Posts tagged vagus nerve
Articles and news from the latest research reports.
'Tickling' your ear could be good for your heart
Stimulating nerves in your ear could improve the health of your heart, researchers have discovered.
A team at the University of Leeds used a standard TENS machine like those designed to relieve labour pains to apply electrical pulses to the tragus, the small raised flap at the front of the ear immediately in front of the ear canal.
The stimulation changed the influence of the nervous system on the heart by reducing the nervous signals that can drive failing hearts too hard.
Professor Jim Deuchars, Professor of Systems Neuroscience in the University of Leeds’ Faculty of Biological Sciences, said: “You feel a bit of a tickling sensation in your ear when the TENS machine is on, but it is painless. It is early days—so far we have been testing this on healthy subjects—but we think it does have potential to improve the health of the heart and might even become part of the treatment for heart failure.”
The researchers applied electrodes to the ears of 34 healthy people and switched on the TENS (Transcutaneous electrical nerve stimulation) machines for 15-minute sessions. They monitored the variability of subjects’ heartbeats and the activity of the part of the nervous system that drives the heart. Monitoring continued for 15 minutes after the TENS machine was switched off.
Lead researcher Dr Jennifer Clancy, of the University of Leeds’ School of Biomedical Sciences, said: “The first positive effect we observed was increased variability in subjects’ heartbeats. A healthy heart does not beat like a metronome. It is continually interacting with its environment—getting a little bit faster or a bit slower depending on the demands on it. An unhealthy heart is more like a machine constantly banging out the same beat. We found that when you stimulate this nerve you get about a 20% increase in heart rate variability.”
The second positive effect was in suppressing the sympathetic nervous system, which drives heart activity using adrenaline.
Dr Clancy said: “We measured the nerve activity directly and found that it reduced by about 50% when we stimulated the ear. This is important because if you have heart disease or heart failure, you tend to have increased sympathetic activity. This drives your heart to work hard, constricts your arteries and causes damage. A lot of treatments for heart failure try to stop that sympathetic activity—beta-blockers, for instance, block the action of the hormones that implement these signals. Using the TENS, we saw a reduction of the nervous activity itself.”
The researchers found significant residual effects, with neither heart rate variability or sympathetic nerve activity returning to the baseline 15 minutes after the TENS machine had been switched off.
The technique works by stimulating a major nerve called the vagus, which has an important role in regulating vital organs such as the heart. There is a sensory branch of the vagus in the outer ear and, by sending electrical current down the nerves and into the brain, researchers were able to influence outflows from the brain that regulate the heart. Vagal nerve stimulation has previously been used to treat conditions including epilepsy.
Professor Deuchars said: “We now need to understand how big and how lasting the residual effect on the heart is and whether this can help patients with heart problems, probably alongside their usual treatments. The next stage will be to conduct a pre-clinical study in heart failure patients.”
(Source: eurekalert.org)
How the gut feeling shapes fear
An unlit, deserted car park at night, footsteps in the gloom. The heart beats faster and the stomach ties itself in knots. We often feel threatening situations in our stomachs. While the brain has long been viewed as the centre of all emotions, researchers are increasingly trying to get to the bottom of this proverbial gut instinct.
It is not only the brain that controls processes in our abdominal cavity; our stomach also sends signals back to the brain. At the heart of this dialogue between the brain and abdomen is the vagus nerve, which transmits signals in both directions – from the brain to our internal organs (via the so called efferent nerves) and from the stomach back to our brain (via the afferent nerves). By cutting the afferent nerve fibres in rats, a team of scientists led by Urs Meyer, a researcher in the group of ETH Zurich professor Wolfgang Langhans, turned this two-way communication into a one-way street, enabling the researchers to get to the bottom of the role played by gut instinct. In the test animals, the brain was still able to control processes in the abdomen, but no longer received any signals from the other direction.
Less fear without gut instinct
In the behavioural studies, the researchers determined that the rats were less wary of open spaces and bright lights compared with controlled rats with an intact vagus nerve. “The innate response to fear appears to be influenced significantly by signals sent from the stomach to the brain,” says Meyer.
