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Humans have devised endless strategies to avoid fatigue in our busy modern world. Whether it’s industrial-grade coffee, supernatural-hued energy drinks, or complex sleep routines, everyone has their own tips for staying alert. Now, researchers say, a new technique to fight fatigue may have emerged in the form of non-invasive electrical brain stimulation.
The research, published by scientists from Air Force Research Laboratory and supplier to the Ministry of Defense Infoscitex, Inc., used a form of nervous system stimulation called cervical vagus nerve stimulation (VNS).
Whereas before studies have shown that transcranial direct current stimulation (tDCS), an electrical stimulation technique that involves passing an electrical current through the scalp, could improve cognitive abilities in fatigue, other brain stimulation techniques should yet to be explored.
The team, including the lead author Lindsey K. McIntire, hypothesized that VNS might be even more effective than tDCS. This is because both techniques target an area of the brainstem called the locus coeruleus (LC) which secretes the arousal hormone norepinephrine.
While tDCS signals must pass through the skin, skull, and the rest of the brain to reach the LC, VNS techniques stimulate the vagus nerve, the central nerve of the parasympathetic nervous system. The device used in this study, the gammaCore Sapphire, stimulates the nerve by placing it against the skin of the neck. The authors hoped that this might be a faster way to activate LC. Additionally, VNS can be self-administered and only takes six minutes, instead of the half hour required for tDCS, making it a more attractive option for fatigue relief.
To test their theory, the team used 40 volunteers, all staff from Wright-Patterson Air Force Base near Dayton, OH. Participants stayed awake for a total of 34 hours. After 12 hours, they received either sets of VNS or a fake stimulation using an identified device that vibrated and clicked like the real thing, with no electrical impulses passing through the skin. The group then received four sets of cognitive tasks to assess their alertness.
The results have been mixed. In two of the tasks, no significant effect of VNS was noted. One was a sustained attention test called the Mackworth clock test and the other a memory test called the N-back test.
On the other two tasks, participants stimulated by VNS performed better at two times approximately 12 and 15 hours after stimulation. The tasks were the psychomotor vigilance task (PVT) and Air Force – Multi-attribute task battery (AF-MATB). The improvement in AF-MATB performance was driven by tasks requiring close visual attention. PVT is also a very visual task, and the authors suggest that the apparent benefits of the VNS device derive from improvements in executive control, which they describe in their article as “the ability to regulate perceptual and motor processes in order to respond to in an adaptive manner to new or changing task demands.
While the results of the behavioral tasks were mixed, the subjective reports of the volunteers were more robust. Significant differences were noted from 21 hours to 31 hours after stimulation, as the VNS group reported much smaller increases in fatigue.
Will VNS devices soon be used to combat fatigue outside of laboratories? The authors stress that their data will need to be confirmed by other laboratories using study groups that are more diverse in terms of sex and age. Additionally, they note that cervical VNS, the specific type of VNS technology used in the study, has only been tested in clinical populations – such devices are medically approved for the treatment of cluster headaches. Until more research is done, keep this coffee grinder handy.
Reference:
McIntire, LK, McKinley, RA, Goodyear, C et al. Stimulation of the cervical transcutaneous vagal nerve (ctVNS) improves human cognitive performance under stress through sleep deprivation. Biology of communications. 2021; 4 (634). do I: 10.1038 / s42003-021-02145-7
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