Age-related changes in midbrain dopaminergic regulation of the human reward system

Age- and sex-driven alterations in alcohol consumption patterns: Role of brain ethanol metabolism and the opioidergic system in the nucleus accumbens

Alcohol consumption leads to significant neurochemical and neurobiological changes, contributing to the development of alcohol use disorders (AUDs), which exhibit sex- and age-dependent variations according to clinical data. However, preclinical studies often neglect these factors when investigating alcohol consumption patterns. In this study, we present data on male and female rats continuously exposed to a 20 % ethanol solution for one month. The animals were divided into two groups based on their age at the onset of drinking (8 and 12 weeks old). Interestingly, 12-week-old males consumed significantly less alcohol than both 12-week-old females and 8-week-old animals, indicating that alcohol consumption patterns vary with sex and age in our model. Additionally, to advance in the study of the neurobiological alterations induced by ethanol intake in the mesocorticolimbic system (MCLS) that may participate in its reinforcing properties and the maintenance of alcohol drinking behavior, we measured catalase activity-an enzyme involved in alcohol metabolism and related to ethanol reinforcement-in the nucleus accumbens (NAc) of these animals. Furthermore, we measured the levels of mu (MOR), kappa (KOR), delta (DOR), and nociceptin (NOP) opioid receptors in the NAc, as the endogenous opioidergic system plays a pivotal role in regulating the MCLS and alcohol reinforcement. MOR levels were lower in high alcohol-consuming groups (8-week-old males and all females). Both DOR and NOP levels decreased with age, whereas KOR levels remained unchanged. Our findings suggest that the age at onset of alcohol consumption critically influences alcohol intake, particularly in males. Additionally, females consistently showed higher alcohol intake regardless of age, highlighting inherent sex-specific differences. The dynamic changes in catalase activity and opioid receptor expression suggest the involvement of these factors in modulating alcohol consumption.

Sex as a Determinant of Age-Related Changes in the Brain

The notion of notable anatomical, biochemical, and behavioral distinctions within male and female brains has been a contentious topic of interest within the scientific community over several decades. Advancements in neuroimaging and molecular biological techniques have increasingly elucidated common mechanisms characterizing brain aging while also revealing disparities between sexes in these processes. Variations in cognitive functions; susceptibility to and progression of neurodegenerative conditions, notably Alzheimer's and Parkinson's diseases; and notable disparities in life expectancy between sexes, underscore the significance of evaluating aging within the framework of gender differences. This comprehensive review surveys contemporary literature on the restructuring of brain structures and fundamental processes unfolding in the aging brain at cellular and molecular levels, with a focus on gender distinctions. Additionally, the review delves into age-related cognitive alterations, exploring factors influencing the acceleration or deceleration of aging, with particular attention to estrogen's hormonal support of the central nervous system.

Memory and automatic processing of valuable information in younger and older adults

People often engage in the selective remembering of valuable or important information, whether strategic and/or automatic. We examined potential age-related differences in the automatic processing of value during encoding on later remembering by presenting participants with words paired with point values (range: 1-10 twice or 1-20) to remember for a later test. On the first three lists, participants were told that they would receive the points associated with each word if they recalled it on the test (their goal was to maximize their score). On the last three lists, we told participants that all words were worth the same number of points if recalled on the tests, thus making the point value paired with each word meaningless. Results revealed that selective memory may be impaired in older adults using procedures with larger value ranges. Additionally, we demonstrated that the automatic effects of value may have a greater effect on younger adults relative to older adults, but there may be instances where older adults also exhibit these automatic effects. Finally, strategic and automatic processes may not be related within each learner, suggesting that these processes may rely on different cognitive mechanisms. This indicates that these processes could be underpinned by distinct cognitive mechanisms: strategic processes might engage higher-level cognitive operations like imagery, while automatic processes appear to be more perceptually driven.

Slowing of Movements in Healthy Aging as a Rational Economic Response to an Elevated Effort Landscape

Why do we move slower as we grow older? The reward circuits of the brain, which tend to invigorate movements, decline with aging, raising the possibility that reduced vigor is due to the diminishing value that our brain assigns to movements. However, as we grow older, it also becomes more effortful to make movements. Is age-related slowing principally a consequence of increased effort costs from the muscles, or reduced valuation of reward by the brain? Here, we first quantified the cost of reaching via metabolic energy expenditure in human participants (male and female), and found that older adults consumed more energy than the young at a given speed. Thus, movements are objectively more costly for older adults. Next, we observed that when reward increased, older adults, like the young, responded by initiating their movements earlier. Yet, unlike the young, they were unwilling to increase their movement speed. Was their reluctance to reach quicker for rewards due to the increased effort costs, or because they ascribed less value to the movement? Motivated by a mathematical model, we next made the young experience a component of aging by making their movements more effortful. Now the young responded to reward by reacting faster but chose not to increase their movement speed. This suggests that slower movements in older adults are partly driven by an adaptive response to an elevated effort landscape. Moving slower may be a rational economic response the brain is making to mitigate the elevated effort costs that accompany aging.

The effect of loss incentives on prospective memory in healthy older adults: study protocol of a randomized controlled trial using ultra-high field fMRI

BACKGROUND

Prospective memory is important for our health and independence but declines with age. Hence, interventions to enhance prospective memory, for example by providing an incentive, may promote healthy ageing. The neuroanatomical correlates of prospective memory and the processing of incentive-related prospective memory changes in older adults are not fully understood. In an fMRI study, we will therefore test whether incentives improve prospective memory in older adults and how prospective memory is processed in the brain in general, and when incentives are provided. Since goals and interests change across adulthood, avoiding losses is becoming more important for older adults than achieving gains. We therefore posit that loss-related incentives will enhance prospective memory, which will be subserved by increased prefrontal and midbrain activity.

METHODS

We will include n = 60 healthy older adults (60-75 years of age) in a randomized, single-blind, and parallel-group study. We will acquire 7T fMRI data in an incentive group and a control group (n = 30 each, stratified by education, age, and sex). Before and after fMRI, all participants will complete questionnaires and cognitive tests to assess possible confounders (e.g., income, personality traits, sensitivity to reward or punishment).

DISCUSSION

The results of this study will clarify whether loss-related incentives can enhance prospective memory and how any enhancement is processed in the brain. In addition, we will determine how prospective memory is processed in the brain in general. The results of our study will be an important step towards a better understanding of how prospective memory changes when we get older and for developing interventions to counteract cognitive decline.

Biphasic patterns of age-related differences in dopamine D1 receptors across the adult lifespan

Age-related alterations in D1-like dopamine receptor (D1DR) have distinct implications for human cognition and behavior during development and aging, but the timing of these periods remains undefined. Enabled by a large sample of in vivo assessments (n = 180, age 20 to 80 years of age, 50% female), we discover that age-related D1DR differences pivot at approximately 40 years of age in several brain regions. Focusing on the most age-sensitive dopamine-rich region, we observe opposing pre- and post-forties interrelations among caudate D1DR, cortico-striatal functional connectivity, and memory. Finally, particularly caudate D1DR differences in midlife and beyond, but not in early adulthood, associate with manifestation of white matter lesions. The present results support a model by which excessive dopamine modulation in early adulthood and insufficient modulation in aging are deleterious to brain function and cognition, thus challenging a prevailing view of monotonic D1DR function across the adult lifespan.

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.

