A new study provides evidence of what many moms and dads already know - that babies respond in a measurable way to soft and gentle caressing, or what scientists call "pleasant touch," and that this helps cement bonds between infants and parents to ensure their healthy development.
Reporting in the journal Psychological Science, the researchers conclude:
"Our results provide physiological and behavioral evidence that sensitivity to pleasant touch emerges early in development and therefore plays an important role in regulating human social interactions."
Previous research on adults shows that stroking the skin activates a particular receptor, which responds only when the stroking is of a speed that feels "pleasant" or like a caress.
Other studies have also investigated how the brain responds to touch. For instance, when we experience a sensual caress, we only perceive it as such if it comes from someone we like or love - in other words, the brain must somehow also be able to perceive the "social meaning" of the touch.
In a study Medical News Today reported in 2012, researchers from the US and the Netherlands used MRI scans to show for the first time that the brain region encoding basic touch properties - like rough and smooth - is also sensitive to the social meaning of a touch. Before that, it was generally assumed that this perception of pleasant or repulsive touch occurred via a separate pathway to the physical sensation.
Such a study is significant because it shows that emotion is involved at the primary stage of social touch, reinforcing the importance of social development alongside physiological development.
Mechanisms for infants' responses to pleasant touch not previously well known
Babies bond with their parents through soft and gentle caressing.
In this latest study, the researchers wanted to explore how babies respond to pleasant touch, because while studies have shown caregiving touch is essential for healthy growth and development of babies, the physiological and behavioral mechanisms that underpin their sensitivity to it are still poorly understood.
Dr. Merle Fairhurst, a cognitive neuroscientist at the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany, and colleagues asked parents to sit with their babies in their laps while the researchers stroked the infants' arms with a paintbrush.
The researchers monitored the babies' responses to three speeds of stroking - 0.3, 3 and 30 cm per second.
The results showed that the babies' heart rate slowed while they were being stroked with the paintbrush, but only at the medium speed (3 cm per second).
The babies also showed more interest in the paintbrush - measured by how long and how often they looked at it - when the researcher stroked their arm at the medium speed.
Strong link between baby's response and parent's sensitivity to touch
However, what the researchers found particularly interesting about the results was the strong link between the infants' lower heart rate during medium-speed stroking, and the parents' own description of how the touch felt.
It seems that the more sensitive the parent was to touch, the more their baby's heart rate slowed in response to the medium-speed brushstroke.
The researchers suggest a combination of "nature and nurture" could be working here.
Dr. Fairhurst says one possibility is that babies become sensitive to touch in relation to their parents' sensitivity to social touch.
"Another possibility is that social touch is genetically heritable and therefore correlated between caregivers and infants," she adds.
The team now wants to explore how pleasant touch is processed in the brain and how it affects social functioning in babies.