Is Low-Grade Inflammation Making You Mentally Sluggish?

New research finds a link between mild inflammation and cognitive sluggishness.

Posted Nov 17, 2019

Certain types of cognitive sluggishness, mental fatigue, and "brain fog" may be linked to systemic inflammation, according to a new study. These findings were published in the November issue of NeuroImage.

For this study, scientists from the University of Birmingham and the University of Amsterdam collaborated to uncover possible neurophysiological links between inflammation and mental sluggishness.

"Scientists have long suspected a link between inflammation and cognition, but it is very difficult to be clear about the cause and effect," senior co-author Ali Mazaheri said in a news release. "Our research has identified a specific critical process within the brain that is clearly affected when inflammation is present." 

The researchers found that acute low-grade inflammation appears to slow down the brain's visual attention processing, which is associated with maintaining an alert state.

Mazaheri and Jane Raymond of the University of Birmingham's Centre for Human Brain Health and Cognitive Neurophysiology Lab are the senior co-authors of this study. The first author of this study, Leonie Balter, conducted this research as part of her Ph.D. 

adike/Shutterstock
Source: adike/Shutterstock

For this study, a small group of volunteers received an injection of a substance known to trigger temporary (but acute) low-grade inflammation. Then, participants had their brain activity monitored with EEG while they performed various tests in the lab.

As a control, each participant performed the same neuro-cognitive assessments on a different day after receiving a placebo injection of water that did not trigger acute low-grade inflammation.

Inflammation levels were measured by assessing interleukin-6 (IL-6) levels in blood samples taken on each day of brain processing and EEG testing.

As mentioned, the results showed that acute low-grade inflammation appears to affect brain activity related to staying alert. "Mild inflammation selectively increased alerting-related alpha suppression; a greater inflammatory response was correlated with more alpha suppression," the authors write.

During this study, each participant completed the Attention Network Test while wearing an EEG monitor six hours after either receiving a placebo or an inflammation-triggering substance.

Brain wave analyses focused on modulations of oscillatory EEG activity in the alpha band (9–12 Hz) for "alerting" and "orienting" attention as well as the frontal theta band (4–8 Hz) which is associated with executive control.

"Inflammation caused significant alterations to task-related brain activity. Specifically, inflammation produced greater cue-induced suppression of alpha power in the alerting aspect of attention and individual variation in the inflammatory response was significantly correlated with the degree of alpha power suppression," the authors write in the paper's summary.

Interestingly, acute low-grade inflammation did not appear to affect orienting (i.e., alpha lateralization) or executive control (i.e., frontal theta activity). As the authors explain, "These results reveal a unique neurophysiological sensitivity to acute mild inflammation of the neural network that underpins attentional alerting functions."

"These results show quite clearly that there's a very specific part of the brain network that's affected by inflammation," Mazaheri said in a news release. "This could explain 'brain fog.'"

These findings suggest that people with systemic inflammation may have to exert more cognitive effort to achieve the same level of attention-related performance as those with less inflammation.

The next step for researchers will be to test how acute low-grade inflammation influences other areas of brain function, such as working memory.

Blogger's note: Although this research doesn't focus on ways to reduce inflammation, one could speculate that lowering inflammation may boost visual attention processing speeds.

Based on other research relating to systemic inflammation and interleukin-6 levels (Koopman et al., 2016), vagus nerve stimulation (VNS) or lifestyle choices that hack the vagus nerve and improve vagal tone—as indexed by heart rate variability (HRV)—could create a domino effect that lowers inflammation and boosts visual attention processing speeds. 

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References

Leonie J. T. Balter, Jos A. Bosch, Sarah Aldred, Mark T. Drayson, Jet JCS. Veldhuijzen van Zanten, Suzanne Higgs, Jane E. Raymond, Ali Mazaheriae. "Selective Effects of Acute Low-Grade Inflammation on Human Visual Attention." NeuroImage (First published online: August 12, 2019) DOI: 10.1016/j.neuroimage.2019.116098