Early Smells Shape Newborn Brains: Olfaction Linked to Touch Development

Summary: Early exposure to odors in newborn mice is crucial for the development of their sense of touch. Researchers found that pleasant smells activate brain areas responsible for touch within the first week of life, influencing sensory processing.

This critical period shows how interconnected our senses are during early development. The findings highlight the importance of olfactory stimuli for proper brain maturation and could inform sensory therapies for premature infants.

Key Facts:

  1. Early exposure to odors in newborn mice is essential for developing the sense of touch.
  2. Odors activate brain areas responsible for touch during the first postnatal week.
  3. Findings suggest olfactory stimuli may aid sensory and cognitive development in humans.

Source: University of Zurich

Smell and touch are the earliest sensations perceived by mammals, enabling newborns to nurse and bond with their mother. If one of these two early senses is defective, various neurodevelopmental disorder may develop in humans.

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

Odors affect the brain of newborns

Previous research has shown the importance of corresponding sensory input for the development of senses – odors for the sense of smell, sounds for the sense of hearing and so on. So far, however, little is known about how the different senses may influence another sense’s maturation.

This shows a baby.
They observed that the odors triggered neural activity across a large part of the cerebral cortex in the mice, including areas responsible for touch. Credit: Neuroscience News

A research team led by Karayannis has now taken a closer look at the effect of olfactory stimuli on the brains of newborn mice.

To do this, the researchers delivered a pleasant odor to the nostrils of the pups and mapped the resulting activity pattern of brain cells using state-of-the-art wide field-of-view imaging of one cortical hemisphere.

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

Critical time window after birth

Furthermore, the researchers observed this phenomenon within only a very short window of time: during the first week after birth. In older pups as well as in adult mice, the 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,” explains Karayannis.

Maturation of sense of smell and touch is linked

To test this assumption, the team investigated whether early olfactory stimulation is also crucial for the maturation of the sense of touch. For this, they trained adult mice to distinguish whether fine or coarse sandpaper was touching their whiskers – a primary way by which mice survey their environment.

The researchers found that mice who had not received any olfactory input in the first week of their lives performed significantly worse than those that had been exposed to odors.

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

The transient functional interaction between the two early senses was also evident in anatomy of the brain: in the first week of life – that is, the critical window of time – the researchers detected a string of nerve connections stretching between the brain areas that process smell and touch. This link then disappeared within a couple of weeks.

Early olfactory stimuli are important

“Our study demonstrates that early-life exposure to odor is essential for touch development and maturation,” says Karayannis.

“This finding perhaps extends to other senses such as hearing or sight, which mature later in life.”

Although the experiments were done with mice, previous findings suggest that similar processes are at work in the human brain.

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

Such deficits can come about by genetic alterations, but are also environmentally induced.

Odor therapy useful in NICUs?

One such example relates to premature babies which are placed in the neonatal intensive care unit (NICU), where they are deprived of a normal sensory environment. This has been shown to potentially leave long-term affective and cognitive marks on individuals.

“While hospitals aim to provide optimal tactile, auditory and visual stimuli to these babies, the sense of smell is not as widely used,” says Karayannis.

“Our results suggest a mechanism by which proper olfactory cues may have a positive effect on supporting the development of various sensory and cognitive skills in babies.”

About this olfaction and sensory development research news

Author: Kurt Bodenmueller
Source: University of Zurich
Contact: Kurt Bodenmueller – University of Zurich
Image: The image is credited to Neuroscience News

Original Research: Closed access.
A nasal chemosensation-dependent critical window for somatosensory development” by Theofanis Karayannis et al. Science


A nasal chemosensation-dependent critical window for somatosensory development

Nasal chemosensation is considered the evolutionarily oldest mammalian sense and, together with somatosensation, is crucial for neonatal well-being before auditory and visual pathways start engaging the brain.

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 (wS1). This effect disappears in adult animals, in line with the loss of excitatory connectivity from olfactory cortex to wS1.

By performing neonatal odor deprivation, followed by electrophysiological and behavioral work in adult animals, we identify a key transient regulation of nasal chemosensory information necessary for the development of wS1 sensory-driven dynamics and somatosensation.

Our work uncovers a cross-modal critical window for nasal chemosensation–dependent somatosensory functional maturation.

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