Effort cost of reaching prompts vigor reduction in older adults

As people age, they move slower. Is age-related reduction in vigor a reflection of a reduced valuation of reward by the brain, or a consequence of increased effort costs by the muscles? Here, we quantified cost of movements objectively via the metabolic energy that young and old participants consumed during reaching and found that in order reach at a given speed, older adults expended more energy than the young. We next quantified how reward modulated movements in the same populations and found that like the young, older adults responded to increased reward by initiating their movements earlier. Yet, their movements were less sensitive to increased reward, resulting in little or no modulation of reach speed. Lastly, we quantified the effect of increased effort on how reward modulated movements in young adults. Like the effects of aging, when faced with increased effort the young adults responded to reward primarily by reacting faster, with little change in movement speed. Therefore, reaching required greater energetic expenditure in the elderly, suggesting that the slower movements and reactions exhibited in aging are partly driven by an adaptive response to an elevation in the energetic landscape of effort. That is, moving slower appears to be a rational economic consequence of aging.

Significance statement

Healthy aging coincides with a reduction in speed, or vigor, of walking, reaching, and eye movements. Here we focused on disentangling two opposing sources of aging-related movement slowing: reduced reward sensitivity due to loss of dopaminergic tone, or increased energy expenditure movements related to mitochondrial or muscular inefficiencies. Through a series of three experiments and construction of a computational model, here we demonstrate that transient changes in reaction time and movement speed together offer a quantifiable metric to differentiate between reward- and effort-based alterations in movement vigor. Further, we suggest that objective increases in the metabolic cost of moving, not reductions in reward valuation, are driving much of the movement slowing occurring alongside healthy aging.

The effects of age on the severity of problem drinking: Mediating effects of positive alcohol expectancy and neural correlates

Aging is associated with reduction in the severity of alcohol misuse. However, the psychological and neural mechanisms underlying the age-related changes remain unclear. Here, we tested the hypothesis that age-related diminution of positive alcohol expectancy (AE) mediated the effects of age on problem drinking and investigated the neural correlates of the mediating effects. Ninety-six drinkers 21-85 years of age, including social drinkers and those with mild/moderate alcohol use disorder (AUD), were assessed for global positive (GP) AE and problem drinking, each with the Alcohol Expectancy Questionnaire and Alcohol Use Disorders Identification Test (AUDIT), and with brain imaging during alcohol cue exposure. We processed imaging data with published routines; identified the correlates shared between whole-brain regression against age, GP and AUDIT scores; and performed mediation and path analyses to explore the interrelationships between the clinical and neural variables. The results showed that age was negatively correlated with both GP and AUDIT scores, with GP score completely mediating the correlation between age and AUDIT score. Lower age and higher GP correlated with shared cue responses in bilateral parahippocampal gyrus and left middle occipital cortex (PHG/OC). Further, higher GP and AUDIT scores were associated with shared cue responses in bilateral rostral anterior cingulate cortex and caudate head (ACC/caudate). Path analyses demonstrated models with significant statistical fit and PHG/OC and ACC/caudate each interrelating age to GP and GP to AUDIT scores. These findings confirmed change in positive AE as a psychological mechanism mitigating alcohol misuse as individuals age and highlighted the neural processes of cue-reactivity interrelating age and alcohol use severity.

Gambling and Aging: An Overview of a Risky Behavior

Gambling is a field of study that has grown since the 2000s. Much research has focused on adolescents and youth as a vulnerable population. The rate of aging gamblers is increasing; however, evidence-based knowledge of this population is still too sparse. After introducing the issue (1), this article provides a narrative review of older adults' gambling through three sections: (2) older adult gamblers (age, characteristics, and motivations), (3) gambling as a risky decision-making situation, and (4) gambling disorder related to older adults. By drawing on the existing literature from a problematization perspective, this type of review can highlight complex and original research topics and provoke thought and controversy to generate avenues for future research. This narrative review provides an overview of the existing literature on gambling among older adults and offers perspectives on how aging can affect decision-making and thus gambling for this population. Older adults are a specific population, not only in terms of the consequences of gambling disorders but also in terms of the motivations and cognitions underlying gambling behaviors. Studies on behavioral science focusing on decision-making in older adults could help in the development of public policy in terms of targeted prevention.

Low-Affinity/High-Selectivity Dopamine Transport Inhibition Sufficient to Rescue Cognitive Functions in the Aging Rat

The worldwide increase in cognitive decline, both in aging and with psychiatric disorders, warrants a search for pharmacological treatment. Although dopaminergic treatment approaches represent a major step forward, current dopamine transporter (DAT) inhibitors are not sufficiently specific as they also target other transporters and receptors, thus showing unwanted side effects. Herein, we describe an enantiomerically pure, highly specific DAT inhibitor, S-CE-123, synthetized in our laboratory. Following binding studies to DAT, NET and SERT, GPCR and kinome screening, pharmacokinetics and a basic neurotoxic screen, S-CE-123 was tested for its potential to enhance and/or rescue cognitive functions in young and in aged rats in the non-invasive reward-motivated paradigm of a hole-board test for spatial learning. In addition, an open field study with young rats was carried out. We demonstrated that S-CE-123 is a low-affinity but highly selective dopamine reuptake inhibitor with good bioavailability. S-CE-123 did not induce hyperlocomotion or anxiogenic or stereotypic behaviour in young rats. Our compound improved the performance of aged but not young rats in a reward-motivated task. The well-described impairment of the dopaminergic system in aging may underlie the age-specific effect. We propose S-CE-123 as a possible candidate for developing a tentative therapeutic strategy for age-related cognitive decline and cognitive dysfunction in psychiatric disorders.

Aging in nucleus accumbens and its impact on alcohol use disorders

Ethanol is one of the most widely consumed drugs in the world and prolonged excessive ethanol intake might lead to alcohol use disorders (AUDs), which are characterized by neuroadaptations in different brain regions, such as in the reward circuitry. In addition, the global population is aging, and it appears that they are increasing their ethanol consumption. Although research involving the effects of alcohol in aging subjects is limited, differential effects have been described. For example, studies in human subjects show that older adults perform worse in tests assessing working memory, attention, and cognition as compared to younger adults. Interestingly, in the field of the neurobiological basis of ethanol actions, there is a significant dichotomy between what we know about the effects of ethanol on neurochemical targets in young animals and how it might affect them in the aging brain. To be able to understand the distinct effects of ethanol in the aging brain, the following questions need to be answered: (1) How does physiological aging impact the function of an ethanol-relevant region (e.g., the nucleus accumbens)? and (2) How does ethanol affect these neurobiological systems in the aged brain? This review discusses the available data to try to understand how aging affects the nucleus accumbens (nAc) and its neurochemical response to alcohol. The data show that there is little information on the effects of ethanol in aged mice and rats, and that many studies had considered 2-3-month-old mice as adults, which needs to be reconsidered since more recent literature defines 6 months as young adults and >18 months as an older mouse. Considering the actual relevance of an aged worldwide population and that this segment is drinking more frequently, it appears at least reasonable to explore how ethanol affects the brain in adult and aged models.

Age-related differences in ERP correlates of value-based decision making

This study evaluates age-related differences in the temporal dynamics underlying neural processing of value for decision-making in younger and older adults. We applied a lottery-choice task with event-related potentials to determine how and when brain activity during choice and outcome processing diverge between younger and older adults. Behaviorally, older adults accepted more losing stakes than younger adults. During choice, younger adults evinced higher P2 ERP-response positivity with a later P3 positivity that monotonically increased with low to middle to high win probability. Older adults evinced lower P2 responses and P3 amplitudes with more positivity for high and low relative to middle win probability. Both age groups showed similar feedback-related negativity and late parietal positivity, indicating intact reward prediction error representations and salience integration. Feedback-P3 showed more complex sensitivity to expectancy violations in older than younger adults, suggesting subjective uncertainty about reward expectations. Reduced early general neural processing of objective stimulus value with greater contribution of downstream subjective processes might underlie older adult risk-taking behaviors.

