Dopamine restores reward prediction errors in old age

Aged mice exhibit faster acquisition of intravenous opioid self-administration with variable effects on intake

Although opioid abuse is more prevalent in young individuals, the rates of opioid use, overdose, and use disorders continue to climb among the elderly. Little is known about the biology underlying abuse potential in a healthy, aged population, in part due to technical and logistical difficulties testing intravenous self-administration in aged rodents. The goal of this study was to address a critical gap in the literature regarding age-dependent effects in opioid (remifentanil and fentanyl) self-administration. Male and female C57Bl/6J and C57Bl/6NJ mice were divided into young (mean: 19 weeks) and old (mean: 101 weeks) groups and were trained to self-administer intravenous fentanyl or remifentanil in daily operant sessions. Acquisition, intake, and cue-responding after forced abstinence were measured for both drugs, and a dose-response curve and dose-escalation were conducted for remifentanil and fentanyl, respectively. Surprisingly, old mice learned to self-administer both remifentanil and fentanyl faster and more accurately than young mice. Baseline intake of remifentanil was also greater in old mice compared to the young group; however, we did not see increased intake of fentanyl with age at either dose tested. Furthermore, old mice showed greater responding for cues previously associated with remifentanil after a forced abstinence, but this result was not observed with fentanyl. This first report of opioid self-administration in greater than 20-month-old mice suggests that old mice have an increased vulnerability for opioid use compared to younger counterparts, underscoring the importance of future work to uncover the biological mechanisms that are responsible.

The precision of hippocampal representations predicts incremental value-learning across the adult lifespan

Correctly assigning value to different options and leveraging this information to guide choice is a cornerstone of adaptive decision-making. Reinforcement learning (RL) has provided a computational framework to study this process, and neural signals linked to RL have been identified in the striatum and medial prefrontal cortex. More recently, hippocampal contributions to this kind of value-learning have been proposed, at least under some conditions. Here, we test whether the hippocampus provides a signal of the option's identity that aids in credit assignment when learning about several perceptually similar items, and evaluate how this process differs across the lifespan. A sample of 251 younger and older adults, including a subset (n = 76) with simultaneous fMRI, completed an RL task in which they learned the value of four houses through trial-and-error. Older adults showed decreased choice accuracy, accompanied by reduced neural signaling of value at choice but not feedback. Using representational similarity analysis, we found that the precision with which choice options were represented in the posterior hippocampus during choice predicted accurate decisions across age groups. Interestingly, despite previous evidence for neural de-differentiation in older adults, we found no support for a "blurring" of these stimulus representations in older adults. Rather, we observed reduced connectivity between the posterior hippocampus and the medial PFC in older adults, and this connectivity correlated with choice consistency. Taken together, these findings identify a hippocampal contribution to incremental value learning, and that reductions in incremental value learning in older adults are associated with the reduced transfer of information between the hippocampus and mPFC, rather than the precision of the information in the hippocampus itself.

Diminished State Space Theory of Human Aging

Many new technologies, such as smartphones, computers, or public-access systems (like ticket-vending machines), are a challenge for older adults. One feature that these technologies have in common is that they involve underlying, partially observable, structures (state spaces) that determine the actions that are necessary to reach a certain goal (e.g., to move from one menu to another, to change a function, or to activate a new service). In this work we provide a theoretical, neurocomputational account to explain these behavioral difficulties in older adults. Based on recent findings from age-comparative computational- and cognitive-neuroscience studies, we propose that age-related impairments in complex goal-directed behavior result from an underlying deficit in the representation of state spaces of cognitive tasks. Furthermore, we suggest that these age-related deficits in adaptive decision-making are due to impoverished neural representations in the orbitofrontal cortex and hippocampus.

Lesion network mapping of REM Sleep Behaviour Disorder

REM Sleep Behaviour Disorder (RBD) is a parasomnia characterised by dream enactment behaviour due to loss of sleep atonia during REM sleep. It is of considerable interest as idiopathic RBD is strongly associated with a high risk of future α-synuclein disorders. Whilst candidate brainstem structures for sleep atonia have been identified in animal studies, the precise mechanisms underpinning RBD in humans remain unclear. Here, we set out to empirically define a candidate anatomical RBD network using lesion network mapping. Our objective was to test the hypothesis that RBD is either due to damage to canonical RBD nodes previously identified in the animal literature, or disruption to the white matter connections between these nodes, or as a consequence of damage to some other brains regions. All published cases of secondary RBD arising due to discrete brain lesions were reviewed and those providing sufficient detail to estimate the original lesion selected. This resulted in lesion masks for 25 unique RBD cases. These were combined to create a lesion probability map, demonstrating the area of maximal overlap. We also obtained MRI lesion masks for 15 pontine strokes that had undergone sleep polysomnography investigations confirming the absence of RBD. We subsequently used these as an exclusion mask and removed any intersecting voxels from the aforementioned region of maximal overlap, creating a single candidate region-of-interest (ROIs) within the pons. This remaining region overlapped directly with the locus coeruleus. As sleep atonia is unlikely to be lateralized, a contralateral ROI was created via a left-right flip, and both were warped to the 100 healthy adult Human Connectome dataset. Probabilistic tractography was run from each ROI to map and characterize the white-matter tracts and connectivity properties. All reported lesions were within the brainstem but there was significant variability in location. Only half of these intersected with at least one of the six a priori RBD anatomical nodes assessed, however 72 % directly intersected with the white matter tracts created from the region of maximum overlap pontine ROIs, and the remainder were within 3.05 mm (±1.51 mm) of these tracts. 92 % of lesions were either at the level of region of maximum overlap or caudal to it. These results suggest that RBD is a brainstem disconnection syndrome, where damage anywhere along the tract connecting the rostral locus coeruleus and medulla may result in failure of sleep atonia, in line with the animal literature. This implies idiopathic disease may emerge through different patterns of damage across this brainstem circuit. This observation may account for the both the paucity of brainstem neuroimaging results reported to date and the observed phenotypic variability seen in idiopathic RBD.

Distinct neural computations scale the violation of expected reward and emotion in social transgressions

Traditional decision-making models conceptualize humans as adaptive learners utilizing the differences between expected and actual rewards (prediction errors, PEs) to maximize outcomes, but rarely consider the influence of violations of emotional expectations (emotional PEs) and how it differs from reward PEs. Here, we conducted a fMRI experiment (n = 43) using a modified Ultimatum Game to examine how reward and emotional PEs affect punishment decisions in terms of rejecting unfair offers. Our results revealed that reward relative to emotional PEs exerted a stronger prediction to punishment decisions. On the neural level, the left dorsomedial prefrontal cortex (dmPFC) was strongly activated during reward receipt whereas the emotions engaged the bilateral anterior insula. Reward and emotional PEs were also encoded differently in brain-wide multivariate patterns, with a more sensitive neural signature observed within fronto-insular circuits for reward PE. We further identified a fronto-insular network encompassing the left anterior cingulate cortex, bilateral insula, left dmPFC and inferior frontal gyrus that encoded punishment decisions. In addition, a stronger fronto-insular pattern expression under reward PE predicted more punishment decisions. These findings underscore that reward and emotional violations interact to shape decisions in complex social interactions, while the underlying neurofunctional PEs computations are distinguishable.

