Inverted-U-shaped dopamine actions on human working memory and cognitive control

The dopaminergic system and Alzheimer's disease

Alzheimer's disease is a common neurodegenerative disorder in older adults. Despite its prevalence, its pathogenesis remains unclear. In addition to the most widely accepted causes, which include excessive amyloid-beta aggregation, tau hyperphosphorylation, and deficiency of the neurotransmitter acetylcholine, numerous studies have shown that the dopaminergic system is also closely associated with the occurrence and development of this condition. Dopamine is a crucial catecholaminergic neurotransmitter in the human body. Dopamine-associated treatments, such as drugs that target dopamine receptor D and dopamine analogs, can improve cognitive function and alleviate psychiatric symptoms as well as ameliorate other clinical manifestations. However, therapeutics targeting the dopaminergic system are associated with various adverse reactions, such as addiction and exacerbation of cognitive impairment. This review summarizes the role of the dopaminergic system in the pathology of Alzheimer's disease, focusing on currently available dopamine-based therapies for this disorder and the common side effects associated with dopamine-related drugs. The aim of this review is to provide insights into the potential connections between the dopaminergic system and Alzheimer's disease, thus helping to clarify the mechanisms underlying the condition and exploring more effective therapeutic options.

The Sustained Attention Paradox: A Critical Commentary on the Theoretical Impossibility of Perfect Vigilance

The human capacity for sustained attention represents a critical cognitive paradox: while essential for numerous high-stakes tasks, perfect vigilance is fundamentally impossible. This commentary explores the theoretical impossibility of maintaining uninterrupted attention, drawing from extensive interdisciplinary research in cognitive science, neuroscience, and psychology. Multiple converging lines of evidence demonstrate that sustained attention is constrained by neural, biological, and cognitive limitations. Neural mechanisms reveal that attention operates through rhythmic oscillations, with inherent fluctuations in frontoparietal networks and default mode network interactions. Neurochemical systems and cellular adaptation effects further underscore the impossibility of continuous, perfect vigilance. Empirical research across domains-including aviation, healthcare, industrial safety, and security-consistently demonstrates rapid declines in attention performance over time, regardless of individual expertise or motivation. Even elite performers like military personnel and experienced meditators exhibit inevitable attention lapses. This paper presents an argument against traditional approaches that seek to overcome these limitations through training or willpower. Instead, it advocates for designing human-technology systems that work harmoniously with cognitive constraints. This requires developing adaptive automation, understanding individual and cultural attention variations, and creating frameworks that strategically balance human capabilities with technological support.

Translational Evidence for Dopaminergic Rewiring of the Basal Ganglia in Persons with Schizophrenia

Importance

In prior work, a transgenic mouse model of the striatal dopamine dysfunction observed in persons with schizophrenia (PSZ) exhibited dopamine-related neuroplasticity in the basal ganglia. This phenotype has never been demonstrated in human PSZ.

Objective

To identify a specific dopamine-related alteration of basal ganglia connectivity via task-based and resting-state functional magnetic resonance imaging (fMRI), neuromelanin-sensitive MRI (NM-MRI), and positron emission tomography (PET), in unmedicated PSZ.

Design

This case-control study of unmedicated PSZ and healthy controls (HC) occurred between November 2014 and June 2018, with analyses performed between April 2023 and February 2025.

Setting

fMRI and NM-MRI were collected at New York State Psychiatric Institute. [ 11 C]-(+)-PHNO PET was collected at Yale University.

Participants

Participants were aged 18-55, and demographically matched. PSZ were antipsychotic drug-naïve or drug-free for at least three weeks prior to recruitment.

Main Outcomes and Measures

1) task-state and resting-state functional connectivity (FC) between dorsal caudate (DCa) and globus pallidus externus (GPe), 2) NM-MRI contrast ratio in substantia nigra voxels associated with psychotic symptom severity, and 3) baseline and amphetamine-induced change in [ 11 C]-(+)-PHNO binding potential in DCa.

Results

37 PSZ (mean±SD age, 32.7±12.7 years, 29.7% female) and 30 HC (32.5±9.7 years, 26.7% female) underwent resting-state fMRI; 29 PSZ (33.4±12.7 years, 31% female) and 29 HC (32.4±9.7 years, 31% female) underwent working memory task-based fMRI. 22 PSZ (35.1±13.9 years, 36.4% female) and 20 HC (29.4±8.5 years, 35% female) underwent NM-MRI. 7 PSZ (23.1±6.3 years, 57.1% female) and 4 HC (31.5±11.9 years, 25% female) underwent [ 11 C]-(+)-PHNO PET with amphetamine challenge. PSZ displayed elevated task-state FC (0.11±0.10 versus 0.05±0.09 in HC; P =0.0252), which was associated with increased NM-MRI contrast ratio (β* [SE] = 0.40 [0.17]; P =0.023), decreased baseline D2 receptor availability (β* [SE] = - 0.45 [0.17]; P =0.039), greater amphetamine-induced dopamine release (β* [SE] = -0.82 [0.27]; P =0.021), and worse task performance (β* [SE] = -0.31 [0.13]; P =0.020).

Conclusions and Relevance

This study provides in-vivo evidence of a dopamine-associated neural abnormality of DCa and GPe connectivity in unmedicated PSZ. This phenotype suggests a potential neurodevelopmental mechanism of working memory deficits in schizophrenia, representing a critical step towards developing treatments for cognitive deficits.

Key Points

Question: Do unmedicated persons with schizophrenia display dopamine-related alterations in basal ganglia functional connectivity?Findings: In this case-control study, we observed hyperconnectivity between the dorsal caudate and globus pallidus externus during a working memory task in unmedicated persons with schizophrenia. This phenotype was associated with worse task performance and measures of subcortical dopamine function obtained via neuromelanin-sensitive magnetic resonance imaging and [ 11 C]-(+)-PHNO positron emission tomography. Meaning: This study provides in-vivo evidence that dopaminergic rewiring of the basal ganglia may be a neurodevelopmental mechanism for working memory deficits in schizophrenia, emulating findings from a transgenic mouse model of striatal dopamine dysfunction.

Methamphetamine-induced adaptation of learning rate dynamics depend on baseline performance

The ability to calibrate learning according to new information is a fundamental component of an organism's ability to adapt to changing conditions. Yet, the exact neural mechanisms guiding dynamic learning rate adjustments remain unclear. Catecholamines appear to play a critical role in adjusting the degree to which we use new information over time, but individuals vary widely in the manner in which they adjust to changes. Here, we studied the effects of a low dose of methamphetamine (MA), and individual differences in these effects, on probabilistic reversal learning dynamics in a within-subject, double-blind, randomized design. Participants first completed a reversal learning task during a drug-free baseline session to provide a measure of baseline performance. Then they completed the task during two sessions, one with MA (20 mg oral) and one with placebo (PL). First, we showed that, relative to PL, MA modulates the ability to dynamically adjust learning from prediction errors. Second, this effect was more pronounced in participants who performed moderately low at baseline. These results present novel evidence for the involvement of catecholaminergic transmission on learning flexibility and highlights that baseline performance modulates the effect of the drug.

Dopaminergic modulation and dosage effects on brain state dynamics and working memory component processes in Parkinson's disease

Parkinson's disease (PD) is primarily diagnosed through its characteristic motor deficits, yet it also encompasses progressive cognitive impairments that profoundly affect quality of life. While dopaminergic medications are routinely prescribed to manage motor symptoms in PD, their influence extends to cognitive functions as well. Here we investigate how dopaminergic medication influences aberrant brain circuit dynamics associated with encoding, maintenance and retrieval working memory (WM) task-phases processes. PD participants, both on and off dopaminergic medication, and healthy controls, performed a Sternberg WM task during fMRI scanning. We employ a Bayesian state-space computational model to delineate brain state dynamics related to different task phases. Importantly, a within-subject design allows us to examine individual differences in the effects of dopaminergic medication on brain circuit dynamics and task performance. We find that dopaminergic medication alters connectivity within prefrontal-basal ganglia-thalamic circuits, with changes correlating with enhanced task performance. Dopaminergic medication also restores engagement of task-phase-specific brain states, enhancing task performance. Critically, we identify an "inverted-U-shaped" relationship between medication dosage, brain state dynamics, and task performance. Our study provides valuable insights into the dynamic neural mechanisms underlying individual differences in dopamine treatment response in PD, paving the way for more personalized therapeutic strategies.