Effects of baclofen on insular gain anticipation in alcohol-dependent patients - a randomized, placebo-controlled, pharmaco-fMRI pilot trial

RATIONALE

One hallmark of addiction is an altered neuronal reward processing. In healthy individuals (HC), reduced activity in fronto-striatal regions including the insula has been observed when a reward anticipation task was performed repeatedly. This effect could indicate a desensitization of the neural reward system due to repetition. Here, we investigated this hypothesis in a cohort of patients with alcohol use disorder (AUD), who have been treated with baclofen or a placebo. The efficacy of baclofen in AUD patients has been shown to have positive clinical effects, possibly via indirectly affecting structures within the neuronal reward system.

OBJECTIVES

Twenty-eight recently detoxified patients (13 receiving baclofen (BAC), 15 receiving placebo (PLA)) were investigated within a longitudinal, double-blind, and randomized pharmaco-fMRI design with an individually adjusted daily dosage of 30-270 mg.

METHODS

Brain responses were captured by functional magnetic resonance imaging (fMRI) during reward anticipation while participating in a slot machine paradigm before (t1) and after 2 weeks of individual high-dose medication (t2).

RESULTS

Abstinence rates were significantly higher in the BAC compared to the PLA group during the 12-week high-dose medication phase. At t1, all patients showed significant bilateral striatal activation. At t2, the BAC group showed a significant decrease in insular activation compared to the PLA group.

CONCLUSIONS

By affecting insular information processing, baclofen might enable a more flexible neuronal adaptation during recurrent reward anticipation, which could resemble a desensitization as previously observed in HC. This result strengthens the modulation of the reward system as a potential mechanism of action of baclofen.

TRIAL REGISTRATION

Identifier of the main trial (the BACLAD study) at clinical.gov: NCT0126665.

Risk-taking in the human brain: An activation likelihood estimation meta-analysis of the balloon analog risk task (BART)

The Balloon Analog Risk Task (BART) is increasingly used to assess risk-taking behavior and brain function. However, the brain networks underlying risk-taking during the BART and its reliability remain controversial. Here, we combined the activation likelihood estimation (ALE) meta-analysis with both task-based and task-free functional connectivity (FC) analysis to quantitatively synthesize brain networks involved in risk-taking during the BART, and compared the differences between adults and adolescents studies. Based on 22 pooled publications, the ALE meta-analysis revealed multiple brain regions in the reward network, salience network, and executive control network underlying risk-taking during the BART. Compared with adult risk-taking, adolescent risk-taking showed greater activation in the insula, putamen, and prefrontal regions. The combination of meta-analytic connectivity modeling with task-free FC analysis further confirmed the involvement of the reward, salience, and cognitive control networks in the BART. These findings demonstrate the core brain networks for risk-taking during the BART and support the utility of the BART for future neuroimaging and developmental research.

Spatial profiles provide sensitive MRI measures of the midbrain micro- and macrostructure

The midbrain is the rostral-most part of the brainstem. It contains numerous nuclei and white matter tracts, which are involved in motor, auditory and visual processing, and changes in their structure and function have been associated with aging, as well as neurodegenerative disorders. Current tools for estimating midbrain subregions and their structure with MRI require high resolution and multi-parametric quantitative MRI measures. We propose an approach that relies on morphology to calculate profiles along the midbrain and show these profiles are sensitive to the underlying macrostructure of the midbrain. First, we show that the midbrain structure can be sampled, within subject space, along three main axes of the left and right midbrain, producing profiles that are similar across subjects. We use two data sets with different field strengths, that contain R1, R2* and QSM maps and show that the profiles are highly correlated both across subjects and between datasets. Next, we compare profiles of the midbrain that sample ROIs, and show that the profiles along the first two axes sample the midbrain in a way that reliably separates the main structures, i.e., the substantia nigra, the red nucleus, and periaqueductal gray. We further show that age differences which are localized to specific nuclei, are reflected in the profiles. Finally, we generalize the same approach to calculate midbrain profiles on a third clinically relevant dataset using HCP subjects, with metrics such as the diffusion tensor and semi-quantitative data such as T1w/T2w maps. Our results suggest that midbrain profiles, both of quantitative and semi-quantitative estimates are sensitive to the underlying macrostructure of the midbrain. The midbrain profiles are calculated in native space, and rely on simple measurements. We show that it is robust and can be easily expanded to different datasets, and as such we hope that it will be of great use to the community and to the study of the midbrain in particular.

Older Barbary macaques show limited capacity for self-regulation to avoid hazardous social interactions

According to the Strength-and-Vulnerability-Integration (SAVI) model, older people are more motivated to avoid negative affect and high arousal than younger people. To explore the biological roots of this effect, we investigate communicative interactions and social information processing in Barbary macaques (Macaca sylvanus) living at 'La Forêt des Singes' in Rocamadour, France. The study combines an analysis of the production of (N = 8185 signals, 84 signallers) and responses to communicative signals (N = 3672 events, 84 receivers) with a field experiment (N = 166 trials, 45 subjects). Here we show that older monkeys are not more likely to specifically ignore negative social information or to employ avoidance strategies in stressful situations, although they are overall less sociable. We suggest that the monkeys have only a limited capacity for self-regulation within social interactions and rather rely on general avoidance strategies to decrease the risk of potentially hazardous social interactions.

Insulin sensitivity in mesolimbic pathways predicts and improves with weight loss in older dieters

Central insulin is critically involved in the regulation of hedonic feeding. Insulin resistance in overweight has recently been shown to reduce the inhibitory function of insulin in the human brain. How this relates to effective weight management is unclear, especially in older people, who are highly vulnerable to hyperinsulinemia and in whom neural target systems of insulin action undergo age-related changes. Here, 50 overweight, non-diabetic older adults participated in a double-blind, placebo-controlled, pharmacological functional magnetic resonance imaging study before and after randomization to a 3-month caloric restriction or active waiting group. Our data show that treatment outcome in dieters can be predicted by baseline measures of individual intranasal insulin (INI) inhibition of value signals in the ventral tegmental area related to sweet food liking as well as, independently, by peripheral insulin sensitivity. At follow-up, both INI inhibition of hedonic value signals in the nucleus accumbens and peripheral insulin sensitivity improved with weight loss. These data highlight the critical role of central insulin function in mesolimbic systems for weight management in humans and directly demonstrate that neural insulin function can be improved by weight loss even in older age, which may be essential for preventing metabolic disorders in later life.

Topographic organization of the human caudate functional connectivity and age-related changes with resting-state fMRI

The striatum is postulated to play a central role in gating cortical processing during goal-oriented behavior. While many human neuroimaging studies have treated the striatum as an undivided whole or several homogeneous compartments, some recent studies showed that its circuitry is topographically organized and has more complex relations with the cortical networks than previously assumed. Here, we took a gradient functional connectivity mapping approach that utilizes the entire anatomical space of the caudate nucleus to examine the organization of its functional relationship with the rest of the brain and how its topographic mapping changes with age. We defined the topography of the caudate functional connectivity using three publicly available resting-state fMRI datasets. We replicated and extended previous findings. First, we found two stable gradients of caudate connectivity patterns along its medial-lateral (M-L) and anterior-posterior (A-P) axes, supporting findings from previous tract-tracing studies of non-human primates that there are at least two main organizational principles within the caudate nucleus. Second, unlike previous emphasis of the A-P topology, we showed that the differential connectivity patterns along the M-L gradient of caudate are more clearly organized with the large-scale neural networks; such that brain networks associated with internal vs. external orienting behavior are respectively more closely linked to the medial vs. lateral extent of the caudate. Third, the caudate's M-L organization showed greater age-related reduction in integrity, which was further associated with age-related changes in behavioral measures of executive functions. In sum, our analysis confirmed a sometimes overlooked M-L functional connectivity gradient within the caudate nucleus, with its lateral longitudinal zone more closely linked to the frontoparietal cortical circuits and age-related changes in cognitive control. These findings provide a more precise mapping of the human caudate functional connectivity, both in terms of the gradient organization with cortical networks and age-related changes in such organization.