Toward a functional future for the cognitive neuroscience of human aging

The cognitive neuroscience of human aging seeks to identify neural mechanisms behind the commonalities and individual differences in age-related behavioral changes. This goal has been pursued predominantly through structural or "task-free" resting-state functional neuroimaging. The former has elucidated the material foundations of behavioral decline, and the latter has provided key insight into how functional brain networks change with age. Crucially, however, neither is able to capture brain activity representing specific cognitive processes as they occur. In contrast, task-based functional imaging allows a direct probe into how aging affects real-time brain-behavior associations in any cognitive domain, from perception to higher-order cognition. Here, we outline why task-based functional neuroimaging must move center stage to better understand the neural bases of cognitive aging. In turn, we sketch a multi-modal, behavior-first research framework that is built upon cognitive experimentation and emphasizes the importance of theory and longitudinal design.

Aged mice exhibit faster acquisition of intravenous opioid self-administration with variable effects on intake

Although opioid abuse is more prevalent in young individuals, opioid use, overdose, and use disorders continue to climb at a rapid rate among the elderly. Little is known about abuse potential in a healthy aged population, in part due to technical and logistical difficulties testing intravenous self-administration in aged rodents. The goal of this study was to address the critical gap in the literature regarding age-dependent differences in opioid (remifentanil and fentanyl) self-administration between old and young mice. Male and female mice were grouped into young (mean: 19 weeks) and old (mean: 101 weeks), and were trained to self-administer intravenous fentanyl or remifentanil in daily sessions. In both old and young mice, acquisition, intake, and cue-responding after forced abstinence were measured for both drugs, and a dose-response curve (remifentanil) and dose-escalation (fentanyl) were conducted. Surprisingly, old mice learned to self-administer both remifentanil and fentanyl faster and more accurately than young mice. Baseline intake of remifentanil was also substantially greater in old mice compared to their young counterparts; however, we did not see increased intake of fentanyl with age at either dose tested. Further, compared to young mice, the old mice showed a greater incubation of responding for cues previously associated with remifentanil after a forced abstinence, but again this was not observed with fentanyl. Together these data suggest that an aged population may have an increased drug-abuse vulnerability for opioids compared to young counterparts and underscore the importance of future work on mechanisms responsible for this increased vulnerability.

Understanding music and aging through the lens of Bayesian inference

Bayesian inference has recently gained momentum in explaining music perception and aging. A fundamental mechanism underlying Bayesian inference is the notion of prediction. This framework could explain how predictions pertaining to musical (melodic, rhythmic, harmonic) structures engender action, emotion, and learning, expanding related concepts of music research, such as musical expectancies, groove, pleasure, and tension. Moreover, a Bayesian perspective of music perception may shed new insights on the beneficial effects of music in aging. Aging could be framed as an optimization process of Bayesian inference. As predictive inferences refine over time, the reliance on consolidated priors increases, while the updating of prior models through Bayesian inference attenuates. This may affect the ability of older adults to estimate uncertainties in their environment, limiting their cognitive and behavioral repertoire. With Bayesian inference as an overarching framework, this review synthesizes the literature on predictive inferences in music and aging, and details how music could be a promising tool in preventive and rehabilitative interventions for older adults through the lens of Bayesian inference.

Assessing the influence of dopamine and mindfulness on the formation of routines in visual search

Given experience in cluttered but stable visual environments, our eye-movements form stereotyped routines that sample task-relevant locations, while not mixing-up routines between similar task-settings. Both dopamine signaling and mindfulness have been posited as factors that influence the formation of such routines, yet quantification of their impact remains to be tested in healthy humans. Over two sessions, participants searched through grids of doors to find hidden targets, using a gaze-contingent display. Within each session, door scenes appeared in either one of two colors, with each color signaling a differing set of likely target locations. We derived measures for how well target locations were learned (target-accuracy), how routine were sets of eye-movements (stereotypy), and the extent of interference between the two scenes (setting-accuracy). Participants completed two sessions, where they were administered either levodopa (dopamine precursor) or placebo (vitamin C), under double-blind counterbalanced conditions. Dopamine and trait mindfulness (assessed by questionnaire) interacted to influence both target-accuracy and stereotypy. Increasing dopamine improved accuracy and reduced stereotypy for high mindfulness scorers, but induced the opposite pattern for low mindfulness scorers. Dopamine also disrupted setting-accuracy invariant to mindfulness. Our findings show that mindfulness modulates the impact of dopamine on the target-accuracy and stereotypy of eye-movement routines, whereas increasing dopamine promotes interference between task-settings, regardless of mindfulness. These findings provide a link between non-human and human models regarding the influence of dopamine on the formation of task-relevant eye-movement routines and provide novel insights into behavior-trait factors that modulate the use of experience when building adaptive repertoires.

Cortical processes of multisensory plausibility modulation of vibrotactile perception in virtual environments in middled-aged and older adults

Digital technologies, such as virtual or augmented reality, can potentially support neurocognitive functions of the aging populations worldwide and complement existing intervention methods. However, aging-related declines in the frontal-parietal network and dopaminergic modulation which progress gradually across the later periods of the adult lifespan may affect the processing of multisensory congruence and expectancy based contextual plausibility. We assessed hemodynamic brain responses while middle-aged and old adults experienced car-riding virtual-reality scenarios where the plausibility of vibrotactile stimulations was manipulated by delivering stimulus intensities that were either congruent or incongruent with the digitalized audio-visual contexts of the respective scenarios. Relative to previous findings observed in young adults, although highly plausible vibrotactile stimulations confirming with contextual expectations also elicited higher brain hemodynamic responses in middle-aged and old adults, this effect was limited to virtual scenarios with extreme expectancy violations. Moreover, individual differences in plausibility-related frontal activity did not correlate with plausibility violation costs in the sensorimotor cortex, indicating less systematic frontal context-based sensory filtering in older ages. These findings have practical implications for advancing digital technologies to support aging societies.

The effect of feedback timing on category learning and feedback processing in younger and older adults

Introduction

Corrective feedback can be received immediately after an action or with a temporal delay. Neuroimaging studies suggest that immediate and delayed feedback are processed by the striatum and medial temporal lobes (MTL), respectively. Age-related changes in the striatum and MTL may influence the efficiency of feedback-based learning in older adults. The current study leverages event-related potentials (ERPs) to evaluate age-related differences in immediate and delayed feedback processing and consequences for learning. The feedback-related negativity (FRN) captures activity in the frontostriatal circuit while the N170 is hypothesized to reflect MTL activation.

Methods

18 younger (Myears  = 24.4) and 20 older (Myears  = 65.5) adults completed learning tasks with immediate and delayed feedback. For each group, learning outcomes and ERP magnitudes were evaluated across timing conditions.

Results

Younger adults learned better than older adults in the immediate timing condition. This performance difference was associated with a typical FRN signature in younger but not older adults. For older adults, impaired processing of immediate feedback in the striatum may have negatively impacted learning. Conversely, learning was comparable across groups when feedback was delayed. For both groups, delayed feedback was associated with a larger magnitude N170 relative to immediate feedback, suggesting greater MTL activation.

Discussion and conclusion

Delaying feedback may increase MTL involvement and, for older adults, improve category learning. Age-related neural changes may differentially affect MTL- and striatal-dependent learning. Future research can evaluate the locus of age-related learning differences and how feedback can be manipulated to optimize learning across the lifespan.

