Brain flexibility and cochlear implants are intertwined. Now we know there might be a reason why cochlear implant success stories vary widely. There are videos of babies crying when they hear their mom’s voice for the first time. For adults, tears of joy may be shed after hearing again for the first time in a long time. But what about the other stories? There are countless others who experience disappointment upon cochlear implant activation because their brain can’t comprehend the electrical signals quite yet.
It has been known that not all implantation success stories are alike. A cochlear implant receives electrical signals, which the mind needs to learn to equate with as sound. This can take time. There are a variety of factors that may shape the success of an implant, such as, the age of patient, time since onset of deafness, cause of the hearing loss, and so on. However, one aspect that researchers agree on is that neuroplasticity of the brain likely contributes to the variability of success for a cochlear implant recipient.
“…neuroplasticity of the brain likely contributes to the variability of success for a cochlear implant recipient.”
The Science of Brain Flexibility and Cochlear Implants
This study decided to look at a very specific structure that lies in the brainstem, called the locus coeruleus (LC). While not uniquely designed for the auditory pathways of the brain, the LC releases a neurotransmitter, norepinephrine. The LC works by increasing the mind’s neuroplasticity to hear by utilizing functions of learning, memory, and arousal.
Researchers at NYU Langone Health led the team and wondered if this deep brainstem structure was stimulated, if it would increase the mind’s ability to understand the electrical signals that travel through a cochlear implant more efficiently.
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Rats with normal hearing were trained to respond to specific sounds for 15 days. These rats used their hearing to press the button if they heard a specific sound, but they were taught to ignore other types of sounds. When these rats pressed the button upon hearing the right tone, they received a reward. Each time the rats chose to press the button correctly, their locus coeruleus (LC) neuronal activity increased. On the other hand, the LC neuronal activity decreased when the rat didn’t press the button or pressed the button for incorrect tones.
Upon completion of these 15 days of training, the rats were made deaf. Then each rat received a cochlear implant. The same training was performed as before. Depending on the tone, the rat either pressed or didn’t press the button. This time however, the rats were deaf with a cochlear implant. Upon activation of the implant, there were two groups studied. The two groups were: the rats with LC stimulated and the rats who did not have their LC stimulated. These two cohorts were compared against each other to see how quickly the rats would be able to complete the task at hand.
Cohort 1: Deaf rat with cochlear implant PLUS locus coeruleus stimulation
Time before sound recognized: 3 days
Cohort 2: Deaf rat with cochlear implant WITHOUT locus coeruleus stimulation
Time before sound recognized: 9 days
This study showed that stimulation of the LC allowed for more neuroplasticity, which caused the rats to adjust to their cochlear implant much quicker!
Co-senior author Mario Svirsky, PhD, notes that the study analyzed rats responding to simple sounds. While the findings of this research on brain flexibility and cochlear implants are exciting, there needs to be more studies done to better analyze hearing in humans. Our hearing is much more complicated with diverse tones, pitches, and patterns.
The next goal is to find a non-invasive way to stimulate the human brain to increase efficacy of the cochlear implant. There is still much research yet to be done to ensure safety and to see if this model holds true for human neuroplasticity. This study gives hope for potential treatment alternatives for new cochlear implant recipients. Not all implantation success stories are alike, but maybe one day, they will be.