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When rat mothers left their pups alone in the nest, infant cortical brain electrical activity
jumped from 50 percent to 100 percent, with brain wave patterns becomming
more erratic and unsynchronized.
'Good mothering' hardwires infant brain
Watching mother rats care for their pups while simultaneously scanning those pups' brains — shows how nuturing molds brain growth.
Reporting in Current Biology, a New York University (NYU) Langone Medical Center research team has shown how a rat mother's presence in her nest regulates and controls electrical signaling in her pups' brains.
By watching nearly a hundred hours of video of mother rats protecting, warming, feeding their pups, and then matching these videos to simultaneous electrical readings of the pups' brains, Langone researchers found a mother rat's presence and social interactions — her nurturing — directly molds neural activity and growth of her offsprings' brain.
Although scientists had identified that maternal-infant bonding affects neural development, the Langone team is believed to be the first to show how early attachment behaviors — nesting, nursing, and grooming of pups — impact key stages in postnatal brain development.
In rats between age 12 and 20 days old, slow-wave-neural-signals are seen in the initial phases of brain development. These waves closely resemble electrical patterns found in humans during meditation, conscious as well as unconscious sleep-wake cycles, and even during periods of highly focused attention.
Permanent neural communication pathways are known to form in the infant brain during this period. As well, an increasing number of nerve axons become sheathed — or myelinated — which speeds up neural signaling.
When rat mothers left their pups alone in the nest, infant cortical brain electrical activity jumped from 50 percent to 100 percent, with brain wave patterns becomming more erratic and unsynchronized. Researchers point out that such desynchronization periods are also key to healthy brain growth.
Infant rat pups calmed down after attaching to their mother's nipple. Brain activity slowed and became more synchronous. Slow brain wave activity increased by 30 percent, while higher brain-wave frequencies decreased by 30 percent. Milk delivery also led to intermittent bursts of electrical brain activity that were double or five times higher than before nursing. Brain spikes of more than 100 percent were also observed in pup rat brains when mothers groomed their infants.
However, these brain surges progressively declined during weaning, as infant pups gained independence from their mothers, left the nest and sought food on their own upon reaching two weeks of age.
Experiments using propranolol to block neural-signaling, confirmed that norepinephrine in the pup brain is responding to maternal nuturing behavior. Norephinephrine is a key hormone and neurotransmitter involved in most basic brain and body functions including regulation of heart rate and cognition.
"The study helps explain how differences in the way mothers nurture their young could account, for the wide variation in infant behavior among animals, including people, with similar backgrounds — even in uniform, tightly knit cultures."
Regina Sullivan, professor, NYU School of Medicine and the Nathan S. Kline Institute for Psychiatric Research
"There are so many factors that go into rearing children," says lead study investigator Emma Sarro, PhD, a postdoctoral research fellow at NYU Langone. "Our findings will help scientists and clinicians better understand the whole-brain implications of quality interactions and bonding between mothers and infants so closely after birth, and how these biological attachment behaviors frame the brain's hard wiring."
•The mother’s presence reduces infant rat cortical desynchronization
•Maternal behaviors (e.g., milk ejection and grooming) increase desynchronization
•Maternal effects on infant cortical activity decline with age
•Norepinephrine receptor blockade reduces impact of dam on infant cortical activity
Patterns of neural activity are critical for sculpting the immature brain, and disrupting this activity is believed to underlie neurodevelopmental disorders [ 1–3 ]. Neural circuits undergo extensive activity-dependent postnatal structural and functional changes [ 4–6 ]. The different forms of neural plasticity [ 7–9 ] underlying these changes have been linked to specific patterns of spatiotemporal activity. Since maternal behavior is the mammalian infant’s major source of sensory-driven environmental stimulation and the quality of this care can dramatically affect neurobehavioral development [ 10 ], we explored, for the first time, whether infant cortical activity is influenced directly by interactions with the mother within the natural nest environment. We recorded spontaneous neocortical local field potentials in freely behaving infant rats during natural interactions with their mother on postnatal days ∼12–19. We showed that maternal absence from the nest increased cortical desynchrony. Further isolating the pup by removing littermates induced further desynchronization. The mother’s return to the nest reduced this desynchrony, and nipple attachment induced a further reduction but increased slow-wave activity. However, maternal simulation of pups (e.g., grooming and milk ejection) consistently produced rapid, transient cortical desynchrony. The magnitude of these maternal effects decreased with age. Finally, systemic blockade of noradrenergic beta receptors led to reduced maternal regulation of infant cortical activity. Our results demonstrate that during early development, mother-infant interactions can immediately affect infant brain activity, in part via a noradrenergic mechanism, suggesting a powerful influence of the maternal behavior and presence on circuit development.
In addition to Sullivan and Sarro, Donald Wilson, PhD, also at NYU Langone, served as co-investigator for this study.
Funding support for the study was provided by the US National Institute of Child Health and Human Development and the National Institute of Mental Health, both parts of the National Institutes of Health. Corresponding federal grant numbers are R01 DC009910 and R01 MH0901451.
About NYU Langone Medical Center:
NYU Langone Medical Center, a world-class, patient-centered, integrated academic medical center, is one of the nation's premier centers for excellence in clinical care, biomedical research, and medical education. Located in the heart of Manhattan, NYU Langone is composed of four hospitals — Tisch Hospital, its flagship acute care facility; Rusk Rehabilitation; the Hospital for Joint Diseases, the Medical Center's dedicated inpatient orthopaedic hospital; and Hassenfeld Children's Hospital, a comprehensive pediatric hospital supporting a full array of children's health services across the Medical Center — plus the NYU School of Medicine, which since 1841 has trained thousands of physicians and scientists who have helped to shape the course of medical history. The Medical Center's tri-fold mission to serve, teach, and discover is achieved 365 days a year through the seamless integration of a culture devoted to excellence in patient care, education, and research. For more information, go to http://www.NYULMC.org, and interact with us on Facebook, Twitter, and YouTube.
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