The role of the basal ganglia in habit formation

The role of fear and dopamine-striatal pathways in grooming

Fear is a fundamental emotion that triggers rapid and automatic behavioral response. Fear is known to suppress reward-seeking behaviors, interrupt previous activities to prioritize defensive responses and lead to rapid switch to defensive reactions. Dopamine (DA) plays a complicated role in the choice and performance of actions and it has a potential interaction of innate actions with the presence of fear. Here, in a series of experiments we explore the role of the different DA striatal pathways in mediating grooming, an innate behavior comprised of a structured sequence of repetitive actions, with or without the presence of fear. Using chemogenetics, we specifically inhibited the DA pathways projecting to the dorsolateral striatum (DLS), dorsomedial striatum (DMS), and ventral striatum (VS), while mice were engaged in a behavioral paradigm inducing grooming during the presentation of a fear related cue. We found that fear related cues consistently reduced grooming proportions and shortened induced grooming bouts, regardless of DA manipulation, indicating prioritization of freezing behavior in fearful contexts. This also suggests that fear responses may be mediated through pathways independent of DA-based action selection. The role of DA, however, varies depending on the specific striatal pathway. Inhibiting DLS DA input delayed grooming initiation and reduced grooming when competing with freezing. In contrast, DMS DA input had no effect on grooming, while inhibition of VS mesolimbic DA input increased grooming proportions and duration. These findings underscore the distinct and sometimes opposing roles of different DA-striatal pathways in modulating innate behaviors. We discuss potential implications of this duality in DA function for both theoretical and clinical fields.

From valence encoding to motivated behavior: A focus on the nucleus accumbens circuitry

How do our brains determine whether something is good or bad? The brain's ability to evaluate stimuli as positive or negative - by attributing valence - is fundamental to survival and decision-making. Different brain regions have been associated with valence encoding, including the nucleus accumbens (NAc). The NAc is predominantly composed of GABAergic medium spiny neurons (MSNs), which segregate into two distinct populations based on their dopamine receptor expression: D1-receptor-expressing (D1-MSNs) and D2-receptor-expressing neurons (D2-MSNs). Classical models propose a binary functional role, where D1-MSNs exclusively mediated reward and positive valence, while D2-MSNs processed aversion and negative valence. However, we now recognize that NAc MSN subpopulations operate in a more complex manner than previously thought, often working cooperatively rather than antagonistically in valence-related behaviors. This review synthesizes our current knowledge of valence-encoding neurocircuitry, with emphasis on the NAc. We examine electrophysiological, calcium imaging, optogenetic, chemogenetic and pharmacological studies detailing the contribution of NAc medium spiny neurons for rewarding and aversive responses. Finally, we explore emerging technical innovations that promise to advance our understanding of how the mammalian brain encodes valence and translates it into behavior.

Neuronal diversity in the caudate nucleus: A comparative study between camel and human brains

Caudate nucleus (CN) neurons in camels and humans were examined using modified Golgi impregnation methods. Neurons were classified based on soma morphology, dendritic characteristics, and spine distribution. Three primary neuron types were identified in both species: rich-spiny (Type I), sparsely-spiny (Type II), and aspiny (Type III), each comprising subtypes with specific features. Comparative analysis revealed significant differences in soma size, dendritic morphology, and spine distribution between camels and humans. The study contributes to our understanding of structural diversity in CN neurons and provides insights into evolutionary neural adaptations.

Disuse-driven plasticity in the human thalamus and putamen

Subcortical plasticity has mainly been studied using invasive electrophysiology in animals. Here, we leverage precision functional mapping (PFM) to study motor plasticity in the human subcortex during 2 weeks of upper-extremity immobilization with daily resting-state and motor task fMRI. We found previously that, in the cortex, limb disuse drastically impacts disused primary motor cortex functional connectivity (FC) and is associated with spontaneous fMRI pulses. It remains unknown whether disuse-driven plasticity pulses and FC changes are cortex specific or whether they could also affect movement-critical nodes in the thalamus and striatum. Tailored analysis methods now show spontaneous disuse pulses and FC changes in the dorsal posterior putamen and central thalamus (centromedian [CM], ventral-intermediate [VIM], and ventroposterior-lateral nuclei), representing a motor circuit-wide plasticity phenomenon. The posterior putamen effects suggest plasticity in stimulus-driven habit circuitry. Importantly, thalamic plasticity effects are focal to nuclei used as deep brain stimulation targets for essential tremor/Parkinson's disease (VIM) and epilepsy/coma (CM).

Multimodal population study reveals the neurobiological underpinnings of chronotype

The rapid shifts in society have altered human behavioural patterns, with increased evening activities, increased screen time and changed sleep schedules. As an explicit manifestation of circadian rhythms, chronotype is closely intertwined with physical and mental health. Night owls often exhibit unhealthier lifestyle habits, are more susceptible to mood disorders and have poorer physical fitness compared with early risers. Although individual differences in chronotype yield varying consequences, their neurobiological underpinnings remain elusive. Here we conducted a pattern-learning analysis with three brain-imaging modalities (grey matter volume, white-matter integrity and functional connectivity) and capitalized on 976 phenotypes in 27,030 UK Biobank participants. The resulting multilevel analysis reveals convergence on the basal ganglia, limbic system, hippocampus and cerebellum. The pattern derived from modelling actigraphy wearables data of daily movement further highlighted these key brain features. Overall, our population-level study comprehensively investigates chronotype, emphasizing its close connections with habit formation, reward processing and emotional regulation.

Erasing "bad memories": reversing aberrant synaptic plasticity as therapy for neurological and psychiatric disorders

Dopamine modulates corticostriatal plasticity in both the direct and indirect pathways of the cortico-striato-thalamo-cortical (CSTC) loops. These gradual changes in corticostriatal synaptic strengths produce long-lasting changes in behavioral responses. Under normal conditions, these mechanisms enable the selection of the most appropriate responses while inhibiting others. However, under dysregulated dopamine conditions, including a lack of dopamine release or dopamine signaling, these mechanisms could lead to the selection of maladaptive responses and/or the inhibition of appropriate responses in an experience-dependent and task-specific manner. In this review, we propose that preventing or reversing such maladaptive synaptic strengths and erasing such aberrant "memories" could be a disease-modifying therapeutic strategy for many neurological and psychiatric disorders. We review evidence from Parkinson's disease, drug-induced parkinsonism, L-DOPA-induced dyskinesia, obsessive-compulsive disorder, substance use disorders, and depression as well as research findings on animal disease models. Altogether, these studies allude to an emerging theme in translational neuroscience and promising new directions for therapy development. Specifically, we propose that combining pharmacotherapy with behavioral therapy or with deep brain stimulation (DBS) could potentially cause desired changes in specific neural circuits. If successful, one important advantage of correcting aberrant synaptic plasticity is long-lasting therapeutic effects even after treatment has ended. We will also discuss the potential molecular targets for these therapeutic approaches, including the cAMP pathway, proteins involved in synaptic plasticity as well as pathways involved in new protein synthesis. We place special emphasis on RNA binding proteins and epitranscriptomic mechanisms, as they represent a new frontier with the distinct advantage of rapidly and simultaneously altering the synthesis of many proteins locally.

Meta-analyses of executive function deficits in chemotherapy-treated rodent models

People diagnosed with cancer who undergo chemotherapy commonly encounter cognitive changes, particularly in executive functions (EFs). EFs support goal-directed behaviours, with EF deficits implicated in various neurocognitive impairments. We conducted five meta-analyses of the rodent models to investigate the impact of chemotherapy across five EF domains. A systematic search across PubMed, Web of Science, Scopus, and PsycINFO yielded 56 eligible papers. Our findings supported the clinical literature suggesting the selective impact of chemotherapy on different EF domains. Specifically, chemotherapy-treated animals performed significantly more poorly than controls in tasks assessing working memory, behavioural flexibility, and problem-solving, with no significant group differences in inhibition or attention. Subgroup analyses revealed that alkylating agents, antitumor antibiotics, and combination therapies were strongly associated with working memory deficits, whereas mitotic inhibitors were not. Rodent species, strain, age, sex, number of treatments, and time of behavioural assessment since the end of treatment did not moderate the drug effect on any assessed EF domains. To increase the generalisability and translational validity of the results, the overall reporting quality of animal studies needs to be improved with more details on randomisation, blinding, sample sizes, and criteria for animal exclusions.