Nevertheless, the loss of their gut instinct did not make the rats completely fearless: the situation for learned fear behaviour looked different. In a conditioning experiment, the rats learned to link a neutral acoustic stimulus – a sound – to an unpleasant experience. Here, the signal path between the stomach and brain appeared to play no role, with the test animals learning the association as well as the control animals. If, however, the researchers switched from a negative to a neutral stimulus, the rats without gut instinct required significantly longer to associate the sound with the new, neutral situation. This also fits with the results of a recently published study conducted by other researchers, which found that stimulation of the vagus nerve facilitates relearning, says Meyer.
These findings are also of interest to the field of psychiatry, as post-traumatic stress disorder (PTSD), for example, is linked to the association of neutral stimuli with fear triggered by extreme experiences. Stimulation of the vagus nerve could help people with PTSD to once more associate the triggering stimuli with neutral experiences. Vagus nerve stimulation is already used today to treat epilepsy and, in some cases, depression.
Stomach influences signalling in the brain
“A lower level of innate fear, but a longer retention of learned fear – this may sound contradictory,” says Meyer. However, innate and conditioned fear are two different behavioural domains in which different signalling systems in the brain are involved. On closer investigation of the rats’ brains, the researchers found that the loss of signals from the abdomen changes the production of certain signalling substances, so called neurotransmitters, in the brain.
“We were able to show for the first time that the selective interruption of the signal path from the stomach to the brain changed complex behavioural patterns. This has traditionally been attributed to the brain alone,” says Meyer. The study shows clearly that the stomach also has a say in how we respond to fear; however, what it says, i.e. precisely what it signals, is not yet clear. The researchers hope, however, that they will be able to further clarify the role of the vagus nerve and the dialogue between brain and body in future studies.
Clinical Trial Brings Positive Results for Tinnitus Sufferers
UT Dallas researchers have demonstrated that treating tinnitus, or ringing in the ears, using vagus nerve stimulation-tone therapy is safe and brought significant improvement to some of the participants in a small clinical trial.
Drs. Sven Vanneste and Michael Kilgard of the School of Behavioral and Brain Sciences used a new method pairing vagus nerve stimulation (VNS) with auditory tones to alleviate the symptoms of chronic tinnitus. Their results were published on Nov. 20 in the journal Neuromodulation: Technology at the Neural Interface.
VNS is an FDA-approved method for treating various illnesses, including depression and epilepsy. It involves sending a mild electric pulse through the vagus nerve, which relays information about the state of the body to the brain.
“The primary goal of the study was to evaluate safety of VNS-tone therapy in tinnitus patients,” Vanneste said. “VNS-tone therapy was expected to be safe because it requires less than 1 percent of the VNS approved by the FDA for the treatment of intractable epilepsy and depression. There were no significant adverse events in our study.”
According to Vanneste, more than 12 million Americans have tinnitus severe enough to seek medical attention, of which 2 million are so disabled that they cannot function normally. He said there has been no consistently effective treatment.
The study, which took place in Antwerp, Belgium, involved implanting 10 tinnitus sufferers with a stimulation electrode directly on the vagus nerve. They received 2 ½ hours of daily treatment for 20 days. The participants had lived with tinnitus for at least a year prior to participating in the study, and showed no benefit from previous audiological, drug or neuromodulation treatments. Electrical pulses were generated from an external device for this study, but future work could involve using internal generators, eliminating the need for clinical visits.
Half of the participants demonstrated large decreases in their tinnitus symptoms, with three of them showing a 44-percent reduction in the impact of tinnitus on their daily lives. Four people demonstrated clinically meaningful reductions in the perceived loudness of their tinnitus by 26 decibels.
Five participants, all of whom were on medications for other problems, did not show significant changes. However, the four participants who benefited from the therapy were not using any medications. The report attributes drug interactions as blocking the effects of the VNS-tone therapy.
