Behavioral and fMRI evidence that arousal enhances bottom-up selectivity in young but not older adults

Functional locus coeruleus imaging to investigate an ageing noradrenergic system

The locus coeruleus (LC), our main source of norepinephrine (NE) in the brain, declines with age and is a potential epicentre of protein pathologies in neurodegenerative diseases (ND). In vivo measurements of LC integrity and function are potentially important biomarkers for healthy ageing and early ND onset. In the present study, high-resolution functional MRI (fMRI), a reversal reinforcement learning task, and dedicated post-processing approaches were used to visualise age differences in LC function (N = 50). Increased LC responses were observed during emotionally and task-related salient events, with subsequent accelerations and decelerations in reaction times, respectively, indicating context-specific adaptive engagement of the LC. Moreover, older adults exhibited increased LC activation compared to younger adults, indicating possible compensatory overactivation of a structurally declining LC in ageing. Our study shows that assessment of LC function is a promising biomarker of cognitive aging.

Eye movements reveal age differences in how arousal modulates saliency priority but not attention processing speed

The arousal-biased competition theory posits that inducing arousal increases attentional priority of salient stimuli while reducing priority of non-pertinent stimuli. However, unlike in young adults, older adults rarely exhibit shifts in priority under increased arousal, and prior studies have proposed different neural mechanisms to explain how arousal differentially modulates selective attention in older adults. Therefore, we investigated how the threat of unpredictable shock differentially modulates attentional control mechanisms in young and older adults by observing eye movements. Participants completed two oculomotor search tasks in which the salient distractor was typically captured by attention (singleton search) or proactively suppressed (feature search). We found that arousal did not modulate attentional priority for any stimulus among older adults nor affect the speed of attention processing in either age group. Furthermore, we observed that arousal modulated pupil sizes and found a correlation between evoked pupil responses and oculomotor function. Our findings suggest age differences in how the locus coeruleus-noradrenaline system interacts with neural networks of attention and oculomotor function.

Parasomnias manifest different phenotypes of sleep-related behaviors in age and sex groups. A YouTube-based video research highlighting the age slope of sleepwalking

STUDY OBJECTIVE

Finding typical patterns - phenotypes - of sleep behaviors characterizing parasomnias in different age and sex groups.

METHODS

We analyzed YouTube videos on sleep-related behaviors likely representing parasomnias. We applied the search terms "sleepwalking", "somnambulism", "sleep eating", "sleep sex", "sleep talking", and "aggression in sleep" in six languages. We classified those persons shown on the videos into estimated biological sex and age (child, adult, elderly) groups. We scored the activity types by a self-made scale and applied binary logistic regression to analyze the association between sleep behaviors versus sex and age groups by the STATA package, providing a 95% confidence interval and the probability of statistical significance.

RESULTS

224 videos (102 women, 68 children, 16 adults, and 40 elderly people) were scored. Elderly people had significantly (P < 0.012) lower odds of sleepwalking compared to adults and children. Adult females performed complex manual activities during sleepwalking more often than males (P < 0.012). Elderly males had 40-fold odds compared to adults and children, to perform aggressive movements and 70-fold odds of complex movements in bed, compared to adults. Elderly people presented emotional behaviors less frequently than adults (P < 0.004), and females showed them twice as often as males. Adults sleep-talked full sentences more often than children and elderly people (P < 0.001).

CONCLUSION

Our results support the existence of age- and sex-specific parasomnia phenotypes, denoting possible safety measures. The remarkably low odds of sleepwalking in the elderly highlight the possibility of different pathomechanisms in higher age groups compared to children.

BRIEF SUMMARY AND STUDY IMPACT

Parasomnias present highly variable clinical forms and often cause injuries. Identifying typical phenotypes may help risk management and imply theoretical conclusions. Our study supports the existence of age-specific parasomnia phenotypes. We found that adult women have a high risk of performing dangerous activities during sleep, and elderly males often move violently in bed, likely representing dream enactment behaviors. Elderly people of both sexes have low odds of sleep ambulation- likely representing somnambulism; compared to adults and children, constituting a descending "age slope" of somnambulism that might reflect different underlying pathomechanisms in children versus adults and the elderly.

Age-related reductions in arousal-enhanced memory are moderated by trait emotion regulation

Emotional arousal is known to enhance episodic memory in young adults. However, compared to valence, little is known about how healthy aging impacts arousal-enhanced memory effects. Furthermore, while emotion regulation is believed to improve with age, it is unclear how individual differences in emotion regulation influence arousal-enhanced memory. In this large-scale online study, we investigated the impact of age and individual differences in emotion regulation on arousal-enhanced memory. During encoding, participants made arousal ratings about negative, neutral, and positive images, and we compared their subsequent memory of high and low-arousal images. We found the impact of emotional arousal on memory was reduced with age, especially for older adults who habitually suppress their emotions. Our findings show that arousal-related memory benefits are reduced with advancing age, and that individual differences in habitual usage of emotion regulation impact these age-related alterations.