Behavioral Bias for Exploration Is Associated with Enhanced Signaling in the Lateral and Medial Frontopolar Cortex

Should we keep doing what we know works for us, or should we risk trying something new as it could work even better? The exploration-exploitation dilemma is ubiquitous in daily life decision-making, and balancing between the two is crucial for adaptive behavior. Yet, we only have started to unravel the neurocognitive mechanisms that help us to find this balance in practice. Analyzing BOLD signals of healthy young adults during virtual foraging, we could show that a behavioral tendency for prolonged exploitation was associated with weakened signaling during exploration in central node points of the frontoparietal attention network, plus the frontopolar cortex. These results provide an important link between behavioral heuristics that we use to balance between exploitation and exploration and the brain function that supports shifts from one tendency to the other. Importantly, they stress that interindividual differences in behavioral strategies are reflected in differences in brain activity during exploration and should thus be more in the focus of basic research that aims at delineating general laws governing visual attention.

L-DOPA and oxytocin influence the neural correlates of performance monitoring for self and others

RATIONALE

The ability to monitor the consequences of our actions for others is imperative for flexible and adaptive behavior, and allows us to act in a (pro)social manner. Yet, little is known about the neurochemical mechanisms underlying alterations in (pro)social performance monitoring.

OBJECTIVE

The aim of this functional magnetic resonance imaging (fMRI) study was to improve our understanding of the role of dopamine and oxytocin and their potential overlap in the neural mechanisms underlying performance monitoring for own versus others' outcomes.

METHOD

Using a double-blind placebo-controlled cross-over design, 30 healthy male volunteers were administered oxytocin (24 international units), the dopamine precursor L-DOPA (100 mg + 25 mg carbidopa), or placebo in three sessions. Participants performed a computerized cannon shooting game in two recipient conditions where mistakes resulted in negative monetary consequences for (1) oneself or (2) an anonymous other participant.

RESULTS

Results indicated reduced error-correct differentiation in the ventral striatum after L-DOPA compared to placebo, independent of recipient. Hence, pharmacological manipulation of dopamine via L-DOPA modulated performance-monitoring activity in a brain region associated with reward prediction and processing in a domain-general manner. In contrast, oxytocin modulated the BOLD response in a recipient-specific manner, such that it specifically enhanced activity for errors that affected the other in the pregenual anterior cingulate cortex (pgACC), a region previously implicated in the processing of social rewards and prediction errors. Behaviorally, we also found reduced target sizes-indicative of better performance-after oxytocin, regardless of recipient. Moreover, after oxytocin lower target sizes specifically predicted higher pgACC activity when performing for others.

CONCLUSIONS

These different behavioral and neural patterns after oxytocin compared to L-DOPA administration highlight a divergent role of each neurochemical in modulating the neural mechanisms underlying social performance monitoring.

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 time constraints on value-directed long-term memory in younger and older adults

We often encounter more information than we can remember, making it critical that we are selective in what we remember. Being selective about which information we consolidate into our long-term memory becomes even more important when there is insufficient time to encode and retrieve information. We investigated whether older and younger adults differ in how time constraints, whether at encoding (Experiment 1) or retrieval (Experiment 2), affect their ability to be selective when remembering important information that they need to recall later. In Experiment 1, we found that younger and older adults exhibited similar selectivity, and the participants remained selective when rushed at encoding. In Experiment 2, older adults maintained their selectivity when given insufficient time at retrieval, but younger adults' selectivity was increased when given limited recall time. Altogether, the present experiments provide new support for negligible, and in some cases, even beneficial, effects of time constraints on older and younger adults' ability to selectively encode and retrieve the most valuable information. These findings may provide insight into a mechanism that allows older adults to use their long-term memory efficiently, despite age-related cognitive declines, even when faced with constraining encoding and retrieval situations. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Dopamine release in human associative striatum during reversal learning

The dopaminergic system is firmly implicated in reversal learning but human measurements of dopamine release as a correlate of reversal learning success are lacking. Dopamine release and hemodynamic brain activity in response to unexpected changes in action-outcome probabilities are here explored using simultaneous dynamic [11C]Raclopride PET-fMRI and computational modelling of behavior. When participants encounter reversed reward probabilities during a card guessing game, dopamine release is observed in associative striatum. Individual differences in absolute reward prediction error and sensitivity to errors are associated with peak dopamine receptor occupancy. The fMRI response to perseverance errors at the onset of a reversal spatially overlap with the site of dopamine release. Trial-by-trial fMRI correlates of absolute prediction errors show a response in striatum and association cortices, closely overlapping with the location of dopamine release, and separable from a valence signal in ventral striatum. The results converge to implicate striatal dopamine release in associative striatum as a central component of reversal learning, possibly signifying the need for increased cognitive control when new stimuli-responses should be learned.

Associations of Frailty with Neuropsychiatric Symptoms of Alzheimer's Disease: A Longitudinal Study

Background

Frailty is a vulnerability state increasing the risk of many adverse health outcomes, but little is known about the effects of frailty on neuropsychiatric health.

Objective

To explore the associations between frailty and the risk of neuropsychiatric symptoms (NPSs) in Alzheimer's disease (AD), especially in its different clinical stages.

Methods

We included 2,155 individuals assessed using modified frailty index-11 (mFI-11), Neuropsychiatric Inventory (NPI) and Neuropsychiatric Inventory Questionnaire (NPI-Q) in the Alzheimer's Disease Neuroimaging Initiative (ADNI). The relationships between frailty and NPSs were explored with logistic regression models and Cox proportional hazard regression models. Causal mediation analyses were conducted to explore the mediation factors between frailty and NPSs.

Results

Among mild cognitive impairment (MCI) participants, frailty was cross-sectionally associated with an increased risk of apathy, and longitudinally associated with increased risk of depression and apathy. Among AD participants, frailty was cross-sectionally associated with increased risk of depression and anxiety, and longitudinally associated with an increased risk of apathy. Among participants with cognitive progression, frailty was associated with increased risk of depression and apathy. In MCI participants, the influence of frailty on NPSs was partially mediated by hippocampus volume, whole brain volume, and monocytes, with mediating proportions ranging from 8.40% to 9.29%.

Conclusions

Frailty was associated with NPSs such as depression, anxiety, and apathy among MCI, AD, and cognitive progression participants. Atrophy of the hippocampus and whole brain, as well as peripheral immunity may be involved in the potential mechanisms underlying the above associations.

Dopamine dysregulation in Parkinson's disease flattens the pleasurable urge to move to musical rhythms

The pleasurable urge to move to music (PLUMM) activates motor and reward areas of the brain and is thought to be driven by predictive processes. Dopamine in motor and limbic networks is implicated in beat-based timing and music-induced pleasure, suggesting a central role of basal ganglia (BG) dopaminergic systems in PLUMM. This study tested this hypothesis by comparing PLUMM in participants with Parkinson's disease (PD), age-matched controls, and young controls. Participants listened to musical sequences with varying rhythmic and harmonic complexity (low, medium and high), and rated their experienced pleasure and urge to move to the rhythm. In line with previous results, healthy younger participants showed an inverted U-shaped relationship between rhythmic complexity and ratings, with preference for medium complexity rhythms, while age-matched controls showed a similar, but weaker, inverted U-shaped response. Conversely, PD showed a significantly flattened response for both the urge to move and pleasure. Crucially, this flattened response could not be attributed to differences in rhythm discrimination and did not reflect an overall decrease in ratings. For harmonic complexity, PD showed a negative linear pattern for both the urge to move and pleasure while healthy age-matched controls showed the same pattern for pleasure and an inverted U for the urge to move. This contrasts with the pattern observed in young healthy controls in previous studies, suggesting that both healthy aging and PD also influence affective responses to harmonic complexity. Together, these results support the role of dopamine within cortico-striatal circuits in the predictive processes that form the link between the perceptual processing of rhythmic patterns and the affective and motor responses to rhythmic music.

