Linking the impact of aging on visual short-term memory capacity with changes in the structural connectivity of posterior thalamus to occipital cortices

Aging impacts both visual short-term memory (vSTM) capacity and thalamo-cortical connectivity. According to the Neural Theory of Visual Attention, vSTM depends on the structural connectivity between posterior thalamus and visual occipital cortices (PT-OC). We tested whether aging modifies the association between vSTM capacity and PT-OC structural connectivity. To do so, 66 individuals aged 20–77 years were assessed by diffusion-weighted imaging used for probabilistic tractography and performed a psychophysical whole-report task of briefly presented letter arrays, from which vSTM capacity estimates were derived. We found reduced vSTM capacity, and aberrant PT-OC connection probability in aging. Critically, age modified the relationship between vSTM capacity and PT-OC connection probability: in younger adults, vSTM capacity was negatively correlated with PT-OC connection probability while in older adults, this association was positive. Furthermore, age modified the microstructure of PT-OC tracts suggesting that the inversion of the association between PT-OC connection probability and vSTM capacity with aging might reflect age-related changes in white-matter properties. Accordingly, our results demonstrate that age-related differences in vSTM capacity links with the microstructure and connectivity of PT-OC tracts

Using neuro-cognitive modelling to link attention deficits to structural and functional brain changes

‘Visual attention’ is an emerging property of interconnected neural networks, in which the interconnections are biased to promote targets over distracting stimuli. It has been shown that efficiency of the attention system is lost after many kinds of brain damage, with each presumably effecting different aspects of basic visual attention functions. Yet, our understanding of these processes is limited by the methodological shortcomings of classical neuropsychological assessment. The overarching goal of the current thesis was to overcome these constrains and thereby extend the link between attention deficits and underlying brain changes. The here used approach incorporates parametric measurement of visual attention derived from the computational Theory of Visual Attention (TVA, Bundesen, 1990) and modern magnetic resonance imaging techniques. Project 1 of the current thesis applied a combined TVA–neuroimaging analysis in a neurodevelopmental model (preterm birth) to relate attention deficits with changes in functional connectivity networks. We found that pre- versus full-term born adults show a selective reduction of visual short-term memory capacity. The remarkable changes we observed in attention-related large-scale brain networks of the occipital and posterior parietal cortices were most pronounced in those preterm born individuals with the most preserved attention functions. This finding was interpreted as evidence for a compensatory reorganization of functional connectivity in order to ameliorate the advert consequences of preterm birth on visual short-term memory. Project 2 of this thesis applied a combined TVA-neuroimaging analysis in a neurodegenerative model (posterior cortical atrophy) to relate attention deficits with structural changes in grey and white matter morphometry. Compared to healthy control participants, patients with posterior cortical atrophy suffered from a selective disturbance of visual processing speed. The individual rate of processing speed slowing was a valid predictor for the severity of simultanagnosia, the core symptom in this clinical condition. We further found wide-spread atrophy in occipital as well as parietal and to a smaller degree in temporal brain areas. White matter degeneration in the superior parietal lobe, rather than atrophy of any grey matter cluster, was significantly associated with patients’ impaired processing speed. Based on these results we propose that disruption of white matter pathways especially within the superior parietal lobe leads to reduced processing speed which then results in the overt clinical symptoms of simultanagnosia. Altogether, projects of the current thesis expanded the link between specific attention deficits and underlying brain damage by using neuro-cognitive modelling. We demonstrated that parametric measurements of attention facilitate, in the role of intermediate cognitive constructs, the mapping between etiological factors and behavioral outcomes. Identifying predictable behavior-brain relationships in attention disorders may offer new perspectives for diagnosis and treatment. The clinical application of an integrated TVA-neuroimaging analysis could additionally compliment insights from healthy participants toward understanding the principles of normal visual attention as well as identifying their neuronal basis

The relevance of posterior thalamo-cortical connectivity for visual short-term memory capacity