Reward System Dysfunction and the Motoric-Cognitive Risk Syndrome in Older Persons

During aging, many physiological systems spontaneously change independent of the presence of chronic diseases. The reward system is not an exception and its dysfunction generally includes a reduction in dopamine and glutamate activities and the loss of neurons of the ventral tegmental area (VTA). These impairments are even more pronounced in older persons who have neurodegenerative diseases and/or are affected by cognitive and motoric frailty. All these changes may result in the occurrence of cognitive and motoric frailty and accelerated progression of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases. In particular, the loss of neurons in VTA may determine an acceleration of depressive symptoms and cognitive and motor frailty trajectory, producing an increased risk of disability and mortality. Thus, we hypothesize the existence of a loop between reward system dysfunction, depression, and neurodegenerative diseases in older persons. Longitudinal studies are needed to evaluate the determinant role of the reward system in the onset of motoric-cognitive risk syndrome.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.

Distinct alterations in cerebellar connectivity with substantia nigra and ventral tegmental area in Parkinson’s disease

In Parkinson’s disease (PD), neurodegeneration of dopaminergic neurons occurs in the midbrain, specifically targeting the substantia nigra (SN), while leaving the ventral tegmental area (VTA) relatively spared in early phases of the disease. Although the SN and VTA are known to be functionally dissociable in healthy adults, it remains unclear how this dissociation is altered in PD. To examine this issue, we performed a whole-brain analysis to compare functional connectivity in PD to healthy adults using resting-state functional magnetic resonance imaging (rs-fMRI) data compiled from three independent datasets. Our analysis showed that across the sample, the SN had greater connectivity with the precuneus, anterior cingulate gyrus, and areas of the occipital cortex, partially replicating our previous work in healthy young adults. Notably, we also found that, in PD, VTA-right cerebellum connectivity was higher than SN-right cerebellum connectivity, whereas the opposite trend occurred in healthy controls. This double dissociation may reflect a compensatory role of the cerebellum in PD and could provide a potential target for future study and treatment.

A bias toward the unknown: individual and environmental factors influencing exploratory behavior

With limited resources, exploring new opportunities is crucial for survival. Exploring novel options, however, comes at the cost of uncertainty. Therefore, there is a trade‐off between exploiting options with a known beneficial outcome and exploring novel options with a potentially higher gain. Computational models have suggested that novelty may promote exploratory behavior by inducing a so‐called novelty bonus through reward‐related processes. So far, few studies have provided behavioral evidence for such a novelty bonus. In this study, we aimed to investigate whether spatial novelty can stimulate exploratory behavior (Experiment 1), and whether age, novelty‐seeking, and reduced action radius or social interactions due to COVID‐19 restrictions influenced the exploration–exploitation trade‐off (Experiment 2). In both experiments, we employed a novel paradigm in which participants made binary decisions between food items, while on rare trials, a surprise option was presented. Results from Experiment 1 are in line with a novelty bonus, with spatial novelty promoting exploratory behavior. In Experiment 2, we found that exploratory behavior declined with age, high novelty seekers made more exploratory choices than low novelty seekers, and participants with a smaller action radius made fewer exploratory choices. These findings are consistent with previous findings in animals and predictions from computational models.

The Acute Effects of Breakfast Drinks with Varying Protein and Energy Contents on Appetite and Free-Living Energy Intake in UK Older Adults

Proposed strategies for preventing protein deficiencies in older patients include increasing protein intake at breakfast. However, protein is highly satiating and the effects of very high protein intakes at breakfast on subsequent appetite and free-living energy intake (EI) in older adults are unclear. This study compared the acute effects of two breakfast drinks varying in protein and energy contents on appetite and free-living EI in healthy older adults using a randomized 2 × 2 crossover design. Participants (n = 48 (20 men, 28 women); mean ± SD age: 69 ± 3 years; BMI: 22.2 ± 2.0 kg·m⁻²; fat-free mass: 45.5 ± 8.0 kg) consumed two drinks for breakfast (high-protein (30.4 ± 5.3 g), low-energy (211.2 ± 37.1 kcal) content (HPLE) and very high-protein (61.8 ± 9.9 g), fed to energy requirements (428.0 ± 68.9 kcal) (VHPER)) one week apart. Appetite perceptions were assessed for 3 h post-drink and free-living EI was measured for the remainder of the day. Appetite was lower in VHPER than HPLE from 30 min onwards (p < 0.01). Free-living energy and protein intake did not differ between conditions (p = 0.814). However, 24 h EI (breakfast drink intake + free-living intake) was greater in VHPER than HPLE (1937 ± 568 kcal vs. 1705 ± 490 kcal; p = 0.001), as was 24 h protein intake (123.0 ± 26.0 g vs. 88.6 ± 20.9 g; p < 0.001). Consuming a very high-protein breakfast drink acutely suppressed appetite more than a low-energy, high-protein drink in older adults, though free-living EI was unaffected. The long-term effects of adopting such a breakfast strategy in older adults at high risk of energy and protein malnutrition warrants exploration.

Reward Processing as an Indicator of Vulnerability or Compensatory Resilience in Psychoses? Results From a Twin Study

Background

Findings of reward disturbances in unaffected relatives of patients with schizophrenia suggest reward disturbances as an endophenotype for schizophrenia. Twin studies, where 1 twin has been diagnosed with a schizophrenia spectrum disorder, can further explore this.

Methods

We used Danish registries to identify twin pairs with at least 1 twin having a schizophrenia spectrum disorder diagnosis and control twin pairs matched on age, sex, and zygosity. The analyses included data from 34 unaffected co-twins (16 females), 42 probands with schizophrenia spectrum disorder (17 females), and 83 control twins (42 females). Participants performed a modified incentive delay task during functional magnetic resonance imaging. Whole-brain group differences were analyzed by performing comparisons between co-twins and control twins. Correlations with cognitive flexibility were tested.

Results

Compared with control twins, co-twins showed no differences in striatal regions, but increased signal in the dorsolateral prefrontal cortex (DLPFC) during missed target contrast was observed. In co-twins, increased DLPFC signal was associated with lower intra-extra dimensional set-shifting scores indicative of higher cognitive flexibility.

Conclusions

Unaffected co-twins did not have decreased striatal activity during anticipation as previously reported for patients with schizophrenia. Instead, they showed increased activity in the DLPFC during evaluation of missed target contrast, which correlated with their level of cognitive flexibility. Unaffected co-twins had no diagnosis at a mean age of 40 years. This could indicate that greater cognitive flexibility and increased activity in the right DLPFC during processing of unexpected negative outcome represents a compensatory resilience mechanism in predisposed twins.

Age-Related Changes in the Role of Social Motivation: Implications for Healthy Aging

Prior research has established the importance of social relations and social embeddedness for motivation in healthy aging. Thus, social orientation appears to be essential for understanding healthy aging. This article focuses particularly on age-related changes in goals concerning social orientation, such as increased prioritization of emotional goals, increased prosociality/altruistic motives, generativity, and ego transcendence. We then consider open questions regarding gaps in the links between goals related to social orientation and healthy aging, as well as the implications of theories and research on social goals for leveraging motivation to promote healthy aging. In particular, interventions to promote healthy behavior in late life may be most effective when they match the themes of older adults' strivings to find meaning and purpose in their personal goals.

