Role of the dorsomedial striatum in behavioral flexibility for response and visual cue discrimination learning

Neurostimulation to Improve Cognitive Flexibility

Cognitive flexibility, the capacity to adapt behaviors in response to changing environments, is impaired across mental illnesses, including depression, anxiety, addiction, and obsessive-compulsive disorder. Cortico-striatal-cortical circuits are integral to cognition and goal-directed behavior and disruptions in these circuits are linked to cognitive inflexibility in mental illnesses. We review evidence that neurostimulation of these circuits can improve cognitive flexibility and ameliorate symptoms, and that this may be a mechanism of action of current clinical therapies. Further, we discuss how animal models can offer insights into the mechanisms underlying cognitive flexibility and effects of neurostimulation. We review research from animal studies that may, if translated, yield better approaches to modulating flexibility. Future research should focus on refining definitions of cognitive flexibility, improving detection of impaired flexibility, and developing new methods for optimizing neurostimulation parameters. This could enhance neurostimulation therapies through more personalized treatments that leverage cognitive flexibility to improve patient outcomes.

Temporally and Functionally Distinct Contributions to Value Based Choice Along the Anterior-Posterior Dorsomedial Striatal Axis

While the dorsoventral and mediolateral organization of striatum has resolved clear functional distinctions, far less is known about how the anterior-posterior striatal axis contributes to behavioral control. We explore this within the dorsomedial striatum (DMS), a key region for value-based choice, by comparing population neuronal activity and function within anterior (A-DMS) and posterior (P-DMS) subregions while mice operantly seek reward. Neural recordings show that P-DMS encoded action values and strategy information prior to choice selection while A-DMS activity represented recently selected choices and their anticipated values via a dynamic population reorganization immediately following action selection. Optogenetic perturbations were consistent with these temporally distinct coding properties as unilateral manipulation of the P-DMS prior to choice biased choice contralaterally in a value-dependent manner and unilateral inhibition of the A-DMS following choice impaired future value-based action selection. Using anterograde tracing, we found that the A-DMS and P-DMS projected to a common region within the ventromedial substantia nigra pars reticulata (vmSNr), which contained value-related signals combining aspects of upstream DMS processing. Together, our results support a model for temporally distributed influence on value-based choice across the anterior-posterior axis of the DMS.

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.

Dorsomedial Striatum (DMS) CB1R Signaling Promotes Pavlovian Devaluation Sensitivity in Male Long Evans Rats and Reduces DMS Inhibitory Synaptic Transmission in Both Sexes

Cannabinoid receptor-1 (CB1R) signaling in the dorsal striatum regulates the shift from flexible to habitual behavior in instrumental outcome devaluation. Based on prior work establishing individual-, sex-, and experience-dependent differences in pavlovian behaviors, we predicted a role for dorsomedial striatum (DMS) CB1R signaling in driving rigid responding in pavlovian autoshaping and outcome devaluation. We trained male and female Long Evans rats in pavlovian lever autoshaping (PLA). We gave intra-DMS infusions of the CB1R inverse agonist, rimonabant, before satiety-induced outcome devaluation test sessions, where we sated rats on training pellets or home cage chow and tested them in brief nonreinforced PLA sessions. Overall, inhibition of DMS CB1R signaling prevented pavlovian outcome devaluation but did not affect behavior in reinforced PLA sessions. Males were sensitive to devaluation while females were not, and DMS CB1R blockade impaired devaluation sensitivity in males. Because these results suggest DMS CB1R signaling supports flexible responding, we investigated how DMS CB1R signaling impacts local inhibitory synaptic transmission in male and female Long Evans rats. We recorded spontaneous inhibitory postsynaptic currents (sIPSC) from DMS neurons at baseline and after application of a CB1R agonist, WIN 55,212-2. We found that male rats showed decreased sIPSC frequency compared with females and that CB1R activation reduced DMS inhibitory transmission independent of sex. Altogether our results demonstrate that DMS CB1Rs regulate pavlovian devaluation sensitivity and DMS inhibitory synaptic transmission and suggest that basal sex differences in inhibitory synaptic transmission may underly sex differences in DMS function and behavioral flexibility.

Flexible and Adaptive Behavioral Strategies: A Personal Journey

The ground-breaking research of patient H.M. brought to light the importance of the hippocampus for our memories of everyday and special events. Three quarters of a century of intense neurobiological and neuropsychological research would follow as scientists sought to understand why the hippocampus is such an important memory structure in the brain. Navigating a career during this time required adaptive research strategies as new evidence emerged. Although exciting progress has been made, complex challenges remain.

Org24598, a Selective Glycine Transporter 1 (GlyT1) Inhibitor, Reverses Object Recognition and Spatial Memory Impairments Following Binge-like Ethanol Exposure in Rats

The N-methyl-D-aspartate (NMDA) glutamate receptor is a major target of ethanol, and it is implicated in learning and memory formation, and other cognitive functions. Glycine acts as a co-agonist for this receptor. We examined whether Org24598, a selective inhibitor of glycine transporter1 (GlyT1), affects ethanol withdrawal-induced deficits in recognition memory (Novel Object Recognition (NOR) task) and spatial memory (Barnes Maze (BM) task) in rats, and whether the NMDA receptor glycine site participates in this phenomenon. Male Wistar rats were habituated to NOR or BM tasks, and then received binge-like intragastric ethanol administration (5 days, 5 g/kg). After ethanol withdrawal, Org24598 (0.1, 0.3, and 0.6 mg/kg) was administered 30 min before NOR (day 10 of withdrawal) or the reversal learning phase of BM (day 11-13 of withdrawal) task. The expression of GluN1 and GluN2B subunits of NMDA receptors were measured in the perirhinal cortex (PRC) and hippocampus (HIP) after termination of NOR. In the BM task, a glycine antagonist, L-701,324 (5 mg/kg), was administered 30 min before Org24598 to confirm the involvement of the NMDA receptor glycine site in the effects of Org24598. Our study showed that binge-like ethanol administration induced recognition and spatial memory impairments after withdrawal in rats. Additionally, an up-regulation of GluN1 and GluN2B subunits of the NMDA receptor was observed in the HIP and PRC on day 11 of abstinence. Org24598 ameliorated memory loss and normalized the expression of these subunits. L-701,324 reversed the effect of Org24598. Thus, NMDA receptor glycine sites are important in ethanol withdrawal-induced memory impairments.

Alcohol, flexible behavior, and the prefrontal cortex: Functional changes underlying impaired cognitive flexibility

Cognitive flexibility enables individuals to alter their behavior in response to changing environmental demands, facilitating optimal behavior in a dynamic world. The inability to do this, called behavioral inflexibility, is a pervasive behavioral phenotype in alcohol use disorder (AUD), driven by disruptions in cognitive flexibility. Research has repeatedly shown that behavioral inflexibility not only results from alcohol exposure across species but can itself be predictive of future drinking. Like many high-level executive functions, flexible behavior requires healthy functioning of the prefrontal cortex (PFC). The scope of this review addresses two primary themes: first, we outline tasks that have been used to investigate flexibility in the context of AUD or AUD models. We characterize these based on the task features and underlying cognitive processes that differentiate them from one another. We highlight the neural basis of flexibility measures, focusing on the PFC, and how acute or chronic alcohol in humans and non-human animal models impacts flexibility. Second, we consolidate findings on the molecular, physiological and functional changes in the PFC elicited by alcohol, that may contribute to cognitive flexibility deficits seen in AUD. Collectively, this approach identifies several key avenues for future research that will facilitate effective treatments to promote flexible behavior in the context of AUD, to reduce the risk of alcohol related harm, and to improve outcomes following AUD. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Dorsomedial Striatum CB1R signaling is required for Pavlovian outcome devaluation in male Long Evans rats and reduces inhibitory synaptic transmission in both sexes

Cannabinoid-1 receptor (CB1R) signaling in the dorsal striatum regulates the shift from flexible to habitual behavior in instrumental outcome devaluation. Based on prior work establishing individual, sex, and experience-dependent differences in Pavlovian behaviors, we predicted a role for dorsomedial striatum CB1R signaling in driving rigid responding in Pavlovian autoshaping and outcome devaluation. We trained male and female Long Evans rats in Pavlovian Lever Autoshaping (PLA). We gave intra-dorsomedial striatum (DMS) infusions of the CB1R inverse agonist, rimonabant, before satiety-induced outcome devaluation test sessions, where we sated rats on training pellets or home cage chow and tested them in brief nonreinforced Pavlovian Lever Autoshaping sessions. Overall, inhibition of DMS CB1R signaling prevented Pavlovian outcome devaluation but did not affect behavior in reinforced PLA sessions. Males were sensitive to devaluation while females were not and DMS CB1R inhibition impaired devaluation sensitivity in males. We then investigated how DMS CB1R signaling impacts local inhibitory synaptic transmission in male and female Long Evans rats. We recorded spontaneous inhibitory postsynaptic currents (sIPSC) from DMS neurons at baseline and before and after application of a CB1R agonist, WIN 55,212-2. We found that male rats showed decreased sIPSC frequency compared to females, and that CB1R activation reduced DMS inhibitory transmission independent of sex. Altogether our results demonstrate that DMS CB1Rs regulate Pavlovian devaluation sensitivity and inhibitory synaptic transmission and suggest that basal sex differences in inhibitory synaptic transmission may underly sex differences in DMS function and behavioral flexibility.

Double dissociation between P300 components and task switch error type in healthy but not psychosis participants

Event-related potentials (ERPs) during oddball tasks and the behavioral performance on the Penn Conditional Exclusion Task (PCET) measure context-appropriate responding: P300 ERPs to oddball targets reflect detection of input changes and context updating in working memory, and PCET performance indexes detection, adherence, and maintenance of mental set changes. More specifically, PCET variables quantify cognitive functions including inductive reasoning (set 1 completion), mental flexibility (perseverative errors), and working memory maintenance (regressive errors). Past research showed that both P300 ERPs and PCET performance are disrupted in psychosis. This study probed the possible neural correlates of 3 PCET abnormalities that occur in participants with psychosis via the overlapping cognitive demands of the two study paradigms. In a two-tiered analysis, psychosis (n = 492) and healthy participants (n = 244) were first divided based on completion of set 1 - which measures subjects' ability to use inductive reasoning to arrive at the correct set. Results showed that participants who failed set 1 produced lower parietal P300, independent of clinical status. In the second tier of analysis, a double dissociation was found among healthy set 1 completers: frontal P300 amplitudes were negatively associated with perseverative errors, and parietal P300 was negatively associated with regressive errors. In contrast, psychosis participants showed global P300 reductions regardless of PCET performance. From this we conclude that in psychosis, overall activations evoked by the oddball task are reduced while the cognitive functions required by PCET are still somewhat supported, showing some level of independence or compensatory physiology in psychosis between neural activities underlying the two tasks.

Deep brain stimulation alleviates tics in Tourette syndrome via striatal dopamine transmission

Tourette syndrome is a childhood-onset neuropsychiatric disorder characterized by intrusive motor and vocal tics that can lead to self-injury and deleterious mental health complications. While dysfunction in striatal dopamine neurotransmission has been proposed to underlie tic behaviour, evidence is scarce and inconclusive. Deep brain stimulation (DBS) of the thalamic centromedian parafascicular complex (CMPf), an approved surgical interventive treatment for medical refractory Tourette syndrome, may reduce tics by affecting striatal dopamine release. Here, we use electrophysiology, electrochemistry, optogenetics, pharmacological treatments and behavioural measurements to mechanistically examine how thalamic DBS modulates synaptic and tonic dopamine activity in the dorsomedial striatum. Previous studies demonstrated focal disruption of GABAergic transmission in the dorsolateral striatum of rats led to repetitive motor tics recapitulating the major symptom of Tourette syndrome. We employed this model under light anaesthesia and found CMPf DBS evoked synaptic dopamine release and elevated tonic dopamine levels via striatal cholinergic interneurons while concomitantly reducing motor tic behaviour. The improvement in tic behaviour was found to be mediated by D2 receptor activation as blocking this receptor prevented the therapeutic response. Our results demonstrate that release of striatal dopamine mediates the therapeutic effects of CMPf DBS and points to striatal dopamine dysfunction as a driver for motor tics in the pathoneurophysiology of Tourette syndrome.

The early excitatory action of striatal cholinergic-GABAergic microcircuits conditions the subsequent GABA inhibitory shift

Cholinergic interneurons of the striatum play a role in action selection and associative learning by activating local GABAergic inhibitory microcircuits. We investigated whether cholinergic-GABAergic microcircuits function differently and fulfill a different role during early postnatal development, when GABAA actions are not inhibitory and mice pups do not walk. We focused our study mainly on dual cholinergic/GABAergic interneurons (CGINs). We report that morphological and intrinsic electrophysiological properties of CGINs rapidly develop during the first post-natal week. At this stage, CGINs are excited by the activation of GABAA receptors or GABAergic synaptic inputs, respond to cortical stimulation by a long excitation and are linked by polysynaptic excitations. All these excitations are replaced by inhibitions at P12-P15. Early chronic treatment with the NKCC1 antagonist bumetanide to evoke premature GABAergic inhibitions from P4 to P8, prevented the GABA polarity shift and corticostriatal pause response at control postnatal days. We propose that early excitatory cholinergic-GABAergic microcircuits are instrumental in the maturation of GABAergic inhibition.

Altered striatal actin dynamics drives behavioral inflexibility in a mouse model of fragile X syndrome

The proteome of glutamatergic synapses is diverse across the mammalian brain and involved in neurodevelopmental disorders (NDDs). Among those is fragile X syndrome (FXS), an NDD caused by the absence of the functional RNA-binding protein FMRP. Here, we demonstrate how the brain region-specific composition of postsynaptic density (PSD) contributes to FXS. In the striatum, the FXS mouse model shows an altered association of the PSD with the actin cytoskeleton, reflecting immature dendritic spine morphology and reduced synaptic actin dynamics. Enhancing actin turnover with constitutively active RAC1 ameliorates these deficits. At the behavioral level, the FXS model displays striatal-driven inflexibility, a typical feature of FXS individuals, which is rescued by exogenous RAC1. Striatal ablation of Fmr1 is sufficient to recapitulate behavioral impairments observed in the FXS model. These results indicate that dysregulation of synaptic actin dynamics in the striatum, a region largely unexplored in FXS, contributes to the manifestation of FXS behavioral phenotypes.

Chronic stress causes striatal disinhibition mediated by SOM-interneurons in male mice

Chronic stress (CS) is associated with a number of neuropsychiatric disorders, and it may also contribute to or exacerbate motor function. However, the mechanisms by which stress triggers motor symptoms are not fully understood. Here, we report that CS functionally alters dorsomedial striatum (DMS) circuits in male mice, by affecting GABAergic interneuron populations and somatostatin positive (SOM) interneurons in particular. Specifically, we show that CS impairs communication between SOM interneurons and medium spiny neurons, promoting striatal overactivation/disinhibition and increased motor output. Using probabilistic machine learning to analyze animal behavior, we demonstrate that in vivo chemogenetic manipulation of SOM interneurons in DMS modulates motor phenotypes in stressed mice. Altogether, we propose a causal link between dysfunction of striatal SOM interneurons and motor symptoms in models of chronic stress.

Etiopathogenic Models of Psychosis Spectrum Illnesses Must Resolve Four Key Features

Etiopathogenic models for psychosis spectrum illnesses are converging on a number of key processes, such as the influence of specific genes on the synthesis of proteins important in synaptic functioning, alterations in how neurons respond to synaptic inputs and engage in synaptic pruning, and microcircuit dysfunction that leads to more global cortical information processing vulnerabilities. Disruptions in prefrontal operations then accumulate and propagate over time, interacting with environmental factors, developmental processes, and homeostatic mechanisms, eventually resulting in symptoms of psychosis and disability. However, there are 4 key features of psychosis spectrum illnesses that are of primary clinical relevance but have been difficult to assimilate into a single model and have thus far received little direct attention: 1) the bidirectionality of the causal influences for the emergence of psychosis, 2) the catastrophic clinical threshold seen in first episodes of psychosis and why it is irreversible in some individuals, 3) observed biotypes that are neurophysiologically distinct but clinically both convergent and divergent, and 4) a reconciliation of the role of striatal dopaminergic dysfunction with models of prefrontal cortical state instability. In this selective review, we briefly describe these 4 hallmark features and we argue that theoretically driven computational perspectives making use of both algorithmic and neurophysiologic models are needed to reduce this complexity and variability of psychosis spectrum illnesses in a principled manner.

Oscillation/Coincidence-Detection Models of Reward-Related Timing in Corticostriatal Circuits

The major tenets of beat-frequency/coincidence-detection models of reward-related timing are reviewed in light of recent behavioral and neurobiological findings. This includes the emphasis on a core timing network embedded in the motor system that is comprised of a corticothalamic-basal ganglia circuit. Therein, a central hub provides timing pulses (i.e., predictive signals) to the entire brain, including a set of distributed satellite regions in the cerebellum, cortex, amygdala, and hippocampus that are selectively engaged in timing in a manner that is more dependent upon the specific sensory, behavioral, and contextual requirements of the task. Oscillation/coincidence-detection models also emphasize the importance of a tuned ‘perception’ learning and memory system whereby target durations are detected by striatal networks of medium spiny neurons (MSNs) through the coincidental activation of different neural populations, typically utilizing patterns of oscillatory input from the cortex and thalamus or derivations thereof (e.g., population coding) as a time base. The measure of success of beat-frequency/coincidence-detection accounts, such as the Striatal Beat-Frequency model of reward-related timing (SBF), is their ability to accommodate new experimental findings while maintaining their original framework, thereby making testable experimental predictions concerning diagnosis and treatment of issues related to a variety of dopamine-dependent basal ganglia disorders, including Huntington’s and Parkinson’s disease.