Exploring Habits in Anorexia Nervosa: Promise, Pitfalls, and Progress

PURPOSE OF REVIEW

Habits, characterized by automaticity and insensitivity to outcomes, may be key to the persistence of maladaptive behaviors in anorexia nervosa (AN). This review examines the status of habit research in AN, focusing on insights from task-based assessments.

RECENT FINDINGS

Findings indicate dysfunction in the frontostriatal circuits associated with habitual and goal-directed behaviors, with some studies linking neural disturbances to habit measures or clinically relevant behaviors. Heightened habitual tendencies in AN have consistently been reported using self-reports, while research utilizing experimental paradigms has yielded mixed results and efforts to capture real-world habits in AN remain limited. Some experimental paradigms appear more sensitive than others, but all face challenges associated with studying habits in the lab. Promising new approaches will need to be adopted and efforts made to capture real-world habits. Understanding which habits are problematic, when in illness and for whom they dominate, could make good on the promise of habit-focused treatments for AN.

Phytoestrogens as potential anti-osteoporosis nutraceuticals: Major sources and mechanism(s) of action

By 2050, the global aging population is predicted to reach 1.5 billion, highlighting the need to enhance the quality of life of the elderly population. Osteoporotic fractures are projected to affect one in three women and one in five men over age 50. Initial treatments for osteoporosis in postmenopausal women include antiresorptive agents such as bisphosphonates, strontium ranelate, estrogen replacement therapy (ERT) and selective estrogen receptor modulators (SERMs). However, these do not rebuild bone, limiting their effectiveness. Denosumab, an FDA-approved antiresorptive monoclonal antibody, also has drawbacks including high costs, biannual subcutaneous injections, slow healing, impaired bone growth and side effects like eczema, flatulence, cellulitis, osteonecrosis of the jaw (ONJ) and an increased risk of spinal fractures after discontinuation of treatment. Nutraceuticals, particularly phytoestrogens, are gaining attention for their health benefits and safety in osteoporosis prevention, management and treatment. Phytoestrogens are plant metabolites similar to mammalian estrogens and include isoflavones, coumestans, lignans, stilbenes, and flavonoids. They interact with estrogen receptor isoforms ERα and ERβ, acting as agonists or antagonists based on concentration and bioavailability. Their tissue-selective activities are particularly significant: anti-estrogenic effects in reproductive tissues may lower the risk of hormone-related cancers (such as ovarian, uterine, breast and prostate), while estrogenic effects on bone could contribute to the preservation of bone mineral density.Phytoestrogens are, thus, used in managing breast and prostate cancers, cardiovascular diseases, menopause and osteoporosis. The present review focuses on the botanical origin, classification, sources and mechanism(s) of action of major phytoestrogens, their potential in prevention and management of osteoporosis and the requirement for additional clinical trials to achieve more definitive outcomes in order to confirm their efficacy and dosage safety.

Striatal dopamine represents valence on dynamic regional scales

Adaptive decision making relies on dynamic updating of learned associations where environmental cues come to predict valenced stimuli, such as food or threat. Cue-guided behavior depends on a network of brain systems, including dopaminergic projections to the striatum. Critically, it remains unclear how dopamine signaling across the striatum encodes multi-valent, dynamic learning contexts, where positive and negative associations must be rapidly disambiguated. To understand this, we employed a Pavlovian discrimination paradigm, where cues predicting food or threat were intermingled during conditioning sessions, and their meaning was serially reversed across training. We found that male and female rats readily distinguished these cues and updated their behavior rapidly upon valence reversal. Using fiber photometry, we recorded dopamine signaling in three major striatal subregions - the dorsolateral striatum (DLS), the nucleus accumbens (NAc) core, and the nucleus accumbens medial shell - finding that valence was represented uniquely across all three regions, indicative of local signals biased for value and salience. Further, ambiguity introduced by cue reversals reshaped striatal dopamine on different timelines: nucleus accumbens signals updated more readily than those in the DLS. Together, these results indicate that striatal dopamine flexibly encodes stimulus valence according to region-specific rules, and these signals are dynamically modulated by changing contingencies in the resolution of ambiguity about the meaning of environmental cues.Significance Statement Adaptive decision making relies on updating learned associations to disambiguate predictions of reward or threat. This cue-guided behavior depends on striatal dopamine, but it remains unclear how dopamine signaling encodes multi-valent, dynamic learning contexts. Here, we employed a paradigm where cues predicting positive and negative outcomes were intermingled, and their meaning was serially reversed across time. We recorded dopamine signaling, finding heterogeneous patterns of valence encoding across striatal subregions, and cue reversal reshaped subregional signals on different timelines. Our results suggest that dopamine flexibly encodes dynamic learning contexts to resolve ambiguity about the meaning of environmental cues.

Cognitive load reduces the reinforcement of ventral striatum by anterior insula in taste processing: An fMRI study on self-control

Recent studies have shown that cognitive overload disrupted the affective processing of taste attributes in food-related tasks, which is difficult to explain using dual-system theories with their reflective and impulsive systems (involved in the cognitive and affective processing of stimuli, respectively). The tripartite neurocognitive model proposes an additional interoceptive system that regulates the activities of reflective and impulsive systems. Using this framework, we studied self-control over food choices and hypothesized inferior processing of both affective (taste) and cognitive (health) components of choice-relevant attributes under increased cognitive load. We expected increased cognitive load to decrease the coupling between interoceptive and impulsive systems (represented by anterior insula (AI) and ventral striatum (VS), respectively), and to strengthen decoupling between interoceptive and reflective system (represented by dorsolateral prefrontal cortex (DLPFC)). In an fMRI scanner, 49 participants made 60 food choices requiring self-control (i.e., between a healthier and tastier item) twice: in high (HL) and low working memory load (LL) conditions. We found that functional connectivity between the right AI and VS was weaker in HL compared to LL condition. We also revealed an expected trend towards a stronger negative connectivity between the right AI and DLPFC in HL compared to LL condition. Our findings suggest that cognitively demanding task concurrent to food self-control task overloads AI and reduces the reinforcement of VS by AI. This helps in explaining how and why the affective processing of taste attributes, together with the cognitive processing of health attributes, may be disrupted under cognitive overload.

Emergence of Categorical Representations in Parietal and Ventromedial Prefrontal Cortex across Extended Training

How do the neural representations underlying category learning change as skill develops? We examined perceptual category learning using a prototype learning task known to recruit a corticostriatal system including the posterior striatum, motor cortex, visual cortex, and intraparietal sulcus (IPS). Male and female human participants practiced categorizing stimuli as category members or nonmembers (A vs not-A) across 3 d, with fMRI data collected at the beginning and end. Univariate analyses found that corticostriatal activity in regions associated with habitual instrumental learning was recruited across both sessions, but activity in regions associated with goal-directed instrumental learning decreased from Day 1 to Day 3. Multivoxel pattern analysis (MVPA) indicated that after training, the trained category could be more easily decoded from the IPS when compared with a novel category. Representational similarity analysis (RSA) showed development of category representations in the IPS and motor cortex. In addition, RSA revealed evidence for category-related representations including prototype representation in the ventromedial prefrontal cortex which may reflect parallel development of schematic memory for the category structure. Overall, the results converge to show how performance of category decisions and representations of the category structure emerge after extensive training across the corticostriatal system underlying perceptual category learning.

