Functional brain networks and their structural underpinnings in the aging brain
1Donders Institute, Radboud University, The Netherlands; 2Umeå Center for Functional Brain Imaging (UFBI), Umeå University, Sweden; 3Department of Integrative Medical Biology, Umeå University, Sweden; 4Wallenberg Centre for Molecular Medicine (WCMM), Umeå University, Sweden; 5Department of Experimental Psychology, Ghent University, Belgium; 6Department of Neurology, Duke University, USA; 7Aging Research Center (ARC), Karolinska Institutet, Sweden
For adequate cognitive function, it is essential that there is efficient and effective communication between various brain regions and systems. By investigating coherent signal changes in different brain regions, we can disentangle functional networks; brain regions that tend to show high connectivity to each other and less connectivity to other regions. In this presentation I will use both cross sectional and longitudinal data to show how functional networks change with aging and how these changes are related to differences in structural connectivity. A hallmark of the age-related changes in functional networks, is that different functional networks become less segregated with age, caused by a decrease of within network connectivity and an increase in between network connections. This loss of segregation has implications for cognitive abilities in older adults. Previous studies have shown that functional connectivity is party, but not fully dependent of structural connectivity. And indeed our results show a weak but significant association between segregation and white matter integrity. We also investigated regional differences in the coupling between structural and functional connectivity and how they differ with age. Several clusters of brain regions show prominent age-related structure-function uncoupling, suggesting a gradual divergence between brain structure and function with advancing age. Together, these findings show that there is a complex interplay between age-related changes in brain structure, function and cognition.
The role of domain-general networks in semantic processing in the young and the aging brain
1Lise Meitner Research Group Cognition and Plasticity, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; 2Language & Aphasia Laboratory, Department of Neurology, University of Leipzig Medical Center, Leipzig, Germany
Aging is characterized by a decline of cognitive control functions (Hedden & Gabrieli, 2004). In semantic cognition, this leads to the paradox that older adults usually show poorer task performance than young adults despite their greater semantic knowledge (Verhaegen, 2003). So far, it is poorly understood which neural changes in task-related activity and functional connectivity underlie these behavioral differences. We investigated the age-dependent contribution of domain-general networks to a verbal semantic fluency task in a neuroimaging study. Generalized and modified psycho-physiological interaction (PPI) analyses were applied to examine functional connections between the strongest task-related activation peaks. Furthermore, the relationship between functional connectivity and behavior was investigated. While univariate analyses revealed activation in the multiple-demand system and deactivation in the default mode system during semantic fluency, functional connectivity results demonstrated a strong interaction of these domain-general networks in both groups. This finding suggests that the functional coupling of usually anti-correlated networks is critical for successful task processing, independent of age, when access to semantic memory is required. Strikingly, we found differences in the predictive behavioral relevance of within- and between-network connectivity between groups. Only young adults capitalized on the positive integration of task-relevant networks. This was evident in the form of better processing efficiency during semantic fluency and improved semantic memory. Our results lend novel support to the notion of reduced efficiency due to neural dedifferentiation with age. We demonstrate that an age-related performance decline in semantic cognition is associated with reduced flexibility in the goal-directed functional coupling of task-relevant networks.
Age-related differences at the neural network level underlying the semantic predictability gain under challenging listening conditions
1Lise Meitner Research Group Cognition and Plasticity, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig; 2Department of Psychology, University of Lübeck, Lübeck
Speech comprehension is often challenged by increased background noise, but can be facilitated via the semantic context of a sentence (‘predictability gain’). Previous work demonstrated the contribution of specialized semantic areas as well as domain-general support regions under challenging listening conditions. The recruitment of these areas may change with age. However, the functional interplay between semantic and domain-general areas during challenging listening conditions remains elusive. In young listeners, we could show that the predictability gain was associated with increased inhibition in the cingulo-opercular network. Here, we investigate age-related differences in network interactions under challenging listening conditions.
26 healthy young (19-29 years) and 26 healthy middle-aged and older participants (50-77 years) listened to and repeated sentences with varying semantic predictability and intelligibility during functional neuroimaging. Signal-to-noise ratio was tailored to individual hearing abilities. Psychometric curves, reflecting the behavioural predictability gain across intelligibility levels, did not differ between age groups. Task-related neural activity largely overlapped for both groups. Both groups exhibited increased effective connectivity from left anterior insula to left posterior middle temporal gyrus when highly predictable sentences became more intelligible. However, only young participants showed increased connectivity from left posterior middle temporal gyrus to pre-SMA when low predictable sentences became more intelligible. These findings show that, after controlling for individual hearing abilities, younger and older participants largely recruit the same brain regions. The observed differences in effective connectivity between semantic and domain-general areas may suggest less efficient coupling between networks in the aging brain.
Behavioral and neural effects of tDCS assisted cognitive training interventions in older adults with and without cognitive impairment
Universitätsmedizin Greifswald, Deutschland
The older population worldwide is growing, therefore the prevalence of age-related diseases such as Alzheimer’s disease increases. Thus, the development of non-invasive, cost-efficient interventions against age-associated cognitive decline is highly important. Non-invasive brain stimulation techniques, especially in combination with cognitive training interventions, may present a promising means to modulate cognitive functions and encourage neural plasticity. Addressing this matter, I will introduce a multi-session intensive cognitive training intervention combined with transcranial direct current stimulation in healthy older adults and patients with prodromal Alzheimer’s disease. I will present data from our group, exploring direct training effects, transfer to non-trained domains and long-term effects of the intervention. Moreover, I will discuss possible plasticity-inducing effects of combined brain stimulation and visuo-spatial memory training by presenting structural and functional MRI data. I will further discuss the data in relation to possible factors predicting efficiency of combined training and tDCS interventions in age-related cognitive decline. As an outlook I will present possible home-based applications of tDCS plus training interventions. Taken together, understanding the effects of tDCS and cognitive training in populations with age-related cognitive decline and investigating underlying neural effects may valuably contribute to developing novel approaches to counteract cognitive decline in healthy and pathological aging.