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- Doctoral Thesis (7)
This Ph.D. dissertation investigates the neurobehavioral, psychological, and cognitive factors influencing postural control and its age-related changes through four studies. Postural control is essential for daily activities, and its decline with age increases fall risk, leading to autonomy loss and reduced quality of life.
The first study (Imani & Godde, 2021) explores how self-efficacy mediates the relationship between falls and autonomy in older adults. While falls negatively impact autonomy, higher self-efficacy reduces this effect. Cognitive function predicts autonomy but does not moderate the relationship between falls and autonomy.
The second study examines the bidirectional link between cognitive and physical function. Results show that cognitive decline affects physical abilities over time and vice versa, highlighting the strong connection between executive function and motor control. This reinforces how cognitive decline, falls, and depressive mood contribute to reduced social participation.
The third study investigates the effects of transcranial direct current stimulation (tDCS) combined with balance training in younger adults. Targeting the sensorimotor cortex and dorsolateral prefrontal cortex (DLPFC), the study assesses how anodal tDCS enhances balance. Resting-state EEG is also explored as a predictor of training effects.
The fourth study extends this research to older adults, revealing age-related differences in neural activation during balance training. Results suggest individualized stimulation protocols may improve balance outcomes.
Overall, these studies emphasize the cognitive-motor link in postural control and propose targeted interventions to enhance balance and autonomy, particularly in older adults at risk of falls.
In our daily life, we are continuously required to learn new motor skills and adapt these skills to new situations, such as during tool-use. Tool-use as one of the hallmark skills in humans serves to functionally extend our body to overcome physical limitations to interact or manipulate other objects or organisms in an environment.
In the present dissertation, I used behavioral and neural oscillation correlates of body schema plasticity during virtual tool-use in young and older adults to investigate the embodiment of virtual tools into the body schema, body image and the association between body ownership and agency as well as their mutual dependency on action-related sensory feedback.
To do so, an arm-shaped virtual tool-use paradigm was employed in order to study forearm sensorimotor body schema, and its level of plasticity in young and older individuals during a sequential motor learning task.
Overall, our findings suggest that virtual tools can be incorporated into the existing body schema of the forearm in younger adults but not in older adults, while showcasing how future work may further disambiguate the contributions of tactile and visual feedback. Additionally, resting-state beta power and task-related theta, alpha and beta power predicts stronger practice effect during virtual tool-use in younger adults compared to older adults.
All together, I conclude that a sense of agency may strongly relate to improvement in tool-use in older adults dependent on practice effect but independent of alterations in the body schema, while ownership did not emerge due to a lack of body schema plasticity. Additionally, I concluded that the stronger practice effect during virtual tool-use training is positively related with resting-state relative beta power, higher task-related relative theta power and lower task-related alpha across frontal, parietal and occipital regions in younger adults but not in older adults.
The present dissertation aimed to contribute to the attempt of decomposing interindividual aging trajectories and to provide empirical evidence about the potential role of brain aging in emotion processing by using different methodological approaches.
Study 1 revealed attenuated arousal-modulated BOLD signals in older adults with low (vs. high) levels of executive functioning, for both negative and positive emotional stimuli in different brain areas, including bilateral premotor area (BA 6), dorsolateral prefrontal cortex, inferior parietal lobule, and left putamen. Functional connectivity of amygdala and visual cortex with various other brain regions was as well found.
Study 2 revealed that brain functioning related to executive functioning moderates the relation between subjective arousal and level of executive functioning. Moderation effects were found for brain activity in several brain regions including lateral and medial frontal cortex, medial temporal cortex, occipital cortex, insula, and cerebellum. Older adults with brain functioning associated with brain aging and low executive functioning showed high levels of positive as well as negative arousal.
Study 3 investigated changes in subjective negative arousal after a 12-month aerobic intervention training. It revealed that, overall, older adults decreased in negative arousal, most likely due to improvements in emotion regulation. However, one subgroup increased in negative arousal. This subgroup showed high levels of executive functioning and compensatory brain activity at T0.
The preliminary results of study 4 revealed that lower white matter in the frontal cortex went along with higher negative arousal.
Models of cognition-based brain networks and functions are enormous in number and intricate in function. However, it is possible to compare modules of hierarchically segregated models against one another and model them based on a range of empirical data.
It is essential to elucidate the neurobiological contribution of executive functions (EFs) to cognitive functions such as decision making (DM) and creative thinking.
The prefrontal cortex (PFC) is associated with several EFs. The PFC is part of a deliberate inhibitory control (IC) network; it is also a central node for problem-solving and the creative ideation process. Nevertheless, several cognitive domains for inhibition and flexibility correspond to distinct cortico-frontal networks. An integrated computational–experimental framework could provide insight into the root of EFs.
