Baby marmosets begin to practice the facial and mouth movements needed to call their family for help before they are born, a study published today in. eLife.
This discovery may also apply to humans, as third-trimester ultrasounds have shown that developing humans in the womb make movements similar to crying.
The first calls of humans and other primates are essential for their survival. In addition to allowing them to call their family members for help, these vocalizations and interactions with parents and other caregivers lay the groundwork for more complex communication later in life.
“We wanted to know how the first neonatal vocalizations develop,” says lead author Darshana Narayanan, who conducted the study as a graduate student in the Department of Psychology and Princeton Neuroscience Institute, Princeton University, New Jersey, USA.
Narayanan and colleagues performed ultrasounds two to three times a week on four pregnant marmosets for a total of 14-17 ultrasound sessions for the marmosets, starting when the face became visible on the ultrasound and ending the day before birth. The team used ultrasound scans to longitudinally track the head, face and mouth movements of developing marmosets and compared them to the movements of newborn marmosets when they called.
Using frame-by-frame analysis, the team found that the developing marmosets’ head and mouth movements were initially coordinated, but mouth movement became distinct over time. Eventually, they became almost indistinguishable from the movements made by crying newborn marmosets briefly separated from their mothers within the first 24 hours after birth.
To verify that these movements were not general head and mouth movements, the team also compared pre- and post-natal flapping and flapping movements associated with another marmoset vocalization called “twitter”. Their results showed that the pattern of crying movements before and after birth was different from licking or twittering movements.
“Our experiments show that marmosets begin to practice the movements required for socially important calls even before they generate a sound,” says Narayanan. She adds that further study of these movements in marmosets could help scientists learn more about the development of social vocalizations in other primates, including humans.
“Marmosets provide a unique opportunity to study primate vocal development,” concludes senior author Asif Ghazanfar, professor at the Princeton Neuroscience Institute, Princeton University. “Like humans, marmosets are highly social and learn to vocalize through interactions with their parents.”
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