Androgen effects on mesoprefrontal dopamine systems in the adult male brain

Epidemiological data show that males are more often and/or more severely affected by symptoms of prefrontal cortical dysfunction in schizophrenia, Parkinson's disease and other disorders in which dopamine circuits associated with the prefrontal cortex are dysregulated. This review focuses on research showing that these dopamine circuits are powerfully regulated by androgens. It begins with a brief overview of the sex differences that distinguish prefrontal function in health and prefrontal dysfunction or decline in aging and/or neuropsychiatric disease. This review article then spotlights data from human subjects and animal models that specifically identify androgens as potent modulators of prefrontal cortical operations and of closely related, functionally critical measures of prefrontal dopamine level or tone. Candidate mechanisms by which androgens dynamically control mesoprefrontal dopamine systems and impact prefrontal states of hypo- and hyper-dopaminergia in aging and disease are then considered. This is followed by discussion of a working model that identifies a key locus for androgen modulation of mesoprefrontal dopamine systems as residing within the prefrontal cortex itself. The last sections of this review critically consider the ways in which the organization and regulation of mesoprefrontal dopamine circuits differ in the adult male and female brain, and highlights gaps where more research is needed.

Sustained effects of repeated levodopa (L-DOPA) administration on reward circuitry, effort-based motivation, and anhedonia in depressed patients with higher inflammation

Inflammatory biomarkers like C-reactive protein (CRP) are elevated in a subset of patients with depression and have been associated with lower functional connectivity (FC) in a ventral striatum (VS) to ventromedial prefrontal cortex (vmPFC) reward circuit and symptoms of anhedonia. Evidence linking these relationships to the effects of inflammation on dopamine is consistent with our recent findings that acute levodopa (L-DOPA) increased VS-vmPFC FC in association with deceased anhedonia in depressed patients with higher but not lower CRP (>2 versus ≤ 2 mg/L). To determine whether repeated L-DOPA administration caused sustained effects on FC and behavior in these patients, medically stable depressed outpatients with CRP > 2 mg/L and anhedonia (n = 18) received one week of three doses of L-DOPA (150-450 mg/day/week with carbidopa) or placebo in a randomized order. Resting-state (rs) and task-based (tb; monetary incentive delay) fMRI, effort-based motivation, and exploratory measures of anhedonia and depression severity were assessed at baseline and after one week of placebo and each dose of L-DOPA. Responses to individual doses of L-DOPA varied across outcomes. For example, VS-vmPFC rs-FC was significantly increased by L-DOPA at 150 and 450 mg/day/week (p < 0.01), whereby approximately half of patients responded optimally to 150 mg/day L-DOPA and approximately half required higher doses for maximum effect. While effort-based motivation was only significantly increased by L-DOPA at 150 mg/day (p < 0.05), it correlated with VS-vmPFC rs-FC at this dose (r = 0.64, p = 0.024), and all L-DOPA doses met a clinically significant threshold of ≥ 10 % increase versus placebo. When comparing the maximum response at any L-DOPA dose to placebo, high effect sizes were observed for these primary outcomes and tb-FC during reward anticipation (dz = 0.82-0.98, p < 0.01), as well as secondary and exploratory measures of anhedonia and depression severity (dz = 0.48-0.97, p < 0.05). Sustained effects on reward circuitry, effort-based motivation, and anhedonia by repeated L-DOPA administration support the therapeutic potential of agents that increase dopamine in depressed patients with higher inflammation.

Acute Administration of 10 mg Methylphenidate on Cognitive Performance and Visual Scanning in Healthy Adults: Randomised, Double-Blind, Placebo-Controlled Study

OBJECTIVE

To examine the effect of a low dose (10 mg) of methylphenidate on cognitive performance, visuospatial working memory (VSWM) and gaze behaviour capabilities in healthy adults.

METHODS

This randomised, double-blind, placebo-controlled and crossover study examined the effects of 10 mg methylphenidate on cognitive performance, VSWM and gaze behaviour. Fixation duration and rate, gaze transition entropy, and stationary gaze entropy were used to quantify visual scanning efficiency in 25 healthy adults (36% female, mean ± SD age = 33.5 ± 7.8 years, BMI = 24.1 ± 2.9 kg/m2). Attention, memory, and reaction time were assessed using the E-CogPro test battery.

RESULTS

Methylphenidate significantly enhanced performance in numeric working memory tasks, reflected by reduced errors and increased accuracy relative to placebo. No significant changes were observed in other cognitive or visual scanning metrics.

CONCLUSIONS

A low dose of methylphenidate improves limited domains of psychomotor speed and accuracy but does not affect visual scanning efficiency. This suggests limited usefulness as a general pro-cognitive aid and raises the possibility of a lower threshold of effect for measurable psychostimulant-induced changes to visual scanning behaviour. Further research is needed to explore these potential dose-response relationships and effects across diverse populations.

TRIAL REGISTRATION

ACTRN12620000499987.

Scopolamine animal model of memory impairment

In this study, we reassessed the suitability of a commonly used pharmacological animal model of Alzheimer's disease (AD) - scopolamine-induced memory impairment. The goal of the study was to explore if this animal model induces other behavioral changes associated with AD. One of the key behavioral features of AD, manifesting already during the early stages of the illness, is apathy-like behavior. We also evaluated how behavioral alterations induced by scopolamine compare to those seen in healthy aging animals. To achieve these goals, locomotor activity and short-term memory of young male Wistar rats were tested in the open field, novel object recognition (NOR) and T-maze spontaneous alternation tests before, during and after 21 daily administrations of scopolamine. Three-, ten- and nineteen-month-old male and female rats were used to measure age-related changes in these behaviors. Our data showed that although both scopolamine treatment and aging reduced the number of approaches to the objects and their exploration time during the NOR test, correlation with impaired object recognition memory was only observed in the scopolamine treated animals. Furthermore, treatment with scopolamine significantly increased the locomotor activity, which could be observed even one week after treatment discontinuation. Contrary, locomotor activity in older rats was significantly lower than that of younger rats. These findings demonstrate that the animal model of scopolamine-induced memory impairment fails to incorporate apathy-like symptoms characteristic to the AD and age-related reduction in physical activity of older rats.

Methylphenidate in Borderline Personality Disorder: Assessing Its Therapeutic Potential and Limitations

Impulsivity is increasingly recognized as a transdiagnostic feature that spans multiple psychiatric disorders, including borderline personality disorder (BPD), bipolar disorder, and substance use disorders. In BPD, impulsive behaviors manifest as substance misuse, risky sexual activity, self-injury, and other maladaptive patterns. This review article updates the clinical and preclinical literature to explore the biological and psychological bases of impulsivity in BPD and considers whether methylphenidate (MPH) can be used as a treatment in this context. Although no medication is specifically approved for BPD, limited evidence from patients with comorbid BPD and attention-deficit/hyperactivity disorder (ADHD) indicates that MPH may reduce impulsivity and improve key symptoms. In addition, real-world data indicate that MPH may be associated with better outcomes and a lower risk of suicidal behaviors in patients with BPD. Nevertheless, such evidence remains scant, particularly among those with a primary diagnosis of BPD without a diagnosis of ADHD. Larger, methodologically rigorous studies are needed to clarify the efficacy and safety of MPH in targeting impulsivity within this population. An improved understanding of dopaminergic mechanisms may eventually shed light on MPH's therapeutic role in BPD, although current data remain preliminary. Overall, recognizing impulsivity as a core symptom rather than focusing exclusively on diagnostic boundaries may facilitate more tailored and effective interventions for BPD.

Negative affect-driven impulsivity as hierarchical model-based overgeneralization

'If your mouth is burned by milk, you blow before you eat yogurt' ('Sütten ağzı yanan yoğurdu üfleyerek yer'). This Turkish proverb advises caution based on past experiences when similar situations are encountered. However, although we may infer similarities across experiences, each situation is a complex combination of many features, and generalizing across situations based on perceived similarities may not achieve desired outcomes when obtaining them depends on more subtle or overlooked features. Here, we examine how models of generalization can uncover the model-based (MB) processes underlying reactive and rigid behaviors traditionally considered model-free (MF). Our novel conceptualization suggests that emotionally driven impulsive behaviors stem from a propensity to overgeneralize based on surface-level similarities, hindering the incorporation of other informative, discriminant cues.

Pharmacological Modulation of Dopamine Receptors Reveals Distinct Brain-Wide Networks Associated with Learning and Motivation in Nonhuman Primates

The neurotransmitter dopamine (DA) has a multifaceted role in healthy and disordered brains through its action on multiple subtypes of dopaminergic receptors. How the modulation of these receptors influences learning and motivation by altering intrinsic brain-wide networks remains unclear. Here, we performed parallel behavioral and resting-state functional MRI experiments after administration of two different DA receptor antagonists in male and female macaque monkeys. Systemic administration of SCH-23390 (D1 antagonist) slowed probabilistic learning when subjects had to learn new stimulus-reward associations and diminished functional connectivity (FC) in corticocortical and frontostriatal connections. In contrast, haloperidol (D2 antagonist) improved learning and broadly enhanced FC in cortical connections. Further comparisons between the effect of SCH-23390/haloperidol on behavioral and resting-state FC revealed specific cortical and subcortical networks associated with the cognitive and motivational effects of DA manipulation, respectively. Thus, we reveal distinct brain-wide networks that are associated with the dopaminergic control of learning and motivation via DA receptors.

