Sorg, C. | bioRxiv Science

bioRxiv2019

Decoupling of inter-regional functional connectivity and regional neural activity in Alzheimer Disease

Alzheimers disease (AD) and mild cognitive impairment (MCI) are characterized by aberrant regional neural activity and disrupted inter-regional functional connectivity (FC). It is, however, poorly understood how changes in regional neural activity and inter-regional FC interact in AD and MCI. Here, we investigated the link between regional neural activity and nodal topological measures of FC through simultaneous PET/MR measurement in 20 patients with MCI, 33 patients with AD, and 26 healthy individuals. First, we assessed regional glucose metabolism identified through FDG-PET (rFDG) (as a proxy of regional neural activity), and regional FC topology through clustering coefficient (CC) and degree centrality (DC) (as surrogates of local segregation and global connectivity, respectively). Next, we examined the potential moderating effect of disease status (AD or MCI) on the link between rFDG and FC topology using hierarchical moderated multiple regression analysis. Alterations in rFDG, CC, and DC were widespread in patients, and AD alters physiological coupling between regional metabolism and functional connectivity particularly in the inferior temporal gyus and supplementary motor areas. While rFDG correlated with CC in healthy subjects, this correlation was lost in AD patients. We suggest that AD pathology decouples the normal association between regional neural activity and functional segregation.

neuroscience↗

bioRxiv2019

Predictability of salient distractor increases top-down control in healthy younger and older adults

Younger adults are able to shield attentional selection against distractors when they have preknowledge about the upcoming distractor location. For older adults, who suffer from an overall decrease in attentional capacity and who are, in addition, particularly prone to attentional capture, such an adaptive shielding ability would be of particular importance. However, it is an open question whether healthy older adults can utilise the predictability of distractor locations to improve top-down controlled selection to the same degree as younger adults. The theory of visual attention (TVA) framework provides a systematic way to measure an individuals efficiency of top-down control. The present study combined a TVA-based partial-report paradigm with abrupt-onset cues rendering the indicated location highly salient in a bottom-up fashion. Experiment 1, in which (on cued trials) the cue was invariably followed by a distractor at the cued location, showed that the cueing increased the weight of the distractor in the competition for selection compared to uncued distractors (on trials without a cue). In Experiment 2, the probability with which the abrupt-onset cue indicated the upcoming distractor location (1/3 vs. 2/3 of trials) was manipulated between experimental blocks. Participants were able to learn these statistical contingencies and exert top-down control more efficiently in blocks with highly valid distractor location cues, as compared to low-validity blocks. This finding suggests that, even though abrupt-onset spatial cues increase the attentional weights of distractors, participants can acquire and use pre-knowledge about the likelihood that a distractor will appear at an indicated location to down-weight the bottom-up attentional-capture signal. This ability turned out to be comparable across age groups, suggesting that efficient use of predictive information to shield against distracting information is preserved in normal ageing.

neuroscience↗