“In all, four of the 10 patients showed relevant decreases on tinnitus questionnaires and audiological measures,” Vanneste said. “The observation that these improvements were stable for more than two months after the end of the one month therapy is encouraging.”
Head hurts? Zap the wonder nerve in your neck
"It was like red-hot pokers needling one side of my face," says Catherine, recalling the cluster headaches she experienced for six years. "I just wanted it to stop." But it wouldn’t – none of the drugs she tried had any effect.
Thinking she had nothing to lose, last year she enrolled in a pilot study to test a handheld device that applies a bolt of electricity to the neck, stimulating the vagus nerve – the superhighway that connects the brain to many of the body’s organs, including the heart.
The results of the trial were presented last month at the International Headache Congress in Boston, and while the trial is small, the findings are positive. Of the 21 volunteers, 18 reported a reduction in the severity and frequency of their headaches, rating them, on average, 50 per cent less painful after using the device daily and whenever they felt a headache coming on.
This isn’t the first time vagal nerve stimulation has been used as a treatment – but it is one of the first that hasn’t required surgery. Some people with epilepsy have had a small generator that sends regular electrical signals to the vagus nerve implanted into their chest. Implanted devices have also been approved to treat depression. What’s more, there is increasing evidence that such stimulation could treat many more disorders from headaches to stroke and possibly Alzheimer’s disease.
The latest study suggests it is possible to stimulate the nerve through the skin, rather than resorting to surgery. “What we’ve done is figured out a way to stimulate the vagus nerve with a very similar signal, but non-invasively through the neck,” says Bruce Simon, vice-president of research at New Jersey-based ElectroCore, makers of the handheld device. “It’s a simpler, less invasive way to stimulate the nerve.”
Cluster headaches are thought to be triggered by the overactivation of brain cells involved in pain processing. The neurotransmitter glutamate, which excites brain cells, is a prime suspect. ElectroCore turned to the vagus nerve as previous studies had shown that stimulating it in people with epilepsy releases neurotransmitters that dampen brain activity.
When the firm used a smaller version of ElectroCore’s device on rats, it found it reduced glutamate levels and excitability in these pain centres. Other studies have shown that vagus nerve stimulation causes the release of inhibitory neurotransmitters which counter the effects of glutamate.
The big question is whether a non-implantable device can really trigger changes in brain chemistry in humans, or whether people are simply experiencing a placebo effect. “The vagus nerve is buried deep in the neck, and something that’s delivering currents through the skin can only go so deep,” says Mike Kilgard of the University of Texas at Dallas. As you turn up the voltage, there’s a risk of it activating muscle fibres that trigger painful cramps, he adds.
Simon says that volunteers using the device haven’t reported any serious side effects. He adds that ElectroCore will soon publish data showing changes in brain activity in humans after using the device. Placebo-controlled trials are also about to start.
Catherine has been using it for a year without ill effect. “I can now function properly as a human being again,” she says.
The many uses of the wonder nerve
Coma, irritable bowel syndrome, asthma and obesity are just some of the disparate conditions that vagus nerve stimulation may benefit and for which human trials are under way.
It might also help people with tinnitus. Although people with tinnitus complain of ringing in their ears, the problem actually arises because too many neurons fire in the auditory part of the brain when certain frequencies are heard.
Mike Kilgard of the University of Texas at Dallas reasoned that if people were played tones that didn’t trigger tinnitus while the vagus nerve was stimulated, this might coax the rogue neurons into firing in response to these frequencies instead. “By activating this nerve we can enhance the brain’s ability to rewire itself,” he says.
He has so far tested the method in rats and in 10 people with tinnitus, using an implanted device to stimulate the nerve. Not everyone noticed an improvement, but even so Kilgard is planning a larger trial. The work was presented at a meeting of the International Union of Physiological Sciences in Birmingham, UK, last month. The technique is also being tested in people who have had a stroke.
"If these studies stand up it could be worth changing the name of the vagus nerve to the wonder nerve," says Sunny Ogbonnaya at Cork University Hospital in Ireland.