Neurobiological influences on event perception: the role of catecholamines

BACKGROUND

Event segmentation, the cognitive process of parsing continuous experiences into discrete events, plays a fundamental role in how humans perceive and interact with their environment. Guided by Event Segmentation Theory, this study investigates the modulation of event segmentation by the catecholaminergic system by methylphenidate (MPH).

METHODS

Healthy adult participants (N = 52) engaged in a double-blind, counter-balanced, placebo-controlled experiment in which they watched a movie and identified event boundaries under placebo and MPH conditions.

RESULTS

With the same information given, MPH increased the likelihood that the information was considered meaningful. Crucially, the number of situational changes and participant's prior experience had an interactive effect on the probability of event segmentation. There was a stronger relationship between environmental information and segmentation probability when catecholaminergic levels were elevated by MPH in addition to previous experience.

CONCLUSIONS

The catecholaminergic system modulates how incoming information is segmented to build meaningful episodes. Prior experience supports the effects of MPH to unfold. These findings underscore the complex interplay between neurochemical modulation and cognitive processes involved in event perception.

Self-prioritization in working memory gating

Working memory (WM) involves a dynamic interplay between temporary maintenance and updating of goal-relevant information. The balance between maintenance and updating is regulated by an input-gating mechanism that determines which information should enter WM (gate opening) and which should be kept out (gate closing). We investigated whether updating and gate opening/closing are differentially sensitive to the kind of information to be encoded and maintained in WM. Specifically, since the social salience of a stimulus is known to affect cognitive performance, we investigated if self-relevant information differentially impacts maintenance, updating, or gate opening/closing. Participants first learned to associate two neutral shapes with two social labels (i.e., "you" vs. "stranger"), respectively. Subsequently they performed the reference-back paradigm, a well-established WM task that disentangles WM updating, gate opening, and gate closing. Crucially, the shapes previously associated with the self or a stranger served as target stimuli in the reference-back task. We replicated the typical finding of a repetition benefit when consecutive trials require opening the gate to WM. In Study 1 (N = 45) this advantage disappeared when self-associated stimuli were recently gated into WM and immediately needed to be replaced by stranger-associated stimuli. However, this was not replicated in a larger sample (Study 2; N = 90), where a repetition benefit always occurred on consecutive gate-opening trials. Overall, our results do not provide evidence that the self-relevance of stimuli modulates component processes of WM. We discuss possible reasons for this null finding, including the importance of continuous reinstatement and task-relevance of the shape-label associations.

Noradrenergic and Dopaminergic modulation of meta-cognition and meta-control

Humans and animals use multiple control systems for decision-making. This involvement is subject to meta-cognitive regulation - as a form of control over control or meta-control. However, the nature of this meta-control is unclear. For instance, Model-based (MB) control may be boosted when decision-makers generally lack confidence as it is more statistically efficient; or it may be suppressed, since the MB controller can correctly assess its own unreliability. Since control and metacontrol are themselves subject to the influence of neuromodulators, we examined the effects of perturbing the noradrenergic (NE) and dopaminergic (DA) systems with propranolol and L-DOPA, respectively. We first administered a simple perceptual task to examine the effects of the manipulations on meta-cognitive ability. Using Bayesian analyses, we found that 81% of group M-ratio samples were lower under propranolol relative to placebo, suggesting a decrease of meta-cognitive ability; and 60% of group M-ratio samples were higher under L-DOPA relative to placebo, considered as no effect of L-DOPA on meta-cognitive ability . We then asked subjects to provide choices and confidence ratings in a two-outcome decision-making task that has been used to dissociate Model-free (MF) and MB control. MB behavior was enhanced by propranolol, while MF behavior was not significantly affected by either drug. The interaction between confidence and MF/MB behavior was highly variable under propranolol, but under L-DOPA, the interaction was significantly lower/higher relative to placebo. Our results suggest a decrease in metacognitive ability under the influence of propranolol and an enhancement of MB behavior and meta-control under the influence of propranolol and L-DOPA, respectively. These findings shed light on the role of NE and DA in different aspects of control and meta-control and suggest potential avenues for mitigating dysfunction.

Methylphenidate stabilizes dynamic brain network organization during tasks probing attention and reward processing in stimulant-naïve children with ADHD

Children with ADHD often exhibit fluctuations in attention and heightened reward sensitivity. Psychostimulants, such as methylphenidate (MPH), improve these behaviors in many, but not all, children with ADHD. Given the extent to which psychostimulants are prescribed for children, coupled with variable efficacy on an individual level, a better understanding of the mechanisms through which MPH changes brain function and behavior is necessary. MPH's primary action is on catecholamines, including dopamine and norepinephrine. Catecholaminergic signaling can influence the tradeoff between flexibility and stability of brain function, which is one candidate mechanism through which MPH may alter brain function and behavior. Time-varying functional connectivity, which models how functional brain networks reconfigure on short timescales, can be used to examine brain flexibility versus stability, and is thus well-suited to test how MPH impacts brain function. Here, we scanned stimulant-naïve children with ADHD (8-12 years) on and off a single dose of MPH. In the MRI machine, participants completed two attention-demanding tasks: 1) a standard go/no-go task and 2) a rewarded go/no-go task. For both tasks, using a within-subjects design, we compared the degree to which brain organization changed throughout the course of the MRI scan, termed whole brain flexibility, on and off MPH. We found that whole brain flexibility decreased on MPH. Further, individuals with greater decreases in whole brain flexibility on MPH exhibited greater improvements in task performance. Together, these results provide novel insights into the neurobiological mechanisms underlying the effectiveness of MPH administration for children with ADHD.

Age-Related Changes in Caudate Glucose Metabolism: Insights from Normative Modeling Study in Healthy Subjects

BACKGROUND

As the global population ages, the prevalence of neurodegenerative conditions, such as Alzheimer's disease (AD), Parkinson's disease (PD), dementia with Lewy bodies, and frontotemporal dementia, continues to rise. Understanding the impact of aging on striatal glucose metabolism is pivotal in identifying potential biomarkers for the early detection of these disorders.

METHODS

We investigated age-related changes in striatal glucose metabolism using both region of interest (ROI)-based and voxel-wise correlation analyses. Additionally, we employed a normative modeling approach to establish age-related metabolic trajectories and assess individual deviations from these normative patterns. In vivo cerebral glucose metabolism was quantified using a molecular neuroimaging technique, 18F-FDG PET.

RESULTS

Our results revealed significant negative correlations between age and glucose metabolism in the bilateral caudate. Furthermore, the normative modeling demonstrated a clear, progressive decline in caudate metabolism with advancing age, and the most pronounced reductions were observed in older individuals.

CONCLUSIONS

These findings suggest that metabolic reductions in the caudate may serve as a sensitive biomarker for normal aging and offer valuable insights into the early stages of neurodegenerative diseases. Moreover, by establishing age-specific reference values for caudate glucose metabolism, the normative model provides a framework for detecting deviations from expected metabolic patterns, which may facilitate the early identification of metabolic alterations that could precede clinical symptoms of neurodegenerative processes.

Impairment of neuronal activity in the dorsolateral prefrontal cortex occurs early in parkinsonism

Background

Parkinson's disease (PD) is often characterized by altered rates and patterns of neuronal activity in the sensorimotor regions of the basal ganglia thalamocortical network. Little is known, however, regarding how neuronal activity in the executive control network of the brain changes in the parkinsonian condition.

Objective

Investigate the impact of parkinsonism on neuronal activity in the dorsolateral prefrontal cortex (DLPFC), a key region in executive control, during a go/nogo reaching task.

Methods

Using a within-subject design, single and multi-unit neuronal activity was recorded in the DLPFC of a nonhuman primate (n = 1) before and after the induction of mild parkinsonism using the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

Results

Coincident with development of mild parkinsonian motor signs, there was a marked reduction in the percentage of DLPFC cells with significant task-related firing rate modulation during go and nogo conditions.

Conclusion

These results suggest that DLPFC dysfunction may occur early in parkinsonism and contribute to cognitive impairments and disrupted executive function often observed in PD patients.

