Many of you will have heard of neurotransmitters, chemicals that neurons use to communicate with each other. The best known neurotransmitters of our brains include serotonin, acetylcholine, dopamine and norepinephrine. All of these neurotransmitters have been linked to cognitive functions, which is why they are also called neuromodulators. The neuromodulator that I will focus on in this blog is norepinephrine. Norepinephrine has been related to cognitive functions, such as attention, cognitive control and flexibility, working memory, response inhibition and emotional memory. If norepinephrine is such an important chemical for our brains, how can we investigate its effects on cognitive processes in a safe manner?

Some researchers have used drugs to influence the release of norepinephrine. Unfortunately, there are some major disadvantages of using drugs for research purposes in healthy individuals. First, drug research always needs to be performed in a hospital, where medical aid is available in case of an emergency. Secondly, the specific action mechanisms of most drugs are not precisely known. Last, certainly there are some ethical concerns when using drugs for research purposes in healthy individuals. So, are there any other ways to study the effects of norepinephrine on cognitive processes?

Indeed there are. Another technique to examine norepinephrine’s effects on cognition is vagal nerve stimulation. This technique uses an electrical stimulator to increase the activity of the cranial vagal nerve; this nerve subsequently influences a brain area related to norepinephrine. Vagal nerve stimulation has been used successfully as a treatment for epileptic patients that did not respond to medicine therapy. However, until recently an invasive surgery was always needed to implant the nerve stimulator into the body. Recently, a device has been engineered that can stimulate the vagal nerve through the skin, so without implanting a stimulator into the body. This has been termed transcutaneous vagal nerve stimulation (t-VNS).

Now, how does t-VNS work? As I already mentioned in the previous paragraph, vagal nerve stimulation uses electricity to increase the activity of the vagal nerve. The vagal nerve originates from the brain stem, a part of the brain where many of the more basal functions are housed (think of breathing, heart rate, etc.). Because the nerve originates from an area that is very close to the locus coeruleus – the brain area that is the primary source of norepinephrine in the brain – it also influences the activity in this area. Increased activity in this brain stem area leads to more norepinephrine being released into other brain areas. Since the locus coeruleus has connections with many areas in our brain, stimulation with t-VNS has an effect on cognitive processes such as attention and cognitive control.

This means that with t-VNS we can study norepinephrine’s effect on cognitive processes, without needing invasive surgery or the disadvantages research with medicines bring about. Concluding, norepinephrine is an important neuromodulator, and we can study this neuromodulator in a safe way by using t-VNS as a research technique.

Do you want to know more about this topic? The articles below give a good overview of the research area:

van Leusden, J. W. R., Sellaro, R. & Colzato, L. S. (2015). Transcutaneous Vagal Nerve Stimulation (tVNS): a new neuromodulation tool in healthy humans? Frontiers in Psychology

Chamberlain, S. R., & Robbins, T. W. (2013). Noradrenergic modulation of cognition: therapeutic implications. Journal of Psychopharmacology, 0269881113480988.

Vonck, K., Raedt, R., Naulaerts, J., De Vogelaere, F., Thiery, E., Van Roost, D., ... & Boon, P. (2014). Vagus nerve stimulation… 25 years later! What do we know about the effects on cognition?. Neuroscience & Biobehavioral Reviews, 45, 63-71.