Neural markers of attentional parameters in the ageing brain

The studies presented in the current PhD thesis aimed at investigating the neural correlates of distinct aspects of visual attention, i.e., spatial bias, efficiency of top-down control and visual processing speed and how they change with healthy ageing. The presented studies are theoretically grounded on Bundesen's Theory of Visual Attention, which provides a mathematical framework enabling quantifying various visual attention functions as the independent parameters of the model. A more recent neural interpretation of these attentional processes – NTVA – served as a basis for investigating attentional processing in combination with neurophysiological techniques. In the presented thesis, we combined TVA-based partial- and whole-report tasks with briefly presented letter arrays that enable mathematically independent estimations of the attentional parameters with simultaneous EEG recording. Extracting event-related lateralizations (ERL) from the signal provided fine-graded neurophysiological signatures of the attentional processes involved in the tasks. In the first empirical study, we combined a partial report task with ERP measurement and aimed at investigating how attentional spatial bias and top-down control efficiency are reflected in the electrophysiological brain activity of healthy participants of between 20 and 35 years of age. We divided participants into groups with more and less efficient top-down control and left- and rightward spatial bias, respectively. First, an ERL component – the PCN wave – reflecting interindividual differences in top-down control efficiency was identified by comparing participants with more relative to less efficient top-down control. Participants with more, compared to less efficient top-down control showed higher PCN amplitudes. Second, we identified asymmetries in earlier visual ERLs reflecting the direction of the spatial bias by comparing participants with a biastowards left or towards right hemifield. Our results show that these two distinct functions of attention are exclusively reflected by the amplitudes of the distinct ERLs. In the second study, we aimed at investigating whether top-down control efficiency is affected by healthy ageing and whether it is similarly reflected in older adults by the amplitude of the lateralized components PCN and Ppc, as reported for younger adults. To pursue this goal we employed an identical methodology as in the first study to additionally test older adults ranging between 33 and 77 years of age. To control for a potential influence of (the amount of) cognitive reserve, we included crystallized IQ as a common proxy for cognitive reserve in the analyses. We divided participants into individuals with more relative to less efficient top-down control and lower versus higher level of cognitive reserve. We found comparable top-down control efficiency values across age groups and, furthermore, that across all age groups, participants with more efficient top-down control showed higher amplitudes of both the Ppc and the PCN waves. We further found that the amount of cognitive reserve modulated the relation between age, top-down control efficiency, and ERLs amplitudes. More precisely, only in participants with higher crystallized IQ Ppc amplitude was higher in participants with more efficient compared to less efficient top-down control. In contrast, in participants with lower crystallized IQ the PCN amplitude decreased significantly with age. In the third study, we combined a whole report task with ERP assessment. We aimed at investigating whether and how visual processing speed is reflected in the neural activity of the brain as indexed by ERLs, and whether this potential relation is affected by healthy ageing. We assessed visual processing speed in a sample of participants ranging from 20 to 78 years of age. Participants were divided into groups with relatively low versus high visual processing speed. Data revealed that visual processing speed declines with age. Further, we identified two lateralized components indexing individual differences in visual processing speed: N1pc and PCN. Both components had increased amplitudes in participants with higher processing speed. Furthermore, amplitudes of the N1pc was increased and latency of the PCN was delayed in older, compared to younger, participants. These age-related changes in the components reflecting visual processing speed may suggest that younger versus older participants employ different mechanisms while performing the whole-report task. More precisely, younger participants may encode the entire display at the early stage of processing and then select relevant information, whereas older ones rather preselect relevant information during an initial phase. The evidence collected across the three ERP studies provides valuable insights into the relation between efficiency of attentional functions, brain activity, and healthy ageing. We found that trajectories of age-related changes of distinct attentional functions are substantially different. Age also does not affect all electrophysiological correlates of functions of attention equally. Finally, our studies show that the relation between efficiency of attentional functions and their neurophysiological correlates is influenced by the amount cognitive reserve