Probing the Neurodynamic Mechanisms of Cognitive Flexibility in Depressed Individuals with Autism Spectrum Disorder

Introduction: Autism spectrum disorder (ASD) is characterized by deficits in social behavior and executive function (EF), particularly in cognitive flexibility. Whether transcranial magnetic stimulation (TMS) can improve cognitive outcomes in patients with ASD remains an open question. We examined the acute effects of prefrontal TMS on cortical excitability and fluid cognition in individuals with ASD who underwent TMS for refractory major depression. Methods: We analyzed data from an open-label pilot study involving nine participants with ASD and treatment-resistant depression who received 30 sessions of accelerated theta burst stimulation of the dorsolateral prefrontal cortex, either unilaterally or bilaterally. Electroencephalography data were collected at baseline and 1, 4, and 12-weeks posttreatment and analyzed using a mixed-effects linear model to assess changes in regional cortical excitability using three models of spectral parametrization. Fluid cognition was measured using the National Institutes of Health Toolbox Cognitive Battery. Results: Prefrontal TMS led to a decrease in prefrontal cortical excitability and an increase in right temporoparietal excitability, as measured using spectral exponent analysis. This was associated with a significant improvement in the NIH Toolbox Fluid Cognition Composite score and the Dimensional Change Card Sort subtest from baseline to 12 weeks posttreatment (t = 3.79, p = 0.005, n = 9). Improvement in depressive symptomatology was significant (HDRS-17, F (3, 21) = 28.49, p < 0.001) and there was a significant correlation between cognitive improvement at week 4 and improvement in depression at week 12 (r = 0.71, p = 0.05). Conclusion: These findings link reduced prefrontal excitability in patients with ASD and improvements in cognitive flexibility. The degree to which these mechanisms can be generalized to ASD populations without Major Depressive Disorder remains a compelling question for future research.

How dopamine shapes trust beliefs

Learning whom to trust is integral for healthy relationships and social cohesion, and atypicalities in trust learning are common across a range of clinical conditions, including schizophrenia spectrum disorders, Parkinson's disease, and depression. Persecutory delusions - rigid, unfounded beliefs that others are intending to harm oneself - significantly impact affected individuals' lives as they are associated with a range of negative health outcomes, including suicidal behaviour and relapse. Recent advances in computational modelling and psychopharmacology have significantly extended our understanding of the brain bases of dynamic trust learning, and the neuromodulator dopamine has been suggested to play a key role in this. However, the specifics of this role on a computational and neurobiological level remain to be fully established. The current review article provides a comprehensive summary of novel conceptual developments and empirical findings regarding the computational role of dopamine in social learning processes. Research findings strongly suggest a conceptual shift, from dopamine as a reward mechanism to a teaching signal indicating which information is relevant for learning, and shed light on the neurocomputational mechanisms via which antipsychotics may alleviate symptoms of aberrant social learning processes such as persecutory delusions. Knowledge gaps and inconsistencies in the extant literature are examined and the most pressing issues highlighted, laying the foundation for future research that will further advance our understanding of the neuromodulation of social belief updating processes.

Effect of individual variations in genes related to dopamine brain transmission on performance with and without rewards during motor sequence and probabilistic learning tasks in children and young adults with and without cerebral palsy

Children with cerebral palsy (CP) often participate in training to improve mobility, hand function and other motor abilities. However, responses to these interventions vary considerably across individuals even those with similar brain injuries, ages and functional levels. Dopamine is a neurotrasmitter known to affect motor skill acquistion in animals and humans and may be influenced by individual variations in genes related to brain transmission of dopamine. To evaluate potential genetic influences on learning in young people with and without CP, we calculated individual dopamine-related gene scores and compared these to the ability to learn two different tasks, an implicit sequence learning task and a probablistic classification task. Each task was also administered in an unrewarded condition and a rewarded one known to increase circulating levels of dopamine. The main finding was an interaction between gene score and condition for the sequence task such that those with low gene scores were poorer learners without rewards but responded positively to rewards whereas the converse was true for those with high gene scores. This is the first prospective study in CP suggesting that genetic variability may influence neurorehabilitation outcomes and could potentially be modulated using rewards or medications for those with poorer learning at baseline, thus promoting more personalized approaches to enhancing motor training in CP and other neurological conditions.

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.

The developing mouse dopaminergic system: Cortical-subcortical shift in D1/D2 receptor balance and increasing regional differentiation

The dopaminergic system of the brain is involved in complex cognitive functioning and undergoes extensive reorganization during development. Yet, these changes are poorly characterized. We have quantified the density of dopamine 1- and 2-receptor (D1 and D2) positive cells across the forebrain of male and female mice at five developmental stages using validated transgenic mice expressing green fluorescent protein in cells producing D1 or D2 mRNA. After analyzing >4,500 coronal brain images, a cortico-subcortical shift in D1/D2 balance was discovered, with increasing D1 dominance in cortical regions as a maturational pattern that occurs earlier in females. We describe postnatal trajectories of D1 and D2 cell densities across major brain regions and observe increasing regional differentiation of D1 densities through development. Our results provide the most comprehensive overview of the developing dopaminergic system to date, and an empirical foundation for further experimental and computational investigations of dopaminergic signaling.

Static and Dynamic Dysconnectivity in Early Psychosis: Relationship With Symptom Dimensions

BACKGROUND AND HYPOTHESIS

Altered functional connectivity (FC) has been frequently reported in psychosis. Studying FC and its time-varying patterns in early-stage psychosis allows the investigation of the neural mechanisms of this disorder without the confounding effects of drug treatment or illness-related factors.

STUDY DESIGN

We employed resting-state functional magnetic resonance imaging (rs-fMRI) to explore FC in individuals with early psychosis (EP), who also underwent clinical and neuropsychological assessments. 96 EP and 56 demographically matched healthy controls (HC) from the Human Connectome Project for Early Psychosis database were included. Multivariate analyses using spatial group independent component analysis were used to compute static FC and dynamic functional network connectivity (dFNC). Partial correlations between FC measures and clinical and cognitive variables were performed to test brain-behavior associations.

STUDY RESULTS

Compared to HC, EP showed higher static FC in the striatum and temporal, frontal, and parietal cortex, as well as lower FC in the frontal, parietal, and occipital gyrus. We found a negative correlation in EP between cognitive function and FC in the right striatum FC (pFWE = 0.009). All dFNC parameters, including dynamism and fluidity measures, were altered in EP, and positive symptoms were negatively correlated with the meta-state changes and the total distance (pFWE = 0.040 and pFWE = 0.049).

CONCLUSIONS

Our findings support the view that psychosis is characterized from the early stages by complex alterations in intrinsic static and dynamic FC, that may ultimately result in positive symptoms and cognitive deficits.

Volatile oil from Acori graminei Rhizoma affected the synaptic plasticity of rats with tic disorders by modulating dopaminergic and glutamatergic systems

ETHNOPHARMACOLOGICAL RELEVANCE

Acori graminei Rhizoma is a commonly used traditional Chinese medicine for treating TD, with its main component being calamus volatile oil. Volatile Oil from Acori graminei Rhizoma (VOA)can protect nerve cells and alleviate learning and memory disorders. However, the mechanism of anti-tic of VOA is still unclear.

AIM OF THE STUDY

We aimed to explore the effects of Volatile Oil from Acori Tatarinowii Rhizoma (VOA) on striatal dopaminergic and glutamatergic systems and synaptic plasticity of rats with Tic Disorder (TD), as well as its pharmaceutical mechanism against TD.

MATERIALS AND METHODS

This study involved 48 (three-week-old) Sprague Dawley (SD) rats, which were randomly divided into two primary groups: Control (8) and TD (40). Rats in the TD group were injected intraperitoneally with 3,3-iminodipropionitrile (IDPN) to construct the TD rat model. They were divided into five subgroups: Model, Tiapride, VOA-high, VOA-medium, and VOA-low (N = 8). After modeling, VOA was administrated to rats in the VOA groups through gavage (once/day for four consecutive weeks), while rats in the blank control and model groups received normal saline of the same volume. The animals' behavioral changes were reflected using the stereotypic and motor behavior scores. After interferences, patterns of striatal neurons and the density of dendritic spines were investigated using H&E and Golgi staining, and the ultrastructure of striatal synapses was examined using Transmission Electron Microscopy (TEM). Furthermore, Ca2+ content was determined using the Ca2+ detector, and Dopamine (DA) and Glutamate (GLU) contents in serum and striatum were detected through ELISA. Finally, DRD1, DRD2, AMPAR1, NMPAR1, DAT, VMAT2, CAMKⅡ, and CREB expression in the striatum was detected using Quantitative real-time PCR (qRT-PCR), Western Blotting (WB) and Immunohistochemical (IHC) methods.

RESULTS

Compared to rats in the blank control and model groups, rats in the VOA groups showed lower stereotypic behavior scores. Furthermore, rats in the VOA groups exhibited relieved, neuron damage and increased quantities of neuronal dendrites and dendritic spines Additionally, based on TEM images show that, the VOA groups showed a clear synaptic structure and increased amounts of postsynaptic dense substances and synaptic vesicles. The VOA groups also exhibited reduced Ca2+ contents, and upregulation of DRD1, DRD2, DAT, AMPAR1, and NMPAR1 and downregulation of VMAT-2, CAMKⅡ, and CREB in the striatum.

CONCLUSIONS

In summary, VOA could influence synaptic plasticity by tuning the dopaminergic and glutamatergic systems, thus relieving TD.

Amygdala activity after subchronic escitalopram administration in healthy volunteers: A pharmaco-functional magnetic resonance imaging study

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are used for the treatment of several conditions including anxiety disorders, but the basic neurobiology of serotonin function remains unclear. The amygdala and prefrontal cortex are strongly innervated by serotonergic projections and have been suggested to play an important role in anxiety expression. However, serotonergic function in behaviour and SSRI-mediated neurobiological changes remain incompletely understood.

