- Scientists discover 3 subclasses of Type I neurons and the Type II neurons.
- They conducted comparative studies on adult mice to show that these neuron types are present since birth.
- It can open new doors for developing genetic tools, which can be used to treat multiple hearing impairments.
The perception of sound is necessary to receive external information and communicate. It depends on a sequence of complex steps that converts sound waves in the air to electrical signals. Then, the auditory nerve carries these signals to the brain through hearing nerve. The brain tells us that we’re hearing a sound and what that sound represents.
Most of the nerve cells in cochlea (a portion of the inner ear) were thought to be of two types – Type I and Type II neurons. Also, it was considered that Type 1 neurons carry most of the auditory data.
Now, researchers at Karolinska Institutet have shown that the Type I cells are actually made of 3 different types of cells. This explains the variations recorded in Type I cell’s properties and sonic response in previous studies.
The researchers performed several tests on mice using a single-cell RNA sequencing method combined with genetic labeling. They discovered 4 different neurons types, including 3 subclasses of Type I neurons and the Type II neurons, and several new marker genes. They conducted comparative studies on adult mice to show that these neuron types are present since birth.
They also developed a comprehensive genetic framework that could enhance the synaptic communication patterns. Using newly discovered markers, they determined the differential projection patterns of all Type I neurons and captured their electrophysiological properties.
More generally, this research uncovers a molecular heterogeneity in the cochlear afferent
system, which represents discrete channels that convey different auditory information. It also constitutes a tool to build genetic techniques to analyze the functions of distinct spiral ganglion neuron types in hearing.
How It Is Useful?
The research indicates that the three newly discovered neuron types play a crucial role in decoding sonic intensity, an important function that helps you make conversations in a loud surrounding, which depends on the capability to filter out the background noise.
This helps scientists better understand the human auditory mechanism and develop new therapies and drugs. It can open new doors for developing genetic tools, which can be used to treat speech-in-noise recognition disabilities and other hearing impairments like hyperacusis (oversensitivity to sound) and tinnitus. Moreover, the mapping can lead to a variety of techniques to influence the individual nerve cells’ function in the body.
Once the cause of hearing disorder(s) has been addressed, investigation on new therapies to block and repair them could be started. In the coming years, researchers will try to figure out how exactly these individual nerve cells affects the auditory system, which will further help in developing enhanced auditory aids like cochlear implants.