Striatum expresses region-specific plasticity consistent with distinct memory abilities

The striatum mediates two learning modalities: goal-directed behavior in dorsomedial (DMS) and habits in dorsolateral (DLS) striata. The synaptic bases of these learnings are still elusive. Indeed, while ample research has described DLS plasticity, little remains known about DMS plasticity and its involvement in procedural learning. Here, we find symmetric and asymmetric anti-Hebbian spike-timing-dependent plasticity (STDP) in DMS and DLS, respectively, with opposite plasticity dominance upon increasing corticostriatal activity. During motor-skill learning, plasticity is engaged in DMS and striatonigral DLS neurons only during early learning stages, whereas striatopallidal DLS neurons are mobilized only during late phases. With a mathematical modeling approach, we find that symmetric anti-Hebbian STDP favors memory flexibility, while asymmetric anti-Hebbian STDP favors memory maintenance, consistent with memory processes at play in procedural learning.

Developmental impact of glutamate transporter overexpression on dopaminergic neuron activity and stereotypic behavior

Obsessive-compulsive disorder (OCD) is a disabling condition that often begins in childhood. Genetic studies in OCD have pointed to SLC1A1, which encodes the neuronal glutamate transporter EAAT3, with evidence suggesting that increased expression contributes to risk. In mice, midbrain Slc1a1 expression supports repetitive behavior in response to dopaminergic agonists, aligning with neuroimaging and pharmacologic challenge studies that have implicated the dopaminergic system in OCD. These findings suggest that Slc1a1 may contribute to compulsive behavior through altered dopaminergic transmission; however, this theory has not been mechanistically tested. To examine the developmental impact of Slc1a1 overexpression on compulsive-like behaviors, we, therefore, generated a novel mouse model to perform targeted, reversible overexpression of Slc1a1 in dopaminergic neurons. Mice with life-long overexpression of Slc1a1 showed a significant increase in amphetamine (AMPH)-induced stereotypy and hyperlocomotion. Single-unit recordings demonstrated that Slc1a1 overexpression was associated with increased firing of dopaminergic neurons. Furthermore, dLight1.1 fiber photometry showed that these behavioral abnormalities were associated with increased dorsal striatum dopamine release. In contrast, no impact of overexpression was observed on anxiety-like behaviors or SKF-38393-induced grooming. Importantly, overexpression solely in adulthood failed to recapitulate these behavioral phenotypes, suggesting that overexpression during development is necessary to generate AMPH-induced phenotypes. However, doxycycline-induced reversal of Slc1a1/EAAT3 overexpression in adulthood normalized both the increased dopaminergic firing and AMPH-induced responses. These data indicate that the pathologic effects of Slc1a1/EAAT3 overexpression on dopaminergic neurotransmission and AMPH-induced stereotyped behavior are developmentally mediated, and support normalization of EAAT3 activity as a potential treatment target for basal ganglia-mediated repetitive behaviors.

Planning in the brain

Recent breakthroughs in artificial intelligence (AI) have enabled machines to plan in tasks previously thought to be uniquely human. Meanwhile, the planning algorithms implemented by the brain itself remain largely unknown. Here, we review neural and behavioral data in sequential decision-making tasks that elucidate the ways in which the brain does-and does not-plan. To systematically review available biological data, we create a taxonomy of planning algorithms by summarizing the relevant design choices for such algorithms in AI. Across species, recording techniques, and task paradigms, we find converging evidence that the brain represents future states consistent with a class of planning algorithms within our taxonomy-focused, depth-limited, and serial. However, we argue that current data are insufficient for addressing more detailed algorithmic questions. We propose a new approach leveraging AI advances to drive experiments that can adjudicate between competing candidate algorithms.

Chronic alcohol drinking persistently suppresses thalamostriatal excitation of cholinergic neurons to impair cognitive flexibility

Exposure to addictive substances impairs flexible decision making. Cognitive flexibility is mediated by striatal cholinergic interneurons (CINs). However, how chronic alcohol drinking alters cognitive flexibility through CINs remains unclear. Here, we report that chronic alcohol consumption and withdrawal impaired reversal of instrumental learning. Chronic alcohol consumption and withdrawal also caused a long-lasting (21 days) reduction of excitatory thalamic inputs onto CINs and reduced pause responses of CINs in the dorsomedial striatum (DMS). CINs are known to inhibit glutamatergic transmission in dopamine D1 receptor–expressing medium spiny neurons (D1-MSNs) but facilitate this transmission in D2-MSNs, which may contribute to flexible behavior. We discovered that chronic alcohol drinking impaired CIN-mediated inhibition in D1-MSNs and facilitation in D2-MSNs. Importantly, in vivo optogenetic induction of long-term potentiation of thalamostriatal transmission in DMS CINs rescued alcohol-induced reversal learning deficits. These results demonstrate that chronic alcohol drinking reduces thalamic excitation of DMS CINs, compromising their regulation of glutamatergic transmission in MSNs, which may contribute to alcohol-induced impairment of cognitive flexibility. These findings provide a neural mechanism underlying inflexible drinking in alcohol use disorder.