Computational model for control of hand movement in Parkinson's disease using deep brain stimulation

Parkinson's disease (PD) is a progressive neurological disorder characterized by the loss of dopamine in the substantia nigra resulting in movement disorder. Although several computational models have been proposed to explore different aspects of PD, a comprehensive computational model of PD and its suppression remains elusive. This study presents a computational model of the Cortico-Basal Ganglia Thalamus (CBGT) network, and demonstrates the effects of close-loop deep brain stimulation (DBS) as a potential therapeutic intervention. The model focuses on addressing abnormal brain wave patterns associated with PD-related hand movement through DBS. To assess the model performance, a three-link manipulator is incorporated into the CBGT model, with the joints corresponding to shoulder, elbow and wrist of human arm. PD-like symptoms are simulated by modulating the dopaminergic input. The striatal (STR) neurons were selected as target neurons for application of DBS. A proportional-integral (PI) controller regulates DBS at different frequencies in striatal neurons based on errors in manipulator movement. The effectiveness of DBS at STR was compared with the DBS at globus pallidus externus and subthalamic nucleus. DBS suppressed neuronal signal oscillations at 13-30 Hz and reduced abnormal hand movements. The results demonstrate that application of DBS at STR could correct manipulator movement. Additionally, the trajectory of movement by the end-effector were compared with DBS at different target neurons in CBGT. These findings suggest the therapeutic potential of the proposed computational model in development of neuroprosthesis for PD patients.

Variable schedules of reinforcement do not reliably distinguish habit from goal-directed behavior

Contemporary analyses of neurophysiological mechanisms of associative learning suggest that instrumental behavior can be controlled by separable action and habit processes. An increasingly broad range of human psychiatric and neurological disorders are now associated with maladaptive habit formation. The question of how the brain controls transitions into habit is thus relevant. Widely used training procedures that might differentially generate goal-directed actions or habits are variable schedules of reinforcement. Random interval schedules are known to generate habitual behavior compared with random ratio schedules Here, we report attempt to identify the behavioral characteristics of the bifurcation point of habitual and goal-directed behavior. We compared the time courses of learning in random ratio and random interval schedules with more common for neurophysiological researches parameters. Behavioral differences between schedules emerge early in learning. However, in outcome devaluation test we found that training in the random ratio schedule, but not in the random interval schedule, led to results interpreted as habitual behavior. This result is the opposite of what we expected based on previous research. We assume that the most commonly used variable schedules of reinforcement cannot serve as a reliable tool for analyzing neural mechanisms of habitual and goal-directed behavior.

Pallidal prototypic neuron and astrocyte activities regulate flexible reward-seeking behaviors

Behavioral flexibility allows animals to adjust actions to changing environments. While the basal ganglia are critical for adaptation, the specific role of the external globus pallidus (GPe) is unclear. This study examined the contributions of two major GPe cell types-prototypic neurons projecting to the subthalamic nucleus (ProtoGPe→STN neurons) and astrocytes-to behavioral flexibility. Using longitudinal operant conditioning with context reversals, we found that ProtoGPe→STN neurons dynamically represent contextual information correlating with behavioral optimality. In contrast, GPe astrocytes exhibited gradual contextual encoding independent of performance. Deleting ProtoGPe→STN neurons impaired adaptive responses to changing action-outcome contingencies without altering initial reward-seeking acquisition, highlighting their specific role in enabling behavioral flexibility. Furthermore, we discovered that ProtoGPe→STN neurons integrate inhibitory striatal and excitatory subthalamic inputs, modulating downstream basal ganglia circuits to support flexible behavior. This research elucidates the complementary roles of ProtoGPe→STN neurons and astrocytes in cellular mechanisms of flexible reward-seeking behavior.

Body Satisfaction, Exercise Dependence, and White Matter Microstructure in Young Adults

BACKGROUND

Self-body satisfaction is considered a psychological factor for exercise dependence (EXD). However, the potential neuropsychological mechanisms underlying this association remain unclear.

PURPOSE

To investigate the role of white matter microstructure in the association between body satisfaction and EXD.

STUDY TYPE

Prospective.

POPULATION

One hundred eight regular exercisers (age 22.11 ± 2.62 years; 58 female).

FIELD STRENGTH/SEQUENCE

3.0 Tesla; diffusion-weighted echo planar imaging with 30 directions.

ASSESSMENT

The Body Shape Satisfaction (BSS) and Exercise Dependence Scale (EDS); whole-brain tract-based spatial statistics (TBSS) and correlational tractography analyses; average fractional anisotropy (FA) and quantitative anisotropy (QA) values of obtained tracts.

STATISTICAL TESTS

The whole-brain regression model, mediation analysis, and simple slope analysis. P values <0.05 were defined as statistically significant.

RESULTS

The BSS and EDS scores were 37.33 ± 6.32 and 68.22 ± 13.88, respectively. TBSS showed negative correlations between EDS and FA values in the bilateral corticospinal tract (CST, r = -0.41), right cingulum (r = -0.41), and left superior thalamic radiation (STR, r = -0.50). Correlational tractography showed negative associations between EDS and QA values of the left inferior frontal occipital fasciculus (r = -0.35), STR (r = -0.42), CST (r = -0.31), and right cingulum (r = -0.28). The FA values, rather than QA values, mediated the BSS-EDS association (indirect effects = 0.30). The BSS was significantly associated with the EDS score at both low (β = 1.02) and high (β = 0.43) levels of FA value, while the association was significant only at the high level of QA value (β = 1.26).

DATA CONCLUSION

EXD was correlated with white matter in frontal-subcortical and sensorimotor networks, and these tracts mediated the body satisfaction-EXD association. White matter microstructure could be a promising neural signature for understanding the underlying neuropsychological mechanisms of EXD.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 1.

Causal contributions of cell-type-specific circuits in the posterior dorsal striatum to auditory decision-making

In the dorsal striatum (DS), the direct- and indirect-pathway striatal projection neurons (dSPNs and iSPNs) play crucial opposing roles in controlling actions. However, it remains unclear whether and how dSPNs and iSPNs provide distinct and specific contributions to decision-making, a process transforming sensory inputs to actions. Here, we perform causal interrogations on the roles of dSPNs and iSPNs in the posterior DS (pDS) in auditory-guided decision-making. Unilateral activation of dSPNs or iSPNs produces strong opposite drives to choice behaviors regardless of task difficulty. However, inactivation of dSPNs or iSPNs leads to pronounced choice bias preferentially in difficult trials, suggesting decision-specific contributions. Indeed, temporally specific iSPN activation within, but not outside, the decision period significantly biased choices. Finally, concurrent disinhibition of both pathways via inactivating parvalbumin (PV)-positive interneurons leads to contralateral bias primarily in difficult trials. These results reveal specific contributions by coordinated dSPN and iSPN activity to decision-making processes.

Maturation of striatal dopamine supports the development of habitual behavior through adolescence

Developmental trajectories during the transition from adolescence to adulthood contribute to the establishment of stable, adult forms of operation. Understanding the neural mechanisms underlying this transition is crucial for identifying variability in normal development and the onset of psychiatric disorders, which typically emerge during this time. Habitual behaviors can serve as a model for understanding brain mechanisms underlying the stabilization of adult behavior, while also conferring risk for psychopathologies. Dopaminergic (DA) processes in the basal ganglia are thought to facilitate the formation of habits; however, developmental trajectories of habits and the brain systems supporting them have not been characterized in vivo in developing humans. The current study examined trajectories of habitual behavior from adolescence to adulthood and sought to understand how the maturing striatal DA system may act as a potential mechanism in the process of habit formation. We used data from two longitudinal studies (combined n = 217, 10 - 32 years of age, 1-3 visits each, 320 total sessions) to characterize normative developmental trajectories of basal ganglia tissue iron concentration (a proxy for DA-related neurophysiology) and goal-direct and habitual control behaviors in a two-stage decision-making task. Tissue iron concentrations across the basal ganglia and habitual responding during the two-stage sequential decision-making task both increased with age (all p < 0.001). Importantly, habitual responding was associated with tissue iron concentrations in the putamen (F = 4.34, p = 0.014), such that increases in habitual responding were supported by increases in putamen tissue iron concentration during childhood through late adolescence. Exploratory analyses of further subdivisions of anatomical regions found that this association was specific to the posterior putamen. These results provide novel evidence in humans that habitual behavior continues to mature into adulthood and may be supported by increased specialization of reward systems.

