How a mother’s depression affects language development in babies
By the time a baby is born, she is capable of learning any of the world’s languages. In the following weeks and months of life, this ability becomes more and more specific to her given environment: she responds to the languages of her surroundings and ignores foreign sounds. The small window of opportunity for heightened language acquisition, where the brain is especially receptive to learning, is known as a ‘sensitive period.’ Sensitive periods for language are particularly prominent in the first year of life.
Understanding how the brain facilitates language learning has been a fascination for two CIFAR Fellows, psychologist Janet Werker and neuroscientist Takao Hensch in the Experience-based Brain and Biological Development program. In a recent study published in the prestigious Proceedings of the National Academy of Science, Drs. Werker and Hensch, along with their colleagues, examined how a mother’s depression during pregnancy changes the timing of when a baby learns to speak.
In the study, three groups of mothers were examined. One group was depressed but not taking medication. A second group was being treated for depression with a common class of antidepressants known as serotonin reuptake inhibitors (SRIs). The control group was comprised of mothers with no symptoms of depression and who were not taking SRIs.
Babies were studied at three stages of development. First, at 36 weeks into pregnancy, fetuses were exposed to sounds of different consonants as their heart rates were recorded. Then, infants at 6 and then 10 months of age were exposed to non-native languages while their eye movements were recorded.
Researchers found that infants of depressed and untreated mothers were slow to reach the known language development milestones. These infants only began to tune into language at 10 months, meaning that the sensitive period for language acquisition was starting later. Conversely, infants of mothers taking SRIs reached the milestones months earlier than the norm. By 6 months of age, these babies were no longer able to tell languages apart, indicating that the sensitive period for language learning had already begun to pass.
From this work, Dr. Hensch and his collaborators are working to identify the specific circuits responsible for language learning in the brain. They are particularly interested in understanding how SRIs affect certain circuits in the brain to change normal language development, and whether there are other types of experiences that can affect learning in a similar way.
“This study shows how transdisciplinary partnerships between scientists can yield a much deeper understanding of some of the questions at the heart of what we do,” says Dr. Werker. “The research was years in the making, and having the opportunity to meet several times a year with other CIFAR researchers to get feedback on this project really moved this work forward.”
This paper appeared in a special edition of the Proceedings of the National Academy of Science titled ‘Biological Embedding of Early Social Adversity: From Fruit Flies to Kindergartners.’ The volume featured a multidisciplinary collection of 25 thought-provoking papers, many written by CIFAR researchers, that will influence a broad range of scientific inquiry: from molecular genetics, evolutionary biology and neuroscience to social and behavioural science, epidemiology and social policy. The implications of the research are far reaching, from new approaches to learning and language acquisition, to new considerations for the health effects of social environments affecting large populations, and policies for early childhood care and education.
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