Research shows better cognition with non-invasive vagal nerve stimulation

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Ruth Klaming, lead author

In a study published this week in Neuromodulation: Technology at the Neutral Interface, authors report that they have initial evidence that non-invasive vagal nerve stimulation (nVNS) is linked to better performance on visuospatial reasoning and memory recognition tasks.

This study aimed to assess whether nVNS enhances complex visuospatial problem solving within a normative sample of healthy patients.

Authors of this study, led by Ruth Klaming, University of California, USA, report that this study, and further research in this area, has potential implications for the treatment and management of cognitive disorders due to incidences such as stroke, traumatic brain injury, or dementia. Klaming said, “Our study has important implications for a potential new approach of treating cognitive disorders with non-invasive neuromodulation in the near future.”

The study included 30 participants, half of which received transcutaneous cervical nVNS, the other half received a sham stimulation in the same area. The nVNS and sham devices were similar in appearance, and produced similar sensations on the skin.

Stimulation lasted two minutes at 24V for nVNS, and at 4.5V for sham stimulation. In both cases stimulation would have a ramp-up period of 30 seconds, followed by 90 seconds of peak stimulation.

Approximately 35 minutes after this stimulation, subjects had to complete a number of tasks. Participants completed a matrix reasoning (MR) task in a magnetic resonance imaging (MRI) scanner, and a forced-choice recognition task outside the scanner.

According to the study, the MR task comprised 30 different matrices, including geometric shapes arranged around specific patterns in a three by three panel. Fifteen shapes had one dimension of difficulty (shape, colour, or orientation), and 15 had two dimensions of difficulty (colour and orientation, orientation and shape, etc.). Subjects completed the tasks by selecting one of four shape options and pushing the corresponding button. Responses were fed into a computer; subjects did not receive feedback if answers were correct or incorrect.

The forced-choice recognition task took place approximately 10 minutes after the MR session. Subjects were presented with images of the shapes from the MR task as well as new shapes and asked to indicate which they had remembered seeing. Subjects were not previously told that they would be tested on the items from the MR task, allowing researchers to assess participant’s incidental learning.

From their research, authors were able to determine that those with nVNS showed higher accuracy on both easy and hard MR items, compared to the sham group. Additionally, on the forced-choice recognition task, the nVNS group was able to correctly reject more items than the sham group.

This study also looked at subjects’ functional MRI scans, to see if nVNS had any effects on brain activation patterns while completing the problem solving task. While they were able to see nVNS providing some sort of cognitive difference, there was not a significant difference in brain pattern activation.

In their discussion, the authors comment, “based on these behavioural observations, we hypothesize that nVNS increased alertness and improved attention, which led to more engagement in the tasks and consequently enhanced higher order executive processes, such as visuospatial problem solving. It is possible that this effect lasted for at least 50 minutes following stimulation and led to more efficient recognition and less errors compared to sham.”

Despite their overall positive findings, the authors note in their conclusion, “these are proof-of-principle findings and further research is needed before nVNS can be implemented in clinical practice.”

 


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