AIMS

To investigate the neural correlates of subchronic antidepressant administration.

METHODS

We investigated whether the 2- to 3-week administration of a highly selective SSRI (escitalopram) would alter brain activation on a task robustly shown to recruit the bilateral amygdala and frontal cortices in a large healthy volunteer sample. Participants performed the task during a functional magnetic resonance imaging acquisition before (n = 96) and after subchronic escitalopram (n = 46, days of administration mean (SD) = 15.7 (2.70)) or placebo (n = 40 days of administration mean (SD) = 16.2 (2.90)) self-administration.

RESULTS

Compared to placebo, we found an elevation in right amygdala activation to the task after escitalopram administration without significant changes in mood. This effect was not seen in the left amygdala, the dorsomedial region of interest, the subgenual anterior cingulate cortex or the right fusiform area. There were no significant changes in connectivity between the dorsomedial cortex and amygdala or the subgenual anterior cingulate cortex after escitalopram administration.

CONCLUSIONS

To date, this most highly powered study of subchronic SSRI administration indicates that, contrary to effects often seen in patients with anxiety disorders, subchronic SSRI treatment may increase amygdala activation in healthy controls. This finding highlights important gaps in our understanding of the functional role of serotonin.

Reward Reinforcement Creates Enduring Facilitation of Goal-directed Behavior

Stimulus-response habits benefit behavior by automatizing the selection of rewarding actions. However, this automaticity can come at the cost of reduced flexibility to adapt behavior when circumstances change. The goal-directed system is thought to counteract the habit system by providing the flexibility to pursue context-appropriate behaviors. The dichotomy between habitual action selection and flexible goal-directed behavior has recently been challenged by findings showing that rewards bias both action and goal selection. Here, we test whether reward reinforcement can give rise to habitual goal selection much as it gives rise to habitual action selection. We designed a rewarded, context-based perceptual discrimination task in which performance on one rule was reinforced. Using drift-diffusion models and psychometric analyses, we found that reward facilitates the initiation and execution of rules. Strikingly, we found that these biases persisted in a test phase in which rewards were no longer available. Although this facilitation is consistent with the habitual goal selection hypothesis, we did not find evidence that reward reinforcement reduced cognitive flexibility to implement alternative rules. Together, the findings suggest that reward creates a lasting impact on the selection and execution of goals but may not lead to the inflexibility characteristic of habits. Our findings demonstrate the role of the reward learning system in influencing how the goal-directed system selects and implements goals.

COMT Val158Met polymorphism protects the impact of a mother's history of childhood trauma on emotional and behavioural problems in preschool children

Childhood trauma has a well-established negative impact on mental health outcomes across the lifespan. Cumulative evidence suggests an intergenerational transmission of trauma to descendants. In this way, considering the child's COMT Val158Met (rs4680: G > A) variant, the study aims to investigate the interactive effect of maternal childhood trauma on the emotional/behavioural problems of their offspring in preschoolers age (4-5 and 11 years old) from a population-based dyad of pregnant adolescent women. The behaviour problems of 310 children were assessed using the Child Behaviour Checklist (CBCL) instrument, and maternal trauma was assessed with the Child Trauma Questionnaire (CTQ) between the 20 to 22° gestational weeks. Maternal childhood trauma increases the risk for all emotional/behavioural problems in the offspring, and no direct association between the child's Val158Met genotypes with emotional/behavioural problems. Interestingly, in moderation analysis adjusted by sex, age and skin colour, children of mothers exposed to childhood trauma, carrying the Val/Met genotype, are less likely to develop externalising (p = .020) and total problems (p = .041) when compared to homozygous (Val/Val and Met/Met). Thus, our findings reinforce evidence on the intergenerational impact of maternal trauma on emotional/behavioural problems and demonstrate that this risk is influenced by the genetic background of the individual, varying according to the functional COMT genotype, which confers a protective profile for the development of externalising and total problems.

Striatal Cholinergic Interneurons Control Physical Nicotine Withdrawal via Muscarinic Receptor Signaling

Striatal cholinergic interneurons (ChIs) provide acetylcholine tone to the striatum and govern motor functions. Nicotine withdrawal elicits physical symptoms that dysregulate motor behavior. Here, the role of striatal ChIs in physical nicotine withdrawal is investigated. Mice under RNAi-dependent genetic inhibition of striatal ChIs (ChIGI) by suppressing the sodium channel subunit NaV1.1, lessening action potential generation and activity-dependent acetylcholine release is first generated. ChIGI markedly reduced the somatic signs of nicotine withdrawal without affecting other nicotine-dependent or striatum-associated behaviors. Multielectrode array (MEA) recording revealed that ChIGI reversed ex vivo nicotine-induced alterations in the number of neural population spikes in the dorsal striatum. Notably, the drug repurposing strategy revealed that a clinically-approved antimuscarinic drug, procyclidine, fully mimicked the therapeutic electrophysiological effects of ChIGI. Furthermore, both ChIGI and procyclidine prevented the nicotine withdrawal-induced reduction in striatal dopamine release in vivo. Lastly, therapeutic intervention with procyclidine dose-dependently diminished the physical signs of nicotine withdrawal. The data demonstrated that the striatal ChIs are a critical substrate of physical nicotine withdrawal and that muscarinic antagonism holds therapeutic potential against nicotine withdrawal.

Within-Individual BOLD Signal Variability and its Implications for Task-Based Cognition: A Systematic Review

Within-individual blood oxygen level-dependent (BOLD) signal variability, intrinsic moment-to-moment signal fluctuations within a single individual in specific voxels across a given time course, is a relatively new metric recognized in the neuroimaging literature. Within-individual BOLD signal variability has been postulated to provide information beyond that provided by mean-based analysis. Synthesis of the literature using within-individual BOLD signal variability methodology to examine various cognitive domains is needed to understand how intrinsic signal fluctuations contribute to optimal performance. This systematic review summarizes and integrates this literature to assess task-based cognitive performance in healthy groups and few clinical groups. Included papers were published through October 17, 2022. Searches were conducted on PubMed and APA PsycInfo. Studies eligible for inclusion used within-individual BOLD signal variability methodology to examine BOLD signal fluctuations during task-based functional magnetic resonance imaging (fMRI) and/or examined relationships between task-based BOLD signal variability and out-of-scanner behavioral measure performance, were in English, and were empirical research studies. Data from each of the included 19 studies were extracted and study quality was systematically assessed. Results suggest that variability patterns for different cognitive domains across the lifespan (ages 7-85) may depend on task demands, measures, variability quantification method used, and age. As neuroimaging methods explore individual-level contributions to cognition, within-individual BOLD signal variability may be a meaningful metric that can inform understanding of neurocognitive performance. Further research in understudied domains/populations, and with consistent quantification methods/cognitive measures, will help conceptualize how intrinsic BOLD variability impacts cognitive abilities in healthy and clinical groups.

Brain state and cortical layer-specific mechanisms underlying perception at threshold

Identical stimuli can be perceived or go unnoticed across successive presentations, producing divergent behavioral outcomes despite similarities in sensory input. We sought to understand how fluctuations in behavioral state and cortical layer and cell class-specific neural activity underlie this perceptual variability. We analyzed physiological measurements of state and laminar electrophysiological activity in visual area V4 while monkeys were rewarded for correctly reporting a stimulus change at perceptual threshold. Hit trials were characterized by a behavioral state with heightened arousal, greater eye position stability, and enhanced decoding performance of stimulus identity from neural activity. Target stimuli evoked stronger responses in V4 in hit trials, and excitatory neurons in the superficial layers, the primary feed-forward output of the cortical column, exhibited lower variability. Feed-forward interlaminar population correlations were stronger on hits. Hit trials were further characterized by greater synchrony between the output layers of the cortex during spontaneous activity, while the stimulus-evoked period showed elevated synchrony in the feed-forward pathway. Taken together, these results suggest that a state of elevated arousal and stable retinal images allow enhanced processing of sensory stimuli, which contributes to hits at perceptual threshold.

Thalamocortical dysrhythmia and reward deficiency syndrome as uncertainty disorders

A common anatomical core has been described for psychiatric disorders, consisting of the dorsal anterior cingulate cortex (dACC) and anterior insula, processing uncertainty. A common neurophysiological core has been described for other brain related disorders, called thalamocortical dysrhythmia (TCD), consisting of persistent cross-frequency coupling between low and high frequencies. And a common genetic core has been described for yet another set of hypodopaminergic pathologies called reward deficiency syndromes (RDS). Considering that some RDS have the neurophysiological features of TCD, it can be hypothesized that TCD and RDS have a common anatomical core, yet a differentiating associated neurophysiological mechanism. The EEGs of 683 subjects are analysed in source space for both differences and conjunction between TCD and healthy controls, RDS and healthy controls, and between TCD and RDS. A balance between current densities of the pregenual anterior cingulate cortex (pgACC) extending into the ventromedial prefrontal cortex (vmPFC) and dACC is calculated as well. TCD and RDS share a common anatomical and neurophysiological core, consisting of beta activity in the dACC and theta activity in dACC extending into precuneus and dorsolateral prefrontal cortex. TCD and RDS differ in pgACC/vmPFC activity and demonstrate an opposite balance between pgACC/vmPFC and dACC. Based on the Bayesian brain model TCD and RDS can be defined as uncertainty disorders in which the pgACC/vmPFC and dACC have an opposite balance, possibly explained by an inverted-U curve profile of both pgACC/vmPFC and dACC.