Neuronal encoding of behaviors and instrumental learning in the dorsal striatum

The dorsal striatum is instrumental in regulating motor control and goal-directed behaviors. The classical description of the two output pathways of the dorsal striatum highlights their antagonistic control over actions. However, recent experimental evidence implicates both pathways and their coordinated activities during actions. In this review, we examine the different models proposed for striatal encoding of actions during self-paced behaviors and how they can account for evidence harvested during goal-directed behaviors. We also discuss how the activation of striatal ensembles can be reshaped and reorganized to support the formation of instrumental learning and behavioral flexibility. Future work integrating these considerations may resolve controversies regarding the control of actions by striatal networks.

Early life racial/ethnic discrimination effects on behavioral control and health outcomes in young adults

Early life trauma has been shown to facilitate habitual behavior, which may predispose individuals toward perpetuating maladaptive behaviors. However, previous investigations did not account for other traumatic childhood experiences like racial/ethnic discrimination exposure, nor have they examined the interaction of trauma and habits on real-world adverse outcomes. To examine these effects, we recruited 96 young adults (20.06 ± 1.89 years old) in a study probing early life racial/ethnic discrimination influences on habitual learning, and the conjunctive influences of early life discrimination and habit on disordered eating and substance use. To measure habit responses, participants completed a noise avoidance task during which they responded to abstract stimuli via associated keyboard presses to avoid an aversive screaming sound, after which they performed a devaluation test to measure avoidance habit responses. Participants then completed a series of questionnaires examining early life racial/ethnic discrimination exposure, disordered eating and substance use, and other psychological characteristics. Hierarchical regression results showed that certain early life discrimination subtypes, particularly threat/aggression experienced due to racial/ethnic background, significantly predicted habitual responding above and beyond the effects of psychological confounds. Additionally, overall early life discrimination exposure positively predicted binge eating, but no variables of interest predicted alcohol and drug use. These results expand on extant literature showing the negative impacts of childhood stressors on behavioral control and real-world outcomes.

Aberrant glutamatergic systems underlying impulsive behaviors: Insights from clinical and preclinical research

Impulsivity is a broad construct that often refers to one of several distinct behaviors and can be measured with self-report questionnaires and behavioral paradigms. Several psychiatric conditions are characterized by one or more forms of impulsive behavior, most notably the impulsive/hyperactive subtype of attention-deficit/hyperactivity disorder (ADHD), mood disorders, and substance use disorders. Monoaminergic neurotransmitters are known to mediate impulsive behaviors and are implicated in various psychiatric conditions. However, growing evidence suggests that glutamate, the major excitatory neurotransmitter of the mammalian brain, regulates important functions that become dysregulated in conditions like ADHD. The purpose of the current review is to discuss clinical and preclinical evidence linking glutamate to separate aspects of impulsivity, specifically motor impulsivity, impulsive choice, and affective impulsivity. Hyperactive glutamatergic activity in the corticostriatal and the cerebro-cerebellar pathways are major determinants of motor impulsivity. Conversely, hypoactive glutamatergic activity in frontal cortical areas and hippocampus and hyperactive glutamatergic activity in anterior cingulate cortex and nucleus accumbens mediate impulsive choice. Affective impulsivity is controlled by similar glutamatergic dysfunction observed for motor impulsivity, except a hyperactive limbic system is also involved. Loss of glutamate homeostasis in prefrontal and nucleus accumbens may contribute to motor impulsivity/affective impulsivity and impulsive choice, respectively. These results are important as they can lead to novel treatments for those with a condition characterized by increased impulsivity that are resistant to conventional treatments.

Environmental complexity modulates information processing and the balance between decision-making systems

Behavior in naturalistic scenarios occurs in diverse environments. Adaptive strategies rely on multiple neural circuits and competing decision systems. However, past studies of rodent decision making have largely measured behavior in simple environments. To fill this gap, we recorded neural ensembles from hippocampus (HC), dorsolateral striatum (DLS), and dorsomedial prefrontal cortex (dmPFC) while rats foraged for food under changing rules in environments with varying topological complexity. Environmental complexity increased behavioral variability, lengthened HC nonlocal sequences, and modulated action caching. We found contrasting representations between DLS and HC, supporting a competition between decision systems. dmPFC activity was indicative of setting this balance, in particular predicting the extent of HC non-local coding. Inactivating mPFC impaired short-term behavioral adaptation and produced long-term deficits in balancing decision systems. Our findings reveal the dynamic nature of decision-making systems and how environmental complexity modulates their engagement with implications for behavior in naturalistic environments.

Addressing Inconsistency in Functional Neuroimaging: A Replicable Data-Driven Multi-Scale Functional Atlas for Canonical Brain Networks

The advent of multiple neuroimaging methodologies has greatly aided in the conceptualization of large-scale functional brain networks in the field of cognitive neuroscience. However, there is inconsistency across studies in both nomenclature and the functional entities being described. There is a need for a unifying framework that standardizes terminology across studies while also bringing analyses and results into the same reference space. Here we present a whole-brain atlas of canonical functional brain networks derived from more than 100,000 resting-state fMRI datasets. These data-driven functional networks are highly replicable across datasets and capture information from multiple spatial scales. We have organized, labeled, and described the networks with terms familiar to the fields of cognitive and affective neuroscience in order to optimize their utility in future neuroimaging analyses and enhance the accessibility of new findings. The benefits of this atlas are not limited to future template-based or reference-guided analyses, but also extend to other data-driven neuroimaging approaches across modalities, such as those using blind independent component analysis (ICA). Future studies utilizing this atlas will contribute to greater harmonization and standardization in functional neuroimaging research.

The primate putamen processes cognitive flexibility alongside the caudate and ventral striatum with similar speeds of updating values

The putamen is thought to generate habitual actions by processing value information relayed from the ventral striatum through the caudate nucleus. However, it is a question what value the putamen neurons process and whether the putamen receives serially processed value through the striatal structures. We found that neurons in the primate putamen, caudate, and ventral striatum selectively encoded flexibly updated values for adaptive behaviors with similar learning speeds, rather than stably sustained values for habit. In reversal value learning, rostral striatum neurons dynamically adjusted their responses to object values in alignment with changes in saccade reaction times following reversals. Notably, the value acquisition speeds within trials were similar, proposing a parallel value update in each striatal region. However, in stable value retrieval, most did not encode the values for habitual saccades. Our findings suggest that the rostral striatum including the putamen is selectively involved in the parallel processing of cognitive flexibility.

Sex and estradiol effects in the rodent dorsal striatum

17β-Estradiol (E2) is a sex hormone that acts on many brain regions to produce changes in neuronal activity and learning. A key brain region sensitive to E2 is the dorsal striatum (also called caudate-putamen), which controls motor behaviour, goal-directed learning and habit learning. In adult rodents, oestrogen receptors (ERs) in the dorsal striatum are localized to the plasma membrane and include ERα, ERβ and G protein-coupled ER (GPER). E2, either naturally produced or exogenously applied, may influence neuronal excitability, basal synaptic transmission and long-term synaptic potentiation. These effects may be due to direct action on signalling pathways or may be due to changes in dopamine availability. In particular, estradiol influences dopamine release, dopamine receptor expression and dopamine transporter expression. We review the cellular effects that E2 has in the dorsal striatum, distinguishing between exogenously applied E2 and the oestrous cycle, as well as its influence on dorsal striatal-dependent motor and learning behaviour.