Transmission of amyloid-beta and tau pathologies is associated with cognitive impairments in a primate

Amyloid-β (Aβ) pathology transmission has been described in patients following iatrogenic exposure to compounds contaminated with Aβ proteins. It can induce cerebral Aβ angiopathy resulting in brain hemorrhages and devastating clinical impacts. Iatrogenic transmission of tau pathology is also suspected but not experimentally proven. In both scenarios, lesions were detected several decades after the putatively triggering medico-surgical act. There is however little information regarding the cognitive repercussions in individuals who do not develop cerebral hemorrhages. In the current study, we inoculated the posterior cingulate cortex and underlying corpus callosum of young adult primates (Microcebus murinus) with either Alzheimer's disease or control brain extracts. This led to widespread Aβ and tau pathologies in all of the Alzheimer-inoculated animals following a 21-month-long incubation period (n = 12) whereas none of the control brain extract-inoculated animals developed such lesions (n = 6). Aβ deposition affected almost all cortical regions. Tau pathology was also detected in Aβ-deposit-free regions distant from the inoculation sites (e.g. in the entorhinal cortex), while some regions adjacent, but not connected, to the inoculation sites were spared (e.g. the occipital cortex). Alzheimer-inoculated animals developed cognitive deficits and cerebral atrophy compared to controls. These pathologies were induced using two different batches of Alzheimer brain extracts. This is the first experimental demonstration that tau can be transmitted by human brain extracts inoculations in a primate. We also showed for the first time that the transmission of widespread Aβ and tau pathologies can be associated with cognitive decline. Our results thus reinforce the need to organize a systematic monitoring of individuals who underwent procedures associated with a risk of Aβ and tau iatrogenic transmission. They also provide support for Alzheimer brain-inoculated primates as relevant models of Alzheimer pathology.

Parallel and hierarchical neural mechanisms for adaptive and predictive behavioral control

Our brain can be recognized as a network of largely hierarchically organized neural circuits that operate to control specific functions, but when acting in parallel, enable the performance of complex and simultaneous behaviors. Indeed, many of our daily actions require concurrent information processing in sensorimotor, associative, and limbic circuits that are dynamically and hierarchically modulated by sensory information and previous learning. This organization of information processing in biological organisms has served as a major inspiration for artificial intelligence and has helped to create in silico systems capable of matching or even outperforming humans in several specific tasks, including visual recognition and strategy-based games. However, the development of human-like robots that are able to move as quickly as humans and respond flexibly in various situations remains a major challenge and indicates an area where further use of parallel and hierarchical architectures may hold promise. In this article we review several important neural and behavioral mechanisms organizing hierarchical and predictive processing for the acquisition and realization of flexible behavioral control. Then, inspired by the organizational features of brain circuits, we introduce a multi-timescale parallel and hierarchical learning framework for the realization of versatile and agile movement in humanoid robots.

Dorsolateral Striatal Task-initiation Bursts Represent Past Experiences More than Future Action Plans

The dorsolateral striatum (DLS) is involved in learning and executing procedural actions. Cell ensembles in the DLS, but not the dorsomedial striatum (DMS), exhibit a burst of firing at the start of a well-learned action sequence ("task-bracketing"). However, it is currently unclear what information is contained in these bursts. Some theories suggest that these bursts should represent the procedural action sequence itself (that they should be about future action chains), whereas others suggest that they should contain representations of the current state of the world, taking into account primarily past information. In addition, the DLS local field potential shows transient bursts of power in the 50 Hz range (γ50) around the time a learned action sequence is initiated. However, it is currently unknown how bursts of activity in DLS cell ensembles and bursts of γ50 power in the DLS local field potential are related to each other. We found that DLS bursts at lap initiation in rats represented recently experienced reward locations more than future procedural actions, indicating that task-initiation DLS bursts contain primarily retrospective, rather than prospective, information to guide procedural actions. Furthermore, representations of past reward locations increased during periods of increased γ50 power in the DLS. There was no evidence of task-initiation bursts, increased γ50 power, or retrospective reward location information in the neighboring dorsomedial striatum. These data support a role for the DLS in model-free theories of procedural decision-making over planned action-chain theories, suggesting that procedural actions derive from representations of the current and recent past.SIGNIFICANCE STATEMENT While it is well-established that the dorsolateral striatum (DLS) plays a critical role in procedural decision-making, open questions remain about the kinds of representations contained in DLS ensemble activity that guide procedural actions. We found that DLS, but not DMS, cell ensembles contained nonlocal representations of past reward locations that appear moments before task-initiation DLS bursts. These retrospective representations were temporally linked to a rise in γ50 power that also preceded the characteristic DLS burst at task-initiation. These results support models of procedural decision-making based on associations between available actions and the current state of the world over models based on planning over action-chains.

Inactivation of posterior but not anterior dorsomedial caudate-putamen impedes learning with self-administered nicotine stimulus in male rats

The rodent caudate-putamen is a large heterogeneous neural structure with distinct anatomical connections that differ in their control of learning processes. Previous research suggests that the anterior and posterior dorsomedial caudate-putamen (a- and p-dmCPu) differentially regulate associative learning with a non-contingent nicotine stimulus. The current study used bilateral NMDA-induced excitotoxic lesions to the a-dmCPu and p-dmCPu to determine the functional involvement of a-dmCPu and p-dmCPu in appetitive learning with contingent nicotine stimulus. Rats with a-dmCPu, p-dmCPu, or sham lesions were trained to lever-press for intravenous nicotine (0.03 mg/kg/inf) followed by access to sucrose 30 s later. After 1, 3, 9, and 20 nicotine-sucrose training sessions, appetitive learning in the form of a goal-tracking response was assessed using a non-contingent nicotine-alone test. All rats acquired nicotine self-administration and learned to retrieve sucrose from a receptacle at equal rates. However, rats with lesions to p-dmCPu demonstrated blunted learning of the nicotine-sucrose association. Our primary findings show that rats with lesions to p-dmCPu had a blunted goal-tracking response to a non-contingent nicotine administration after 20 consecutive days of nicotine-sucrose pairing. Our findings extend previous reports to a contingent model of nicotine self-administration and show that p-dmCPu is involved in associative learning with nicotine stimulus using a paradigm where rats voluntarily self-administer nicotine infusions that are paired with access to sucrose-a paradigm that closely resembles learning processes observed in humans.

Differential effects of d- and l-enantiomers of govadine on distinct forms of cognitive flexibility and a comparison with dopaminergic drugs

RATIONALE

There is an urgent need for novel drugs for treating cognitive deficits that are defining features of schizophrenia. The individual d- and l-enantiomers of the tetrahydroprotoberberine (THPB) d,l-govadine have been proposed for the treatment of cognitive deficiencies and positive symptoms of schizophrenia, respectively.