The interplay of dopaminergic genotype and parent-child relationship in relation to intra-individual response time variability in preschoolers: A replication study

Intra-individual response time variability (IIRTV) during cognitive performance is increasingly recognized as an important indicator of attentional control (AC) and related brain region function. However, what determinants contribute to preschoolers' IIRTV received little attention. The present study explored the interaction of dopaminergic polygenic composite score (DPCS) and the parent-child relationship in relation to preschoolers' IIRTV. In the initial sample, 452 preschoolers (M age = 5.17, SD = 0.92) participated in the study. The modified Flanker task was used to evaluate children's IIRTV and their parents were requested to complete the Parent-Child Relationship Scale to assess the parent-child relationship (closeness/conflict). DNA data were extracted from children's saliva samples, and a DPCS was created by the number of COMT, DAT1, and DRD2 alleles associated with lower dopamine levels. Results showed that DPCS significantly interacted with the parent-child closeness to impact preschoolers' IIRTV. Specifically, preschoolers with higher DPCS exhibited lower IIRTV under higher levels of the parent-child closeness, and greater IIRTV under lower levels of the parent-child closeness compared to those with lower DPCS, which supported the differential susceptibility theory (DST). A direct replication attempt with 280 preschoolers (M age = 4.80, SD = 0.86) was conducted to investigate whether the results were in accordance with our exploratory outcomes. The interactive effect of DPCS and the parent-child closeness on IIRTV was confirmed. Additionally, the significant interactive effect of DPCS and the parent-child conflict on IIRTV was found in the replication study. The findings indicate that preschoolers' IIRTV, as an indicator of AC and related brain region function, is influenced by the interactions of dopaminergic genotypes and the parent-child relationship. RESEARCH HIGHLIGHTS: We investigated the Gene × Environment mechanism to underline the intra-individual response time variability as an indicator of attentional control (AC) in Chinese preschoolers. Dopaminergic polygenic composite score (COMT, DAT1, and DRD2) interacted with the parent-child relationship to predict preschoolers' intra-individual reaction time variability. A direct replication attempt has been conducted, and the results were in accordance with our exploratory outcomes, which increased the credibility of the present findings. The findings highlight the importance of considering precursors, including polygenic and environmental factors, which contribute to the development of early cognitive performance such as AC.

Neural correlates of working memory training: An fMRI meta-analysis

Working memory (WM) can be improved by cognitive training. Numerous studies examined neural mechanisms underlying WM training, although with differing conclusions. Therefore, we conducted a meta-analysis to examine the neural substrates underlying WM training in healthy adults. Findings from global analyses showed substantial neural changes in the frontoparietal and subcortical regions. Results from training dosage analyses of WM training showed that shorter WM training could produce neural changes in the frontoparietal regions, whereas longer WM training could produce changes in the subcortical regions (striatum, anterior cingulate cortex, and insula). WM training-induced neural changes were also moderated by the type of training task, with updating tasks inducing neural changes in more regions than maintenance tasks. Overall, these results indicate that the neural changes associated with WM training occur in the frontoparietal network and dopamine-related brain areas, extending previous meta-analyses on WM training and advancing our understanding of the neural underpinnings of WM training effects.

Dopamine in Sports: A Narrative Review on the Genetic and Epigenetic Factors Shaping Personality and Athletic Performance

This narrative review examines the relationship between dopamine-related genetic polymorphisms, personality traits, and athletic success. Advances in sports genetics have identified specific single nucleotide polymorphisms (SNPs) in dopamine-related genes linked to personality traits crucial for athletic performance, such as motivation, cognitive function, and emotional resilience. This review clarifies how genetic variations can influence athletic predisposition through dopaminergic pathways and environmental interactions. Key findings reveal associations between specific SNPs and enhanced performance in various sports. For example, polymorphisms such as COMT Val158Met rs4680 and BDNF Val66Met rs6265 are associated with traits that could benefit performance, such as increased focus, stress resilience and conscientiousness, especially in martial arts. DRD3 rs167771 is associated with higher agreeableness, benefiting teamwork in sports like football. This synthesis underscores the multidimensional role of genetics in shaping athletic ability and advocates for integrating genetic profiling into personalized training to optimize performance and well-being. However, research gaps remain, including the need for standardized training protocols and exploring gene-environment interactions in diverse populations. Future studies should focus on how genetic and epigenetic factors can inform tailored interventions to enhance both physical and psychological aspects of athletic performance. By bridging genetics, personality psychology, and exercise science, this review paves the way for innovative training and performance optimization strategies.

Impairment of Neuronal Activity in the Dorsolateral Prefrontal Cortex Occurs Early in Parkinsonism

Background

Parkinson's disease (PD) is often characterized by altered rates and patterns of neuronal activity in the sensorimotor regions of the basal ganglia thalamocortical network. Little is known, however, regarding how neuronal activity in the executive control network of the brain changes in the parkinsonian condition.

Objective

Investigate the impact of parkinsonism on neuronal activity in the dorsolateral prefrontal cortex (DLPFC), a key region in executive control, during a go/nogo reaching task.

Methods

Using a within-subject design, single and multi-unit neuronal activity was recorded in the DLPFC of a nonhuman primate before and after the induction of mild parkinsonism using the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

Results

Coincident with development of mild parkinsonian motor signs, there was a marked reduction in the percentage of DLPFC cells with significant task-related firing rate modulation during go and nogo conditions.

Conclusions

These results suggest that DLPFC dysfunction may occur early in parkinsonism and contribute to cognitive impairments and disrupted executive function often observed in PD patients.

Working memory gating in obesity is moderated by striatal dopaminergic gene variants

Everyday life requires an adaptive balance between distraction-resistant maintenance of information and the flexibility to update this information when needed. These opposing mechanisms are proposed to be balanced through a working memory gating mechanism. Prior research indicates that obesity may elevate the risk of working memory deficits, yet the underlying mechanisms remain elusive. Dopaminergic alterations have emerged as a potential mediator. However, current models suggest these alterations should only shift the balance in working memory tasks, not produce overall deficits. The empirical support for this notion is currently lacking, however. To address this gap, we pooled data from three studies (N = 320) where participants performed a working memory gating task. Higher BMI was associated with overall poorer working memory, irrespective of whether there was a need to maintain or update information. However, when participants, in addition to BMI level, were categorized based on certain putative dopamine-signaling characteristics (single-nucleotide polymorphisms [SNPs]; specifically, Taq1A and DARPP-32), distinct working memory gating effects emerged. These SNPs, primarily associated with striatal dopamine transmission, appear to be linked with differences in updating, specifically, among high-BMI individuals. Moreover, blood amino acid ratio, which indicates central dopamine synthesis capacity, combined with BMI shifted the balance between distractor-resistant maintenance and updating. These findings suggest that both dopamine-dependent and dopamine-independent cognitive effects exist in obesity. Understanding these effects is crucial if we aim to modify maladaptive cognitive profiles in individuals with obesity.

Dopaminergic manipulations affect the modulation and meta-modulation of movement speed: Evidence from two pharmacological interventions

A body of research implicates dopamine in the average speed of simple movements. However, naturalistic movements span a range of different shaped trajectories and rarely proceed at a single constant speed. Instead, speed is reduced when drawing "corners" compared to "straights" (i.e., speed modulation), and the extent of this slowing down is dependent upon the global shape of the movement trajectory (i.e., speed meta-modulation) - for example whether the shape is an ellipse or a rounded square. At present, it is not known how (or whether) dopaminergic function controls continuous changes in speed during movement execution. The current paper reports effects on these kinematic features of movement following two forms of dopamine manipulation: Study One highlights movement differences in individuals with PD both ON and OFF their dopaminergic medication (N = 32); Study Two highlights movement differences in individuals from the general population on haloperidol (a dopamine receptor blocker, or "antagonist") and placebo (N = 43). Evidence is presented implicating dopamine in speed, speed modulation and speed meta-modulation, whereby low dopamine conditions are associated with reductions in these variables. These findings move beyond vigour models implicating dopamine in average movement speed, and towards a conceptualisation that involves the modulation of speed as a function of contextual information.