The peptide Acein promotes dopamine secretion through clec-126 to extend the lifespan of elderly C. elegans

Dopamine plays a crucial role in regulating brain activity and movement and modulating human behavior, cognition and mood. Regulating dopamine signaling may improve cognitive abilities and physical functions during aging. Acein, a nonapeptide of sequence H-Pro-Pro-Thr-Thr-Thr-Lys-Phe-Ala-Ala-OH is able to stimulate dopamine secretion in the brain. By using genetic editing and lifespan investigation in C. elegans, we showed that the lack of the C-type lectin domain-containing protein clec-126 significantly suppressed the aging phenotype and prolonged lifespan, while overexpression of clec-126 promoted aging-related phenotypes and accelerated the aging process. We examined the aging phenotype of C. elegans and showed that Acein could induce a decrease in clec-126 expression, prolonging the lifespan of aged C. elegans. The mechanism proceeds through the Acein-induced stimulation of dopamine secretion that ameliorates motor function decline and extends the healthy lifespan of aged C. elegans. In addition, we also observed an increase in brood number. Our study has shown that Acein regulates dopamine secretion and has good antiaging activity by decreasing clec-126 expression.

Reduced neural encoding of utility prediction errors in cocaine addiction

Influential accounts of addiction posit alterations in adaptive behavior driven by deficient dopaminergic prediction errors (PEs), signaling the discrepancy between actual and expected reward. Dopamine neurons encode these error signals in subjective terms, calibrated by individual risk preferences, as "utility" PEs. It remains unclear, however, whether people with drug addiction have PE deficits or their computational source. Here, using an analogous task to prior single-unit studies with known expectancies, we show that fMRI-measured PEs similarly reflect utility PEs. Relative to control participants, people with chronic cocaine addiction demonstrate reduced utility PEs in the dopaminoceptive ventral striatum, with similar trends in orbitofrontal cortex. Dissecting this PE signal into its subcomponent terms attributed these reductions to weaker striatal responses to received reward/utility, whereas suppression of activity with reward expectation was unchanged. These findings support that addiction may fundamentally disrupt PE signaling and reveal an underappreciated role for perceived reward value in this mechanism.

Improving social reward responsivity and social connectedness in psychotherapies for late-life depression: Engage & Connect as an example

Psychotherapies are effective in reducing late-life depression. Yet, about half of patients remain depressed at treatment end. Advances in neuroscience can inform simplified interventions that target key brain networks impacted by depression. Behavioral activation therapies that increase social connectedness may improve social reward responsivity and alter abnormalities of the Positive Valence System (PVS). Engage & Connect is an example for a scalable and simple neuroscience-informed psychotherapy, aimed to improve PVS functions and social reward responsivity by increasing engagement in rewarding social activities. Interventions that improve social reward responsivity can be promising first-line treatments for late-life depression in the community.

How does apathy impact exploration-exploitation decision-making in older patients with neurocognitive disorders?

Apathy is a pervasive clinical syndrome in neurocognitive disorders, characterized by a quantitative reduction in goal-directed behaviors. The brain structures involved in the physiopathology of apathy have also been connected to the brain structures involved in probabilistic reward learning in the exploration-exploitation dilemma. This dilemma in question involves the challenge of selecting between a familiar option with a more predictable outcome, and another option whose outcome is uncertain and may yield potentially greater rewards compared to the known option. The aim of this study was to combine experimental procedures and computational modeling to examine whether, in older adults with mild neurocognitive disorders, apathy affects performance in the exploration-exploitation dilemma. Through using a four-armed bandit reinforcement-learning task, we showed that apathetic older adults explored more and performed worse than non-apathetic subjects. Moreover, the mental flexibility assessed by the Trail-making test-B was negatively associated with the percentage of exploration. These results suggest that apathy is characterized by an increased explorative behavior and inefficient decision-making, possibly due to weak mental flexibility to switch toward the exploitation of the more rewarding options. Apathetic participants also took longer to make a choice and failed more often to respond in the allotted time, which could reflect the difficulties in action initiation and selection. In conclusion, the present results suggest that apathy in participants with neurocognitive disorders is associated with specific disturbances in the exploration-exploitation trade-off and sheds light on the disturbances in reward processing in patients with apathy.

Parietal stimulation reverses age-related decline in exploration, learning, and decision-making

Aging can compromise decision-making and learning, potentially due to reduced exploratory behaviors crucial for novel problem-solving. We posit that invigorating exploration could mitigate these declines. Supporting this hypothesis, we found that older mice mirrored human aging, displaying less exploration and learning during decision-making, but optogenetic stimulation of their posterior parietal cortex boosted initial exploration, subsequently improving learning. Thus, enhancing exploration-driven learning could be a key to countering cognitive aging.

Functional Organization of Auditory and Reward Systems in Aging

The intrinsic organization of functional brain networks is known to change with age, and is affected by perceptual input and task conditions. Here, we compare functional activity and connectivity during music listening and rest between younger (n = 24) and older (n = 24) adults, using whole-brain regression, seed-based connectivity, and ROI-ROI connectivity analyses. As expected, activity and connectivity of auditory and reward networks scaled with liking during music listening in both groups. Younger adults show higher within-network connectivity of auditory and reward regions as compared with older adults, both at rest and during music listening, but this age-related difference at rest was reduced during music listening, especially in individuals who self-report high musical reward. Furthermore, younger adults showed higher functional connectivity between auditory network and medial prefrontal cortex that was specific to music listening, whereas older adults showed a more globally diffuse pattern of connectivity, including higher connectivity between auditory regions and bilateral lingual and inferior frontal gyri. Finally, connectivity between auditory and reward regions was higher when listening to music selected by the participant. These results highlight the roles of aging and reward sensitivity on auditory and reward networks. Results may inform the design of music-based interventions for older adults and improve our understanding of functional network dynamics of the brain at rest and during a cognitively engaging task.

Neural correlates of valence-dependent belief and value updating during uncertainty reduction: An fNIRS study

Selective use of new information is crucial for adaptive decision-making. Combining a gamble bidding task with assessing cortical responses using functional near-infrared spectroscopy (fNIRS), we investigated potential effects of information valence on behavioral and neural processes of belief and value updating during uncertainty reduction in young adults. By modeling changes in the participants' expressed subjective values using a Bayesian model, we dissociated processes of (i) updating beliefs about statistical properties of the gamble, (ii) updating values of a gamble based on new information about its winning probabilities, as well as (iii) expectancy violation. The results showed that participants used new information to update their beliefs and values about the gambles in a quasi-optimal manner, as reflected in the selective updating only in situations with reducible uncertainty. Furthermore, their updating was valence-dependent: information indicating an increase in winning probability was underweighted, whereas information about a decrease in winning probability was updated in good agreement with predictions of the Bayesian decision theory. Results of model-based and moderation analyses showed that this valence-dependent asymmetry was associated with a distinct contribution of expectancy violation, besides belief updating, to value updating after experiencing new positive information regarding winning probabilities. In line with the behavioral results, we replicated previous findings showing involvements of frontoparietal brain regions in the different components of updating. Furthermore, this study provided novel results suggesting a valence-dependent recruitment of brain regions. Individuals with stronger oxyhemoglobin responses during value updating was more in line with predictions of the Bayesian model while integrating new information that indicates an increase in winning probability. Taken together, this study provides first results showing expectancy violation as a contributing factor to sub-optimal valence-dependent updating during uncertainty reduction and suggests limitations of normative Bayesian decision theory.

