Imagery in a pair of aphantasic and non-aphantasic identical twins: Neural similarities and differences

Aphantasia is defined as a lack of voluntary visual imagery, with otherwise normal perception and visual recognition (Zeman et al., 2015). Aphantasics will often describe semantic but not perceptual detail when recalling visual stimuli (Bainbridge et al., 2021). However, the neural correlates that underpin this difference in visual recall remain largely unknown. To understand the neural correlates of aphantasia, we used fMRI to study a pair of identical twins (female, 31 years old) where one twin has typical visual imagery but the other has aphantasia as diagnosed by the Vividness of Visual Imagery Questionnaire and a drawing recall behavioral task. In the scanner, participants completed two visual imagery tasks - imagery for novel object and scene images and for familiar people and places (Bainbridge et al., 2020; Steel et al., 2021) – and a resting state scan to examine differences in functional connectivity. Both participants show anterior shifts in peak voxel activity for category-selective visual cortex during visual recall compared to perception, suggesting similar transformations of stimulus representations from encoding to recall. However, using whole-brain searchlight decoding, we found late perceptual and memory regions that differently decoded information from perception and recall between the two subjects, revealing differences in memory representations between aphantasia and typical imagery. A representational similarity analysis within those regions showed discriminable stimulus information during recall between both participants, which suggests some visual information is retrieved by the aphantasic twin during imagery. Overall, we see that the imager and aphantasic have different regions that share information across perception and recall, but both retain some level of visual information during recall, despite their different experiences.