OBJECTIVES

We examined the effects of d-, l-, or d,l-govadine on two distinct forms of cognitive flexibility perturbed in schizophrenia and compared them to those induced by a selective D1 receptor agonist and D2 receptor antagonist.

METHODS

Male rats received d-, l-, or d,l-govadine (0.3, 0.5, and 1.0 mg/kg), D1 agonist SKF81297(0.1, 0.3, and 1.0 mg/kg), or D2 antagonist haloperidol (0.1-0.2 mg/kg). Experiment 1 used a strategy set-shifting task (between-subjects). In experiment 2, well-trained rats were tested on a probabilistic reversal task (within-subjects).

RESULTS

d-Govadine improved set-shifting across all doses, whereas higher doses of l-govadine impaired set-shifting. SKF81297 reduced perseverative errors at the lowest dose. Low/high doses of haloperidol increased/decreased set-shifting errors, the latter "improvement" attributable to impaired retrieval of a previous acquired rule. Probabilistic reversal performance was less affected by these drugs, but d-govadine reduced errors during the first reversal, whereas l-govadine impaired initial discrimination learning. d,l-Govadine had no reliable cognitive effects but caused psychomotor slowing like l-govadine and haloperidol.

CONCLUSIONS

These findings further highlight differences between two enantiomers of d,l-govadine that may reflect differential modulation of D1 and D2 receptors. These preclinical findings give further impetus to formal clinical evaluation of d-govadine as a treatment for cognitive deficiencies related to schizophrenia.

Place vs. Response Learning: History, Controversy, and Neurobiology

The present article provides a historical review of the place and response learning plus-maze tasks with a focus on the behavioral and neurobiological findings. The article begins by reviewing the conflict between Edward C. Tolman's cognitive view and Clark L. Hull's stimulus-response (S-R) view of learning and how the place and response learning plus-maze tasks were designed to resolve this debate. Cognitive learning theorists predicted that place learning would be acquired faster than response learning, indicating the dominance of cognitive learning, whereas S-R learning theorists predicted that response learning would be acquired faster, indicating the dominance of S-R learning. Here, the evidence is reviewed demonstrating that either place or response learning may be dominant in a given learning situation and that the relative dominance of place and response learning depends on various parametric factors (i.e., amount of training, visual aspects of the learning environment, emotional arousal, et cetera). Next, the neurobiology underlying place and response learning is reviewed, providing strong evidence for the existence of multiple memory systems in the mammalian brain. Research has indicated that place learning is principally mediated by the hippocampus, whereas response learning is mediated by the dorsolateral striatum. Other brain regions implicated in place and response learning are also discussed in this section, including the dorsomedial striatum, amygdala, and medial prefrontal cortex. An exhaustive review of the neurotransmitter systems underlying place and response learning is subsequently provided, indicating important roles for glutamate, dopamine, acetylcholine, cannabinoids, and estrogen. Closing remarks are made emphasizing the historical importance of the place and response learning tasks in resolving problems in learning theory, as well as for examining the behavioral and neurobiological mechanisms of multiple memory systems. How the place and response learning tasks may be employed in the future for examining extinction, neural circuits of memory, and human psychopathology is also briefly considered.

Whole-Brain Mapping of Direct Inputs to Dopamine D1 and D2 Receptor-Expressing Medium Spiny Neurons in the Posterior Dorsomedial Striatum

The posterior dorsomedial striatum (pDMS) is mainly composed of medium spiny neurons (MSNs) expressing either dopamine D1 receptors (D1Rs) or D2Rs. Activation of these two MSN types produces opposing effects on addictive behaviors. However, it remains unclear whether pDMS D1-MSNs or D2-MSNs receive afferent inputs from different brain regions or whether the extrastriatal afferents express distinct dopamine receptors. To assess whether these afferents also contained D1Rs or D2Rs, we generated double transgenic mice, in which D1R-expressing and D2R-expressing neurons were fluorescently labeled. We used rabies virus-mediated retrograde tracing in these mice to perform whole-brain mapping of direct inputs to D1-MSNs or D2-MSNs in the pDMS. We found that D1-MSNs preferentially received inputs from the secondary motor, secondary visual, and cingulate cortices, whereas D2-MSNs received inputs from the primary motor and primary sensory cortices, and the thalamus. We also discovered that the bed nucleus of the stria terminalis (BNST) and the central nucleus of the amygdala (CeA) contained abundant D2R-expressing, but few D1R-expressing, neurons in a triple transgenic mouse model. Remarkably, although limited D1R or D2R expression was observed in extrastriatal neurons that projected to D1-MSNs or D2-MSNs, we found that cortical structures preferentially contained D1R-expressing neurons that projected to D1-MSNs or D2-MSNs, while the thalamus, substantia nigra pars compacta (SNc), and BNST had more D2R-expressing cells that projected to D2-MSNs. Taken together, these findings provide a foundation for future understanding of the pDMS circuit and its role in action selection and reward-based behaviors.

Dorsomedial striatal contributions to different forms of risk/reward decision making

Optimal decision making involving reward uncertainty is integral to adaptive goal-directed behavior. In some instances, these decisions are guided by internal representations of reward history, whereas in other situations, external cues inform a decision maker about how likely certain actions are to yield reward. Different regions of the frontal lobe form distributed networks with striatal and amygdalar regions that facilitate different types of risk/reward decision making. The dorsal medial striatum (DMS) is one key output region of the prefrontal cortex, yet there have been few preclinical studies investigating the involvement of the DMS in different forms of risk/reward decision making. The present study addressed this issue, wherein separate groups of male rats were trained on one of two tasks where they chose between a small/certain or a large/risky reward. In a probabilistic discounting task, reward probabilities changed systematically over blocks of trials (100-6.25% or 6.25-100%), requiring rats to use internal representations of reward history to guide choice. Cue-guided decision-making was assessed with a "Blackjack" task, where different auditory cues indicated the odds associated with the large/risky option (50 or 12.5%). Inactivation of the DMS with GABA agonists impaired adjustments in choice biases during probabilistic discounting, resulting in either increases or decreases in risky choice as the probabilities associated with the large/risky reward decreased or increased over a session. In comparison, DMS inactivation increased risky choices on poor-odds trials on the Blackjack task, which was associated with a reduced impact that non-rewarded choices had on subsequent choices. DMS inactivation also impaired performance of an auditory conditional discrimination. These findings highlight a previously uncharacterized role for the DMS in facilitating flexible action selection during multiple forms of risk/reward decision making.