Dopamine regulates decision thresholds in human reinforcement learning in males

Dopamine fundamentally contributes to reinforcement learning, but recent accounts also suggest a contribution to specific action selection mechanisms and the regulation of response vigour. Here, we examine dopaminergic mechanisms underlying human reinforcement learning and action selection via a combined pharmacological neuroimaging approach in male human volunteers (n = 31, within-subjects; Placebo, 150 mg of the dopamine precursor L-dopa, 2 mg of the D2 receptor antagonist Haloperidol). We found little credible evidence for previously reported beneficial effects of L-dopa vs. Haloperidol on learning from gains and altered neural prediction error signals, which may be partly due to differences experimental design and/or drug dosages. Reinforcement learning drift diffusion models account for learning-related changes in accuracy and response times, and reveal consistent decision threshold reductions under both drugs, in line with the idea that lower dosages of D2 receptor antagonists increase striatal DA release via an autoreceptor-mediated feedback mechanism. These results are in line with the idea that dopamine regulates decision thresholds during reinforcement learning, and may help to bridge action selection and response vigor accounts of dopamine.

Adult age differences in event memory updating: The roles of prior-event retrieval and prediction

Remembering past events can lead to predictions of what is to come and to experiencing prediction errors when things change. Previous research has shown enhanced memory updating for ongoing events that are inconsistent with predictions based on past experiences. According to the Event Memory Retrieval and Comparison (EMRC) Theory, such memory updating depends on the encoding of configural representations that bind retrieved features of the previous event, changed features, and the relationship between the two. We investigated potential age-related differences in these mechanisms by showing older and younger adults two movies of everyday activities. Activities in the second movie either repeated from the first movie or included changed endings. During the second movie, before activities ended, participants were instructed to predict the upcoming action based on the first movie. One week later, participants were instructed to recall activity endings from the second movie. For younger adults, having predicted endings consistent with the first movie before seeing changed endings was subsequently associated with better recall of these changed endings and recollection that activities had changed. Conversely, for older adults, making such predictions prior to changes was associated with intruding details from the first movie endings and was less strongly associated with change recollection. Consistent with EMRC, these findings suggest that retrieval of relevant experiences when events change can trigger prediction errors that prompt associative encoding of existing memories and current perceptions. These mechanisms were less efficient in older adults, which may account for their poorer event memory updating than younger adults. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

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.

Effects of positive and negative social feedback on motivation, evaluative learning, and socio-emotional processing

Social rewards and punishments are strong motivators. Since experimental work has focused on young adults using simplistic feedback, the effects of more naturalistic stimuli on motivation, evaluative learning, and socio-emotional processing with advanced age remain unclear. Therefore, we compared the effects of static (photos) vs dynamic (videos) social feedback in a social incentive delay (SID) task in young (18-35 years) and older adults (50-84 years) with neutral, positive, and negative feedback, on response times (RTs), and assessed the emotional valence of feedback cues and feedback videos. We found that anticipating positive and negative social feedback accelerated RTs regardless of age and without additional effects of video feedback. Furthermore, the results suggest a valence transfer from positive feedback videos to predictive cues in both groups (i.e., evaluative learning). Finally, older adults reported less pronounced negative affect for negative feedback videos, indicating age differences in socio-emotional processing. As such, our findings foster our understanding of the underlying cognitive and emotional aspects involved in the processing of social rewards and punishments.

Graph Theoretical Network Structures Underlie Age-Related Differences in the Functional Connectome During Rest and Music Listening

Aging is associated with decreased functional connectivity within the default mode network, as well as auditory and reward systems which are involved in music listening. Understanding how music listening affects network organization of the aging brain, both globally and specific to the brain networks, will have implications for designing lifestyle interventions that tap into distinct networks in the brain. Here we apply graph-theory metrics of modularity, global efficiency, clustering coefficients, degrees, and betweenness centrality to compare younger and older adults (YA/OA, N=24 per group) in fMRI connectivity during rest and a music listening task. Results show a less modular but more globally efficient connectome in OAs, especially during music listening, resulting in main effects of group and task, as well as group-by-task interactions. ROI analyses indicated that the posterior cingulate is more centrally located than the medial prefrontal cortex in OAs. Overall, reduced modularity and increased global efficiency with age is in keeping with previously-observed functional reorganizations, and interaction effects show that age-related differences in baseline network organization are reflected in, potentially magnified by, music listening.

Aging, uncertainty, and decision making-A review

There is a great deal of uncertainty in the world. One common source of uncertainty results from incomplete or missing information about probabilistic outcomes (i.e., outcomes that may occur), which influences how people make decisions. The impact of this type of uncertainty may particularly pronounced for older adults, who, as the primary leaders around the world, make highly impactful decisions with lasting outcomes. This review examines the ways in which uncertainty about probabilistic outcomes is perceived, handled, and represented in the aging brain, with an emphasis on how uncertainty may specifically affect decision making in later life. We describe the role of uncertainty in decision making and aging from four perspectives, including 1) theoretical, 2) self-report, 3) behavioral, and 4) neuroscientific. We report evidence of any age-related differences in uncertainty among these contexts and describe how these changes may affect decision making. We then integrate the findings across the distinct perspectives, followed by a discussion of important future directions for research on aging and uncertainty, including prospection, domain-specificity in risk-taking behaviors, and choice overload.

Multivariate associations between dopamine receptor availability and risky investment decision-making across adulthood

Enhancing dopamine increases financial risk taking across adulthood but it is unclear whether baseline individual differences in dopamine function are related to risky financial decisions. Here, thirty-five healthy adults completed an incentive-compatible risky investment decision task and a PET scan at rest using [11C]FLB457 to assess dopamine D2-like receptor availability. Participants made choices between a safe asset (bond) and a risky asset (stock) with either an expected value less than the bond ("bad stock") or expected value greater than the bond ("good stock"). Five measures of behavior (choice inflexibility, risk seeking, suboptimal investment) and beliefs (absolute error, optimism) were computed and D2-like binding potential was extracted from four brain regions of interest (midbrain, amygdala, anterior cingulate, insula). We used canonical correlation analysis to evaluate multivariate associations between decision-making and dopamine function controlling for age. Decomposition of the first dimension (r = 0.76) revealed that the strongest associations were between measures of choice inflexibility, incorrect choice, optimism, amygdala binding potential, and age. Follow-up univariate analyses revealed that amygdala binding potential and age were both independently associated with choice inflexibility. The findings suggest that individual differences in dopamine function may be associated with financial risk taking in healthy adults.