Neural markers of attentional parameters in the ageing brain

The studies presented in the current PhD thesis aimed at investigating the neural correlates of distinct aspects of visual attention, i.e., spatial bias, efficiency of top-down control and visual processing speed and how they change with healthy ageing. The presented studies are theoretically grounded on Bundesen's Theory of Visual Attention, which provides a mathematical framework enabling quantifying various visual attention functions as the independent parameters of the model. A more recent neural interpretation of these attentional processes – NTVA – served as a basis for investigating attentional processing in combination with neurophysiological techniques. In the presented thesis, we combined TVA-based partial- and whole-report tasks with briefly presented letter arrays that enable mathematically independent estimations of the attentional parameters with simultaneous EEG recording. Extracting event-related lateralizations (ERL) from the signal provided fine-graded neurophysiological signatures of the attentional processes involved in the tasks. In the first empirical study, we combined a partial report task with ERP measurement and aimed at investigating how attentional spatial bias and top-down control efficiency are reflected in the electrophysiological brain activity of healthy participants of between 20 and 35 years of age. We divided participants into groups with more and less efficient top-down control and left- and rightward spatial bias, respectively. First, an ERL component – the PCN wave – reflecting interindividual differences in top-down control efficiency was identified by comparing participants with more relative to less efficient top-down control. Participants with more, compared to less efficient top-down control showed higher PCN amplitudes. Second, we identified asymmetries in earlier visual ERLs reflecting the direction of the spatial bias by comparing participants with a biastowards left or towards right hemifield. Our results show that these two distinct functions of attention are exclusively reflected by the amplitudes of the distinct ERLs. In the second study, we aimed at investigating whether top-down control efficiency is affected by healthy ageing and whether it is similarly reflected in older adults by the amplitude of the lateralized components PCN and Ppc, as reported for younger adults. To pursue this goal we employed an identical methodology as in the first study to additionally test older adults ranging between 33 and 77 years of age. To control for a potential influence of (the amount of) cognitive reserve, we included crystallized IQ as a common proxy for cognitive reserve in the analyses. We divided participants into individuals with more relative to less efficient top-down control and lower versus higher level of cognitive reserve. We found comparable top-down control efficiency values across age groups and, furthermore, that across all age groups, participants with more efficient top-down control showed higher amplitudes of both the Ppc and the PCN waves. We further found that the amount of cognitive reserve modulated the relation between age, top-down control efficiency, and ERLs amplitudes. More precisely, only in participants with higher crystallized IQ Ppc amplitude was higher in participants with more efficient compared to less efficient top-down control. In contrast, in participants with lower crystallized IQ the PCN amplitude decreased significantly with age. In the third study, we combined a whole report task with ERP assessment. We aimed at investigating whether and how visual processing speed is reflected in the neural activity of the brain as indexed by ERLs, and whether this potential relation is affected by healthy ageing. We assessed visual processing speed in a sample of participants ranging from 20 to 78 years of age. Participants were divided into groups with relatively low versus high visual processing speed. Data revealed that visual processing speed declines with age. Further, we identified two lateralized components indexing individual differences in visual processing speed: N1pc and PCN. Both components had increased amplitudes in participants with higher processing speed. Furthermore, amplitudes of the N1pc was increased and latency of the PCN was delayed in older, compared to younger, participants. These age-related changes in the components reflecting visual processing speed may suggest that younger versus older participants employ different mechanisms while performing the whole-report task. More precisely, younger participants may encode the entire display at the early stage of processing and then select relevant information, whereas older ones rather preselect relevant information during an initial phase. The evidence collected across the three ERP studies provides valuable insights into the relation between efficiency of attentional functions, brain activity, and healthy ageing. We found that trajectories of age-related changes of distinct attentional functions are substantially different. Age also does not affect all electrophysiological correlates of functions of attention equally. Finally, our studies show that the relation between efficiency of attentional functions and their neurophysiological correlates is influenced by the amount cognitive reserve

Dual Task Effects on Visual Attention Capacity in Normal Aging

Older adults show higher dual task performance decrements than younger adults. While this is assumed to be related to attentional capacity reductions, the precise affected functions are not specified. Such specification is, however, possible based on the "theory of visual attention" (TVA) which allows for modeling of distinct attentional capacity parameters. Furthermore, it is unclear whether older adults show qualitatively different attentional effects or whether they show the same effects as younger adults experience under more challenging conditions. By varying the complexity of the secondary task, it is possible to address this question. In our study, participants performed a verbal whole report of briefly presented letter arrays. TVA-based fitting of report performance delivered parameters of visual threshold to, processing speed C, and visual short-term memory (VSTM) storage capacity K. Furthermore, participants performed a concurrent motor task consisting of continuous tapping of a (simple or complex) sequence. Both TVA and tapping tasks were performed under single and dual task conditions. Two groups of 30 younger adults each performed either the simple or complex tapping, and a group of 30 older adults performed the simple tapping condition. In older participants, VSTM storage capacity declined under dual task conditions. While no such effect was found in younger subjects performing the simple tapping sequence under dual task conditions, the younger group performing the complex tapping task under dual task conditions also showed a significant VSTM capacity reduction. Generally, no significant effect on other TVA parameters or on tapping accuracy was found. Comparable goodness-of-fit measures were obtained for the TVA modeling data in single and dual tasks, indicating that tasks were executed in a qualitatively similar, continuous manner, although quantitatively less efficiently under dual- compared to single-task conditions. Taken together, our results show that the age-specific effects of motor-cognitive dual task interference are reflected by a stronger decline of VSTM storage capacity. They support an interpretation of VSTM as central attentional capacity, which is shared across visual uptake and concurrent motor performance. Capacity limits are reached earlier, and already under lower motor task complexity, in older compared to younger adults

