Cortical excitability controls the strength of mental imagery
Keogh, Bergmann and PearsonMay 2020
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.
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What This Study Is About
How They Studied It
- Imagery strength came from an objective test, binocular rivalry: people imagined a red horizontal or green vertical striped pattern for 6 to 7 seconds, then briefly saw a different pattern in each eye. The more often the imagined pattern dominated, the stronger the imagery. The authors say this sensory measure is not a direct proxy for vividness.
- 31 people had resting brain scans (fMRI). A separate 32 had TMS, magnetic pulses over visual cortex that make people see faint flashes of light; a more excitable cortex needs weaker pulses.
- Five experiments (16 to 26 people each) used tDCS, a weak current through the scalp, to lower or raise excitability in visual cortex, prefrontal cortex or both.
What They Found
- Lower resting activity in visual cortex, and lower excitability on TMS (r = -0.43), went with stronger imagery.
- Lowering visual cortex excitability at 1.5 mA strengthened imagery in two experiments; raising it did the opposite. A first experiment at 1 mA found no significant effect. Sham (fake) stimulation weakened imagery, so practice was an unlikely cause.
- In prefrontal cortex the pattern reversed: raising excitability strengthened imagery. People with lower visual and higher frontal resting activity had stronger imagery.
- Stimulating both regions together had no significant effect, and stimulation did not change vividness ratings.
What This Might Mean
One Interesting Detail
This summary was written with AI and may contain errors. Check the original paper.
Authors
Rebecca Keogh
17 papers in the libraryJohanna Bergmann
4 papers in the libraryJoel Pearson
35 papers in the library
Cite this paper
Keogh, R., Bergmann, J., & Pearson, J. (2020). Cortical excitability controls the strength of mental imagery. eLife, 9. doi:10.7554/eLife.50232
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