A dopaminergic basis of behavioral control

Both goal-directed and automatic processes shape human behavior, but these processes often conflict. Behavioral control is the decision about which process guides behavior. Despite the importance of behavioral control for adaptive decision-making, its neural mechanisms remain unclear. Critically, it is unknown if there are mechanisms for behavioral control that are distinct from those supporting the formation of goal-relevant knowledge. We performed deep phenotyping of individual dopamine system function by combining multiple PET scans, fMRI, and dopaminergic drug administration in a within-subject, double-blind, placebo-controlled design. Subjects performed a rule-based response time task, with goal-directed and automatic decision-making operationalized as model-based and model-free influences on behavior. We found a double dissociation between two aspects of ventral striatal dopamine physiology: D2/3 receptor availability and dopamine synthesis capacity. Convergent and causal evidence indicated that D2/3 receptors regulate behavioral control by enhancing model-based and blunting model-free influences on behavior but do not affect model-based knowledge formation. In contrast, dopamine synthesis capacity was linked to the formation of model-based knowledge but not behavioral control. D2/3 receptors also modulated frontostriatal functional connectivity, suggesting they regulate behavioral control by gating prefrontal inputs to the striatum. These results identify central mechanisms underlying individual and state differences in behavioral control and point to striatal D2/3 receptors as targets for interventions for improving goal-directed behavior.

Contextual control demands determine whether stability and flexibility trade off against each other

Cognitive stability, the ability to focus on a current task, and cognitive flexibility, the ability to switch between different tasks, are traditionally conceptualized as opposing end-points on a one-dimensional continuum. This assumption obligates a stability-flexibility trade-off - greater stability equates to less flexibility, and vice versa. In contrast, a recent cued task-switching study suggested that stability and flexibility can be regulated independently, evoking a two-dimensional perspective where trade-offs are optional (Geddert & Egner, Journal of Experimental Psychology: General, 151, 3009-3027, 2022). This raises the question of under what circumstances trade-offs occur. We here tested the hypothesis that trade-offs are guided by cost-of-control considerations whereby stability and flexibility trade off in contexts that selectively promote stability or flexibility, but not when neither or both are promoted. This proposal was probed by analyzing whether a trial-level metric of a stability-flexibility trade-off, an interaction between task-rule congruency and task sequence, varied as a function of a broader block-level context that independently varied demands on stability or flexibility by manipulating the proportion of incongruent and switch trials, respectively. In Experiment 1, we reanalyzed data from Geddert and Egner, Journal of Experimental Psychology: General, 151, 3009-3027, (2022); Experiment 2 was a conceptual replication with a design tweak that controlled for potential confounds due to local trial history effects. The experiments produced robust evidence for independent stability and flexibility adaptation, and for a context-dependent expression of trial-level stability-flexibility trade-offs that generally conformed to the cost-of-control predictions. The current study thus documents that stability-flexibility trade-offs are not obligatory but arise in contexts where either stability or flexibility are selectively encouraged.

Factors associated with cognitive dysfunction in treatment-responsive and -resistant schizophrenia: A pilot cross-sectional study

BACKGROUND

Cognitive dysfunction is a core feature of schizophrenia. Although treatment-resistant schizophrenia (TRS) exhibits wide-ranging neuropsychological deficits, factors defining cognitive prognosis in TRS are unclear. We aimed to clarify the association between cognitive dysfunction and factors, such as plasma concentrations of clozapine (CLZ), N-desmethylclozapine (NDMC), and homovanillic acid (HVA), due to differences in antipsychotic responses in patients with schizophrenia.

METHODS

This pilot cross-sectional study included 60 Japanese patients (35 with TRS and 25 with non-CLZ antipsychotic responders (AR)). Cognitive function was evaluated using the Brief Assessment of Cognition Short Form (BAC-SF). Plasma concentrations of HVA, CLZ, and NDMC were analyzed by high-performance liquid chromatography.

RESULTS

The cognitive performance of patients with AR was better than that of patients with TRS in all tasks. No significant cognitive differences were detected between the CLZ responders and non-responders. The severity of negative and extrapyramidal symptoms was found to be potentially negatively associated with BAC-SF composite and several subtest scores. In patients with TRS, chlorpromazine equivalents and the CLZ/NDMC ratio were identified as factors negatively associated with Digit Sequencing and the Symbol Coding subtest scores of the BAC-SF, respectively.

CONCLUSIONS

Our study suggests that patients with TRS experience worse cognitive dysfunction than those with AR, and CLZ responsiveness in TRS may be not associated with cognitive dysfunction. Additionally, higher chlorpromazine equivalents and the CLZ/NDMC ratio may be associated with severity of cognitive dysfunction in patients with TRS. Further studies are required to clarify the relationship between treatment response and cognitive dysfunction in schizophrenia.

Multi-modal and bi-directional effects of a synthetic Δ9-Tetrahydrocannabinol (THC) analogue, Nabilone, on spatio-temporal binding windows: Evidence from the projected hand illusion

Abnormally widened spatial and temporal binding windows (SBW/TBWs; length of space/time whereby stimuli are considered part of the same percept) are observed in schizophrenia. TBW alterations have been associated with altered sense of agency (hereafter referred to as agency), and an associative relationship between embodiment (body ownership) and agency has been proposed. SBWs/TBWs are investigated separately, but no evidence exists of these being separate in mechanism, system or function. The underlying neural substrate of schizophrenia remains unclear. The literature claims either pro-psychotic or anti-psychotic effects of Δ9-Tetrahydrocannabinol (THC) in patients and healthy individuals, but major support for cannabis in the aetiology of schizophrenia is associative, not causal. To clarify if THC is pro- or anti-psychotic, this single-blind, placebo-controlled within-subjects cross-over study tested several hypotheses. 1) Competing hypotheses that a synthetic THC analogue, Nabilone (NAB, 1-2 mg), would alter measures of agency and embodiment in healthy volunteers (n = 32) similarly, or opposite, to that of in patients with schizophrenia. 2) That there would be significant associations between any NAB-induced alterations in individual agency and embodiment measures in the Projected Hand Illusion (PHI). 3) That there is a unitary spatio-temporal binding window (STBW). A large proportion of individuals did not experience the PHI. Multimodal and bi-directional effects of NAB on the PHI were observed. Evidence of a unitary spatio-temporal binding window (STBW) was observed. NAB widened the STBW in some but narrowed it in others as a function of space and delay. No associations were found between agency and embodiment.

Changes in electrophysiological aperiodic activity during cognitive control in Parkinson's disease

Cognitive symptoms in Parkinson's disease are common and can significantly affect patients' quality of life. Therefore, there is an urgent clinical need to identify a signature derived from behavioural and/or neuroimaging indicators that could predict which patients are at increased risk for early and rapid cognitive decline. Recently, converging evidence identified that aperiodic activity of the EEG reflects meaningful physiological information associated with age, development, cognitive and perceptual states or pathologies. In this study, we aimed to investigate aperiodic activity in Parkinson's disease during cognitive control and characterize its possible association with behaviour. Here, we recorded high-density EEG in 30 healthy controls and 30 Parkinson's disease patients during a Simon task. We analysed task-related behavioural data in the context of the activation-suppression model and extracted aperiodic parameters (offset, exponent) at both scalp and source levels. Our results showed lower behavioural performances in cognitive control as well as higher offsets in patients in the parieto-occipital areas, suggesting increased excitability in Parkinson's disease. A small congruence effect on aperiodic parameters in pre- and post-central brain areas was also found, possibly associated with task execution. Significant differences in aperiodic parameters between the resting-state, pre- and post-stimulus phases were seen across the whole brain, which confirmed that the observed changes in aperiodic activity are linked to task execution. No correlation was found between aperiodic activity and behaviour or clinical features. Our findings provide evidence that EEG aperiodic activity in Parkinson's disease is characterized by greater offsets, and that aperiodic parameters differ depending on arousal state. However, our results do not support the hypothesis that the behaviour-related differences observed in Parkinson's disease are related to aperiodic changes. Overall, this study highlights the importance of considering aperiodic activity contributions in brain disorders and further investigating the relationship between aperiodic activity and behaviour.

Monoaminergic Modulation of Learning and Cognitive Function in the Prefrontal Cortex

Extensive research has shed light on the cellular and functional underpinnings of higher cognition as influenced by the prefrontal cortex. Neurotransmitters act as key regulatory molecules within the PFC to assist with synchronizing cognitive state and arousal levels. The monoamine family of neurotransmitters, including dopamine, serotonin, and norepinephrine, play multifaceted roles in the cognitive processes behind learning and memory. The present review explores the organization and signaling patterns of monoamines within the PFC, as well as elucidates the numerous roles played by monoamines in learning and higher cognitive function.

