Just like musicians train to recognize subtle pitch differences more effectively, mammals can also sharpen their skills in hearing, vision, and other senses through practice. This improvement, known as perceptual learning, may be further enhanced by stimulating a key nerve that links the brain to almost every organ in the body, as suggested by a recent mouse study.
Similar to how musicians hone their ability to identify nuanced pitch variations, mammals can enhance their interpretation of senses like hearing and vision through practice. This enhancement, referred to as perceptual learning, could potentially be boosted by activating a significant nerve that connects the brain to nearly every organ in the body, according to new research conducted on mice.
The research, conducted by scientists at NYU Langone Health, focuses on the vagus nerve, responsible for transmitting signals between the brain and various organs, including the heart and digestive system. Researchers have been exploring the use of gentle electrical pulses on this nerve to address a wide range of issues, such as epilepsy, depression, post-traumatic stress disorder, and hearing problems. However, results have been inconsistent, and the exact mechanisms for enhancing hearing remained unclear until now.
To investigate whether vagus nerve stimulation could enhance perceptual learning, the research team trained 38 mice to differentiate musical tones. Initially, all the mice showed improvement, making fewer mistakes over time. However, while those who did not receive treatment reached a plateau after about a week, the mice that were stimulated by the nerve continued to improve, averaging 10% fewer errors in most tests compared to their pre-stimulation performance. Furthermore, in the toughest assessments, where the tones were closely related, these mice made 50% fewer mistakes than their counterparts.
“Our results indicate that stimulating the vagus nerve during training can help surpass the limits of learning in animals, and potentially in humans as well,” stated Kathleen Martin, BS, the lead author of the study and a graduate student at the NYU Grossman School of Medicine’s Neuroscience Institute.
In a subsequent part of the study, researchers looked at how vagus nerve stimulation impacts the brain. The findings showed increased activity in the cholinergic basal forebrain, which is important for attention and memory. When this area was suppressed during nerve stimulation, the mice did not experience any additional learning benefits.
Additionally, the team discovered that the stimulation enhanced neuroplasticity, a crucial process that allows brain cells to adapt and form memories, particularly in the auditory cortex, the primary auditory processing area of the brain. This could result in lasting cellular modifications, enabling the retention of new skills long after training, according to Martin.
She pointed out that the effectiveness of targeting the vagus nerve to enhance hearing has been a topic of debate among experts, with earlier studies on animals not demonstrating significant improvements.
The new research, published online on September 16 in the journal Nature Neuroscience, indicates that this approach can indeed be effective, though the results took longer to manifest than the researchers had anticipated. Martin suggests that this delay might be partly due to the electrical pulses used in the technique, potentially distracting the animals, which may require some time to adapt to the sensation.
The authors believe that using vagus nerve stimulation to boost hearing may have broader implications beyond improving musical skills. Perceptual learning is essential for acquiring new languages and adapting to cochlear implants—neuroprosthetic devices intended to restore hearing. Importantly, patients often need months to adjust to these devices and many encounter difficulties in conversations even after years of use.
“These findings underscore the potential of vagus nerve stimulation to accelerate hearing improvements for cochlear implant users,” remarked senior study author Robert Froemke, PhD. “By enhancing perceptual learning, this technique could facilitate communication for implant recipients, help them detect approaching vehicles, and improve their interaction with their surroundings.”
Froemke, who holds the Skirball Professorship of Genetics in the Department of Neuroscience and Physiology at NYU Grossman School of Medicine, mentioned that the current electrical stimulation devices for activating the vagus nerve are small, only a few centimeters in size, and can be implanted with an outpatient procedure. Some devices, like those for migraine relief, are even less invasive, being simply positioned against the neck’s skin.
Building on their findings, the researchers’ next step is to test the effect of vagus nerve stimulation in rodents with cochlear implants to determine if it enhances their functionality, stated Froemke, who is also a professor in the Department of Otolaryngology – Head and Neck Surgery at NYU Grossman School of Medicine.
Froemke, also an associated member of NYU Langone’s Neuroscience Institute, cautioned that because the vagus nerve is significantly larger and more complex in humans than in mice, the effects of its stimulation may differ and require further investigation in humans.
The study received funding from the National Institutes of Health grant DC012557, with additional support from the United States Department of Defense and the National Science Foundation.
Alongside Martin and Froemke, other researchers from NYU Langone involved in the study include Eleni Papadoyannis, MA; Jennifer Schiavo, PhD; Saba Shokat Fadaei, MS; Habon Issa, BS; Soomin Song, PhD; and Sofia Orrey Valencia, BS. Co-investigators from other institutions include Nesibe Temiz, PhD, at the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland; Matthew McGinley, PhD, at Baylor College of Medicine in Houston, Texas; and David McCormick, PhD, at the University of Oregon in Eugene.