Visual short-term memory (vSTM) capacity represents the maximum number of visual items that can be perceived and stored into vSTM. One way to measure it is by using simple psycho-physical experiments together with the theory of visual attention (TVA) computational framework in which visual processing is conceived as a race between objects to be consciously perceived and stored into vSTM. The neural theory of visual attention (NTVA), which gives an interpretation of the TVA at both the cellular and systemic level, suggests that recurrent loops between posterior thalamus and visual cortices are relevant for vSTM capacity. Nevertheless, no clear evidence for the role of posterior thalamus and its connection to visual cortices in vSTM capacity has been found thus far. This thesis investigated the role of posterior thalamo-cortical connectivity in vSTM capacity in healthy young individuals as well as in two populations that have shown to exhibit both vSTM capacity impairments and posterior cortical and subcortical white matter damages: healthy aging and premature birth. We found that vSTM capacity in healthy young adults was significantly associated with the tracts connecting posterior thalamus to occipital cortices and their microstructure. However, this association was modified in elderly individuals and in young adults born prematurely, in which the recruitment of additional, cortico-cortical, tracts, takes place. Together, these findings bring the first structural evidence for the NTVA model with respect to the relevance of posterior thalamo-cortical tracts for vSTM capacity and show how alterations of these tracts affect vSTM capacity

Using neuro-cognitive modelling to link attention deficits to structural and functional brain changes

‘Visual attention’ is an emerging property of interconnected neural networks, in which the interconnections are biased to promote targets over distracting stimuli. It has been shown that efficiency of the attention system is lost after many kinds of brain damage, with each presumably effecting different aspects of basic visual attention functions. Yet, our understanding of these processes is limited by the methodological shortcomings of classical neuropsychological assessment. The overarching goal of the current thesis was to overcome these constrains and thereby extend the link between attention deficits and underlying brain changes. The here used approach incorporates parametric measurement of visual attention derived from the computational Theory of Visual Attention (TVA, Bundesen, 1990) and modern magnetic resonance imaging techniques. Project 1 of the current thesis applied a combined TVA–neuroimaging analysis in a neurodevelopmental model (preterm birth) to relate attention deficits with changes in functional connectivity networks. We found that pre- versus full-term born adults show a selective reduction of visual short-term memory capacity. The remarkable changes we observed in attention-related large-scale brain networks of the occipital and posterior parietal cortices were most pronounced in those preterm born individuals with the most preserved attention functions. This finding was interpreted as evidence for a compensatory reorganization of functional connectivity in order to ameliorate the advert consequences of preterm birth on visual short-term memory. Project 2 of this thesis applied a combined TVA-neuroimaging analysis in a neurodegenerative model (posterior cortical atrophy) to relate attention deficits with structural changes in grey and white matter morphometry. Compared to healthy control participants, patients with posterior cortical atrophy suffered from a selective disturbance of visual processing speed. The individual rate of processing speed slowing was a valid predictor for the severity of simultanagnosia, the core symptom in this clinical condition. We further found wide-spread atrophy in occipital as well as parietal and to a smaller degree in temporal brain areas. White matter degeneration in the superior parietal lobe, rather than atrophy of any grey matter cluster, was significantly associated with patients’ impaired processing speed. Based on these results we propose that disruption of white matter pathways especially within the superior parietal lobe leads to reduced processing speed which then results in the overt clinical symptoms of simultanagnosia. Altogether, projects of the current thesis expanded the link between specific attention deficits and underlying brain damage by using neuro-cognitive modelling. We demonstrated that parametric measurements of attention facilitate, in the role of intermediate cognitive constructs, the mapping between etiological factors and behavioral outcomes. Identifying predictable behavior-brain relationships in attention disorders may offer new perspectives for diagnosis and treatment. The clinical application of an integrated TVA-neuroimaging analysis could additionally compliment insights from healthy participants toward understanding the principles of normal visual attention as well as identifying their neuronal basis

The relevance of posterior thalamo-cortical connectivity for visual short-term memory capacity

