The project used a novel imaging technique that combines traditional fMRI with a simultaneous measurement of glucose consumption using a PET scan. Our assumption throughout the project was that signal changes in fMRI reflect neural activity if they are paralleled in space and time by transient changes in glucose metabolism. If they are not, they are likely to reflect altered neuro-vascular coupling, either through different mediating mechanisms or through cardiovascular events. For WP1, SIMULTAN collected data from 30 healthy young adults. Confirming our hypothesis and providing proof of concept for the novel hybrid imaging technique, we found good agreement between fMRI signal increases and increased glucose metabolism in frontal-parietal areas that are active during cognitive control compared to rest. Interestingly, we found that task-induced fMRI deactivations, which have been difficult to fully understand, are not paralleled by overlapping task-induced changes in glucose metabolism. This showed that task-induced deactivations are not antagonistic to fMRI activations and highlight a special role for deactivated areas (also known as default mode areas). The results have been presented in oral presentations at two different international conferences (OHBM 2019 in Rome and The Conference for Neuroreceptor Mapping in London 2018) and are published in PNAS in 2021.
For WP2 we collected data from 40 healthy older adults. The finding that cognitively healthy older adults often show widespread fMRI activity during task performance has been interpreted as neural compensation. We tested this hypothesis using a modern human imaging technique in which the fMRI data were again simultaneously complemented with measures of glucose consumption as a proxy for synaptic activity. It was found that patterns of additional fMRI activity in older adults that were not detectable in young controls were not accompanied by synaptic activity. The main results are published in the Journal of Neuroscience in 2023.
WP 3 supplements WP2 with a longitudinal component which means that the 40 older adults were invited back toward the end of the project for a second scan. Here, the aim was to compare fMRI and glucose metabolims in older adults to themselves over a period of 3 years. The longitudinal analysis of cognitive and physical health from the project's own data collection was complemented by data from large publicly available data sources (the PPMI, results published in Andersson et al. 2021 Frontiers in Psychology, and ongoing work with data from the Survey of Health and Retirement in Europe SHARE). Preliminary results confirm our results from WP2 that trajectories of cognitive stability over time are not accompanied by compensatory neural activity but rather reflect a maintained healthy brain.
