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Principal Components Analysis Relates Hippocampal Trisynaptic Circuit to Vividness of Visual Mental Imagery
1Research, National Coalition of Independent Scholars, South Bend, Indiana, USA.
Purpose:
The hippocampal formation serves fundamental processes to support scene construction, learning, memory, and imagination. Here, we use principal components analysis (PCA) to investigate the relation of the trisynaptic circuit, and other hippocampal zones, to individual differences in visual mental imagery ability.
Method:
The data from 53 healthy, middle- to older-aged adults with MRI scans of 36 hippocampal subfield volumes were entered into a PCA, which extracted information about individual differences in subfield volumes and their support, or not, of visual mental imagery ability.
Findings:
A seven-factor solution explained 85% of the variance in hippocampal subfield volumes. The first principal component explained 37% of the variance in referencing trisynaptic circuit subfields. The subjects' ability to form vivid visual mental imagery was indexed with the Vividness of Visual Imagery Questionnaire (VVIQ), which we used to compare the component scores of the 10 highest scoring VVIQ subjects to those of the 10 lowest scoring VVIQ subjects. The high VVIQ group possessed significantly larger component scores than the low VVIQ subjects, with the component referencing the trisynaptic pathway yielding significant differences between the high and low imagery groups. The second principal component indexed a previously unidentified hippocampal region, which referenced four neighboring subfields: the molecular layer, hippocampal tail, presubiculum, and subiculum. All four subfields had strong loadings of between 0.625 and 0.821 on Component 2, which appears to have pinpointed a cohesive structure performing as an integrated network.
Conclusion:
These findings suggest that the trisynaptic circuit is critical for the formation of vivid visual imagery with a lesser role for the parasubiculum, while another site consisting of four neighboring subfields (the molecular layer, hippocampal tail, presubiculum, and subiculum) serves alternative functions yet to be established.
