Study may speed improved treatments for hearing loss and symptoms of PTSD
According to researchers at NYU Langone Medical Center, even brief exposure to sudden sounds or mild trauma can form permanent, long-term brain connections, or memories, in a specific region of the brain. The research team was also able to chemically stimulate those biological pathways in rats—in the locus coeruleus—the area of the brain best known for releasing the “fight or flight” hormone noradrenaline—to improve the animals’ hearing.
The study was featured in the cover article in the journal Nature Neuroscience online. The research team believe this study is the first of its kind to explore an apparent connection between hearing and memory formation in the locus coeruleus as well as the first to successfully improve hearing in rats by manipulating the centrally located brain region whose neural network projects throughout the body.
“Our study gives us deeper insight into the functions of the locus coeruleus as a powerful amplifier in the brain, controlling how and where the brain stores and transforms sudden, traumatizing sounds and events into memories,” says senior study investigator and neuroscientist Robert C. Froemke, PhD, an assistant professor at NYU Langone and its Skirball Institute of Biomolecular Medicine. “Our findings, if confirmed by future studies in animals and people, should help us better understand how to improve hearing and memory abilities in those suffering from hearing loss or possibly even Alzheimer’s disease, as well as how to alter or minimize memories involved in disorders like post-traumatic stress disorder.”
As part of the Froemke team’s four-year investigation, led by Ana Raquel O. Martins, PhD, PharmD, the researchers chemically stimulated the locus coeruleus in rats while simultaneously playing them a sound paired with a food reward. After a two-week training period to ensure that the rats associated the sound with food, the same sound was played much more quietly. The researchers recorded activity in the same regions of their brain, as well as in the auditory cortex area responsible for interpreting sounds. They found that the locus coeruleus and auditory cortex still responded to the sound, even at nearly imperceptible levels, for the subsequent and remaining two weeks of the experiments. Chemically stimulating the locus coeruleus led to 100 per cent neural activity in the auditory cortex, even in the absence of the same triggering sounds. Neural activity in the auditory cortex in response to the sounds was at least 10 times greater than when activity in the locus coeruleus was chemically suppressed.
Froemke says these results clearly demonstrate that the memory of the sound and its associated reward was encoded by the locus coeruleus, which helped improve the rats’ ability to perceive the sound.
