Microstructural Correlates and Laterality Effect of Prospective Memory in Non-Demented Adults with Memory Complaints

An increasing number of studies suggest the importance of prospective memory (ProM) due to its functional relevance and sensitivity to neuropathology. However, its relevant neural substrates have not been sufficiently explored.

The present study aimed to investigate the relationship between structural connectivity and both objective and subjective ProM measures in a group of non-demented people with subjective memory complaints, and to examine the potential of ProM measures to detect the difference between subjective cognitive decline (SCD) and mild cognitive impairment (MCI) in the pre-dementia stage.

Thirty-sevennon-dementedparticipants aged above 50 years were recruited from an outpatient Neurology Clinic; 13 of them fulfilled the criteria of MCI and 24 of SCD. All subjects received comprehensive neuropsychological tests, including the adapted version of the Cambridge Prospective Memory Test, as well as the Taiwan version of the Prospective and Retrospective Memory Questionnaire. The diffusion tensor imaging technique with tract-based spatial statistics was applied to measure cerebral microstructural changes.

Time-based ProM performance was significantly correlated with microstructural integrity of the right superior longitudinal fasciculus, while the event-based one was associated with that of the left superior longitudinal fasciculus and the genu of the corpus callosum among all participants and in the SCD group. After controlling for age, the correlation remained significant between event-based ProM performance and the left superior longitudinal fasciculus among all participants and in the MCI group, as well as between event-based ProM performance and the genu among all participants. Although self-reported ProM failures in real life was associated with fiber disruption of the left superior longitudinal fasciculus among all participants and within the MCI group, an inverse relationship was also observed with that of the corpus callosum in the SCD group even after controlling for age. As compared to the SCD group, people with MCI performed significantly worse on time-based ProM tasks and reported more ProM failures in daily life.

ProM was related to the integrity of interhemispheric commissural fibers and association fibers that connect the frontal lobe with posterior regions, with a task-specific laterality effect. Time-based ProM tasks and self-reported ProM questionnaire may be sensitive to early pathological cognitive deterioration, while the concomitant aging process and individual awareness level may respectively confound the results of evaluation.