Age-related differences in the social associative learning of trust information

Trust is a key component of social interaction. Older adults, however, often exhibit excessive trust relative to younger adults. One explanation is that older adults may learn to trust differently than younger adults. Here, we examine how younger (N = 33) and older adults (N = 30) learn to trust over time. Participants completed a classic iterative trust game with 3 partners. Younger and older adults shared similar amounts but differed in how they shared money. Compared to younger adults, older adults invested more with untrustworthy partners and less with trustworthy partners. As a group, older adults displayed less learning than younger adults. However, computational modeling suggests that this is not because older adults learn differently from positive and negative feedback than younger adults. Model-based fMRI analyses revealed several age- and learning-related differences in neural processing. Specifically, we found that older learners (N = 19), relative to older non-learners (N = 11), had greater reputation-related activity in metalizing/memory areas while making their decisions. Collectively, these findings suggest that older adult learners use social cues differently from non-learners.

l-DOPA and oxytocin influence the neurocomputational mechanisms of self-benefitting and prosocial reinforcement learning

Humans learn through reinforcement, particularly when outcomes are unexpected. Recent research suggests similar mechanisms drive how we learn to benefit other people, that is, how we learn to be prosocial. Yet the neurochemical mechanisms underlying such prosocial computations remain poorly understood. Here, we investigated whether pharmacological manipulation of oxytocin and dopamine influence the neurocomputational mechanisms underlying self-benefitting and prosocial reinforcement learning. Using a double-blind placebo-controlled cross-over design, we administered intranasal oxytocin (24 IU), dopamine precursor l-DOPA (100 mg + 25 mg carbidopa), or placebo over three sessions. Participants performed a probabilistic reinforcement learning task with potential rewards for themselves, another participant, or no one, during functional magnetic resonance imaging. Computational models of reinforcement learning were used to calculate prediction errors (PEs) and learning rates. Participants behavior was best explained by a model with different learning rates for each recipient, but these were unaffected by either drug. On the neural level, however, both drugs blunted PE signaling in the ventral striatum and led to negative signaling of PEs in the anterior mid-cingulate cortex, dorsolateral prefrontal cortex, inferior parietal gyrus, and precentral gyrus, compared to placebo, and regardless of recipient. Oxytocin (versus placebo) administration was additionally associated with opposing tracking of self-benefitting versus prosocial PEs in dorsal anterior cingulate cortex, insula and superior temporal gyrus. These findings suggest that both l-DOPA and oxytocin induce a context-independent shift from positive towards negative tracking of PEs during learning. Moreover, oxytocin may have opposing effects on PE signaling when learning to benefit oneself versus another.

Dopamine differentially modulates medial temporal lobe activity and behavior during spatial navigation in young and older adults

Aging is associated with changes in spatial navigation behavior. In addition to an overall performance decline, older adults tend to rely more on proximal location cue information than on environmental boundary information during spatial navigation compared to young adults. The fact that older adults are more susceptible to errors during spatial navigation might be partly attributed to deficient dopaminergic modulation of hippocampal and striatal functioning. Hence, elevating dopamine levels might differentially modulate spatial navigation and memory performance in young and older adults. In this work, we administered levodopa (L-DOPA) in a double-blind within-subject, placebo-controlled design and recorded functional neuroimaging while young and older adults performed a 3D spatial navigation task in which boundary geometry or the position of a location cue were systematically manipulated. An age by intervention interaction on the neural level revealed an upregulation of brain responses in older adults and a downregulation of responses in young adults within the medial temporal lobe (including hippocampus and parahippocampus) and brainstem, during memory retrieval. Behaviorally, L-DOPA had no effect on older adults' overall memory performance; however, older adults whose spatial memory improved under L-DOPA also showed a shift towards more boundary processing under L-DOPA. In young adults, L-DOPA induced a decline in spatial memory performance in task-naïve participants. These results are consistent with the inverted-U-shaped hypothesis of dopamine signaling and cognitive function and suggest that increasing dopamine availability improves hippocampus-dependent place learning in some older adults.

Opportunity cost determines free-operant action initiation latency and predicts apathy

BACKGROUND

Apathy, a disabling and poorly understood neuropsychiatric symptom, is characterised by impaired self-initiated behaviour. It has been hypothesised that the opportunity cost of time (OCT) may be a key computational variable linking self-initiated behaviour with motivational status. OCT represents the amount of reward which is foregone per second if no action is taken. Using a novel behavioural task and computational modelling, we investigated the relationship between OCT, self-initiation and apathy. We predicted that higher OCT would engender shorter action latencies, and that individuals with greater sensitivity to OCT would have higher behavioural apathy.

METHODS

We modulated the OCT in a novel task called the 'Fisherman Game', Participants freely chose when to self-initiate actions to either collect rewards, or on occasion, to complete non-rewarding actions. We measured the relationship between action latencies, OCT and apathy for each participant across two independent non-clinical studies, one under laboratory conditions (n = 21) and one online (n = 90). 'Average-reward' reinforcement learning was used to model our data. We replicated our findings across both studies.

RESULTS

We show that the latency of self-initiation is driven by changes in the OCT. Furthermore, we demonstrate, for the first time, that participants with higher apathy showed greater sensitivity to changes in OCT in younger adults. Our model shows that apathetic individuals experienced greatest change in subjective OCT during our task as a consequence of being more sensitive to rewards.

CONCLUSIONS

Our results suggest that OCT is an important variable for determining free-operant action initiation and understanding apathy.

Angiotensin blockade enhances motivational reward learning via enhancing striatal prediction error signaling and frontostriatal communication

Adaptive human learning utilizes reward prediction errors (RPEs) that scale the differences between expected and actual outcomes to optimize future choices. Depression has been linked with biased RPE signaling and an exaggerated impact of negative outcomes on learning which may promote amotivation and anhedonia. The present proof-of-concept study combined computational modeling and multivariate decoding with neuroimaging to determine the influence of the selective competitive angiotensin II type 1 receptor antagonist losartan on learning from positive or negative outcomes and the underlying neural mechanisms in healthy humans. In a double-blind, between-subjects, placebo-controlled pharmaco-fMRI experiment, 61 healthy male participants (losartan, n = 30; placebo, n = 31) underwent a probabilistic selection reinforcement learning task incorporating a learning and transfer phase. Losartan improved choice accuracy for the hardest stimulus pair via increasing expected value sensitivity towards the rewarding stimulus relative to the placebo group during learning. Computational modeling revealed that losartan reduced the learning rate for negative outcomes and increased exploitatory choice behaviors while preserving learning for positive outcomes. These behavioral patterns were paralleled on the neural level by increased RPE signaling in orbitofrontal-striatal regions and enhanced positive outcome representations in the ventral striatum (VS) following losartan. In the transfer phase, losartan accelerated response times and enhanced VS functional connectivity with left dorsolateral prefrontal cortex when approaching maximum rewards. These findings elucidate the potential of losartan to reduce the impact of negative outcomes during learning and subsequently facilitate motivational approach towards maximum rewards in the transfer of learning. This may indicate a promising therapeutic mechanism to normalize distorted reward learning and fronto-striatal functioning in depression.

Mechanisms Underlying Brain Aging Under Normal and Pathological Conditions

Aging is a major risk factor for many human diseases, including cognitive impairment, which affects a large population of the elderly. In the past few decades, our understanding of the molecular and cellular mechanisms underlying the changes associated with aging and age-related diseases has expanded greatly, shedding light on the potential role of these changes in cognitive impairment. In this article, we review recent advances in understanding of the mechanisms underlying brain aging under normal and pathological conditions, compare their similarities and differences, discuss the causative and adaptive mechanisms of brain aging, and finally attempt to find some rules to guide us on how to promote healthy aging and prevent age-related diseases.