The Hippocampus and Dorsolateral Striatum Integrate Distinct Types of Memories through Time and Space, Respectively

Several decades of research have established that different kinds of memories result from the activity of discrete neural networks. Studying how these networks process information in experiments that target specific types of mnemonic representations has provided deep insights into memory architecture and its neural underpinnings. However, in natural settings reality confronts organisms with problems that are not neatly compartmentalized. Thus, a critical problem in memory research that still needs to be addressed is how distinct types of memories are ultimately integrated. Here we demonstrate how two memory networks, the hippocampus and dorsolateral striatum, may accomplish such a goal. The hippocampus supports memory for facts and events, collectively known as declarative memory and often studied as spatial memory in rodents. The dorsolateral striatum provides the basis for habits that are assessed in stimulus-response types of tasks. Expanding previous findings, the current work revealed that in male Long-Evans rats, the hippocampus and dorsolateral striatum use time and space in distinct and largely complementary ways to integrate spatial and habitual representations. Specifically, the hippocampus supported both types of memories when they were formed in temporal juxtaposition, even if the learning took place in different environments. In contrast, the lateral striatum supported both types of memories if they were formed in the same environment, even at temporally distinct points. These results reveal for the first time that by using fundamental aspects of experience in specific ways, the hippocampus and dorsolateral striatum can transcend their attributed roles in information storage.SIGNIFICANCE STATEMENT The current paradigm in memory research postulates that different types of memories reflected in separate types of behavioral strategies result from activity in distinct neural circuits. However, recent data have shown that when rats concurrently acquired in the same environment of hippocampal-dependent spatial navigation and striatal-dependent approach of a visual cue, each of the two types of memories became dependent on both the hippocampus and dorsolateral striatum. The current work reveals that the hippocampus and dorsolateral striatum use distinct and complementary principles to integrate different types of memories in time and space: the hippocampus integrates memories formed in temporal proximity, while the lateral striatum integrates memories formed in the same space.

Catechol-O-methyltransferase genotype differentially contributes to the flexibility and stability of cognitive sets in patients with psychotic disorders and their first-degree relatives

Dopaminergic activity in prefrontal cortex is modulated by the low (Met) and high (Val) activity of the rs4680 Val158Met single nucleotide polymorphism (SNP) in the Catechol-O-Methyltransferase (COMT) gene. While this has been related to working memory maintenance in patients with schizophrenia, the familial pattern, impact across the psychosis spectrum, and the role of this genotype on other aspects of behavior, such as cognitive flexibility, remains unclear. The relationship between COMT Val158Met genotype and both cognitive stability and flexibility were assessed using the Penn Conditional Exclusion Test (PCET) in healthy controls (n = 241), patients with psychotic disorders (n = 542), and their first-degree relatives (n = 613) from the Bipolar-Schizophrenia Network on Intermediate Phenotypes (B-SNIP) consortium. Higher rates of perseverative errors (poor flexibility) were associated with the low-activity COMT genotype (Met allele carriers) in probands compared to their first-degree relatives with the same genotype. Probands and first-degree relatives homozygous for the high-activity COMT enzyme (Val/Val) showed elevated rates of regressive errors (poor stability) compared to controls. Conversely, heterozygous relatives had comparable regressive error rates to controls, with probands showing elevated errors in comparison. These findings suggest that impaired suppression of learned response patterns and reduced stability of mental sets may be a familial intermediate cognitive phenotype related to Val COMT allele genotype.

Attentional set shifting in HAP3, LAP3, and cHAP mice is unaffected by either genetic differences in alcohol preference or an alcohol drinking history

Alcohol consumption may precede, or result from, behavioral inflexibility and contribute to individuals' difficulties ceasing drinking. Attentional set shifting tasks are an animal analog to a human behavioral flexibility task requiring recognition of a previous strategy as inappropriate, and the formation and maintenance of a novel strategy (Floresco, Block, & Tse, 2008). Abstinent individuals with alcohol use disorder, nonalcoholic individuals with a family history of alcoholism, and mice exposed to chronic-intermittent alcohol vapor show impaired behavioral flexibility (Gierski et al., 2013; Hu, Morris, Carrasco, & Kroener, 2015; Oscar-Berman et al., 2009). Behavioral flexibility deficits can be linked to frontal cortical regions connected to the striatum (Ragozzino, 2007), and alterations to the endocannabinoid system, implicated in drug seeking and consumption (Economidou et al., 2006; Serrano & Parsons, 2011), may affect these behaviors. Alcohol-preferring and nonpreferring rodents exhibit differences in CB1 receptor expression (CB1R; Hansson et al., 2007; Hungund & Basavarajappa, 2000), but whether dorsal striatal CB1Rs are important for other alcohol-related behaviors such as attentional set shifting tasks remains unclear. This study assesses whether selectively bred high (HAP) versus low alcohol-preferring mice differ in an operant attentional set shifting task or CB1R levels in the dorsal striatum and whether a history of voluntary alcohol consumption in crossed HAP mice exacerbates inflexibility. Contrary to our hypothesis, neither genetic differences in alcohol preference nor drinking affected set shifting. However, high alcohol-preferring mice-3 mice showed reduced levels of dorsal striatal CB1R compared with low alcohol-preferring-3 mice, suggesting that genetic differences in alcohol consumption may be mediated in part by striatal CB1R. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Aging is not equal across memory systems