Brain activations associated with anticipation and delivery of monetary reward: A systematic review and meta-analysis of fMRI studies

BACKGROUND

While multiple studies have examined the brain functional correlates of reward, meta-analyses have either focused on studies using the monetary incentive delay (MID) task, or have adopted a broad strategy, combining data from studies using both monetary and non-monetary reward, as probed using a wide range of tasks.

OBJECTIVE

To meta-analyze fMRI studies that used monetary reward and in which there was a definable cue-reward contingency. Studies were limited to those using monetary reward in order to avoid potential heterogeneity from use of other rewards, especially social rewards. Studies using gambling or delay discounting tasks were excluded on the grounds that reward anticipation is not easily quantifiable.

STUDY ELIGIBILITY

English-language fMRI studies (i) that reported fMRI findings on healthy adults; (ii) that used monetary reward; and (iii) in which a cue that was predictive of reward was compared to a no win (or lesser win) condition. Only voxel-based studies were included; those where brain coverage was incomplete were excluded.

DATA SOURCES

Ovid, Medline and PsycInfo, from 2000 to 2020, plus checking of review articles and meta-analyses.

DATA SYNTHESIS

Data were pooled using Seed-based d Mapping with Permutation of Subject Images (SDM-PSI). Heterogeneity among studies was examined using the I2 statistic. Publication bias was examined using funnel plots and statistical examination of asymmetries. Moderator variables including whether the task was pre-learnt, sex distribution, amount of money won and width of smoothing kernel were examined.

RESULTS

Pooled data from 45 studies of reward anticipation revealed activations in the ventral striatum, the middle cingulate cortex/supplementary motor area and the insula. Pooled data from 28 studies of reward delivery again revealed ventral striatal activation, plus cortical activations in the anterior and posterior cingulate cortex. There was relatively little evidence of publication bias. Among moderating variables, only whether the task was pre-learnt exerted an influence.

CONCLUSIONS

According to this meta-analysis monetary reward anticipation and delivery both activate the ventral but not the dorsal striatum, and are associated with different patterns of cortical activation.

Ageing is associated with disrupted reinforcement learning whilst learning to help others is preserved

Reinforcement learning is a fundamental mechanism displayed by many species. However, adaptive behaviour depends not only on learning about actions and outcomes that affect ourselves, but also those that affect others. Using computational reinforcement learning models, we tested whether young (age 18-36) and older (age 60-80, total n = 152) adults learn to gain rewards for themselves, another person (prosocial), or neither individual (control). Detailed model comparison showed that a model with separate learning rates for each recipient best explained behaviour. Young adults learned faster when their actions benefitted themselves, compared to others. Compared to young adults, older adults showed reduced self-relevant learning rates but preserved prosocial learning. Moreover, levels of subclinical self-reported psychopathic traits (including lack of concern for others) were lower in older adults and the core affective-interpersonal component of this measure negatively correlated with prosocial learning. These findings suggest learning to benefit others is preserved across the lifespan with implications for reinforcement learning and theories of healthy ageing.

The Biology and Pathobiology of Glutamatergic, Cholinergic, and Dopaminergic Signaling in the Aging Brain

The elderly population is growing worldwide, with important health and socioeconomic implications. Clinical and experimental studies on aging have uncovered numerous changes in the brain, such as decreased neurogenesis, increased synaptic defects, greater metabolic stress, and enhanced inflammation. These changes are associated with cognitive decline and neurobehavioral deficits. Although aging is not a disease, it is a significant risk factor for functional worsening, affective impairment, disease exaggeration, dementia, and general disease susceptibility. Conversely, life events related to mental stress and trauma can also lead to accelerated age-associated disorders and dementia. Here, we review human studies and studies on mice and rats, such as those modeling human neurodegenerative diseases, that have helped elucidate (1) the dynamics and mechanisms underlying the biological and pathological aging of the main projecting systems in the brain (glutamatergic, cholinergic, and dopaminergic) and (2) the effect of defective glutamatergic, cholinergic, and dopaminergic projection on disabilities associated with aging and neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Detailed knowledge of the mechanisms of age-related diseases can be an important element in the development of effective ways of treatment. In this context, we briefly analyze which adverse changes associated with neurodegenerative diseases in the cholinergic, glutaminergic and dopaminergic systems could be targeted by therapeutic strategies developed as a result of our better understanding of these damaging mechanisms.

Temporal discounting in adolescents and adults with Tourette syndrome

Tourette syndrome is a neurodevelopmental disorder associated with hyperactivity in dopaminergic networks. Dopaminergic hyperactivity in the basal ganglia has previously been linked to increased sensitivity to positive reinforcement and increases in choice impulsivity. In this study, we examine whether this extends to changes in temporal discounting, where impulsivity is operationalized as an increased preference for smaller-but-sooner over larger-but-later rewards. We assessed intertemporal choice in two studies including nineteen adolescents (age: mean[sd] = 14.21[±2.37], 13 male subjects) and twenty-five adult patients (age: mean[sd] = 29.88 [±9.03]; 19 male subjects) with Tourette syndrome and healthy age- and education matched controls. Computational modeling using exponential and hyperbolic discounting models via hierarchical Bayesian parameter estimation revealed reduced temporal discounting in adolescent patients, and no evidence for differences in adult patients. Results are discussed with respect to neural models of temporal discounting, dopaminergic alterations in Tourette syndrome and the developmental trajectory of temporal discounting. Specifically, adolescents might show attenuated discounting due to improved inhibitory functions that also affect choice impulsivity and/or the developmental trajectory of executive control functions. Future studies would benefit from a longitudinal approach to further elucidate the developmental trajectory of these effects.

The impact of dietary macronutrient intake on cognitive function and the brain

Macronutrients - carbohydrates, fats, and proteins - supply the nutrients required for optimal functioning. Inadequate intake compromises both physical and brain health. We synthesized research on macronutrients from whole meals on cognitive function in healthy adults and identified underlying mechanisms. Intake of simple carbohydrates ('sugars') is consistently associated with decreased global cognition whereas consumption of complex carbohydrates correlates with successful brain aging and improved memory both in the short- and long-term. Saturated fatty acid intake correlates with decreased memory and learning scores whereas omega-3 intake correlates positively with memory scores. Protein intake boosts executive function and working memory when task-demands are high. Individual differences affecting the macronutrient-cognition relationship are age, physical activity, and glucose metabolism. Neural correlates reflect findings on cognitive functions: cortical thickness and cerebral amyloid burden correlate with sugar intake, inflammatory status and cerebral glucose metabolism correlate with fatty acid intake. Key mechanisms by which dietary macronutrients affect the brain and cognition include glucose and insulin metabolism, neurotransmitter actions, and cerebral oxidation and inflammation. In conclusion, macronutrient intake affects cognitive function both acutely and in the long-term, involving peripheral and central mechanisms. A healthy diet supports brain integrity and functionality, whereas inadequate nutrition compromises it. Studying diet can be key to nutritional recommendations, thereby improving the landscape of mental health and healthy brain aging.

Reconsidering delay discounting in bulimia nervosa

Delay discounting measures one's preference for smaller-sooner versus larger-later reward and is a facet of impulsivity. Studying delay discounting in bulimia nervosa (BN) may enhance clinical understanding of BN, as BN is characterized by engagement in behaviors that provide immediate reward (i.e., binge eating, purging) at the expense of future well-being. Prior research suggests that individuals with BN prefer smaller amounts of money available sooner compared to psychiatrically healthy (HC) persons. Here, we aimed to replicate and extend previous work by studying delay discounting of both monetary and food reward in women with BN relative to HC women. We also compared delay discounting of monetary and food reward, and examined associations among delay discounting, trait impulsivity, and eating disorder symptom expression in women with BN. Participants were 20 women with sub- or full-threshold DSM-5 BN and 20 HC women who completed a diagnostic interview, paper-and-pencil measures of delay discounting of monetary and food commodities, and a measure of trait impulsivity. Contrary to previous work, we found that women with BN showed decreased delay discounting of monetary and food reward relative to HC women. Within-group analyses demonstrated that women with BN showed elevated delay discounting of food reward relative to monetary reward. Within women with BN, elevated delay discounting of food, but not money, was associated with elevated negative and positive urgency, two facets of trait impulsivity that relate to acting rashly when experiencing strong emotion. Results suggest that delay discounting may be more variable in BN than previously assumed.

