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Visual mental imagery in typical imagers and in aphantasia: A millimeter-scale 7-T fMRI study

DOI: 10.1101/2023.06.14.544909
Liu, J., Zhan, M., Hajhajate, D., Spagna, A., Dehaene, S., Cohen, L., & Bartolomeo, P. (n.d.). Visual mental imagery in typical imagers and in aphantasia: a millimeter-scale 7-t fmri study. doi:10.1101/2023.06.14.544909

Abstract

Most of us effortlessly describe visual objects, whether seen or remembered. Yet, around 4% of people report congenital aphantasia: they struggle to visualize objects despite being able to describe their visual appearance. What neural mechanisms create this disparity between subjective experience and objective performance? Aphantasia can provide novel insights into conscious processing and awareness. We used ultra-high field 7T fMRI to establish the neural circuits involved in visual mental imagery and perception, and to elucidate the neural mechanisms associated with the processing of internally generated visual information in the absence of imagery experience in congenital aphantasia. Ten typical imagers and 10 aphantasic individuals performed imagery and perceptual tasks in five domains: object shape, object color, written words, faces, and spatial relationships. In typical imagers, imagery tasks activated left-hemisphere frontoparietal areas, the relevant domain-preferring areas in the ventral temporal cortex partly overlapping with the perceptual domain-preferring areas, and a domain-general area in the left fusiform gyrus (the Fusiform Imagery Node). The results were valid for each individual participant. In aphantasic individuals, imagery activated similar visual areas, but there was reduced functional connectivity between the Fusiform Imagery Node and frontoparietal areas. Our results unveil the domain-general and domain-specific circuits of visual mental imagery, their functional disorganization in aphantasia, and support the general hypothesis that conscious visual experience - whether perceived or imagined - depends on the integrated activity of high-level visual cortex and frontoparietal networks.

Authors

  • Jianghao Liu4
  • Minye Zhan1
  • Dounia Hajhajate1
  • Alfredo Spagna1
  • Stanislas Dehaene1
  • Laurent Cohen1
  • Paolo Bartolomeo4

Understanding Visual Imagery and Aphantasia: A Study on Brain Activity

Overview/Introduction

Visual mental imagery is the ability to visualize objects in the mind without any external visual input. While most people can do this effortlessly, about 4% of the population experiences congenital aphantasia, a condition where individuals cannot visualize images in their minds. Despite this, they can still describe objects accurately. This study explores the brain mechanisms behind this phenomenon using advanced brain imaging techniques.

Methodology

Researchers used ultra-high field 7-Tesla fMRI to study the brain activity of 20 participants—10 with typical imagery abilities and 10 with aphantasia. Participants engaged in tasks involving visualizing and perceiving objects across five domains: shapes, colors, words, faces, and spatial relationships. The study aimed to identify the neural circuits involved in visual imagery and how they differ in individuals with aphantasia.

Key Findings

  • Typical Imagers: In individuals with typical imagery abilities, tasks activated specific brain areas, including the left hemisphere's frontoparietal regions and the ventral temporal cortex. These areas are involved in both imagery and perception.
  • Aphantasic Individuals: Although similar brain areas were activated during imagery tasks, aphantasic individuals showed reduced connectivity between the Fusiform Imagery Node (FIN) and frontoparietal areas. This suggests a disconnect in the network that integrates visual information.
  • Functional Connectivity: Typical imagers displayed strong connections between the FIN and other brain regions during imagery tasks, which was not observed in aphantasic individuals.
  • Behavioral Performance: Despite their inability to visualize, aphantasic individuals performed imagery tasks with accuracy comparable to typical imagers, indicating that they process visual information differently.

Implications

  • Understanding Conscious Experience: The study provides insights into how conscious visual experience is generated in the brain. It suggests that aphantasia may result from a functional disconnection in the brain's imagery network.
  • Potential Applications: These findings could inform therapeutic strategies for individuals with aphantasia and enhance our understanding of other cognitive conditions involving imagery deficits.

Limitations

  • Sample Size and Diversity: The study involved a small sample size, which may not represent the diversity of experiences in aphantasia.
  • Brain Coverage: The imaging technique used did not cover the entire brain, potentially missing relevant areas.
  • Variability in Vividness Ratings: The study faced challenges in analyzing vividness ratings due to consistently low scores in aphantasic individuals and high scores in typical imagers.
In conclusion, this research highlights the complex neural mechanisms underlying visual mental imagery and the uniq...