This PhD thesis aims to explore the role of models of cognition-related brain networks and functions. The thesis addresses 1) the computational perspective on decision-making and creative thinking and 2) the experimental perspective on creative thinking, supported by relevant peer-reviewed publications.
The computational perspective on DM and creative thinking is concerned with validating computational modeling through spiking neural network (SNN) and connectionist models.
The experimental perspective on creative thinking is concerned with the relationships among creative cognition, creative drive, and their associated neuromodulator systems––a subject on which information has, until now, remained scattered and elusive. The experimental study used a non-invasive brain stimulation method (transcranial direct current stimulation [tDCS]) to examine the role of the inferior frontal gyrus (IFG) in divergent thinking (DT) and whether changes in the activity of the IFGs and IC would mediate variations in DT.
Diverse adaptive visual processing mechanisms allow us to complete simple discrimination and more complex visual search tasks in a wide visual photopic range (> 0.6 cd/m2). Despite extensive research ranging from the psychophysical to neurophysiological disciplines, none has examined how these processes behave in the scotopic and low - mesopic luminance ranges, even though we still utilize these processes daily albeit facing considerable decreases in performance. Characterization of perceptual and environmental limitations are needed. Furthermore, visual performance is often enhanced by innate visual - tactile mechanisms, and if patterned properly, application of additional tactile information could attenuate observed decreases in the low luminance spectral ranges. This dissertation will first demonstrate novel behavioural performance efficiency functions for visual discrimination and visual search as one traverses the scotopic to low - mesopic luminance ranges. Second, will demonstrate how various properties of tactile encoding can either attenuate behavioural deficiencies or even facilitate normal performance. Third, these results are supported from both behavioural (eye tracking) and neurophysiological (event related potential) analyses, isolating critical temporal gating windows with more efficient search patterns mediated via a central - parietal network.
In this work, I studied the organization, development and robustness of cortical, as well as other biological networks, using methods of network analysis. First, I examined the organization of neural systems and important constraints for shaping them. Area positions in the macaque cortical as well as the C. elegans neural networks could be rearranged so that total wiring length can be reduced by up to 64% of the original value. Although causing such non-optimal wiring, long-distance connections help to minimize the number of intermediate nodes, which leads to lower time delay, less interference, and higher synchrony in the network. Second, I observed growth of networks in space. I designed a developmental algorithm that takes into account distance between nodes and which yields networks that are alike various spatial networks from metabolic networks to the German highway system. Such spatial growth can generate networks that are comparable to cat and macaque cortical networks. In addition, the inclusion of time windows for development can lead to a defined cluster architecture. Finally, I analyzed the measurement of robustness in biological networks as well as possible underlying causes for high robustness towards unspecific removal of edges or nodes. The existence of clusters and of highly-connected nodes results in enhanced average-case robustness after removal of edges or nodes. Using multiple lesions, I found that in some cases the effect differed from the effect that was predicted from single lesions. Therefore, multiple lesion analysis could become a framework to predict or explain 'unexpected' effects of experimental lesions (or multiple gene knock-outs in metabolic systems).
The ability to direct attention to different locations in space appears to require the involvement of cortical networks located in the parietal lobe in the human brain. The cognitive deficits of neglect and extinction suggest that the right parietal cortex supports to a greater degree the ability to attend to contralateral space than the left parietal cortex. Using the technique of Transcranial Magnetic Stimulation II conducted a series of experiments aimed at establishing the effectiveness of different experimental paradigms for biasing the attentional function. In another series of experiments, using only behavioral methods without TMS, I studied the nature of the interhemispheric connections and the interactions between the two brain hemispheres by testing the effects of symmetry perception (symmetrical arrangement of the stimuli as well as symmetry of the perceived objects) on performance. Based on the findings from the experiments I was able to delineate a contiguous region in right parietal cortex whose deactivation results in a significant bias of spatial attention towards the ipsilateral side of space, thus confirming the hypothesis that spatial attention is functionally lateralized. The findings also support the idea of the competitive nature of the interactions between the two hemisphere resulting in a dynamic balance in the intact state. This balance can be perturbed by unilateral deactivation, with the right hemisphere being more susceptible to modulation than the left hemisphere, and it can be paradoxically restored by bilateral deactivation. The interhemispheric connections mediate the competitive balance between the two hemispheres by exchanging predominantly excitatory signals, but the facilitation and inhibition effects on performance seem to involve higher-order representations of distributed neural activity, which do not necessarily result in a low-level point-to-point activation exchange between homologous regions in the two hemispheres.