Effects of aging on the cholinergic innervation of the rat ventral tegmental area: A stereological study

Dopamine neurons in the ventral tegmental area (VTA) play a main role in processing both rewarding and aversive stimuli, and their response to salient stimuli is significantly shaped by afferents originating in the brainstem cholinergic nuclei. Aging is associated with a decline in dopaminergic activity and reduced response to positive reinforcement. We have used stereological techniques to examine, in adult and aged rats, the dopaminergic neurons and the cholinergic innervation of the VTA, and the cholinergic populations of the pedunculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei, which are the only source of cholinergic inputs to the VTA. In the VTA, there were no age-related variations in the number and size of tyrosine hydroxylase (TH)-immunoreactive neurons, but the density of cholinergic varicosities was reduced in aged rats. The total number of choline acetyltransferase (ChAT)-immunoreactive neurons in the PPT and LDT was unchanged, but their somas were hypertrophied in aged rats. Our results suggest that dysfunction of the cholinergic system might contribute for the age-associated deterioration of the brain reward system.

Human aging alters social inference about others' changing intentions

Decoding others' intentions accurately in order to adapt one's own behavior is pivotal throughout life. In this study, we asked how younger and older adults deal with uncertainty in dynamic social environments. We used an advice-taking paradigm together with Bayesian modeling to characterize effects of aging on learning about others' time-varying intentions. We observed age differences when comparing learning on two levels of social uncertainty: the fidelity of the adviser and the volatility of intentions. Older adults expected the adviser to change his/her intentions more frequently (i.e., a higher volatility of the adviser). They also showed higher confidence (i.e., precision) in their volatility beliefs and were less willing to change their beliefs about volatility over the course of the experiment. This led them to update their predictions about the fidelity of the adviser more quickly. Potentially indicative of stereotype effects, we observed that older advisers were perceived as more volatile, but also more faithful than younger advisers. This offers new insights into adult age differences in response to social uncertainty.

Dopaminergic modulation of working memory and cognitive flexibility in a zebrafish model of aging-related cognitive decline

Healthy aging is associated with a decline in memory and executive function, which have both been linked with aberrant dopaminergic signaling. We examined the relationship between cognitive performance and dopamine function of young and aging zebrafish (Danio rerio). We revealed age-related decreases in working memory and cognitive flexibility in the Free-Movement Pattern (FMP) Y-maze. An increase in drd5 gene expression in aging adults coincided with a decrease in cognitive performance. Treatment with a D1/D5 receptor agonist (SKF-38393, 35 µM) 30 minutes prior to behavioral assessment resulted in improved working memory in aging zebrafish, but no effect in younger adults. However, an "overdosing" effect caused by agonist treatment resulted in downregulation of dat expression in 6-month old, treated zebrafish. The translational relevance of these findings was tested in humans by analyzing exploratory behavior in young-adult, 18-35-year olds, and aged adults, 70+ year olds, in a virtual FMP Y-maze. Our findings revealed similar age-related decline in working memory. Thus, strongly supporting zebrafish as a translational model of aging and cognitive decline.

Polycystic Ovary Syndrome and Brain: An Update on Structural and Functional Studies

CONTEXT

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder of women in reproductive age and is associated with reproductive, endocrine, metabolic, cardiovascular, and psychological outcomes. All these disorders are thought to be affected by central mechanisms which could be a major contributor in pathogenesis of PCOS.

EVIDENCE ACQUISITION

This mini-review discusses the relevance of central nervous system imaging modalities in understanding the neuroendocrine origins of PCOS as well as their relevance to understanding its comorbidities.

EVIDENCE SYNTHESIS

Current data suggest that central nervous system plays a key role in development of PCOS. Decreased global and regional brain volumes and altered white matter microstructure in women with PCOS is shown by structural imaging modalities. Functional studies show diminished reward response in corticolimbic areas, brain glucose hypometabolism, and greater opioid receptor availability in reward-related regions in insulin-resistant patients with PCOS. These structural and functional disturbances are associated with nonhomeostatic eating, diminished appetitive responses, as well as cognitive dysfunction and mood disorders in women with PCOS.

CONCLUSION

Structural and functional brain imaging is an emerging modality in understanding pathophysiology of metabolic disorders such as diabetes and obesity as well as PCOS. Neuroimaging can help researchers and clinicians for better understanding the pathophysiology of PCOS and related comorbidities as well as better phenotyping PCOS.

Sex-Specific Functional Connectivity in the Reward Network Related to Distinct Gender Roles

Gender roles are anti-dichotomous and malleable social constructs that should theoretically be constructed independently from biological sex. However, it is unclear whether and how the factor of sex is related to neural mechanisms involved in social constructions of gender roles. Thus, the present study aimed to investigate sex specificity in gender role constructions and the corresponding underlying neural mechanisms. We measured gender role orientation using the Bem Sex-Role Inventory, used a voxel-based global brain connectivity method based on resting-state functional magnetic resonance imaging to characterize the within-network connectivity in the brain reward network, and analyzed how the integration of the reward network is related to gender role scores between sex groups. An omnibus analysis of voxel-wise global brain connectivity values within a two-level linear mixed model revealed that in female participants, femininity scores were positively associated with integration in the posterior orbitofrontal cortex and subcallosal cortex, whereas masculinity scores were positively associated with integration in the frontal pole. By contrast, in male participants, masculinity was negatively correlated with integration in the nucleus accumbens and subcallosal cortex. For the first time, the present study revealed the sex-specific neural mechanisms underlying distinct gender roles, which elucidates the process of gender construction from the perspective of the interaction between reward sensitivity and social reinforcement.

Longitudinal Cerebral Blood Flow Changes in Normal Aging and the Alzheimer's Disease Continuum Identified by Arterial Spin Labeling MRI

BACKGROUND

Cross-sectional studies have shown lower cerebral blood flow (CBF) in Alzheimer's disease (AD), but longitudinal CBF changes in AD are still unknown.

OBJECTIVE

To reveal the longitudinal CBF changes in normal control (NC) and the AD continuum using arterial spin labeling perfusion magnetic resonance imaging (ASL MRI).

METHODS

CBF was calculated from two longitudinal ASL scans acquired 2.22±1.43 years apart from 140 subjects from the Alzheimer's Disease Neuroimaging Initiative (ADNI). At the baseline scan, the cohort contained 41 NC, 74 mild cognitive impairment patients (MCI), and 25 AD patients. 21 NC converted into MCI and 17 MCI converted into AD at the follow-up. Longitudinal CBF changes were assessed using paired-t test for non-converters and converters separately at each voxel and in the meta-ROI. Age and sex were used as covariates.

RESULTS

CBF reductions were observed in all subjects. Stable NC (n = 20) showed CBF reduction in the hippocampus and precuneus. Stable MCI patients (n = 57) showed spatially more extended CBF reduction patterns in hippocampus, middle temporal lobe, ventral striatum, prefrontal cortex, and cerebellum. NC-MCI converters showed CBF reduction in hippocampus and cerebellum and CBF increase in caudate. MCI-AD converters showed CBF reduction in hippocampus and prefrontal cortex. CBF changes were not related with longitudinal neurocognitive changes.

