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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 Keogh14
  • Johanna Bergmann4
  • Joel Pearson28

Understanding the Strength of Mental Imagery

Overview/Introduction

Mental imagery, or the ability to "see with the mind's eye," is a crucial cognitive tool that helps us remember the past and plan for the future. The vividness of these mental images can vary greatly among individuals and has significant implications for both cognitive functions and mental health. This study explores the role of brain activity, particularly in the visual cortex, in controlling the strength of these mental images.

Methodology

The research employed a combination of brain imaging techniques and non-invasive brain stimulation methods to investigate how the excitability of the visual cortex affects mental imagery strength. Specifically, the study used:
  • Functional Magnetic Resonance Imaging (fMRI) to observe brain activity.
  • Transcranial Magnetic Stimulation (TMS) to measure cortical excitability through phosphene thresholds, which are visual sensations induced by magnetic stimulation.
  • Transcranial Direct Current Stimulation (tDCS) to manipulate cortical excitability and observe changes in imagery strength.

Key Findings

  • Visual Cortex Excitability: Lower resting activity and excitability in the early visual cortex (areas V1-V3) were associated with stronger mental imagery. This suggests that a less excitable visual cortex may reduce neural noise, enhancing the clarity of mental images.
  • Causal Role of Visual Cortex: By decreasing visual cortex excitability through tDCS, researchers were able to increase the strength of mental imagery, indicating a direct causal relationship.
  • Prefrontal Cortex Role: Increasing excitability in the prefrontal cortex, a brain area involved in higher cognitive functions, also enhanced imagery strength, but through a different mechanism than the visual cortex.

Implications

These findings provide a deeper understanding of the neurophysiological mechanisms behind mental imagery. They suggest potential therapeutic applications for enhancing mental imagery in individuals with weaker imagery abilities, which could benefit cognitive and mental health interventions. For instance, targeted brain stimulation could be used to improve visualization skills in educational settings or therapy for mental health conditions.

Limitations

While the study provides valuable insights, it has some limitations:
  • The sample size was relatively small, which may limit the generalizability of the findings.
  • The study focused on specific brain regions, so the role of other areas in mental imagery remains unexplored.
  • The effects of simultaneous stimulation of multiple brain regions were not significant, indicating a need for further research to understand complex brain interactions.
In conclusion, this research highlights the importance of cortical excitability in visual imagery strength and opens new avenues for enhancing cognitive functions through brain stimulation techniques.