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.

From songbird to humans: The multifaceted roles of FOXP2 in speech and motor learning

Motor learning involves a complex network of brain structures and is crucial for tasks like speech. The cerebral cortex, subcortical nuclei, and cerebellum are involved in motor learning and vocalization. Vocal learning has been demonstrated across species. However, it is a task that should be further studied and reevaluated, particularly in species considered non-vocal learners, to potentially uncover new insights. FOXP2, a transcription factor, has been implicated in speech learning and execution. Several variants have been involved in speech and cognitive impairments; the most studied is the R553H, found in the KE family, where more than half of the members show verbal dyspraxia. Brain FOXP2 expression shows consistent patterns across species in regions associated with motor learning and execution. Animal models expressing mutated FOXP2 showed impaired motor learning and vocalization. Genes regulated by FOXP2 are related to neural differentiation, connectivity, and synaptic plasticity, indicating its role in brain development and function. This review explores the intricate relationship between FOXP2, motor learning, and speech in an anatomical and functional context.

Assembloid model to study loop circuits of the human nervous system

Neural circuits connecting the cerebral cortex, the basal ganglia and the thalamus are fundamental networks for sensorimotor processing and their dysfunction has been consistently implicated in neuropsychiatric disorders 1-9 . These recursive, loop circuits have been investigated in animal models and by clinical neuroimaging, however, direct functional access to developing human neurons forming these networks has been limited. Here, we use human pluripotent stem cells to reconstruct an in vitro cortico-striatal-thalamic-cortical circuit by creating a four-part loop assembloid. More specifically, we generate regionalized neural organoids that resemble the key elements of the cortico-striatal-thalamic-cortical circuit, and functionally integrate them into loop assembloids using custom 3D-printed biocompatible wells. Volumetric and mesoscale calcium imaging, as well as extracellular recordings from individual parts of these assembloids reveal the emergence of synchronized patterns of neuronal activity. In addition, a multi-step rabies retrograde tracing approach demonstrate the formation of neuronal connectivity across the network in loop assembloids. Lastly, we apply this system to study heterozygous loss of ASH1L gene associated with autism spectrum disorder and Tourette syndrome and discover aberrant synchronized activity in disease model assembloids. Taken together, this human multi-cellular platform will facilitate functional investigations of the cortico-striatal-thalamic-cortical circuit in the context of early human development and in disease conditions.

Cofilin linked to GluN2B subunits of NMDA receptors is required for behavioral sensitization by changing the dendritic spines of neurons in the caudate and putamen after repeated nicotine exposure

BACKGROUND

Nicotine dependence is associated with glutamatergic neurotransmission in the caudate and putamen (CPu) of the forebrain which includes alterations in the structure of dendritic spines at glutamate synapses. These changes after nicotine exposure can lead to the development of habitual behaviors such as smoking. The present study investigated the hypothesis that cofilin, an actin-binding protein that is linked to the GluN2B subunits of N-methyl-D-aspartate (NMDA) receptors regulates the morphology of dendritic spines in the neurons of the CPu after repeated exposure to nicotine.

RESULTS

Adult male rats received subcutaneous injections of nicotine (0.3 mg/kg/day) or vehicle for seven consecutive days. DiI staining was conducted to observe changes in dendritic spine morphology. Repeated subcutaneous injections of nicotine decreased the phosphorylation of cofilin while increasing the formation of thin spines and filopodia in the dendrites of medium spiny neurons (MSN) in the CPu of rats. Bilateral intra-CPu infusion of the cofilin inhibitor, cytochalasin D (12.5 µg/µL/side), restored the thin spines and filopodia from mushroom types after repeated exposure to nicotine. Similar results were obtained from the bilateral intra-CPu infusion of the selective GluN2B subunit antagonist, Ro 25-6981 (4 µM/µL/side). Bilateral intra-CPu infusion of cytochalasin D that interferes with the actin-cofilin interaction attenuated the repeated nicotine-induced increase in locomotor sensitization in rats.

CONCLUSIONS

These findings suggest that active cofilin alters the structure of spine heads from mushroom to thin spine/filopodia by potentiating actin turnover, contributing to behavioral sensitization after nicotine exposure.

Learning and Control in Motor Cortex across Cell Types and Scales

The motor cortex is essential for controlling the flexible movements underlying complex behaviors. Behavioral flexibility involves the ability to integrate and refine new movements, thereby expanding an animal's repertoire. This review discusses recent strides in motor learning mechanisms across spatial and temporal scales, describing how neural networks are remodeled at the level of synapses, cell types, and circuits and across time as animals' learn new skills. It highlights how changes at each scale contribute to the evolving structure and function of neural circuits that accompanies the expansion and refinement of motor skills. We review new findings highlighted by advanced imaging techniques that have opened new vistas in optical physiology and neuroanatomy, revealing the complexity and adaptability of motor cortical circuits, crucial for learning and control. At the structural level, we explore the dynamic regulation of dendritic spines mediating corticocortical and thalamocortical inputs to the motor cortex. We delve into the role of perisynaptic astrocyte processes in maintaining synaptic stability during learning. We also examine the functional diversity among pyramidal neuron subtypes, their dendritic computations and unique contributions to single cell and network function. Further, we highlight how cortical activation is characterized by increased consistency and reduced strength as new movements are learned and how external inputs contribute to these changes. Finally, we consider the motor cortex's necessity as movements unfold over long time scales. These insights will continue to drive new research directions, enhancing our understanding of motor cortical circuit transformations that underpin behavioral changes expressed throughout an animal's life.

A TAN-dopamine interaction mechanism based computational model of basal ganglia in action selection

The basal ganglia (BG) plays a key role in action selection. Physiological experiments have suggested that the reciprocal interaction between tonically active neurons (TANs) and dopamine (DA) is closely related to reward-based behaviors. However, the functional role of TAN-DA interaction in action selection remains unclear. In this study, a cortico-BG model including TAN-DA interaction mechanism is developed to explore the action selection mechanism of BG. The results show that in the default case, direct, indirect, and hyperdirect pathways are responsible for promoting, suppressing, and stopping the formation of stimulus-action associations, respectively. In the case of reinforcement learning, a single rewarded action is selected according to the combination of the TAN-DA dependent reinforcement mechanism and Hebbian mechanism with a gradual transfer from the former to the latter. Besides, a longer exploratory phase occurs when switching the reward to a new action because additional trials are required to overcome the habituation previously induced by the Hebbian mechanism. In the Parkinsonian state, the reinforcement mechanism is disrupted, and the resting tremor occurs due to dopamine deficiency. Although the model's performance significantly improves due to the levodopa treatment, it is still inferior to the healthy state. This phenomenon is consistent with the experimental results and is explained theoretically via the TAN pause duration and phasic DA release. Furthermore, the model's performances in multi-action selection further verify the rationality of the TAN-DA-dependent reinforcement mechanism. Our work provides a more complete framework for studying the action selection mechanism of basal ganglia.

The genetic landscape of basal ganglia and implications for common brain disorders

The basal ganglia are subcortical brain structures involved in motor control, cognition, and emotion regulation. We conducted univariate and multivariate genome-wide association analyses (GWAS) to explore the genetic architecture of basal ganglia volumes using brain scans obtained from 34,794 Europeans with replication in 4,808 white and generalization in 5,220 non-white Europeans. Our multivariate GWAS identified 72 genetic loci associated with basal ganglia volumes with a replication rate of 55.6% at P < 0.05 and 87.5% showed the same direction, revealing a distributed genetic architecture across basal ganglia structures. Of these, 50 loci were novel, including exonic regions of APOE, NBR1 and HLAA. We examined the genetic overlap between basal ganglia volumes and several neurological and psychiatric disorders. The strongest genetic overlap was between basal ganglia and Parkinson's disease, as supported by robust LD-score regression-based genetic correlations. Mendelian randomization indicated genetic liability to larger striatal volume as potentially causal for Parkinson's disease, in addition to a suggestive causal effect of greater genetic liability to Alzheimer's disease on smaller accumbens. Functional analyses implicated neurogenesis, neuron differentiation and development in basal ganglia volumes. These results enhance our understanding of the genetic architecture and molecular associations of basal ganglia structure and their role in brain disorders.