Nucleus accumbens: a systematic review of neural circuitry and clinical studies in healthy and pathological states

OBJECTIVE

The nucleus accumbens (NAcc) of the ventral striatum is critically involved in goal- and reward-based behavior. Structural and functional abnormalities of the NAcc or its associated neural systems are involved in neurological and psychiatric disorders. Studies of neural circuitry have shed light on the subtleties of the structural and functional derangements of the NAcc across various diseases. In this systematic review, the authors sought to identify human studies involving the NAcc and provide a synthesis of the literature on the known circuity of the NAcc in healthy and diseased states, as well as the clinical outcomes following neuromodulation.

METHODS

A systematic review was conducted using the PubMed, Embase, and Scopus databases. Neuroimaging studies that reported on neural circuitry related to the human NAcc with sample sizes greater than 5 patients were included. Demographic data, aim, design and duration, participants, and clinical and neurocircuitry details and outcomes of the studies were extracted.

RESULTS

Of 3591 resultant articles, 123 were included. The NAcc and its corticolimbic connections to other brain regions, such as the prefrontal cortex, are largely involved in reward and pain processes, with distinct functional circuitry between the shell and core in healthy patients. There is heterogeneity between clinical studies with regard to the NAcc indirect targeting coordinates, methods for postoperative confirmation, and blinded trial design. Neuromodulation studies provided promising clinical results in the context of addiction and substance misuse, obsessive-compulsive disorder, and mood disorders. The most common complications were impaired memory or concentration, and a notable serious complication was hypomania.

CONCLUSIONS

The functional diversity of the NAcc highlights the importance of studying the NAcc in healthy and pathological states. The results of this review suggest that NAcc neuromodulation has been attempted in the management of diverse psychiatric indications. There is promising, emerging evidence that the NAcc may be an effective target for specific reward- or pain-based pathologies with a reasonable risk profile.

L-DOPA enhances neural direction signals in younger and older adults

Previous studies indicate a role of dopamine in spatial navigation. Although neural representations of direction are an important aspect of spatial cognition, it is not well understood whether dopamine directly affects these representations, or only impacts other aspects of spatial brain function. Moreover, both dopamine and spatial cognition decline sharply during age, raising the question which effect dopamine has on directional signals in the brain of older adults. To investigate these questions, we used a double-blind cross-over L-DOPA/Placebo intervention design in which 43 younger and 37 older adults navigated in a virtual spatial environment while undergoing functional magnetic resonance imaging (fMRI). We studied the effect of L-DOPA, a dopamine precursor, on fMRI activation patterns that encode spatial walking directions that have previously been shown to lose specificity with age. This was done in predefined regions of interest, including the early visual cortex, retrosplenial cortex, and hippocampus. Classification of brain activation patterns associated with different walking directions was improved across all regions following L-DOPA administration, suggesting that dopamine broadly enhances neural representations of direction. No evidence for differences between regions was found. In the hippocampus these results were found in both age groups, while in the retrosplenial cortex they were only observed in younger adults. Taken together, our study provides evidence for a link between dopamine and the specificity of neural responses during spatial navigation. SIGNIFICANCE STATEMENT: The sense of direction is an important aspect of spatial navigation, and neural representations of direction can be found throughout a large network of space-related brain regions. But what influences how well these representations track someone's true direction? Using a double-blind cross-over L-DOPA/Placebo intervention design, we find causal evidence that the neurotransmitter dopamine impacts the fidelity of direction selective neural representations in the human hippocampus and retrosplenial cortex. Interestingly, the effect of L-DOPA was either equally present or even smaller in older adults, despite the well-known age related decline of dopamine. These results provide novel insights into how dopamine shapes the neural representations that underlie spatial navigation.

Effects of exploring a novel environment on memory across the lifespan

Exploration of a novel environment has been shown to promote memory formation in healthy adults. Studies in animals have suggested that such novelty-induced memory boosts are mediated by hippocampal dopamine. The dopaminergic system is known to develop and deteriorate over the lifespan, but so far, the effects of novelty on memory across the lifespan have not yet been investigated. In the current study, we had children, adolescents, younger, and older adults (n = 439) explore novel and previously familiarized virtual environments to pinpoint the effects of spatial novelty on declarative memory in humans across different age groups. After exploration, words were presented while participants performed a deep or shallow encoding task. Incidental memory was quantified in a surprise test. Results showed that participants in the deep encoding condition remembered more words than those in the shallow condition, while novelty did not influence this effect. Interestingly, however, children, adolescents and younger adults benefitted from exploring a novel compared to a familiar environment as evidenced by better word recall, while these effects were absent in older adults. Our findings suggest that the beneficial effects of novelty on memory follow the deterioration of neural pathways involved in novelty-related processes across the lifespan.

Altered functional connectivity of nucleus accumbens subregions associates with non-motor symptoms in Parkinson's disease

AIMS

This study aimed to identify the functional connectivity (FC) changes of nucleus accumbens (NAc) subregions and characterize the association of network changes and non-motor symptoms (NMS) in Parkinson's disease (PD).

METHODS

We enrolled 129 PD patients and 106 healthy controls from our center and the PPMI (Parkinson's Progression Markers Initiative) database. The FC of the bilateral core and shell of the NAc were measured and compared between the two groups. We further used partial least squares correlation to reveal the relationships between altered FC of NAc subregions and manifestations of NMS of PD.

RESULTS

The subregions of left core, left shell, and right core had reduced FC with extensive brain regions in PD patients compared with healthy controls. These three subregions were commonly associated with depression, anxiety, apathy, and cognitive impairment. Moreover, the left core and left shell were associated with excessive daytime sleepiness, whereas the right core was associated with olfactory impairment and rapid eye movement sleep behavior disorder.

CONCLUSION

This study for the first time identified the neural network changes of NAc subregions in PD and the associations between network changes and phenotypes of NMS. Our findings provide new insights into the pathogenesis of NMS in PD.

Dopaminergic medication increases motivation to exert cognitive control by reducing subjective effort costs in Parkinson's patients

Engaging in demanding mental activities requires the allocation of cognitive control, which can be effortful and aversive. Individuals thus tend to avoid exerting cognitive effort if less demanding behavioral options are available. Recent accounts propose a key role for dopamine in motivating behavior by increasing the sensitivity to rewards associated with effort exertion. Whether dopamine additionally plays a specific role in modulating the sensitivity to the costs of cognitive effort, even in the absence of any incentives, is much less clear. To address this question, we assessed cognitive effort avoidance in patients (n = 38) with Parkinson's disease, a condition characterized by loss of midbrain dopaminergic neurons, both ON and OFF dopaminergic medication and compared them to healthy controls (n = 24). Effort avoidance was assessed using the Demand Selection Task (DST), in which participants could freely choose between performing a high-demand or a low-demand version of a task-switching paradigm. Critically, participants were not offered any incentives to choose the more effortful option, nor for good performance. While healthy controls and patients OFF their dopaminergic medications consistently preferred the low-demand option, effort avoidance in patients ON dopaminergic medications was reduced compared to patients OFF, a difference which seems to lessen over trials. These differences in preference could not be explained by altered task-switching performance. Although patients ON were less accurate at detecting the different effort levels, as measured during instructed forced-choice blocks, their detection ability was not associated with effort avoidance, unlike in the healthy controls and the patients OFF. Our findings provide evidence that dopamine replacement in Parkinson's patients increases the willingness to engage in cognitively demanding behavior, and that this cannot be explained by possible effects of dopamine replacement on performance nor on the ability to detect effort demands. These results suggest that dopamine plays a role in reducing the sensitivity to effort costs that is independent of its role in enhancing the sensitivity to the benefits of effort exertion.

