Scientists have yet to answer the age-old question of whether or how sound shapes the minds of fetuses in the womb, and expectant mothers often wonder about the benefits of such activities as playing music during pregnancy. Now, in experiments in newborn mice, scientists report that sounds appear to change "wiring" patterns in areas of the brain that process sound earlier than scientists assumed and even before the ear canal opens.
The current experiments involve newborn mice, which have ear canals that open 11 days after birth. In human fetuses, the ear canal opens prenatally, at about 20 weeks gestation.
The findings, published in Science Advances, may eventually help scientists identify ways to detect and intervene in abnormal wiring in the brain that may cause hearing or other sensory problems.
"As scientists, we are looking for answers to basic questions about how we become who we are," says the senior author. "Specifically, I am looking at how our sensory environment shapes us and how early in fetal development this starts happening."
In development, the white matter also contains so-called subplate neurons, some of the first to develop in the brain -- at about 12 weeks gestation for humans and the second embryonic week in mice. These primordial subplate neurons eventually die off during development in mammals, including mice. In humans, this happens shortly before birth through the first few months of life. But before they die off, they make connections between a key gateway in the brain for all sensory information, the thalamus, and the middle layers of the cortex.
"The thalamus is the intermediary of information from the eyes, ears and skin into the cortex," says the author. "When things go wrong in the thalamus or its connections with the cortex, neurodevelopmental problems occur." In adults, the neurons in the thalamus stretch out and project long, arm like structures called axons to the middle layers of the cortex, but in fetal development, subplate neurons sit between the thalamus and cortex, acting as a bridge. At the end of the axons is a nexus for communication between neurons called synapses. Working in ferrets and mice, the author previously mapped the circuitry of subplate neurons and found that subplate neurons can receive electrical signals related to sound before any other cortical neurons did.
In the new research, first, the scientists used genetically engineered mice that lack a protein on hair cells in the inner ear. The protein is integral for transforming sound into an electric pulse that goes to the brain; from there it is translated into our perception of sound. Without the protein, the brain does not get the signal.
In the deaf, 1-week-old mice, the researchers saw about 25% - 30% more connections among subplate neurons and other cortex neurons, compared with 1-week-old mice with normal hearing and raised in a normal environment. This suggests that sounds can change brain circuits at a very young age, says the author.
In addition, say the researchers, these changes in neural connections were happening about a week earlier than typically seen. Scientists had previously assumed that sensory experience can only alter cortical circuits after neurons in the thalamus reach out to and activate the middle layers of the cortex, which in mice is around the time when their ear canals open (at around 11 days).
"When neurons are deprived of input, such as sound, the neurons reach out to find other neurons, possibly to compensate for the lack of sound," says the author. "This is happening a week earlier than we thought it would, and tells us that the lack of sound likely reorganizes connections in the immature cortex."
In the same way that lack of sound influences brain connections, the scientists thought it was possible that extra sounds could influence early neuron connections in normal hearing mice, as well.
To test this, the scientists put normal hearing, 2-day-old mouse pups in a quiet enclosure with a speaker that sounds a beep or in a quiet enclosure without a speaker. The scientists found that the mouse pups in the quiet enclosure without the beeping sound had stronger connections between subplate and cortical neurons than in the enclosure with the beeping sound. However, the difference between the mice housed in the beeping and quiet enclosures was not as large as between the deaf mice and ones raised in a normal sound environment.
These mice also had more diversity among the types of neural circuits that developed between the subplate and cortical neurons, compared with normal hearing mouse pups raised in a quiet enclosure with no sound. The normal hearing mice raised in the quiet enclosure also had neuron connectivity in the subplate and cortex regions similar to that of the genetically-engineered deaf mice.
"In these mice we see that the difference in early sound experience leaves a trace in the brain, and this exposure to sound may be important for neurodevelopment," says the author.
The research team is planning additional studies to determine how early exposure to sound impacts the brain later in development. Ultimately, they hope to understand how sound exposure in the womb may be important in human development and how to account for these circuit changes when fitting cochlear implants in children born deaf. They also plan to study brain signatures of premature infants and develop biomarkers for problems involving miswiring of subplate neurons.
https://www.hopkinsmedicine.org/news/newsroom/news-releases/study-in-newborn-mice-suggests-sounds-influence-the-developing-brain-earlier-than-previously-thought
https://advances.sciencemag.org/content/7/7/eabc9155
http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Fearly-peripheral&filter=22
Sounds influence the developing brain earlier than previously thought
- 1,558 views
- Added
Edited
Latest News
AI to analyze clumping prot…
By newseditor
Posted 26 May
Reversible, non-hormonal ma…
By newseditor
Posted 26 May
Dissection of the schizophr…
By newseditor
Posted 26 May
Protease action on controll…
By newseditor
Posted 25 May
Maternal inflammation activ…
By newseditor
Posted 25 May
Other Top Stories
Genes Responsible for Severe Congenital Heart Disease Identified
Read more
Genetic variant that protects against heart disease identified!
Read more
CRISPR gene editing can cause hundreds of unintended mutations
Read more
Insomnia genes found!
Read more
Scientists Tie 52 Genes to Human Intelligence
Read more
Protocols
SEMORE: SEgmentation and MO…
By newseditor
Posted 26 May
Spatially resolved lipidomi…
By newseditor
Posted 24 May
Efficient expansion and CRI…
By newseditor
Posted 21 May
Massively parallel in vivo…
By newseditor
Posted 20 May
Breast cancer-on-chip for p…
By newseditor
Posted 16 May
Publications
The thalamic reticular nucl…
By newseditor
Posted 26 May
PMI-controlled mannose meta…
By newseditor
Posted 26 May
Protein-membrane interactio…
By newseditor
Posted 26 May
Toward an interventional sc…
By newseditor
Posted 26 May
Cryo-EM reveals that iRhom2…
By newseditor
Posted 25 May
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar