Ziel

Abstract (2018-2021):
The overall objective of this project is to better understand mechanisms of age-related decrements in dual-task performance between postural control and working memory. We will specifically disentangle age-related differences in domain-specific resource limitations, as operationalized by mental versus physical fatigue, from specific central mapping-related crosstalk in modality incompatible compared to modality compatible stimulus-response mappings within cognitive-motor dual-task performance. For this purpose, two experiments will be conducted in a biomechanics laboratory and in an fMRI facility. Fatigue protocols will be similar in both experiments. The physical fatigue protocol comprises old (65-75 years) and young (20-30 years) adults to perform a repeated sit-to-stand task until failure. While the old adults will be asked to perform the fatigue protocol without any extra load, the young adults will receive an adjustable weighted vest with a load that corresponds to 30% of their individual body mass. The mental fatigue protocol affords young and old subjects to complete a variant of the Attentional Network Test. An administration time of 35 minutes is expected to induce selective effects in executive attention. Pre, post fatigue and during recovery, experiment 1 includes standing on a force plate and performing postural single tasks, cognitive-postural dual tasks, and cognitive-cognitive postural triple tasks. Postural sway (i.e., centre of pressure displacements), lower limb muscle activity using surface electromyography and brain activity using electroencephalography will be monitored. In all conditions, the cognitive task will include a spatial one-back working memory task (i.e., cognitive single or cognitive dual-task), with either modality compatible or modality incompatible input-output modality pairings. During lying position in the MRI scanner, participants will perform single and dual one-back tasks.
Abstract (2015-2018):
Aging is associated with marked decrements in both postural control and working memory capacity as well as dual-task performance, i.e., the concurrent performance of two tasks. Dual-task decrements in balance and working memory have ample significance for everyday activities and critical outcomes such as falls. At the same time, there is increasing evidence that working memory shows significant training-induced plasticity in old adults, and several intervention studies in motor-cognitive dual-tasks have indicated that dual-task performance can be improved by practice. However, the underlying mechanisms and neural correlates of both age-related decrements in dual-task performance between postural control and working memory, as well as effects of training on motor-cognitive dual-task performance are poorly understood. Extant theories of dual-task processes and empirical research on the neural mechanisms underlying dual-task interference indicate that both interference related to the compatibility of stimulus and response modalities within working memory (in that e.g., visual stimuli facilitate motor responses) as well as limited central capacities within working memory may modulate dual-task performance. The overall objective of this project is to better understand mechanisms of such age-related decrements in dual-task performance between postural control and working memory. Using a behavioral and a neurophysiological approach, we will specifically disentangle effects of compatible versus incompatible stimulus-response mappings within working memory on dual-task performance from effects of the degree of central interference of these working memory tasks with postural control. Furthermore, within old adults, we will explore effects of dual-task training as a function of stimulus-response mappings and the degree of central processing constraints for upright posture and will be able to relate individual differences in cross-sectional behavior and associated neural changes. This approach will allow us to differentially test effects of stimulus-response and central processing modality and hence allow us to directly assess the effects predicted by a common-coding account versus the effects of central interference as predicted by central processing theories. We will test 30 young and 40 older adults in dual-task paradigms involving working memory and postural control and will investigate neural activation patterns associated with working memory capacity (central processing constraints) and stimulus-response modality mappings. We will then train dual-task performance in 60 older adults in either compatible or incompatible modality mappings. Our results will elucidate underlying mechanisms of decline in both working memory capacity and in dual-task performance involving postural control, and will inform both theoretical accounts of modality compatibility as well as future training and falls prevention studies in older adults.

