Researchers publishing in Aging have found that stresses, both biological and in daily life, harm one of our fundamental abilities to correctly process what’s going on around us.
What is sensory gating?
Sensory gating is the brain’s ability to filter out irrelevant stimuli after the first time it experiences them. It reflects our ability to stop paying attention to repetitive things. Without sensory gating, we would be constantly aware of everything, even the very mundane things, that our senses detect. This would leave us unable to focus on the important and different elements of our environment [1].
Previous studies have discovered a link between cognitive abilities and sensory gating [2], and the links between aging and stress have also been explored [3]. However, the link between sensory gating and the combined problems aging and stress has not yet been thoroughly examined. Here, the researchers endeavored to study this link in order to better understand how our brains change as we age.
Direct nerve stimulation
To measure sensory gating directly, the researchers didn’t rely on behavior, even unconscious behavior. Instead, they measured the effects of electrical stimulation on the right median nerve. They stimulated the nerve in the same way twice and analyzed how it reacted both times. The comparison between these two reactions is called the gating ratio. A lower gating ratio is almost always better, as it means that the redundant stimulus is being naturally, automatically filtered out.
The results
Both stress and aging were found to be predictive of a high gating ratio, although in different ways. People who live stressful lives did not respond as much as the average person to the first stimulus, although they responded as much during the second. People who are suffering from accelerated aging respond as much as the average person to the first stimulus, but they have greater responses during the second. Both of these phenomena lead to the same outcome in this study: a higher gating ratio.
The researchers then used an intensive testing system to analyze the test participants’ cognitive abilities. Interestingly, some parts of brain function were not linked to gating ratio: executive function and motor skills. Processing speed was only slightly affected. However, learning, memory, and attention were all significantly, negatively affected by a high gating ratio, which concurs with the results of a previous study [2].
Conclusion
While they did not perform a biochemical analysis, the researchers point to the amino acid GABA, which is the main inhibitory transmitter in humans. They also suggest that hypermethylation of neurons may be responsible for a lack of GABA, leading to a higher gating ratio.
It is clear that the most basic, fundamental abilities of our neurons are affected by both stress and aging. This isn’t a matter of how our neurons are configured. The gating ratio is a fundamental result of how our neurons themselves react to stimuli. As the researchers themselves note, future studies may make use of the gating ratio to test stress-reducing or anti-aging interventions that affect the brain.
Literature
[1] Cromwell, H. C., Mears, R. P., Wan, L., & Boutros, N. N. (2008). Sensory gating: a translational effort from basic to clinical science. Clinical EEG and neuroscience, 39(2), 69-72.
[2] Cheng, C. H., Chan, P. Y. S., Niddam, D. M., Tsai, S. Y., Hsu, S. C., & Liu, C. Y. (2016). Sensory gating, inhibition control and gamma oscillations in the human somatosensory cortex. Scientific reports, 6(1), 1-8.
[3] Booth, T., Royle, N. A., Corley, J., Gow, A. J., Hernández, M. D. C. V., Maniega, S. M., … & Deary, I. J. (2015). Association of allostatic load with brain structure and cognitive ability in later life. Neurobiology of aging, 36(3), 1390-1399.
