MSGID: 1:317/3 64a4f1ee   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    How the ear can inform the brain of whether hearing is impaired    
      
     Date:   
         July 4, 2023   
     Source:   
         Linko"ping University   
     Summary:   
         A cochlear signal, the exact role of which has been unclear   
         since its discovery around 70 years ago, probably gives the brain   
         information on whether the ear is functioning normally or not. These   
         new findings are an important piece of the puzzle in explaining what   
         happens in the ear in hearing impairment caused by harmful noise,   
         and may in the long run contribute to diagnosing noise-induced   
         hearing injury.   
      
      
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   FULL STORY   
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   A cochlear signal, the exact role of which has been unclear since its   
   discovery around 70 years ago, probably gives the brain information on   
   whether the ear is functioning normally or not. This is the conclusion of   
   a study from Linko"ping University, Sweden. Its findings are an important   
   piece of the puzzle in explaining what happens in the ear in hearing   
   impairment caused by harmful noise, and may in the long run contribute   
   to diagnosing noise-induced hearing injury.   
      
   When the ear is exposed to loud sounds, as at a concert or when being in a   
   noisy environment, hearing can be temporarily impaired. Being repeatedly   
   exposed to loud sounds may cause permanent damage to hearing. There is   
   research to indicate that more than one billion young people are at risk   
   of damaging their hearing by listening to loud music with headphones   
   and at venues. But although noise damage is a major cause of impaired   
   hearing, the exact mechanisms are largely unclear. Pierre Hakizimana at   
   Linko"ping University is one of the researchers aiming to find out how   
   these damages occur and whether they can be prevented.   
      
   The inner ear, or cochlea, has around 15,000 hair cells. When hit by   
   sound waves, the hair cells transform the vibrations to electric nerve   
   signals. These signals are led to the brain, which interprets them, and   
   not until then can we hear the sound. The hair cell signal consists of   
   two parts, called AC and DC.   
      
   The AC signal is well researched. It gives the brain information on   
   sound loudness and frequency, i.e. how high or low pitched the sound   
   is. But the DC signal has remained something of a mystery. Ever since   
   its discovery some 70 years ago, researchers have been wondering what   
   its function could be.   
      
   When measuring the electrical signals from the cochlea hair cells, the   
   DC signal is noticeable as it causes a slight shift in the AC signal   
   in either a positive or a negative direction. Various studies trying to   
   characterise the DC signal have come to different conclusions as to its   
   polarity. In the current study, Pierre Hakizimana shows that DC signal   
   polarity changes from positive to negative when the cochlea has been   
   exposed to harmful noise. In other words, the signal can provide an   
   indication of ear health status.   
      
   "It seems like this signal could be a way for the body to inform the   
   brain whether the ear is healthy or not, and in that way facilitate the   
   brain's ability to decode faint sounds. The brain can amplify a weak   
   signal from the cochlea. If informed that the ear isn't functioning   
   normally, the brain doesn't have to spend resources trying to improve   
   the signal to decode sound from an injured ear," says Pierre Hakizimana,   
   principal research engineer in the Department of Biomedical and Clinical   
   Sciences at Linko"ping University.   
      
   This discovery may hopefully contribute to new research on how the   
   DC signal could be used to diagnose hearing loss caused by harmful   
   noise. This has so far not been solved, as it has not been known how   
   to interpret this signal, or how to reliably isolate and measure it   
   in humans.   
      
   In his study, Pierre Hakizimana also shows that the DC signal is created   
   by potassium ion channels releasing potassium ions through hair cell   
   membranes.   
      
   The research was funded by Stiftelsen Tysta Skolan.   
      
       * RELATED_TOPICS   
             o Health_&_Medicine   
                   # Hearing_Loss # Disability # Diseases_and_Conditions #   
                   Nervous_System   
             o Mind_&_Brain   
                   # Hearing_Impairment # Tinnitus # Perception #   
                   Brain_Injury   
       * RELATED_TERMS   
             o Hearing_impairment o Auditory_system o Ear o Middle_ear o   
             Brain_damage o Eardrum o Ultrasound o Tinnitus   
      
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   Materials provided by Linko"ping_University. Original written by Karin   
   So"derlund Leifler. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Pierre Hakizimana. The summating potential polarity encodes the ear   
         health condition. Cellular and Molecular Life Sciences, 2023; 80   
         (6) DOI: 10.1007/s00018-023-04809-5   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230704110920.htm   
      
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