Zusammenfassung

Altersbezogene Verluste in Gleichgewichtskontrolle und Arbeitsgedächtnisleistung sowie der simultanen Ausführung von Aufgaben (Doppelaufgaben) haben für Alltagsaktivitäten und kritische Ereignisse wie Stürze eine zentrale Bedeutung. Dabei ist die Gleichgewichtskontrolle ein multimodales System, das von altersbezogenen Veränderungen in Kognition und Sensomotorik beeinflusst wird. Ausgehend von Theorien zu Doppelaufgabenprozessen zur Vereinbarkeit von Reiz-Reaktions-Zuordnungen im Arbeitsgedächtnis (zum Beispiel erleichtern visuelle Reize motorische Reaktionen, d.h. sind kompatibel) konnten wir in der ersten Phase des Schwerpunktprogramms zeigen, dass Reiz-Reaktions-Zuordnungen die Doppelaufgabenperformanz hinsichtlich der Gleichgewichtskontrolle bei jungen und älteren Erwachsenen beeinflussen, und dass diese Effekte mit Aktivierungsveränderungen im lateralen präfrontalen Kortex (PFC) einhergehen. Um die Interaktion zwischen Effekten auf das Gleichgewicht durch verminderte zentrale Ressourcen in Abgrenzung von Effekten von Reiz-Reaktions-Zuordnungen mit dem Alter besser zu verstehen, wollen wir in der zweiten Phase des Schwerpunktprogramms Effekte von ressourcenspezifischer Ermüdung zusammen mit Effekten von Reiz-Reaktions-Zuordnungen untersuchen. Wir werden anhand von zwei experimentellen Serien zur ressourcenspezifischen Ermüdung (körperliche vs. mentale Ermüdung) Alterseffekte kompatibler gegenüber inkompatibler Reiz-Reaktions-Zuordnungen innerhalb des Arbeitsgedächtnisses und Effekte der zentralen Arbeitsgedächtniskapazität auf die Doppelaufgabenperformanz in der Gleichgewichtskontrolle untersuchen. Wir sagen für die körperliche Ermüdung ähnliche relative Effekte auf das Gleichgewicht bei jungen und älteren Erwachsenen vorher, aber erwarten spezifische Effekte modalitätsinkompatibler Reiz-Reaktions-Zuordnungen auf das Arbeitsgedächtnis im Alter. Mentale Ermüdung sollte in beiden Altersgruppen die relative Arbeitsgedächtnisleistung beeinflussen, aber wir erwarten selektive Effekte auf die Gleichgewichtskontrolle im Alter. Experimentelle Messungen von Arbeitsgedächtnis und Gleichgewicht in Doppelaufgaben gehen hier mit neuronalen Erfassungen von Gehirnaktivierung mittels funktioneller Magnetresonanztomographie und Elektroenzephalographie (EEG) einher. Wir erwarten Effekte ressourcenspezifischer Ermüdung in der doppelaufgabenspezifischen Aktivierung im PFC und Veränderungen im Alpha und Theta Band im EEG zusammen mit selektiven Effekten körperlicher Ermüdung bei älteren Erwachsenen.
Die Untersuchung ressourcenspezifischer Ermüdung und der Kompatibilität von Reiz-Reaktions-Zuordnungen im Alter soll so die Mechanismen altersbezogener kompensatorischer Prozesse bei Doppelaufgaben in der Gleichgewichtskontrolle besser erklären und gezielte Interventionen für ältere Erwachsene informieren helfen.
(DFG- Projektnummer 274922926)

Zusammenfassung

Age-related decrements in postural control and working memory as well as dual-task performance have ample significance for everyday activities and critical outcomes such as falls. Postural control reflects a multimodal system affected by age-related changes in cognition, sensory input, as well as muscular output. Based on models of content-specific interference (i.e. modality compatibility) as well as models of limited central capacities, during the first period of this priority program, we addressed the question whether the compatibility of input and output modality mappings (i.e. that visual input and motor output are deemed compatible, while e.g. auditory input and motor output are deemed incompatible) differentially affect dual-tasks involving postural control. Overall, we were able to show that modality-specific interference affects continuous dual-task performance in young and more so in old adults, and that these age differences are related to compensatory mechanisms in the lateral prefrontal cortex (PFC).In order to investigate the interaction between central processing limitations and effects of modality compatibility, the current proposal will examine the effects of domain-specific resource depletion operationalized as fatigue interventions on modality-specific cognitive-motor dual-task performance. For this purpose, two experimental series with two domain-specific fatigue interventions (physical vs. mental fatigue) will be launched that i) disentangle the effects of physical and mental fatigue on cognitive-postural performance during dual-task stimulus-response modality compatibility conditions in healthy young and old adults and ii) delineate brain mechanisms underlying these effects. We hypothesize that physical fatigue results in similar relative declines in postural control in young and old adults, but we expect greater physical fatigue-related performance declines with increasing modality incompatibility in old age. Mental fatigue should affect relative cognitive performance in both age groups, but we expect selective age-related effects of mental fatigue with increasing modality incompatibility in postural control due to age-related central resource limitations and larger attentional demands.Behavioral cognitive and motor measures will be complemented by neuronal markers (electroencephalography EEG, functional magnetic resonance imaging fMRI) to assess these effects, and we expect fatigue to suppress dual-task related fMRI activity in PFC regions, and increase alpha and theta band power in EEG in young and old adults, with selective effects of physical fatigue in the old age group. In sum, the investigation of the effects of physical vs. mental fatigue and modality compatibility on cognitive-motor dual-task performance in young and old adults may shed further light on the mechanisms underlying age-related decline and compensatory mechanisms in cognitive-motor multitasking and may inform targeted interventions in old age.
(DFG- Project number 274922926)