Causal effect of COVID-19 on longitudinal volumetric changes in subcortical structures: A mendelian randomization study

A few observational neuroimaging investigations have reported subcortical structural changes in the individuals who recovered from the coronavirus disease-2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the causal relationships between COVID-19 and longitudinal changes of subcortical structures remain unclear. We performed two-sample Mendelian randomization (MR) analyses to estimate putative causal relationships between three COVID-19 phenotypes (susceptibility, hospitalization, and severity) and longitudinal volumetric changes of seven subcortical structures derived from MRI. Our findings demonstrated that genetic liability to SARS-CoV-2 infection had a great long-term impact on the volumetric reduction of subcortical structures, especially caudate. Our investigation may contribute in part to the understanding of the neural mechanisms underlying COVID-19-related neurological and neuropsychiatric sequelae.

Subcortical volume in middle-aged adults with fetal alcohol spectrum disorders

Studies of youth and young adults with prenatal alcohol exposure (PAE) have most consistently reported reduced volumes of the corpus callosum, cerebellum and subcortical structures. However, it is unknown whether this continues into middle adulthood or if individuals with PAE may experience premature volumetric decline with aging. Forty-eight individuals with fetal alcohol spectrum disorders (FASD) and 28 healthy comparison participants aged 30 to 65 participated in a 3T MRI session that resulted in usable T1-weighted and T2-weighted structural images. Primary analyses included volumetric measurements of the caudate, putamen, pallidum, cerebellum and corpus callosum using FreeSurfer software. Analyses were conducted examining both raw volumetric measurements and subcortical volumes adjusted for overall intracranial volume (ICV). Models tested for main effects of age, sex and group, as well as interactions of group with age and group with sex. We found the main effects for group; all regions were significantly smaller in participants with FASD for models using raw volumes (P's < 0.001) as well as for models using volumes adjusted for ICV (P's < 0.046). Although there were no significant interactions of group with age, females with FASD had smaller corpus callosum volumes relative to both healthy comparison females and males with FASD (P's < 0.001). As seen in children and adolescents, adults aged 30 to 65 with FASD showed reduced volumes of subcortical structures relative to healthy comparison adults, suggesting persistent impact of PAE. Moreover, the observed volumetric reduction of the corpus callosum in females with FASD could suggest more rapid degeneration, which may have implications for cognition as these individuals continue to age.

Random interval schedule of reinforcement influences punishment resistance for cocaine in rats

In an animal model of compulsive drug use, a subset of rats continues to self-administer cocaine despite footshock consequences and is considered punishment resistant. We recently found that punishment resistance is associated with habits that persist under conditions that typically encourage a transition to goal-directed control. Given that random ratio (RR) and random interval (RI) schedules of reinforcement influence whether responding is goal-directed or habitual, we investigated the influence of these schedules on punishment resistance for cocaine or food. Male and female Sprague Dawley rats were trained to self-administer either intravenous cocaine or food pellets on a seeking-taking chained schedule of reinforcement, with the seeking lever requiring completion of either an RR20 or RI60 schedule. Rats were then given four days of punishment testing with footshock administered at the completion of seeking on a random one-third of trials. For cocaine-trained rats, the RI60 schedule led to greater punishment resistance (i.e., more trials completed) than the RR20 schedule in males and females. For food-trained rats, the RI60 schedule led to greater punishment resistance (i.e., higher reward rates) than the RR20 schedule in female rats, although male rats showed punishment resistance on both RR20 and RI60 schedules. For both cocaine and food, we found that seeking responses were suppressed to a greater degree than reward rate with the RI60 schedule, whereas response rate and reward rate were equally suppressed with the RR20 schedule. This dissociation between punishment effects on reward rate and response rate with the RI60 schedule can be explained by the nonlinear relation between these variables on RI schedules, but it does not account for the enhanced resistance to punishment. Overall, the results show greater punishment resistance with the RI60 schedule as compared to the RR20 schedule, indicating that schedules of reinforcement are an influencing factor on resistance to negative consequences.

Bridging flexible goal-directed cognition and consciousness: The Goal-Aligning Representation Internal Manipulation theory

Goal-directed manipulation of internal representations is a key element of human flexible behaviour, while consciousness is commonly associated with higher-order cognition and human flexibility. Current perspectives have only partially linked these processes, thus preventing a clear understanding of how they jointly generate flexible cognition and behaviour. Moreover, these limitations prevent an effective exploitation of this knowledge for technological scopes. We propose a new theoretical perspective that extends our 'three-component theory of flexible cognition' toward higher-order cognition and consciousness, based on the systematic integration of key concepts from Cognitive Neuroscience and AI/Robotics. The theory proposes that the function of conscious processes is to support the alignment of representations with multi-level goals. This higher alignment leads to more flexible and effective behaviours. We analyse here our previous model of goal-directed flexible cognition (validated with more than 20 human populations) as a starting GARIM-inspired model. By bridging the main theories of consciousness and goal-directed behaviour, the theory has relevant implications for scientific and technological fields. In particular, it contributes to developing new experimental tasks and interpreting clinical evidence. Finally, it indicates directions for improving machine learning and robotics systems and for informing real-world applications (e.g., in digital-twin healthcare and roboethics).

Amphibian spatial cognition, medial pallium and other supporting telencephalic structures

Vertebrate hippocampal formation is central to conversations on the comparative analysis of spatial cognition, especially in light of variation found in different vertebrate classes. Assuming the medial pallium (MP) of extant amphibians resembles the hippocampal formation (HF) of ancestral stem tetrapods, we propose that the HF of modern amniotes began with a MP characterized by a relatively undifferentiated cytoarchitecture, more direct thalamic/olfactory sensory inputs, and a more generalized role in associative learning-memory processes. As such, hippocampal evolution in amniotes, especially mammals, can be seen as progressing toward a cytoarchitecture with well-defined subdivisions, regional connectivity, and a functional specialization supporting map-like representations of space. We then summarize a growing literature on amphibian spatial cognition and its underlying brain organization. Emphasizing the MP/HF, we highlight that further research into amphibian spatial cognition would provide novel insight into the role of the HF in spatial memory processes, and their supporting neural mechanisms. A more complete reconstruction of hippocampal evolution would benefit from additional research on non-mammalian vertebrates, with amphibians being of particular interest.

Dopamine neurons drive spatiotemporally heterogeneous striatal dopamine signals during learning

Environmental cues, through Pavlovian learning, become conditioned stimuli that invigorate and guide animals toward rewards. Dopamine (DA) neurons in the ventral tegmental area (VTA) and substantia nigra (SNc) are crucial for this process, via engagement of a reciprocally connected network with their striatal targets. Critically, it remains unknown how dopamine neuron activity itself engages dopamine signals throughout the striatum, across learning. Here, we investigated how optogenetic Pavlovian cue conditioning of VTA or SNc dopamine neurons directs cue-evoked behavior and shapes subregion-specific striatal dopamine dynamics. We used a fluorescent biosensor to monitor dopamine in the nucleus accumbens (NAc) core and shell, dorsomedial striatum (DMS), and dorsolateral striatum (DLS). We demonstrate spatially heterogeneous, learning-dependent dopamine changes across striatal regions. Although VTA stimulation-evoked robust dopamine release in NAc core, shell, and DMS, predictive cues preferentially recruited dopamine release in NAc core, starting early in training, and DMS, late in training. Negative prediction error signals, reflecting a violation in the expectation of dopamine neuron activation, only emerged in the NAc core and DMS. Despite the development of vigorous movement late in training, conditioned dopamine signals did not emerge in the DLS, even during Pavlovian conditioning with SNc dopamine neuron activation, which elicited robust DLS dopamine release. Together, our studies show a broad dissociation in the fundamental prediction and reward-related information generated by VTA and SNc dopamine neuron populations and signaled by dopamine across the striatum. Further, they offer new insight into how larger-scale adaptations across the striatal network emerge during learning to coordinate behavior.

