MRI brain scanning sheds light on 'mind blindness'

Aphantasia, or ‘mind blindness’, is a condition where people cannot form mental images.

“If you try and imagine a beach, you can probably ‘see’ it in your mind’s eye,” said Professor Joel Pearson from UNSW Sydney’s School of Psychology. “People with aphantasia don’t get that mental picture — it’s just blank.”

People with aphantasia also report a reduced ability to remember the past, imagine the future and even dream, according to a 2020 study by Pearson’s Future Minds Lab at UNSW. While there is physiological evidence for aphantasia — discovered through previous studies using sensory measures — little is understood about the underlying neural mechanisms of the condition. Now, scientists from UNSW and South China Normal University have used MRI brain scanning to discover more about the neural processes in people with aphantasia.

In a breakthrough for understanding the condition, they found that when people with aphantasia try to conjure a mental image, the primary visual cortex — the part of the brain that processes picture-like visual information — is activated, but any images that are produced remain unconscious to the individual. This finding challenges the existing theory that activity in the primary visual cortex directly produces conscious visual imagery.

Existing research in psychology and neuroscience has demonstrated that visual experiences are closely linked to neural activity in the parts of the brain that process visual input at the earliest stages. The primary visual cortex is particularly important as it processes visual information in a picture-like format during perception and mental imagery, with its activation strength and size both tied to the vividness and strength of imagined content.

Scientists have even decoded and reconstructed visual imagery based on neural activity in these areas, highlighting their role in creating subjective visual experiences. However, until now, it has been unclear whether people with aphantasia have this type of neural activity in their primary visual cortex.

The MRI study tested 14 participants with aphantasia and a control group of 18 participants who had typical mental imagery. The participants underwent two different tests to assess their visual imagery, followed by functional MRI (fMRI) scans. The scans utilised blood oxygen level-dependent (BOLD) fMRI, a technique that measures brain activity by detecting changes in blood oxygenation.

During the scans, participants viewed or imagined coloured striped patterns — which selectively activate the primary visual cortex. BOLD signals were recorded during either passive perception or attempts at imagining these patterns.

When passively looking at the striped patterns, participants with aphantasia showed a reduced BOLD response compared to the control group. When asked to mentally visualise the patterns, individuals with aphantasia reported little to no conscious imagery; however, distinct neural patterns were still generated during their imagery attempts. The researchers were even able to use algorithms to ‘decode’ what people with aphantasia were attempting to imagine from the brain activity in the primary visual cortex.

This suggests that there is indeed an image-specific representation in the brains of people with aphantasia; it just remains unconscious. These neural patterns are fundamentally different from perception and from those of people with mental imagery.

“Our results show that when someone with aphantasia tries to imagine, their brains still seem to create a representation in the early visual cortex. It’s like their brain is doing the maths but skipping the final step of showing the result on a screen,” Pearson said.

“This tells us that mental imagery isn’t just about the brain ‘lighting up’ — it’s about how that activity is formatted into something we can actually experience.”

The results of the research, published in Current Biology, open a door to understanding more about aphantasia, along with a range of other conditions involving altered mental imagery.

“We want and need to know more about how mental imagery is central to many psychological therapies and how superstrong imagery is associated with disorders such as schizophrenia and Parkinson’s disease,” Pearson said. “Understanding the neurological basis of aphantasia could have a major impact on a range of disorders, and treatments to potentially give those with aphantasia mental imagery.”

While the study’s findings are significant, further research is still required, including studies with greater sample sizes.

“Next, we plan to figure out why exactly these representations in the visual brain don’t produce conscious imagery in those with aphantasia,” Pearson said.

Image credit: iStock.com/gaiamoments