laps and listened to recorded non-speech vocalisations that were angry, happy, or neutral in emotionality.
The team also observed the mother-infant pairs during floor play, quantifying the mother’s interactions in terms of both sensitivity to infant behaviour as it changed, and directiveness, or the degree to which the mother sought to control the infant’s behaviour.
They found that both angry and happy vocalisations activated the fronto-cortical network, and the level of activation in response to anger was greater for those infants whose mothers were more directive in their interactions.
The results suggest that greater experience with directive caregiving, or the stress it produces, heightens the infant brain’s ability to detect and respond to angry vocalisations.
“Babies’ brains are sensitive to different emotional tones they hear in voices,” says lead author Chen Zhao.
“Such tones can cause different activation patterns in the infant’s brain areas which are also known to be involved in processing voices in adults and older children.
“These patterns also reveal that the early care experienced by babies can influence brain responses so that the more intrusive and demanding their mother, the stronger the brain response of these 6-month-olds is to hearing angry voices.”