Visual short-term memory (vSTM) capacity represents the maximum number of visual items that can be perceived and stored into vSTM. One way to measure it is by using simple psycho-physical experiments together with the theory of visual attention (TVA) computational framework in which visual processing is conceived as a race between objects to be consciously perceived and stored into vSTM. The neural theory of visual attention (NTVA), which gives an interpretation of the TVA at both the cellular and systemic level, suggests that recurrent loops between posterior thalamus and visual cortices are relevant for vSTM capacity. Nevertheless, no clear evidence for the role of posterior thalamus and its connection to visual cortices in vSTM capacity has been found thus far. This thesis investigated the role of posterior thalamo-cortical connectivity in vSTM capacity in healthy young individuals as well as in two populations that have shown to exhibit both vSTM capacity impairments and posterior cortical and subcortical white matter damages: healthy aging and premature birth. We found that vSTM capacity in healthy young adults was significantly associated with the tracts connecting posterior thalamus to occipital cortices and their microstructure. However, this association was modified in elderly individuals and in young adults born prematurely, in which the recruitment of additional, cortico-cortical, tracts, takes place. Together, these findings bring the first structural evidence for the NTVA model with respect to the relevance of posterior thalamo-cortical tracts for vSTM capacity and show how alterations of these tracts affect vSTM capacity

Effects of Choir Singing and Ageing in the Brain: A Voxel-Based and Surface-Based Morphometry Study

Objectives. Ageing is accompanied by neurobiological changes, such as changes in grey matter (GM) volume and cortical thickness, that mediate a gradual cognitive decline, which can, in turn, be potentially offset by stimulating leisure activities. Choir singing is an especially feasible musical activity with positive effects on physiological, psychological, cognitive, and social functioning in old age. Research investigating the effects of choir singing on the ageing brain is limited. As part of the Brain, Ageing, and Vocal Expression (BRAVE) project, this study aimed to investigate the effect of ageing and choir singing on GM structure. Methods. Using a cross-sectional design and voxel-based morphometry (VBM) and surface-based morphometry (SBM), this study compared GM structure between young (20-39 years; n=35), middle-aged (40-59 years; n=34), and old (60-90 years; n=31) participants and investigated the interaction of age and choir singing on GM structure with amateur choir singer (n=54) and controls (n=46). Results and conclusions. Age had a significant and widespread effect on GM structure, with old participants showing lower GM volume and cortical thickness than young (in bilateral sensorimotor, auditory/language, visual, and limbic areas, midbrain, and cerebellum) and middle-aged (in right visual cortex, thalamus, hippocampus and left auditory cortex) participants. Middle-aged participants also showed lower GM volume and cortical thickness than young participants (in bilateral sensorimotor, language, and visual areas, basal ganglia, cerebellum, and right hippocampus and amygdala). These results corroborate the current understanding of neurobiological ageing. No significant interaction of age and choir singing was found on GM structure, which could be explained by methodological factors. Further research is needed to determine whether choir singing can support brain structure or function across healthy ageing

The meditative mind: a comprehensive meta-analysis of MRI studies

Over the past decade mind and body practices, such as yoga and meditation, have raised interest in different scientific fields; in particular, the physiological mechanisms underlying the beneficial effects observed in meditators have been investigated. Neuroimaging studies have studied the effects of meditation on brain structure and function and findings have helped clarify the biological underpinnings of the positive effects of meditation practice and the possible integration of this technique in standard therapy. The large amount of data collected thus far allows drawing some conclusions about the neural effects of meditation practice. In the present study we used activation likelihood estimation (ALE) analysis to make a coordinate-based meta-analysis of neuroimaging data on the effects of meditation on brain structure and function. Results indicate that meditation leads to activation in brain areas involved in processing self-relevant information, self-regulation, focused problem-solving, adaptive behavior, and interoception. Results also show that meditation practice induces functional and structural brain modifications in expert meditators, especially in areas involved in self-referential processes such as self-awareness and self-regulation. These results demonstrate that a biological substrate underlies the positive pervasive effect of meditation practice and suggest that meditation techniques could be adopted in clinical populations and to prevent disease