The integrity of dopaminergic and noradrenergic brain regions is associated with different aspects of late-life memory performance

Changes in dopaminergic neuromodulation play a key role in adult memory decline. Recent research has also implicated noradrenaline in shaping late-life memory. However, it is unclear whether these two neuromodulators have distinct roles in age-related cognitive changes. Here, combining longitudinal MRI of the dopaminergic substantia nigra-ventral tegmental area (SN-VTA) and noradrenergic locus coeruleus (LC) in younger (n = 69) and older (n = 251) adults, we found that dopaminergic and noradrenergic integrity are differentially associated with memory performance. While LC integrity was related to better episodic memory across several tasks, SN-VTA integrity was linked to working memory. Longitudinally, we found that older age was associated with more negative change in SN-VTA and LC integrity. Notably, changes in LC integrity reliably predicted future episodic memory. These differential associations of dopaminergic and noradrenergic nuclei with late-life cognitive decline have potential clinical utility, given their degeneration in several age-associated diseases.

Effects of Adult Age and Functioning of the Locus Coeruleus Norepinephrinergic System on Reward-Based Learning

Age-related impairments in value representations and updating during decision-making and reward-based learning are often related to age-related attenuation in the catecholamine system such as dopamine (DA) and norepinephrine (NE). However, it is unclear to what extent age-related declines in NE functioning in humans affect reward-based decision-making. We conducted a probabilistic decision-making task and applied a Q-learning model to investigate participants' anticipatory values and value sensitivities. Task-related pupil dilations and locus coeruleus (LC) magnetic resonance imaging (MRI) contrast, which served as a potential window of the LC-NE functions, were assessed in younger and older adults. Results showed that in both choice and feedback phases, younger adults' (N = 42, 22 males) pupil dilations negatively correlated with anticipatory values, indicating uncertainty about outcome probabilities. Uncertainty-evoked pupil dilations in older adults (N = 41, 27 males) were smaller, indicating age-related impairments in value estimation and updating. In both age groups, participants who showed a larger uncertainty-evoked pupil dilation exhibited a higher value sensitivity as reflected in the β parameter of the reinforcement Q-learning model. Furthermore, older adults (N = 34, 29 males) showed a lower LC-MRI contrast than younger adults (N = 25, 15 males). The LC-MRI contrast positively correlated with value sensitivity only in older but not in younger adults. These findings suggest that task-related pupillary responses can reflect age-related deficits in value estimation and updating during reward-based decision-making. Our evidence with the LC-MRI contrast further showed the age-related decline of the LC structure in modulating value representations during reward-based learning.SIGNIFICANCE STATEMENT Age-related impairments in value representation and updating during reward-based learning are associated with declines in the catecholamine modulation with age. However, it is unclear how age-related declines in the LC-NE system may affect reward-based learning. Here, we show that compared with younger adults, older adults exhibited reduced uncertainty-induced pupil dilations, suggesting age-related deficits in value estimation and updating. Older adults showed a lower structural MRI of the LC contrast than younger adults, indicating age-related degeneration of the LC structure. The association between the LC-MRI contrast and value sensitivity was only observed in older adults. Our findings may demonstrate a pioneering model to unravel the role of the LC-NE system in reward-based learning in aging.

Isometric handgrip exercise speeds working memory responses in younger and older adults

Physiological arousal affects attention and memory, sometimes enhancing and other times impairing what we attend to and remember. In the present study, we investigated how changes in physiological arousal-induced through short bursts of isometric handgrip exercise-affected subsequent working memory performance. A sample of 57 younger (ages 18-29) and 56 older (ages 65-85) participants performed blocks of isometric handgrip exercise in which they periodically squeezed a therapy ball, alternating with blocks of an auditory working memory task. We found that, compared with those in a control group, participants who performed isometric handgrip had faster reaction times on the working memory task. Handgrip-speeded responses were observed for both younger and older participants, across working memory loads. Analysis of multimodal physiological responses indicated that physiological arousal increased during handgrip. Our findings suggest that performing short bouts of isometric handgrip exercise can improve processing speed, and they offer testable possibilities for the mechanism underlying handgrip's effects on performance. The potential for acute isometric exercise to temporarily improve processing speed may be of particular relevance for older adults who show declines in processing speed and working memory. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Characterization of an automated method to segment the human locus coeruleus

Following the development of magnetic resonance imaging (MRI) methods to assay the integrity of catecholamine nuclei, including the locus coeruleus (LC), there has been an effort to develop automated methods that can accurately segment this small structure in an automated manner to promote its widespread use and overcome limitations of manual segmentation. Here we characterize an automated LC segmentation approach (referred to as the funnel-tip [FT] method) in healthy individuals and individuals with LC degeneration in the context of Alzheimer's disease (AD, confirmed with tau-PET imaging using [18F]MK6240). The first sample included n = 190 individuals across the AD spectrum from cognitively normal to moderate AD. LC signal assayed with FT segmentation showed excellent agreement with manual segmentation (intraclass correlation coefficient [ICC] = 0.91). Compared to other methods, the FT method showed numerically higher correlation to AD status (defined by presence of tau: Cohen's d = 0.64) and AD severity (Braak stage: Pearson R = -.35, cognitive function: R = .25). In a separate sample of n = 12 control participants, the FT method showed excellent scan-rescan reliability (ICC = 0.82). In another sample of n = 30 control participants, we found that the structure of the LC defined by FT segmentation approximated its expected shape as a contiguous line: <5% of LC voxels strayed >1 voxel (0.69 mm) from this line. The FT LC segmentation shows high agreement with manual segmentation and captures LC degeneration in AD. This practical method may facilitate larger research studies of the human LC-norepinephrine system and has potential to support future use of neuromelanin-sensitive MRI as a clinical biomarker.