Odors influence newborn brain growth in the first week

The first week after birth is a pivotal period for the development of the senses in newborn mammals. Smell and touch are the earliest sensations perceived, enabling newborns to nurse and bond with their mothers.

Defects in these early senses can lead to various neurodevelopmental disorders in humans.

“Our senses are crucial for the proper formation and functioning of brain circuits,” noted Professor Theofanis Karayannis, co-director of the Brain Research Institute at the University of Zurich (UZH).

Impact of odors on newborn brains

Previous research has underscored the importance of sensory input for the development of corresponding senses – odors for smell, sounds for hearing, and so on. However, little is known about how different senses may influence the maturation of each other.

To address this gap, the research team delved into the effects of olfactory stimuli on the brains of newborn mice.

The researchers delivered a pleasant odor to the nostrils of the pups and mapped the resulting brain activity using advanced wide field-of-view imaging of one cortical hemisphere.

They observed that odors triggered neural activity across a large part of the cerebral cortex, including areas responsible for touch.

“Using anatomical and functional approaches in mice, we reveal that odor-driven activity propagates to a large part of the cortex during the first postnatal week and enhances whisker-evoked activation of primary whisker somatosensory cortex,” noted the study authors.

A critical window after birth

This phenomenon was observed within a very short window of time: the first week after birth. In older pups and adult mice, odors affected more restricted areas of the brain.

“This clearly shows that olfactory input in the first postnatal week induces a special pattern of electrical activity in the brain. This indicated to us that it may be essential for the formation of brain circuits for non-olfactory sensory processing,” explained Professor Karayannis.

The link between smell and touch

To test this assumption, the team investigated whether early olfactory stimulation is also crucial for the maturation of the sense of touch.

They trained adult mice to distinguish between fine and coarse sandpaper touching their whiskers – a primary way mice survey their environment.

The researchers found that mice deprived of olfactory input in their first week performed significantly worse than those exposed to odors.

“A deficiency in olfaction during the critical window of time also affects touch processing in later life,” explained Professor Karayannis.

Early sensory interactions and brain anatomy

The transient functional interaction between smell and touch was evident in the brain’s anatomy.

During the first week of life, the researchers detected a string of nerve connections between the brain areas that process smell and touch. This link disappeared within a few weeks.

“Our study demonstrates that early-life exposure to odor is essential for touch development and maturation,” said Professor Karayannis. “This finding perhaps extends to other senses such as hearing or sight, which mature later in life.”

Although the experiments were conducted with newborn mice, previous findings suggest similar processes occur in the human brain. Such sensory deficits can result from genetic alterations or environmental factors.

“Our findings raise attention to assessing the impact of olfactory deficiencies, especially early in life, on the maturation of general sensory and cognitive processing.”

Potential benefits of odor therapy in newborns

One practical implication of this research relates to premature babies in neonatal intensive care units (NICUs), where they are deprived of a normal sensory environment. This deprivation can potentially have long-term cognitive and emotional effects to the newborns.

“While hospitals aim to provide optimal tactile, auditory, and visual stimuli to these babies, the sense of smell is not as widely used,” said Professor Karayannis. “Our results suggest a mechanism by which proper olfactory cues may positively support the development of various sensory and cognitive skills in babies.”

The study emphasizes the crucial role of early sensory experiences in the proper development of brain circuits, highlighting the need for a holistic approach to sensory stimulation in early life, particularly for vulnerable populations such as premature infants.

The study is published in the journal Science.

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