Mariam Malik ‘22

Past research and work has proven the interconnectedness of all senses and their corresponding cortices in the brain. For example, it has been scientifically proven that those lacking in one sense possess advanced abilities in others. Cross-modal learning, or the manipulation of one sense to cause alterations in another, is a key feature of further research. Researchers at the University of Maryland found that a week of complete visual deprivation in mice rewires the networks of cells in the brain to alter hearing sensitivity even after the optimal time for auditory learning has passed. 

Patrick Kanold, professor of biology and senior author of the study, and his team of researchers began the experiment by placing fifteen adult mice in a completely dark space for one week. The mice were in-house bred male and female mixed. The researchers separated the mice into two groups: one kept in the dark for seven days and the other left in a normal 12-hour light/dark cycle. The team played and repeated seventeen different auditory sounds ten times with a few seconds between every repetition, while brain activity was measured in the auditory cortex. Kanold and his team predicted that there would be changes in neural networks, but did not expect that the neural networks were actually changing in multiple ways. In certain areas of the auditory cortex, there were more neurons that were sensitive to high and low frequencies, but fewer neurons that were sensitive to mid-range frequencies. To study the plasticity of the primary auditory cortex (A1), the team used in vivo two-photon calcium imaging. 

Overall, the team found that temporary visual deprivation, or dark exposure (DE), in adult mice enhances the ability of the auditory cortex to select different frequencies and discriminate neurons, specifically in the cortex’s thalamus recipient layer (L4). One week of DE also increased the responses evoked by the sounds and the frequency selectivity of layer ⅔ (L2/3). Thus, the researchers also concluded that the adapting of auditory neurons and can still be changed even after the window for auditory development has passed. 

The findings hold significance for how effectively those with hearing disabilities adapt to hearing aids or cochlear implants. Additionally, Kanold also adds that for further research, the sounds the mice were exposed to could be manipulated and brain activity could be monitored to determine which parts of their soundscape the mice are hearing. This would allow further insight into how focus and attention play a role in the transformation of auditory neurons, which could also hold useful information into how those with cochlear implants or hearing aids adapt. 

References:

1. P. Kanold, et al., Temporary visual deprivation causes decorrelation of spatio-temporal population responses in adult mouse auditory cortex. eNeuro 6, (2019). doi: 10.1523/ENEURO.0269-19.2019
2. Image retrieved from: https://commons.wikimedia.org/wiki/File:In-the-ear_hearing_aid.jpg