R-Squared Equal to One: Substituting a Hippocampal Asymmetry Metric for Subjective Measures of Visual Mental Imagery

For decades, investigators have been wary of subjective measures of visual mental imagery such as the Vividness of Visual Imagery Questionnaire (VVIQ) and have sought an objective alternative. A method for substituting a measure of hippocampal asymmetry for subjective measures of visual mental imagery ability is presented. Individual differences in VVIQ scores were shown to be strongly associated with left-right (L/R) asymmetry in hippocampal subfields. In samples of 20 and 53 healthy people, and 38 people with neurological conditions, a significant relationship was found between L/R hippocampal subfield volume ratios and VVIQ scores. A regression of VVIQ scores against hippocampal subfield asymmetry variance yielded R-squared values of .91, .91 and .99 respectively. A sample of 201 participants with the Memory Experiences Questionnaire yielded R-squared equal to 1.0 for the association between memory imagery experience and hippocampal L/R subfield asymmetry variance. A measure of anterior/posterior hippocampal asymmetry variance also yielded R-squared equal to one for its association with imagery ability. These finding points to a robust link between hippocampal asymmetry variance and the vividness of mental imagery. The greater variability in hippocampal subfield asymmetry may reflect enhanced lateral specialization and functional differentiation to support richer VMI. Individual differences in neuroanatomical asymmetry of the hippocampus appear to play a previously underappreciated role in controlling mental imagery experience.