Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels

Abstract

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

The Effect of Aging on Muscular Dynamics Underlying Movement Patterns Changes

“…In other words, the results might suggest that the set of dynamical repertoires used is the same between age groups but elderly do not switch between them as often or alternatively that a smaller set of dynamical repertoires is available. Only the latter case would be consistent with the dedifferentiation hypotheses (Sleimen-Malkoun et al, 2014) which was also found for the kinematic data presented here. The analyses of muscular synergies allowed answering this question.…”

“…Accordingly, aging is a dynamic process that presents itself with both alterations within all subsystems—though each having their individual timescale—and with changes in their couplings (e.g., Sleimen-Malkoun et al, 2014). These changes lie at the origin of an age-related loss of behavioral adaptability.…”

“…To address this issue, a possible strategy consists of forcing the system to reorganize to accommodate a progressive increase in task constraints (Haken et al, 1985; Kelso and Jeka, 1992; Kelso, 2009; Sleimen-Malkoun et al, 2014). In the present experiment, we adopted a similar strategy to study reorganizations in muscular dynamics in parallel to (before, around, and after) transitions between dynamics regimes in Fitts' task.…”

Dynamic Functional Connectivity between Order and Randomness and its Evolution across the Human Adult Lifespan

“…These reductions in dFC speed and complexity correlate with the level of general cognitive and behavioural performance, as probed by both standard clinical assessments of cognitive impairments (Nasreddine et al, 2005) and a simple visuomotor coordination task (Houweling et al, 2008). The fact that slowing down and complexity loss in dFC are associated with degraded performance can be linked to prominent theories of cognitive aging, speculatively establishing alterations of dFC random walk properties as novel imaging correlates of processing speed reduction (Salthouse, 1996;Finkel et al, 2007) and de-differentiation (Baltes, 1980;Sleimen-Malkoun et al, 2014).…”

Fractal Analysis of Cardiovascular Signals Empowering the Bioengineering Knowledge

“…From the point of view of chaos theory, multiscale and non-linear complexity (structure and interactions of individual subsystems) appears to degrade with ageing and disease [47]. The structures and functions of the individual subsystems are not only affected by the process but also the interactions between them [48]. For this reason, the loss of complexity has even been hypothesized to be an indicator of the transition from normal ageing to frailty [49].…”