Diagnostic yield is dependent on monitoring duration. Insights from a full-disclosure mobile cardiac telemetry system

Background: Despite the advancement of electrocardiogram (ECG) monitoring methods, the most important factor influencing diagnostic yield (DY) may still be monitoring duration. Ambulatory ECG monitoring, typically with 24–48 hours duration, is widely used but may result in underdiagnosis of rare arrhythmias.Aims: This study aimed to examine the relationship between the DY and monitoring duration in a large patient cohort and investigate sex and age differences in the presentation of arrhythmias. Methods: The study population consisted of 25 151 patients (57.8% women; median [interquartile range, IQR], 71 [64–78] years), who were examined with mobile cardiac telemetry during 2017 in the United States, using the PocketECGTM that continuously transmits a signal on a beat-to-beat basis. We investigated the occurrence of atrial fibrillation at a burden of both ≤1% (atrial fibrillation [AF], ≤1%) and ≤10% (AF ≤10%), premature ventricular contractions (PVC; >10 000 per 24 hours), non-sustained ventricular tachycardias (nsVT), sustained ventricular tachycardias (VT ≥30 seconds), atrioventricular blocks (AVB), pauses of >3 seconds duration, and bradycardia  (heart rate <40 beats per minute for ≥60 seconds).Results: The median (IQR) recording duration was 15.4, 8.2–28.2) days. The DY increased gradually with monitoring duration for all types of investigated arrhythmias. Compared to DY after up to 30 days of monitoring, a standard 24 hours monitoring resulted in DY for males/females of 20%/18% for AF ≤1%, 29%/28% for AF ≤10%, 45%/40% for PVCs, 17%/11% for nsVT, 17%/11% for VT ≥30 seconds, 49%/42 for AVB, 27%/20% for pauses, 36%/29% for bradycardia. Conclusion: A substantial number of patients suffering from arrhythmias may remain undiagnosed due to insufficient ECG monitoring time

Diagnostic yield is dependent on monitoring duration. Insights from a full-disclosure mobile cardiac telemetry system

Background: Despite the advancement of electrocardiogram (ECG) monitoring methods, the most important factor influencing diagnostic yield (DY) may still be monitoring duration. Ambulatory ECG monitoring, typically with 24–48 hours duration, is widely used but may result in underdiagnosis of rare arrhythmias. Aims: This study aimed to examine the relationship between the DY and monitoring duration in a large patient cohort and investigate sex and age differences in the presentation of arrhythmias. Methods: The study population consisted of 25 151 patients (57.8% women; median [interquartile range, IQR], 71 [64–78] years), who were examined with mobile cardiac telemetry during 2017 in the United States, using the PocketECGTM that continuously transmits a signal on a beat-to-beat basis. We investigated the occurrence of atrial fibrillation at a burden of both ≤1% (atrial fibrillation [AF], ≤1%) and ≤10% (AF ≤10%), premature ventricular contractions (PVC; >10 000 per 24 hours), non-sustained ventricular tachycardias (nsVT), sustained ventricular tachycardias (VT ≥30 seconds), atrioventricular blocks (AVB), pauses of >3 seconds duration, and bradycardia (heart rate <40 beats per minute for ≥60 seconds). Results: The median (IQR) recording duration was 15.4, 8.2–28.2) days. The DY increased gradually with monitoring duration for all types of investigated arrhythmias. Compared to DY after up to 30 days of monitoring, a standard 24 hours monitoring resulted in DY for males/females of 20%/18% for AF ≤1%, 29%/28% for AF ≤10%, 45%/40% for PVCs, 17%/11% for nsVT, 17%/11% for VT ≥30 seconds, 49%/42 for AVB, 27%/20% for pauses, 36%/29% for bradycardia. Conclusion: A substantial number of patients suffering from arrhythmias may remain undiagnosed due to insufficient ECG monitoring time