Bad habits-good goals? Meta-analysis and translation of the habit construct to alcoholism

Excessive alcohol consumption remains a global public health crisis, with millions suffering from alcohol use disorder (AUD, or simply "alcoholism"), leading to significantly reduced life expectancy. This review examines the interplay between habitual and goal-directed behaviors and the associated neurobiological changes induced by chronic alcohol exposure. Contrary to a strict habit-goal dichotomy, our meta-analysis of the published animal experiments combined with a review of human studies reveals a nuanced transition between these behavioral control systems, emphasizing the need for refined terminology to capture the probabilistic nature of decision biases in individuals with a history of chronic alcohol exposure. Furthermore, we distinguish habitual responding from compulsivity, viewing them as separate entities with diverse roles throughout the stages of the addiction cycle. By addressing species-specific differences and translational challenges in habit research, we provide insights to enhance future investigations and inform strategies for combatting AUD.

A transdiagnostic and translational framework for delineating the neuronal mechanisms of compulsive exercise in anorexia nervosa

OBJECTIVE

The development of novel treatments for anorexia nervosa (AN) requires a detailed understanding of the biological underpinnings of specific, commonly occurring symptoms, including compulsive exercise. There is considerable bio-behavioral overlap between AN and obsessive-compulsive disorder (OCD), therefore it is plausible that similar mechanisms underlie compulsive behavior in both populations. While the association between these conditions is widely acknowledged, defining the shared mechanisms for compulsive behavior in AN and OCD requires a novel approach.

METHODS

We present an argument that a better understanding of the neurobiological mechanisms that underpin compulsive exercise in AN can be achieved in two critical ways. First, by applying a framework of the neuronal control of OCD to exercise behavior in AN, and second, by taking better advantage of the activity-based anorexia (ABA) rodent model to directly test this framework in the context of feeding pathology.

RESULTS

A cross-disciplinary approach that spans preclinical, neuroimaging, and clinical research as well as compulsive neurocircuitry and behavior can advance our understanding of when, why, and how compulsive exercise develops in the context of AN and provide targets for novel treatment strategies.

DISCUSSION

In this article, we (i) link the expression of compulsive behavior in AN and OCD via a transition between goal-directed and habitual behavior, (ii) present disrupted cortico-striatal circuitry as a key substrate for the development of compulsive behavior in both conditions, and (iii) highlight the utility of the ABA rodent model to better understand the mechanisms of compulsive behavior relevant to AN.

PUBLIC SIGNIFICANCE

Individuals with AN who exercise compulsively are at risk of worse health outcomes and have poorer responses to standard treatments. However, when, why, and how compulsive exercise develops in AN remains inadequately understood. Identifying whether the neural circuitry underlying compulsive behavior in OCD also controls hyperactivity in the activity-based anorexia model will aid in the development of novel eating disorder treatment strategies for this high-risk population.

The well-worn route revisited: Striatal and hippocampal system contributions to familiar route navigation

Classic research has shown a division in the neuroanatomical structures that support flexible (e.g., short-cutting) and habitual (e.g., familiar route following) navigational behavior, with hippocampal-caudate systems associated with the former and putamen systems with the latter. There is, however, disagreement about whether the neural structures involved in navigation process particular forms of spatial information, such as associations between constellations of cues forming a cognitive map, versus single landmark-action associations, or alternatively, perform particular reinforcement learning algorithms that allow the use of different spatial strategies, so-called model-based (flexible) or model-free (habitual) forms of learning. We sought to test these theories by asking participants (N = 24) to navigate within a virtual environment through a previously learned, 9-junction route with distinctive landmarks at each junction while undergoing functional magnetic resonance imaging (fMRI). In a series of probe trials, we distinguished knowledge of individual landmark-action associations along the route versus knowledge of the correct sequence of landmark-action associations, either by having absent landmarks, or "out-of-sequence" landmarks. Under a map-based perspective, sequence knowledge would not require hippocampal systems, because there are no constellations of cues available for cognitive map formation. Within a learning-based model, however, responding based on knowledge of sequence would require hippocampal systems because prior context has to be utilized. We found that hippocampal-caudate systems were more active in probes requiring sequence knowledge, supporting the learning-based model. However, we also found greater putamen activation in probes where navigation based purely on sequence memory could be planned, supporting models of putamen function that emphasize its role in action sequencing.

Rethinking dopamine-guided action sequence learning

As opposed to those requiring a single action for reward acquisition, tasks necessitating action sequences demand that animals learn action elements and their sequential order and sustain the behaviour until the sequence is completed. With repeated learning, animals not only exhibit precise execution of these sequences but also demonstrate enhanced smoothness and efficiency. Previous research has demonstrated that midbrain dopamine and its major projection target, the striatum, play crucial roles in these processes. Recent studies have shown that dopamine from the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) serve distinct functions in action sequence learning. The distinct contributions of dopamine also depend on the striatal subregions, namely the ventral, dorsomedial and dorsolateral striatum. Here, we have reviewed recent findings on the role of striatal dopamine in action sequence learning, with a focus on recent rodent studies.

Facial emotion recognition and judgment of affective scenes in Parkinson's disease

Emotional dysfunctions in Parkinson's disease (PD) remain a controversial issue. While previous investigations showed compromised recognition of expressive faces in PD, no studies evaluated potential deficits in recognizing the emotional valence of affective scenes. This study aimed to investigate both facial emotion recognition performance and the ability to judge affective scenes in PD patients. Forty PD patients (mean age ± SD: 64.50 ± 8.19 years; 27 men) and forty healthy subjects (64.95 ± 8.25 years; 27 men) were included. Exclusion criteria were previous psychiatric disorders, previous Deep Brain Stimulation, and cognitive impairment. Participants were evaluated through the Ekman 60-Faces test and the International Affective Picture System. The accuracy in recognizing the emotional valence of facial expressions and affective scenes was compared between groups using linear mixed models. Pearson's correlation was performed to test the association between accuracy measures. The groups did not differ in sex, age, education, and Mini-Mental State Examination scores. Patients showed a lower recognition accuracy of facial expressions (68.54 % ± 15.83 %) than healthy participants (78.67 % ± 12.04 %; p < 0.001). Specifically, the PD group was characterized by lower recognition of faces expressing fear, sadness, and anger than the control group (all p < 0.020). No difference was detected for faces expressing disgust, surprise, and happiness (all p ≥ 0.25). Furthermore, patients showed lower accuracy in recognizing the emotional valence of affective scenes (66.75 % ± 14.59 %) than healthy subjects (74.83 % ± 12.65 %; p = 0.010). Pearson's correlations indicated that higher accuracy in recognizing the emotional facial expressions was associated with higher accuracy in classifying the valence of affective scenes in patients (r = 0.57, p < 0.001) and control participants (r = 0.57, p < 0.001). Our study suggested maladaptive affective processing in PD, leading patients to misinterpret both facial expressions and the emotional valence of complex evocative scenes.

Chronic alcohol induces subcircuit-specific striatonigral plasticity enhancing the sensorimotor basal ganglia role in action execution

Functional deficits in basal ganglia (BG) circuits contribute to cognitive and motor dysfunctions in alcohol use disorder. Chronic alcohol exposure alters synaptic function and neuronal excitability in the dorsal striatum, but it remains unclear how it affects BG output that is mediated by the substantia nigra pars reticulata (SNr). Here, we describe a neuronal subpopulation-specific synaptic organization of striatal and subthalamic (STN) inputs to the medial and lateral SNr. Chronic alcohol exposure (CIE) potentiated dorsolateral striatum (DLS) inputs but did not change dorsomedial striatum and STN inputs to the SNr. Chemogenetic inhibition of DLS direct pathway neurons revealed an enhanced role for DLS direct pathway neurons in execution of an instrumental lever-pressing task. Overall, we reveal a subregion-specific organization of striatal and subthalamic inputs onto the medial and lateral SNr and find that potentiated DLS-SNr inputs are accompanied by altered BG control of action execution following CIE.

