Complexity analysis of heartbeat-related signals in Brain MRI time series as a potential biomarker for ageing and cognitive performance

Abstract

There are multiple magnet resonance imaging (MRI) based approaches to studying the ageing brain. Getting older affects both the structure of the brain and our cognitive capabilities but there is still no solid evidence on how ageing influences the mechanisms underlying the MRI signal. Here, we apply a recently developed long-range zero-quantum coherence (ZQC) weighted MRI sequence that was found to be sensitive to wakefulness. We found that the complexity of the signal time curve is also affected by age. While comparing young and old participants, we found qualitative and quantitative evidence that the dynamics of these quantum fluctuations undergo strong changes with age. Finally, we study how differences in long-range ZQC relate with measures from different cognitive batteries, suggesting that long-range ZQC may be key for cerebral dynamics and cognitive functioning. The profound sensitivity for dynamic changes shows the potential of long-range ZQC and its underlying physiological mechanism with clinical relevance for all neurovascular diseases.[4]) or are slower processing different stimuli (e.g., [5]). At the same time, some aspects of cognition are maintained, such as semantic memory [6] or emotional regulation [7]. However, the cerebral mechanisms that underlie this better or lesser performance are still poorly understood [8].A vast amount of studies have tried to link these structural changes to age differences in cognitive function. Magnetic resonance imaging (MRI) based methods have been mainly used to study changes in the ageing brain. Among the various MRI methods, functional MRI (fMRI), with more than 10000 published papers, is probably the one more widely applied (e.g., [9]). The blood oxygen level-dependent (BOLD) signal obtained from fMRI is an indirect index of neural activity and reflects small metabolic changes in deoxyhaemoglobin concentrations that take place when a specific region of the brain is active [10]. These responses have been found to be similar in both young and older adults [8], but in some cases, the magnitude of the BOLD response was reduced in older adults (e.g., [11]) while sometimes was increased (e.g., [12]). The former is often related to cognitive deficits in older adults (e.g., [13]), while the latter is often interpreted as compensatory (e.g., [14]) or as a reduction in the selectivity of responses [15]. Independently of the direction of these magnitude variations, changes in cerebral vasculature with age (e.g., [16]), are somehow expected to influence the mechanisms underlying the fMRI signal. Although still unknown, these changes should be related to differences in cognitive performance, but no substantial evidence has been found so far.This comes as a surprise because heart functions also alter with age which should, in turn ,affect cerebral blood flow. Even more, it is well known that several heartbeat-related effects influence conscious perception where the cardiac cycle may impact the perception of visual or auditory stimuli (e.g., [17]). The existence of heartbeat-...