CONCLUSION

Normal aging and AD continuum showed common longitudinal CBF reductions in hippocampus independent of disease and its conversion. Disease conversion independent longitudinal CBF reductions escalated in MCI subjects.

Appetite Control across the Lifecourse: The Acute Impact of Breakfast Drink Quantity and Protein Content. The Full4Health Project

Understanding the mechanisms of hunger, satiety and how nutrients affect appetite control is important for successful weight management across the lifecourse. The primary aim of this study was to describe acute appetite control across the lifecourse, comparing age groups (children, adolescents, adults, elderly), weight categories, genders and European sites (Scotland and Greece). Participants (n = 391) consumed four test drinks, varying in composition (15% (normal protein, NP) and 30% (high protein, HP) of energy from protein) and quantity (based on 100% basal metabolic rate (BMR) and 140% BMR), on four separate days in a double-blind randomized controlled study. Ad libitum energy intake (EI), subjective appetite and biomarkers of appetite and metabolism (adults and elderly only) were measured. The adults' appetite was significantly greater than that of the elderly across all drink types (p < 0.004) and in response to drink quantities (p < 0.001). There were no significant differences in EI between age groups, weight categories, genders or sites. Concentrations of glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) were significantly greater in the elderly than the adults (p < 0.001). Ghrelin and fasting leptin concentrations differed significantly between weight categories, genders and sites (p < 0.05), while GLP-1 and PYY concentrations differed significantly between genders only (p < 0.05). Compared to NP drinks, HP drinks significantly increased postprandial GLP-1 and PYY (p < 0.001). Advanced age was concomitant with reduced appetite and elevated anorectic hormone release, which may contribute to the development of malnutrition. In addition, appetite hormone concentrations differed between weight categories, genders and geographical locations.

Motivation and sensitivity to monetary reward in late-life insomnia: moderating role of sex and the inflammatory marker CRP

Insomnia is a well-established risk factor for late-life depression, yet the intermediary mechanisms are not known. One plausible mechanism is dysregulation of the reward system, a common feature of depression. The main objective of the current study was to determine whether late-life insomnia is associated with reduced motivation and reduced sensitivity for monetary reward. Secondary exploratory objectives were to test for sex-specific effects and whether elevated inflammation potentiated these associations. Nondepressed community dwelling older adults (n = 104; aged 60-80) who either met (n = 31) or did not meet (n = 73) criteria for insomnia disorder as assessed by the Structured Clinical Interview for DSM-5 completed the Effort Expenditure for Rewards Task and provided blood samples for the assessment of C-reactive protein (CRP). Older adults with late-life insomnia showed reduced reward motivation 95% CI [-0.955, -0.569] and reduced reward sensitivity 95% CI [-0.430, -0.075] relative to comparison controls. In secondary exploratory analyses, late-life insomnia was associated with reduced motivation to a greater degree in males than in females 95% CI [0.072, 0.775], particularly when CRP was also elevated 95% CI [0.672, 1.551]. Late-life insomnia is associated with reduced motivation and sensitivity for monetary reward, which suggests insomnia may confer risk for late-life depression by dysregulation of reward mechanisms. Exploratory analyses suggest that older males with insomnia and elevated CRP may be particularly vulnerable to deficits in reward motivation. Although in need of replication and further study, results suggest that interventions that target insomnia or deficits in reward processing may mitigate the risk of depression in nondepressed older adults, especially older males with insomnia.

Telomerase and telomeres in aging theory and chronographic aging theory (Review)

The current review focuses on the connection of telomerase and telomeres with aging. In this review, we describe the changes in telomerase and telomere length (TEL) during development, their role in carcinogenesis processes, and the consequences of reduced telomerase activity. More specifically, the connection of TEL in peripheral blood cells with the development of aging‑associated diseases is discussed. The review provides systematic data on the role of telomerase in mitochondria, the biology of telomeres in stem cells, as well as the consequences of the forced expression of telomerase (telomerization) in human cells. Additionally, it presents the effects of chronic stress exposure on telomerase activity, the effect of TEL on fertility, and the effect of nutraceutical supplements on TEL. Finally, a comparative review of the chronographic theory of aging, presented by Olovnikov is provided based on currently available scientific research on telomere, telomerase activity, and the nature of aging by multicellular organisms.

Age-related variability in decision-making: Insights from neurochemistry

Despite dopamine's significant role in models of value-based decision-making and findings demonstrating loss of dopamine function in aging, evidence of systematic changes in decision-making over the life span remains elusive. Previous studies attempting to resolve the neural basis of age-related alteration in decision-making have typically focused on physical age, which can be a poor proxy for age-related effects on neural systems. There is growing appreciation that aging has heterogeneous effects on distinct components of the dopamine system within subject in addition to substantial variability between subjects. We propose that some of the conflicting findings in age-related effects on decision-making may be reconciled if we can observe the underlying dopamine components within individuals. This can be achieved by incorporating in vivo imaging techniques including positron emission tomography (PET) and neuromelanin-sensitive MR. Further, we discuss how affective factors may contribute to individual differences in decision-making performance among older adults. Specifically, we propose that age-related shifts in affective attention ("positivity effect") can, in some cases, counteract the impact of altered dopamine function on specific decision-making processes, contributing to variability in findings. In an effort to provide clarity to the field and advance productive hypothesis testing, we propose ways in which in vivo dopamine imaging can be leveraged to disambiguate dopaminergic influences on decision-making, and suggest strategies for assessing individual differences in the contribution of affective attentional focus.

How does decisional capacity evolve with normal cognitive aging: systematic review of the literature

PURPOSE

Aging is associated with increased needs related to complex decisions, particularly in medical and social issues. However, the complexity of decision-making involves many neurological functions and structures which are potentially altered by cognitive aging.

METHODOLOGY

A systematic review was conducted in accordance with PRISMA guidelines to examine changes in decision-making occurring in normal cognitive aging. The keywords "decision making" and "normal aging" were used to find the clinical studies and literature reviews focused on these changes.

RESULTS

A total of 97 articles were considered in the review, and ultimately 40 articles were selected, including 30 studies and 10 literature reviews. The data from these studies were of uneven quality and too disparate to allow meta-analysis according to PRISMA criteria. Nevertheless, a key result of the analysis is the decrease of processing speed with aging. In ambiguous decision-making situations, the alteration of the ventromedial system is associated with changes in motivation profiles. These changes can be compensated by experience. However, difficulties arise for older adults in the case of one-off decisions, which are very common in the medical or medico-social domains.

CONCLUSIONS

Cognitive aging is associated with a slowdown in processing speed of decision-making, especially in ambiguous situations. However, decision-making processes which are based on experience and cases in which sufficient time is available are less affected by aging. These results highlight the relativity of decision-making capacities in cognitive aging.

Loss of Sensitivity to Rewards by Dopamine Neurons May Underlie Age-Related Increased Probability Discounting

Normative aging is known to affect how decisions are made in risky situations. Although important individual variability exists, on average, aging is accompanied by greater risk aversion. Here the behavioral and neural mechanisms of greater risk aversion were examined in young and old rats trained on an instrumental probability discounting task. Consistent with the literature, old rats showed greater discounting of reward value when the probability of obtaining rewards dropped below 100%. Behaviorally, reward magnitude discrimination was the same between young and old rats, and yet these same rats exhibited reduced sensitivity to positive, but not negative, choice outcomes. The latter behavioral result was congruent with additional findings that the aged ventral tegmental neurons (including dopamine cells) were less responsive to rewards when compared to the same cell types recorded from young animals. In sum, it appears that reduced responses of dopamine neurons to rewards contribute to aging-related changes in risky decisions.