Linking haploinsufficiency of the autism- and schizophrenia-associated gene Cyfip1 with striatal-limbic-cortical network dysfunction and cognitive inflexibility

Impaired behavioural flexibility is a core feature of neuropsychiatric disorders and is associated with underlying dysfunction of fronto-striatal circuitry. Reduced dosage of Cyfip1 is a risk factor for neuropsychiatric disorder, as evidenced by its involvement in the 15q11.2 (BP1-BP2) copy number variant: deletion carriers are haploinsufficient for CYFIP1 and exhibit a two- to four-fold increased risk of schizophrenia, autism and/or intellectual disability. Here, we model the contributions of Cyfip1 to behavioural flexibility and related fronto-striatal neural network function using a recently developed haploinsufficient, heterozygous knockout rat line. Using multi-site local field potential (LFP) recordings during resting state, we show that Cyfip1 heterozygous rats (Cyfip1+/-) harbor disrupted network activity spanning medial prefrontal cortex, hippocampal CA1 and ventral striatum. In particular, Cyfip1+/- rats showed reduced influence of nucleus accumbens and increased dominance of prefrontal and hippocampal inputs, compared to wildtype controls. Adult Cyfip1+/- rats were able to learn a single cue-response association, yet unable to learn a conditional discrimination task that engages fronto-striatal interactions during flexible pairing of different levers and cue combinations. Together, these results implicate Cyfip1 in development or maintenance of cortico-limbic-striatal network integrity, further supporting the hypothesis that alterations in this circuitry contribute to behavioural inflexibility observed in neuropsychiatric diseases including schizophrenia and autism.

Intense training prevents the amnestic effect of inactivation of dorsomedial striatum and induces high resistance to extinction

A large body of evidence has shown that treatments that interfere with memory consolidation become ineffective when animals are subjected to an intense learning experience; this effect has been observed after systemic and local administration of amnestic drugs into several brain areas, including the striatum. However, the effects of amnestic treatments on the process of extinction after intense training have not been studied. Previous research demonstrated increased spinogenesis in the dorsomedial striatum, but not in the dorsolateral striatum after intense training, indicating that the dorsomedial striatum is involved in the protective effect of intense training. To investigate this issue, male Wistar rats, previously trained with low, moderate, or high levels of foot shock, were used to study the effect of tetrodotoxin inactivation of dorsomedial striatum on memory consolidation and subsequent extinction of inhibitory avoidance. Performance of the task was evaluated during seven extinction sessions. Tetrodotoxin produced a marked deficit of memory consolidation of inhibitory avoidance trained with low and moderate intensities of foot shock, but normal consolidation occurred when a relatively high foot shock was used. The protective effect of intense training was long-lasting, as evidenced by the high resistance to extinction exhibited throughout the extinction sessions. We discuss the possibility that increased dendritic spinogenesis in dorsomedial striatum may underly this protective effect, and how this mechanism may be related to the resilient memory typical of post-traumatic stress disorder (PTSD).

Beliefs, compulsive behavior and reduced confidence in control

OCD has been conceptualized as a disorder arising from dysfunctional beliefs, such as overestimating threats or pathological doubts. Yet, how these beliefs lead to compulsions and obsessions remains unclear. Here, we develop a computational model to examine the specific beliefs that trigger and sustain compulsive behavior in a simple symptom-provoking scenario. Our results demonstrate that a single belief disturbance-a lack of confidence in the effectiveness of one's preventive (harm-avoiding) actions-can trigger and maintain compulsions and is directly linked to compulsion severity. This distrust can further explain a number of seemingly unrelated phenomena in OCD, including the role of not-just-right feelings, the link to intolerance to uncertainty, perfectionism, and overestimation of threat, and deficits in reversal and state learning. Our simulations shed new light on which underlying beliefs drive compulsive behavior and highlight the important role of perceived ability to exert control for OCD.

Punishment resistance for cocaine is associated with inflexible habits in rats

Addiction is characterized by continued drug use despite negative consequences. In an animal model, a subset of rats continues to self-administer cocaine despite footshock consequences, showing punishment resistance. We sought to test the hypothesis that punishment resistance arises from failure to exert goal-directed control over habitual cocaine seeking. While habits are not inherently permanent or maladaptive, continued use of habits under conditions that should encourage goal-directed control makes them maladaptive and inflexible. We trained male and female Sprague Dawley rats on a seeking-taking chained schedule of cocaine self-administration. We then exposed them to four days of punishment testing in which footshock was delivered randomly on one-third of trials. Before and after punishment testing (four days pre-punishment and ≥ four days post-punishment), we assessed whether cocaine seeking was goal-directed or habitual using outcome devaluation via cocaine satiety. We found that punishment resistance was associated with continued use of habits, whereas punishment sensitivity was associated with increased goal-directed control. Although punishment resistance for cocaine was not predicted by habitual responding pre-punishment, it was associated with habitual responding post-punishment. In parallel studies of food self-administration, we similarly observed that punishment resistance was associated with habitual responding post-punishment but not pre-punishment in males, although it was associated with habitual responding both pre- and post-punishment in females, indicating that punishment resistance was predicted by habitual responding in food-seeking females. These findings indicate that punishment resistance is related to habits that have become inflexible and persist under conditions that should encourage a transition to goal-directed behavior.

Synergizing habits and goals with variational Bayes

Behaving efficiently and flexibly is crucial for biological and artificial embodied agents. Behavior is generally classified into two types: habitual (fast but inflexible), and goal-directed (flexible but slow). While these two types of behaviors are typically considered to be managed by two distinct systems in the brain, recent studies have revealed a more sophisticated interplay between them. We introduce a theoretical framework using variational Bayesian theory, incorporating a Bayesian intention variable. Habitual behavior depends on the prior distribution of intention, computed from sensory context without goal-specification. In contrast, goal-directed behavior relies on the goal-conditioned posterior distribution of intention, inferred through variational free energy minimization. Assuming that an agent behaves using a synergized intention, our simulations in vision-based sensorimotor tasks explain the key properties of their interaction as observed in experiments. Our work suggests a fresh perspective on the neural mechanisms of habits and goals, shedding light on future research in decision making.

Valence ambiguity dynamically shapes striatal dopamine heterogeneity

Adaptive decision making relies on dynamic updating of learned associations where environmental cues come to predict positive and negatively valenced stimuli, such as food or threat. Flexible cue-guided behaviors depend on a network of brain systems, including dopamine signaling in the striatum, which is critical for learning and maintenance of conditioned behaviors. Critically, it remains unclear how dopamine signaling encodes multi-valent, dynamic learning contexts, where positive and negative associations must be rapidly disambiguated. To understand this, we employed a Pavlovian discrimination paradigm, where cues predicting positive and negative outcomes were intermingled during conditioning sessions, and their meaning was serially reversed across training. We found that rats readily distinguished these cues, and updated their behavior rapidly upon valence reversal. Using fiber photometry, we recorded dopamine signaling in three major striatal subregions -,the dorsolateral striatum (DLS), the nucleus accumbens core, and the nucleus accumbens medial shell - and found heterogeneous responses to positive and negative conditioned cues and their predicted outcomes. Valence ambiguity introduced by cue reversal reshaped striatal dopamine on different timelines: nucleus accumbens core and shell signals updated more readily than those in the DLS. Together, these results suggest that striatal dopamine flexibly encodes multi-valent learning contexts, and these signals are dynamically modulated by changing contingencies to resolve ambiguity about the meaning of environmental cues.