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Cortical excitability controls the strength of mental imagery

DOI: 10.7554/elife.50232
Keogh, R., Bergmann, J., & Pearson, J. (2020). Cortical excitability controls the strength of mental imagery. eLife, 9. doi:10.7554/eLife.50232

Abstract

Mental imagery provides an essential simulation tool for remembering the past and planning the future, with its strength affecting both cognition and mental health. Research suggests that neural activity spanning prefrontal, parietal, temporal, and visual areas supports the generation of mental images. Exactly how this network controls the strength of visual imagery remains unknown. Here, brain imaging and transcranial magnetic phosphene data show that lower resting activity and excitability levels in early visual cortex (V1-V3) predict stronger sensory imagery. Further, electrically decreasing visual cortex excitability using tDCS increases imagery strength, demonstrating a causative role of visual cortex excitability in controlling visual imagery. Together, these data suggest a neurophysiological mechanism of cortical excitability involved in controlling the strength of mental images.

Authors

  • Rebecca Keogh17
  • Johanna Bergmann4
  • Joel Pearson33

What This Study Is About

Researchers wanted to find out why some people have "HD" mental movies while others have a "blank screen" (a condition called aphantasia). They specifically looked at whether the sensitivity or "excitability" of the brain’s visual center determines how clearly we can picture things.

How They Studied It

The team used three different methods to peek inside the brain:
  • Brain Scans (fMRI): They measured the resting activity of 31 people's brains.
  • Magnetic Pulses (TMS): They used magnets on 32 people to see how much "juice" it took to make them see a tiny flash of light (a measure of brain sensitivity).
  • Tiny Electric Currents (tDCS): They applied very weak electricity to about 20 people to see if manually changing their brain activity would change their mental imagery—the ability to picture things in your mind.

What They Found

The results were a bit of a surprise! Usually, we think "more activity = better," but the researchers found the opposite:
  • Quiet is Key: People with *lower* activity in their visual cortex (the back of the brain) actually had *stronger* mental images.
  • The Front-Back Balance: Stronger imagery happened when the "command center" (prefrontal cortex) was very active, but the "movie screen" (visual cortex) was calm.
  • The Electric Boost: When researchers used electricity to "quiet down" the visual cortex, participants' mental images actually became stronger and more vivid!

What This Might Mean

This suggests that aphantasia might not be caused by a "broken" imagination, but rather a "noisy" brain. Think of it like trying to see a faint constellation in the sky—if the "city lights" of your visual cortex are too bright, you can't see the stars.
While this is exciting, we have to be careful: these were small groups of people, and the study didn't focus exclusively on those with total aphantasia. It *suggests* a mechanism for how imagery works, but it doesn't *prove* this is the only cause for everyone.

One Interesting Detail

To measure brain sensitivity, researchers used magnets to create "phosphenes"—harmless, tiny flashes of light in the person's vision. They found that people who were "harder to flash" (meaning their brains were less sensitive) were actually the ones with the most powerful imaginations!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.