Dark Exposure and Its Effects on Auditory Sensitivity in Mice

Research Overview

A recent study published in eNeuro examined the auditory cortex of mice subjected to a week of darkness. The findings revealed that this dark exposure led to changes in neuronal networks, resulting in heightened hearing sensitivity among the mice.

The Role of the Auditory System

The auditory system, comprising the outer, middle, and inner ear, is essential for transforming sound vibrations into neural signals. These signals travel to various layers of the primary auditory cortex (A1) located in the temporal lobe, where sound attributes like pitch and rhythm are processed for perception and understanding.

Previous Findings on Sensory Deprivation

Earlier research indicated that temporary visual deprivation in adult mice enhanced the sensitivity of individual A1 neurons. This phenomenon is also observed in individuals and animals who have experienced vision loss from birth, showcasing a compensatory enhancement in hearing. Such adjustments exemplify the brain’s neuroplasticity—its ability to adapt to environmental changes.

New Discoveries on Neuronal Interaction

Building on previous studies, scientists from Maryland discovered that dark exposure modifies interactions between neurons in two distinct A1 layers, even after the critical period of brain development. This alteration improves sensitivity to both low and high-frequency sounds.

Methodology of the Study

In the study, mice were kept in darkness for one week, after which researchers monitored electrical brain activity in A1 layer 4 (L4) and layer 2/3 (L2/3) while playing 17 different tones. Advanced imaging techniques demonstrated that both neuron types were affected by dark exposure—becoming more responsive and selective to sound.

Key Findings on Frequency Response

The results indicated that an increased proportion of neurons responded to high and low frequencies while largely ignoring mid-range frequencies, which are typically more prevalent. This suggests that dark exposure influences the tuning of individual A1 neurons, enabling the adult brain to reorganize its response to various sound frequencies, akin to how children adapt to their hearing experiences.

Understanding Neuronal Redistribution

While the precise mechanisms behind neuronal redistribution in adult mice remain under investigation, it was noted that interactions between neurons in L4 and L2/3 were modified due to dark exposure.

Implications for Neuroplasticity Research

This study supports the assertion that neuroplasticity is not confined to childhood development but can also be induced in adulthood through sensory manipulation. Further exploration into cross-modal learning mechanisms could offer valuable insights for individuals who have lost one of their senses. For example, temporary visual deprivation may aid deaf and hearing-impaired individuals in adapting to cochlear implants and hearing aids.

Contributors and References

Written by Maria-Elena Bernal B.Sc. (Hons)

References:
Solarana, K., Liu, J., Bowen, Z., Lee, H.-K., & Kanold, P. O. (2019). Temporary visual deprivation causes decorrelation of spatio-temporal population responses in adult mouse auditory cortex. eNeuro. doi: 10.1523/eneuro.0269-19.2019

A week in the dark rewires brain cell networks and changes hearing in adult mice. (2019, December 4). Retrieved from https://www.sciencedaily.com/releases/2019/12/191204145858.htm

The Auditory System. (n.d.). Retrieved from https://explorable.com/auditory-system.

Image by Anemone123 from Pixabay.