Adenosinergic system and nucleoside transporters in attention deficit hyperactivity disorder: Current findings

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder with high heterogeneity that can affect individuals of any age. It is characterized by three main symptoms: inattention, hyperactivity, and impulsivity. These neurobehavioral alterations and neurochemical and pharmacological findings are mainly attributed to unbalanced catecholaminergic signaling, especially involving dopaminergic pathways within prefrontal and striatal areas. Dopamine receptors and transporters are not solely implicated in this imbalance, as evidence indicates that the dopaminergic signaling is modulated by adenosine activity. To this extent, alterations in adenosinergic signaling are probably involved in ADHD. Here, we review the current knowledge about adenosine's role in the modulation of chemical, behavioral and cognitive parameters of ADHD, especially regarding dopaminergic signaling. Current literature usually links adenosine receptors signaling to the dopaminergic imbalance found in ADHD, but there is evidence that equilibrative nucleoside transporters (ENTs) could also be implicated as players in dopaminergic signaling alterations seen in ADHD, since their involvement in other neurobehavioral impairments.

Attenuated responses to attention-modulating drugs in the neuroligin-3R451C mouse model of autism

Attention deficits are frequently reported within the clinical autism population. Despite not being a core diagnostic feature, some aetiological theories place atypical attention at the centre of autism development. Drugs used to treat attention dysfunction are therefore increasingly prescribed to autistic patients, though currently off-label with uncertain efficacy. We utilised a rodent-translated touchscreen test of sustained attention in mice carrying an autism-associated R451C mutation in the neuroligin-3 gene (Nlgn3R451C). In doing so, we replicated their cautious but accurate response profile and probed it using two widely prescribed attention-modulating drugs: methylphenidate (MPH) and atomoxetine (ATO). In wild-type mice, acute administration of MPH (3 mg/kg) promoted impulsive responding at the expense of accuracy, while ATO (3 mg/kg) broadly reduced impulsive responding. These drug effects were absent in Nlgn3R451C mice, other than a small reduction in blank touches to the screen following ATO administration. The absence of drug effects in Nlgn3R451C mice likely arises from their altered behavioural baseline and underlying neurobiology, highlighting caveats to the use of classic attention-modulating drugs across disorders and autism subsets. It further suggests that altered dopaminergic and/or norepinephrinergic systems may drive behavioural differences in the Nlgn3R451C mouse model of autism, supporting further targeted investigation.

Bi-directional and multi-modal effects of dexamphetamine on spatial binding windows in healthy individuals

OBJECTIVES

Stimuli that are separated by a short window of space or time, known as spatial and temporal binding windows (SBW/TBWs), may be perceived as separate. Widened TBWs are evidenced in schizophrenia, although it is unclear if the SBW is similarly affected. The current study aimed to assess if dexamphetamine (DEX) may increase SBWs in a multimodal visuo-tactile illusion, potentially validating usefulness as an experimental model for multimodal visuo-tactile hallucinations in schizophrenia, and to examine a possible association between altered binding windows (BWs) and working memory (WM) suggested by previous research.

METHODS

A placebo-controlled, double-blinded, and counter-balanced crossover design was employed. Permuted block randomisation was used for drug order. Healthy participants received DEX (0.45 mg/kg, PO, b.i.d.) or placebo (glucose powder) in capsules. The Rubber Hand Illusion (RHI) and Wechsler Adult Intelligence Scale Spatial Span was employed to determine whether DEX would alter SBWs and WM, respectively. Schizotypy was assessed with a variety of psychological scales.

RESULTS

Most participants did not experience the RHI even under normal circumstances. Bi-directional and multimodal effects of DEX on individual SBWs and schizotypy were observed, but not on WM.

CONCLUSIONS

Bidirectional multimodal effects of DEX on the RHI and SBWs were observed in individuals, although not associated with alterations in WM.

The relation between stress-induced dopamine release in the ventromedial prefrontal cortex, fronto-striatal functional connectivity, and negative urgency: A multimodal investigation using [18F]Fallypride PET, MRI and experience sampling

Negative urgency (NU), or the tendency to act rashly when stress of negative affect is high, could be the result of an insufficient control of the ventromedial prefrontal cortex (vmPFC) over the striatum, through an impaired dopamine (DA) transmission. Therefore, we investigated in vivo human stress-induced DA release in the vmPFC, its relation with fronto-striatal functional connectivity (FC), and NU in daily life. In total, 12 female healthy participants performed a simultaneous [18 F]fallypride PET and fMRI scan during which stress was induced. Regions displaying stress-induced DA release were identified and used to investigate stress-induced changes in fronto-striatal FC. Additionally, participants enrolled in an experience sampling study, reporting on daily life stress and rash actions over a 12-month-long period. Mixed models explored whether stress-induced DA release and FC moderated NU in daily life. Stress led to a lower FC between the vmPFC and dorsal striatum, but a higher FC between the vmPFC and contralateral ventral striatum. Participants with a higher FC between the vmPFC and dorsal striatum displayed more NU in daily life. A higher stress-induced DA release in the vmPFC was related to a higher stress-induced change in FC between the vmPFC and striatum. Participants with a higher DA release in the vmPFC displayed more NU in daily life. In conclusion, stress could differentially impact fronto-striatal FC whereby the connectivity with the dorsal striatum is especially important for NU in daily life. This could be mediated by a higher, but not a lower, stress-induced DA release in the vmPFC.

Lower Dorsal Putamen D2/3 Receptor Availability and Amphetamine-Induced Dopamine Release are Related to Poorer Cognitive Function in Recently Abstinent People Who Smoke and Healthy Controls

INTRODUCTION

In the dopamine system, the mesolimbic pathway, including the dorsal striatum, underlies the reinforcing properties of tobacco smoking, and the mesocortical pathway, including the dorsolateral prefrontal cortex (dlPFC), is critical for cognitive functioning. Dysregulated dopamine signaling has been linked to drug-seeking behaviors and cognitive deficits. The dorsal striatum and dlPFC are structurally and functionally connected and are key regions for cognitive functioning. We recently showed that people who smoke have lower dlPFC dopamine (D2/3R) receptor availability than people who do not, which is related to poorer cognitive function.

AIMS AND METHODS

The goal of this study was to examine the same brain-behavior relationship in the dorsal striatum. Twenty-nine (18 males) recently abstinent people who smoke and 29 sex-matched healthy controls participated in 2 same-day [11C]-(+)-PHNO positron emission tomography scans before and after amphetamine administration to provoke dopamine release. D2/3R availability (binding potential; BPND) and amphetamine-induced dopamine release (%ΔBPND) were calculated. Cognition (verbal learning and memory) was assessed with the CogState computerized battery.

RESULTS

There were no group differences in baseline BPND. People who smoke have a smaller magnitude %ΔBPND in dorsal putamen than healthy controls (p = .022). People who smoke perform worse on immediate (p = .035) and delayed (p = .011) recall than healthy controls. In all people, lower dorsal putamen BPND was associated with worse immediate (p = .006) and delayed recall (p = .049), and lower %ΔBPND was related to worse delayed recall (p = .022).

CONCLUSIONS

Lower dorsal putamen D2/3R availability and function are associated with disruptions in cognitive function that may underlie difficulty with resisting smoking.

IMPLICATIONS

This study directly relates dopamine imaging outcomes in the dorsal striatum to cognitive function in recently abstinent people who smoke cigarettes and healthy controls. The current work included a well-characterized subject sample in terms of demographics, smoking characteristics, and a validated neurocognitive test of verbal learning and memory. The findings of this study extend previous literature relating dopamine imaging outcomes to cognition in recently abstinent people who smoke and people who do not smoke, expanding our understanding of brain-behavior relationships.

Inter-individual variability in neural response to low doses of LSD

The repeated use of small doses of psychedelics (also referred to as "microdosing") to facilitate benefits in mental health, cognition, and mood is a trending practice. Placebo-controlled studies however have largely failed to demonstrate strong benefits, possibly because of large inter-individual response variability. The current study tested the hypothesis that effects of low doses of LSD on arousal, attention and memory depend on an individual's cognitive state at baseline. Healthy participants (N = 53) were randomly assigned to receive repeated doses of LSD (15 mcg) or placebo on 4 occasions divided over 2 weeks. Each treatment condition also consisted of a baseline and a 1-week follow-up visit. Neurophysiological measures of arousal (resting state EEG), pre-attentive processing (auditory oddball task), and perceptual learning and memory (visual long-term potentiation (LTP) paradigm) were assessed at baseline, dosing session 1 and 4, and follow-up. LSD produced stimulatory effects as reflected by a reduction in resting state EEG delta, theta, and alpha power, and enhanced pre-attentive processing during the acute dosing sessions. LSD also blunted the induction of LTP on dosing session 4. Stimulatory effects of LSD were strongest in individuals with low arousal and attention at baseline, while inhibitory effects were strongest in high memory performers at baseline. Decrements in delta EEG power and enhanced pre-attentive processing in the LSD treatment condition were still present during the 1-week follow-up. The current study demonstrates across three cognitive domains, that acute responses to low doses of LSD depend on the baseline state and provides some support for LSD induced neuroadaptations that sustain beyond treatment.