Neuro Seminar Blog Post
Rathna Kalluri
Article Link: https://www.nationalgeographic.com/animals/article/tree-dwelling-mice-echolocate-study-shows
The ability to hear and distinguish between different pitches is something that we as humans tend to take for granted. However, the mechanisms behind the ability of us to categorize and recognize different voices is widely unfamiliar to neuroscientists. Recently, researcher Wei-Ming Yu and his team have uncovered a molecule that has a hand in the formation of the totonic map, which is the mechanism that allows organisms to distinguish different pitches of voices in mice.
Yu hypothesized that a molecule known as Ephrin (Eph) had a role in establishing the tonotopic map in the cochlear nucleus of a mouse. Ephrin is differentially expressed along the tonotopic axis; this indicates the role that Ephrin has on sound discrimination. This was tested by removing Ephrin A3 and observing the mice’s ability to distinguish between different pitches of auditory stimuli. He found that when Ephrin was removed from the mice, they were able to somewhat discriminate between general pitches, like extremely high or extremely low, but distinguishing between more specific pitches is impaired in the mice.
An article published on June 17, 2021, looks into tonotopic mapping in a different way: this article highlights mice that use echolocation to identify their surroundings. Entitled “These Blind Mice can ‘See’ with Their Ears, a First Among Rodents”, it looked at a species of mice that are almost completely blind. These mice, called Chinese pygmy mice, are able to understand what their surroundings look like by sending high-frequency vocalizations, and then listening to the way they echo off of nearby objects in their surroundings. What makes these mice so remarkable is that to date, only bats and marine animals like whales have been studied in depth on their echolocating ability. A number of studies for these mice were done by researcher Peng Shi of the Chinese Academy of Sciences Kunmig Institute of Zoology. One particular experiment they performed involved placing the mice on an elevated platform with a ramp attached to it and a food reward at the bottom and allowing the mice to explore. When the mice did so freely, they were able to go down the ramp in complete darkness with no issues after increasing their squeaks. When earplugs were placed in their ears, however, they found more difficulty with completing the task. The study also looked at the anatomical qualities that Chinese pygmy mice possessed, and discovered the stylohyal bone in the ears of the mice were fused with the tympanic bone; this quality is only associated with one other mammal: bats. They found that the anatomical similarities between the mice and bats, “suggest homoplasy, a type of convergent evolution, in which similar traits develop in disparate, unrelated species” (Main, 14).
I found this article interesting, because it is a real-life example of the auditory processes from Wei-Ming Yu’s study being discovered in the environment and applied. The difference in the frequency of sounds that are perceived by the mice in this case is incredibly important because their auditory cues also serve as their visual information. In order to survive, their tonotopic map and associated mechanisms must be impeccable. Understanding tonotopic mapping and its molecular mechanisms further will also help us understand how species like these mice are able to improve their reproductive fitness in a “survival of the fittest” environment. I think a combination of these two studies, such as viewing the tonotopic abilities of these pygmy mice would be a really interesting further study to perform as well, and can provide us with even more valuable information regarding vertebrate auditory processing.
Works cited
Hoshino, N., Altarshan, Y., Alzein, A.,Fernando, A. M., Nguyen, H. T., Majewski, E. F., Chen,
V. C.-F.,Rochlin, M. W., & Yu, W.-M. (2021). Ephrin-A3 is required fortonotopic map precision and auditory functions in the mouseauditory brainstem. Journal of Comparative Neurology,1–22.https://doi.org/10.1002/cne.25213
Main, D. (2021, June 17). These blind mice can 'see' with their ears, a first among rodents. Animals. Retrieved October 14, 2022, from https://www.nationalgeographic.com/animals/article/tree-dwelling-mice-echolocate-study-shows
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