The effects of age on reward magnitude processing in the monetary incentive delay task

Previous studies have suggested age-related differences in reward-directed behavior and cerebral processes in support of the age effects. However, it remains unclear how age may influence the processing of reward magnitude. Here, with 54 volunteers (22-74 years of age) participating in the Monetary Incentive Delay Task (MIDT) with explicit cues ($1, ¢1, or nil) and timed response to win, we characterized brain activations during anticipation and feedback and the effects of age on these regional activations. Behaviorally, age was associated with less reaction time (RT) difference between dollar and cent trials, as a result of slower response to the dollar trials; i.e., age was positively correlated with RT dollar - RT cent, with RT nil as a covariate. Both age and the RT difference ($1 - ¢1) were correlated with diminished activation of the right caudate head, right anterior insula, supplementary motor area (SMA)/pre-SMA, visual cortex, parahippocampal gyrus, right superior/middle frontal gyri, and left primary motor cortex during anticipation of $1 vs. ¢1 reward. Further, these regional activities mediated the age effects on RT differences. In responses to outcomes, age was associated with decreases in regional activations to dollar vs. cent loss but only because of higher age-related responses to cent losses. Together, these findings suggest age-related differences in sensitivity to the magnitude of reward. With lower cerebral responses during anticipation to win large rewards and higher responses to outcomes of small loss, aging incurs a constricted sensitivity to the magnitude of reward.

Resilience and the brain: a key role for regulatory circuits linked to social stress and support

Given the high prevalence and burden of mental disorders, fostering the understanding of protective factors is an urgent issue for translational medicine in psychiatry. The concept of resilience describes individual and environmental protective factors against the backdrop of established adversities linked to mental illness. There is convergent evidence for a crucial role of direct as well as indirect adversity impacting the developing brain, with persisting effects until adulthood. Direct adversity may include childhood maltreatment and family adversity, while indirect social adversity can include factors such as urban living or ethnic minority status. Recently, research has begun to examine protective factors which may be able to buffer against or even reverse these influences. First evidence indicates that supportive social environments as well as trait-like individual protective characteristics might impact on similar neural substrates, thus strengthening the capacity to actively cope with stress exposure in order to counteract the detrimental effects evoked by social adversity. Here, we provide an overview of the current literature investigating the neural mechanisms of resilience with a putative social background, including studies on individual traits and genetic variation linked to resilience. We argue that the regulatory perigenual anterior cingulate cortex and limbic regions, including the amygdala and the ventral striatum, play a key role as crucial convergence sites of protective factors. Further, we discuss possible prevention and early intervention approaches targeting both the individual and the social environment to reduce the risk of psychiatric disorders and foster resilience.

Age-differential relationships among dopamine D1 binding potential, fusiform BOLD signal, and face-recognition performance

Facial recognition ability declines in adult aging, but the neural basis for this decline remains unknown. Cortical areas involved in face recognition exhibit lower dopamine (DA) receptor availability and lower blood-oxygen-level-dependent (BOLD) signal during task performance with advancing adult age. We hypothesized that changes in the relationship between these two neural systems are related to age differences in face-recognition ability. To test this hypothesis, we leveraged positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to measure D1 receptor binding potential (BP_ND) and BOLD signal during face-recognition performance. Twenty younger and 20 older participants performed a face-recognition task during fMRI scanning. Face recognition accuracy was lower in older than in younger adults, as were D1 BP_ND and BOLD signal across the brain. Using linear regression, significant relationships between DA and BOLD were found in both age-groups in face-processing regions. Interestingly, although the relationship was positive in younger adults, it was negative in older adults (i.e., as D1 BP_ND decreased, BOLD signal increased). Ratios of BOLD:D1 BP_ND were calculated and relationships to face-recognition performance were tested. Multiple linear regression revealed a significant Group × BOLD:D1 BP_ND Ratio interaction. These results suggest that, in the healthy system, synchrony between neurotransmitter (DA) and hemodynamic (BOLD) systems optimizes the level of BOLD activation evoked for a given DA input (i.e., the gain parameter of the DA input-neural activation function), facilitating task performance. In the aged system, however, desynchronization between these brain systems would reduce the gain parameter of this function, adversely impacting task performance and contributing to reduced face recognition in older adults.

The Role of the Striatum in Learning to Orthogonalize Action and Valence: A Combined PET and 7 T MRI Aging Study

Pavlovian biases influence instrumental learning by coupling reward seeking with action invigoration and punishment avoidance with action suppression. Using a probabilistic go/no-go task designed to orthogonalize action (go/no-go) and valence (reward/punishment), recent studies have shown that the interaction between the two is dependent on the striatum and its key neuromodulator dopamine. Using this task, we sought to identify how structural and neuromodulatory age-related differences in the striatum may influence Pavlovian biases and instrumental learning in 25 young and 31 older adults. Computational modeling revealed a significant age-related reduction in reward and punishment sensitivity and marked (albeit not significant) reduction in learning rate and lapse rate (irreducible noise). Voxel-based morphometry analysis using 7 Tesla MRI images showed that individual differences in learning rate in older adults were related to the volume of the caudate nucleus. In contrast, dopamine synthesis capacity in the dorsal striatum, assessed using [18F]-DOPA positron emission tomography in 22 of these older adults, was not associated with learning performance and did not moderate the relationship between caudate volume and learning rate. This multiparametric approach suggests that age-related differences in striatal volume may influence learning proficiency in old age.

Interaction of Cannabis Use and Aging: From Molecule to Mind

Given the aging Baby Boomer generation, changes in cannabis legislation, and the growing acknowledgment of cannabis for its therapeutic potential, it is predicted that cannabis use in the older population will escalate. It is, therefore, important to determine the interaction between the effects of cannabis and aging. The aim of this report is to describe the link between cannabis use and the aging brain. Our review of the literature found few and inconsistent empirical studies that directly address the impact of cannabis use on the aging brain. However, research focused on long-term cannabis use points toward cumulative effects on multimodal systems in the brain that are similarly affected during aging. Specifically, the effects of cannabis and aging converge on overlapping networks in the endocannabinoid, opioid, and dopamine systems that may affect functional decline particularly in the hippocampus and prefrontal cortex, which are critical areas for memory and executive functioning. To conclude, despite the limited current knowledge on the potential interactive effects between cannabis and aging, evidence from the literature suggests that cannabis and aging effects are concurrently present across several neurotransmitter systems. There is a great need for future research to directly test the interactions between cannabis and aging.

Reproducibility of the correlative triad among aging, dopamine receptor availability, and cognition

The evidence that dopamine function mediates the association between aging and cognition is one of the most cited findings in the cognitive neuroscience of aging. However, few and relatively small studies have directly examined these associations. Here we examined correlations among adult age, dopamine D2-like receptor (D2R) availability, and cognition in two cross-sectional studies of healthy human adults. Participants completed a short cognitive test battery and, on a separate day, a PET scan with either the high-affinity D2R tracer [18F]Fallypride (Study 1) or [11C]FLB457 (Study 2). Digit span, a measure of short-term memory maintenance and working memory, was the only cognitive test for which dopamine D2R availability partially mediated the age effect on cognition. In Study 1, age was negatively correlated with digit span. Striatal D2R availability was positively correlated with digit span controlling for age. The age effect on digit span was smaller when controlling for striatal D2R availability. Although other cognitive measures used here have individually been associated with age and D2R availability in prior studies, we found no consistent evidence for significant associations between low D2R availability and low cognitive performance on these measures. These results at best only partially supported the correlative triad of age, dopamine D2R availability, and cognition. While a wealth of other research in human and nonhuman animals demonstrates that dopamine makes critical contributions to cognition, the present studies suggest caution in interpreting PET findings as evidence that dopamine D2R loss is a primary cause of broad age-related declines in fluid cognition. (PsycINFO Database Record (c) 2019 APA, all rights reserved).