52 Scientific American, June 2022
led the study and is now at the University of Maryland.
Other research indicates that important connections
between very young children and caregivers actually oc-
cur on a neural level. Their brains sync up. Elise Piazza
and her colleagues at the Princeton University Neuro-
science Institute found this out when they used a meth-
od called functional near-infrared spectroscopy that can
track the activity of neurons. The scientists looked at
adults and infants between nine and 15 months old, in
a variety of situations. The brain waves of the infants
and the adult synchronized when the two were direct-
ly playing together or jointly paying attention to the
same object. They did not sync when the adult spoke to
someone else in the room, affirming that overheard lan-
guage does not count. This kind of synchrony has beenlinked to social learning, problem-solving skills and vo-
cabulary development. And when in sync, the adult
turned out to be following the baby’s lead, anticipating
smiles and interest, rather than the other way around.
“We already knew that infant-directed speech is very
important for babies’ learning and that a variety of
communicative cues could be important for them,” says
Piazza, who is now at the University of Rochester. But
“even before they’re fully verbal, there are a lot of ways
in which [babies’] brains are picking up on these dif-
ferent cues in the environment.”
Such research strongly supports the need for par-
ents to have time with their children. It also underlines
why parents also need access to high-quality, affordable
child care. The problem faced by Randy, and millions
like him, was that there was rarely enough time to par-
ent the way he wished. To make ends meet, he was hold-
ing down multiple jobs. His wife, Mayra, worked full-
time, too. Most days Randy saw his kids for all of 30
minutes. And the only child care Randy could afford
was custodial—at pickup he often found Julian in front
of a blaring television. “Here we have this body of re-
search showing over and over that the core adult-child
interactions in the early years of life are critical for brain
development and social development,” Romeo says.
“Anything we can do as a society to create an environ-
ment where [those] relationships can flourish, that’s
the best investment we can make in children’s futures.”EARLY HELP FOR PARENTS
language is just one dimension of the powerful nurtur-
ing interactions between children and caregivers. For
infants, connections begin on the first day of their lives.
That is why paid leave at the birth of a child is consis-tent with policy centered on early brain development.
But few Americans have such leave. Randy and Mayra
didn’t have it. When their two children were born,
Mayra was one of the roughly one quarter of mothers
who return to work within two weeks, and Randy took
only a day or two off each time.
Traditionally research on paid leave has focused on
the economic side of the equation—assessing the im-
pact on employers or on household incomes. Yet more
recently, studies of the effects of paid leave on the health
of mothers and children found it was associated with
lower levels of postpartum depression, improved in-
fant attachment, decreases in infant mortality and re-
hospitalizations, as well as increases in pediatric visits,
timely immunizations and the duration of breastfeed-
ing. When fathers took paid leave at the birth of a child,
it benefited both parents’ mental health, lowering de-
pressive symptoms and stress. Plus, married parents
who both take leave are less likely to divorce.
To this already persuasive evidence, the newest stud-
ies add positive impacts of paid leave on infants’ cogni-
tive development. In 2021 developmental psychologist
Natalie Brito of New York University and her colleagues
published a study of 328 mothers and babies from
across the socioeconomic spectrum, some of whom had
paid leave and some of whom had unpaid leave at the
birth of their child. When the children were two years
old, the researchers asked the mothers to report on
their children’s language abilities, as well as their emo-
tional responses in social situations. Paid leave was as-
sociated with higher language skills for the toddlers at
all socioeconomic status (SES) levels and with better
emotional skills among children whose mothers had
lower education levels. “It seems as though paid leave
was beneficial for every family, but it may have an out-
size effect for lower-SES families,” Brito says.
Paid leave actually changes patterns of brain activ-
ity. In a second study of 80 mothers and babies pub-
lished this past April in Child Development, Brito and
her colleagues used electroencephalography (EEG) to
eaves drop on babies’ brain waves three months after
birth. Interactions between neurons create these waves,
or oscillations. Everyone has high- and low-frequency
waves, and both types are important. But as children
get older, the relative amount of high-frequency activ-
ity tends to increase. Previous studies suggested that
young children with more high-frequency waves, when
tested a little later on in life, tend to have higher scores
on skills necessary for learning and thinking.
In the work by Brito and her co-workers, infants
whose mothers could take paid leave tended to have
more higher-frequency waves, and fewer low-frequen-
cy ones, than babies whose mothers had unpaid leave.
Although the sample was relatively small and not a tru-
ly random selection of babies, the researchers did con-
trol for a range of potentially confounding variables,
such as gestational age at birth, number of children in
the home, maternal relationship status, education and
occupational prestige. The association between paidPaid leave after the birth of a child
was associated with lower infant
mortality and hospitalizations and
improved infant attachment.