Microglia Drive Pockets of Neuroinflammation in Middle Age

During aging, microglia produce inflammatory factors, show reduced tissue surveillance, altered interactions with synapses, and prolonged responses to CNS insults, positioning these cells to have profound impact on the function of nearby neurons. We and others recently showed that microglial attributes differ significantly across brain regions in young adult mice. However, the degree to which microglial properties vary during aging is largely unexplored. Here, we analyze and manipulate microglial aging within the basal ganglia, brain circuits that exhibit prominent regional microglial heterogeneity and where neurons are vulnerable to functional decline and neurodegenerative disease. In male and female mice, we demonstrate that VTA and SNc microglia exhibit unique and premature responses to aging, compared with cortex and NAc microglia. This is associated with localized VTA/SNc neuroinflammation that may compromise synaptic function as early as middle age. Surprisingly, systemic inflammation, local neuron death, and astrocyte aging do not appear to underlie these early aging responses of VTA and SNc microglia. Instead, we found that microglial lysosome status was tightly linked to early aging of VTA microglia. Microglial ablation/repopulation normalized VTA microglial lysosome swelling and suppressed increases in VTA microglial density during aging. In contrast, CX3CR1 receptor KO exacerbated VTA microglial lysosome rearrangements and VTA microglial proliferation during aging. Our findings reveal a previously unappreciated regional variation in onset and magnitude of microglial proliferation and inflammatory factor production during aging and highlight critical links between microglial lysosome status and local microglial responses to aging.SIGNIFICANCE STATEMENT Microglia are CNS cells that are equipped to regulate neuronal health and function throughout the lifespan. We reveal that microglia in select brain regions begin to proliferate and produce inflammatory factors in late middle age, months before microglia in other brain regions. These findings demonstrate that CNS neuroinflammation during aging is not uniform. Moreover, they raise the possibility that local microglial responses to aging play a critical role in determining which populations of neurons are most vulnerable to functional decline and neurodegenerative disease.

Decision neuroscience and neuroeconomics: Recent progress and ongoing challenges

In the past decade, decision neuroscience and neuroeconomics have developed many new insights in the study of decision making. This review provides an overarching update on how the field has advanced in this time period. Although our initial review a decade ago outlined several theoretical, conceptual, methodological, empirical, and practical challenges, there has only been limited progress in resolving these challenges. We summarize significant trends in decision neuroscience through the lens of the challenges outlined for the field and review examples where the field has had significant, direct, and applicable impacts across economics and psychology. First, we review progress on topics including reward learning, explore-exploit decisions, risk and ambiguity, intertemporal choice, and valuation. Next, we assess the impacts of emotion, social rewards, and social context on decision making. Then, we follow up with how individual differences impact choices and new exciting developments in the prediction and neuroforecasting of future decisions. Finally, we consider how trends in decision-neuroscience research reflect progress toward resolving past challenges, discuss new and exciting applications of recent research, and identify new challenges for the field. This article is categorized under: Psychology > Reasoning and Decision Making Psychology > Emotion and Motivation.

Musical reward across the lifespan

Music is ubiquitous. Despite the fact that most people find music enjoyable, there are individual differences in the degree to which listeners derive pleasure from music. However, there has been little focus on how musical reward may change across the lifespan. Some theories predict that there would be little change, or even an increase in musical reward across the lifespan, while others suggest that older adults may have decreased capacity for musical reward. Here, we investigated musical reward across the lifespan. Participants consisted of American adults ranging between 20-85 years old (n = 20 participants in each 10-year age bin). Participants in Study 1 completed the Barcelona Music Reward Questionnaire (BMRQ), which is a multi-dimensional assessment of musical reward. We found a negative correlation between age and BMRQ scores, suggesting decreases in musical reward across the lifespan. When investigating which components were driving this effect, we found that the music seeking subscale was the strongest predictor of age. Participants in Study 2 completed the Aesthetic Experiences in Music Scale (AES-M), which focuses on intense emotional responses to music. In contrast to the BMRQ, we found no relationship between age and scores on the AES-M, suggesting that strong emotional responses to music are consistent across the lifespan. These results have implications for the use of music as a therapeutic tool in older adults. In addition, this work points to the importance of considering age when investigating reward for music and suggests that the ways individuals experience music may change across the lifespan.

Role of dopamine and clinical heterogeneity in cognitive dysfunction in Parkinson's disease

Parkinson's disease (PD) is commonly treated with dopaminergic medication, which enhances some, while impairing other cognitive functions. It can even contribute to impulse control disorder and addiction. We describe the history of research supporting the dopamine overdose hypothesis, which accounts for the large within-patient variability in dopaminergic medication effects across different tasks by referring to the spatially non-uniform pattern of dopamine depletion in dorsal versus ventral striatum. However, there is tremendous variability in dopaminergic medication effects not just within patients across distinct tasks, but also across different patients. In the second part of this chapter we review recent studies addressing the large individual variability in the negative side effects of dopaminergic medication on functions that implicate dopamine, such as value-based learning and choice. These studies begin to unravel the mechanisms of dopamine overdosing, thus revising the strict version of the overdose hypothesis. For example, the work shows that the canonical boosting of reward-versus punishment-based choice by medication is greater in patients with depression and a non-tremor phenotype, which both implicate, among other pathology, more rather than less severe dysregulation of the mesolimbic dopamine system. Future longitudinal cohort studies are needed to identify how to optimally combine different clinical, personality, cognitive, neural, genetic and molecular predictors of detrimental medication effects in order to account for as much of the relevant variability as possible. This will provide a useful tool for precision neurology, allowing individual and contextual tailoring of (the dose of) dopaminergic medication in order to maximize its cognitive benefits, yet minimize its side effects.

Influences of dopaminergic system dysfunction on late-life depression

Deficits in cognition, reward processing, and motor function are clinical features relevant to both aging and depression. Individuals with late-life depression often show impairment across these domains, all of which are moderated by the functioning of dopaminergic circuits. As dopaminergic function declines with normal aging and increased inflammatory burden, the role of dopamine may be particularly salient for late-life depression. We review the literature examining the role of dopamine in the pathogenesis of depression, as well as how dopamine function changes with aging and is influenced by inflammation. Applying a Research Domain Criteria (RDoC) Initiative perspective, we then review work examining how dopaminergic signaling affects these domains, specifically focusing on Cognitive, Positive Valence, and Sensorimotor Systems. We propose a unified model incorporating the effects of aging and low-grade inflammation on dopaminergic functioning, with a resulting negative effect on cognition, reward processing, and motor function. Interplay between these systems may influence development of a depressive phenotype, with an initial deficit in one domain reinforcing decline in others. This model extends RDoC concepts into late-life depression while also providing opportunities for novel and personalized interventions.