The present experiments compared the effects of aging on learning several hippocampus- and striatum-sensitive tasks in young (3-4 month) and old (24-28 month) male Fischer-344 rats. Across three sets of tasks, aging was accompanied not only by deficits on hippocampal tasks but also by maintained or even enhanced abilities on striatal tasks. On two novel object recognition tasks, rats showed impaired performance on a hippocampal object location task but enhanced performance on a striatal object replacement task. On a dual solution task, young rats predominately used hippocampal solutions and old rats used striatal solutions. In addition, on two maze tasks optimally solved using either hippocampus-sensitive place or striatum-sensitive response strategies, relative to young rats, old rats had impaired learning on the place version but equivalent learning on the response version. Because glucose treatments can reverse deficits in learning and memory across many tasks and contexts, levels of available glucose in the brain may have particular importance in cognitive aging observed across tasks and memory systems. During place learning, training-related rises in extracellular glucose levels were attenuated in the hippocampus of old rats compared to young rats. In contrast, glucose levels in the striatum increased comparably in young and old rats trained on either the place or response task. These extracellular brain glucose responses to training paralleled the impairment in hippocampus-sensitive learning and the sparing of striatum-sensitive learning seen as rats age, suggesting a link between age-related changes in learning and metabolic substrate availability in these brain regions.

Cognitive rigidity and BDNF-mediated frontostriatal glutamate neuroadaptations during spontaneous nicotine withdrawal

Cognitive flexibility is the ability to switch strategic responses adaptively in changing environments. Cognitive rigidity imposed by neural circuit adaptations during nicotine abstinence may foster maladaptive nicotine taking in addicts. We systematically examined the effects of spontaneous withdrawal in mice exposed to either nicotine (6.3 or 18 mg/kg/day) or saline for 14 days on cognitive flexibility using an operant strategy set-shifting task. Because frontostriatal circuits are critical for cognitive flexibility and brain-derived neurotrophic factor (BDNF) modulates glutamate plasticity in these circuits, we also explored the effects of nicotine withdrawal on these neurochemical substrates. Mice undergoing nicotine withdrawal required more trials to attain strategy-switching criterion. Error analysis show that animals withdrawn from both nicotine doses committed higher perseverative errors, which correlated with measures of anxiety. However, animals treated with the higher nicotine dose also displayed more strategy maintenance errors that remained independent of negative affect. BDNF mRNA expression increased in the medial prefrontal cortex (mPFC) following nicotine withdrawal. Surprisingly, BDNF protein declined in mPFC but was elevated in dorsal striatum (DS). DS BDNF protein positively correlated with perseverative and maintenance errors, suggesting mPFC-DS overflow of BDNF during withdrawal. BDNF-evoked glutamate release and synapsin phosphorylation was attenuated within DS synapses, but enhanced in the nucleus accumbens, suggesting a dichotomous role of BDNF signaling in striatal regions. Taken together, these data suggest that spontaneous nicotine withdrawal impairs distinct components of cognitive set-shifting and these deficits may be linked to BDNF-mediated alterations in glutamate signaling dynamics in discrete frontostriatal circuits.

Targeting the cholinergic system in Parkinson's disease

Motor control in the striatum is an orchestra played by various neuronal populations. Loss of harmony due to dopamine deficiency is considered the primary pathological cause of the symptoms of Parkinson’s disease (PD). Recent progress in experimental approaches has enabled us to examine the striatal circuitry in a much more comprehensive manner, not only reshaping our understanding of striatal functions in movement regulation but also leading to new opportunities for the development of therapeutic strategies for treating PD. In addition to dopaminergic innervation, giant aspiny cholinergic interneurons (ChIs) within the striatum have long been recognized as a critical node for balancing dopamine signaling and regulating movement. With the roles of ChIs in motor control further uncovered and more specific manipulations available, striatal ChIs and their corresponding receptors are emerging as new promising therapeutic targets for PD. This review summarizes recent progress in functional studies of striatal circuitry and discusses the translational implications of these new findings for the treatment of PD.

Striatal and hippocampal contributions to flexible navigation in rats and humans

The hippocampus has been firmly established as playing a crucial role in flexible navigation. Recent evidence suggests that dorsal striatum may also play an important role in such goal-directed behaviour in both rodents and humans. Across recent studies, activity in the caudate nucleus has been linked to forward planning and adaptation to changes in the environment. In particular, several human neuroimaging studies have found the caudate nucleus tracks information traditionally associated with that by the hippocampus. In this brief review, we examine this evidence and argue the dorsal striatum encodes the transition structure of the environment during flexible, goal-directed behaviour. We highlight that future research should explore the following: (1) Investigate neural responses during spatial navigation via a biophysically plausible framework explained by reinforcement learning models and (2) Observe the interaction between cortical areas and both the dorsal striatum and hippocampus during flexible navigation.

Anabolic-androgenic steroid abuse and cognitive impairment: Testosterone IMPAIRS biconditional task performance in male rats

Our goal is to understand the consequences of anabolic-androgenic steroid (AAS) abuse on cognitive function, using rats as a model. There is relatively little research on how AAS abuse impacts cognition. In the present study, rats were tested for their ability to use contextual information to guide decision-making in biconditional discrimination. The Stroop task is a classic human test for contextual decision-making. In rodents, biconditional discrimination challenges subjects to use contextual cues in the operant chamber to resolve the correct lever response when auditory and visual cues are incongruent. The hypothesis is that chronic high-dose testosterone impairs biconditional discrimination. Rats were trained in 24 trials/day over 14 days, in alternating sessions with each environment. On a flat floor with houselight illuminated, auditory cues (clicker vs tone) signified the active lever. On a barred floor with no light, visual cues from 2 stimulus lights (constant vs blinking) identified the active lever. Rats treated chronically with testosterone (7.5 mg/kg) were unimpaired in task acquisition, and all rats learned to select the correct lever in response to auditory or visual cues. During extinction, controls made significantly more correct than incorrect responses in congruent trials (p < 0.05 by paired t-test), but testosterone-treated rats failed to show a similar preference. This was reflected by significant interactions of drug x cue agreement (F_1,18 = 5.21, p < 0.05) and drug x cue agreement x response accuracy (F_1,18 = 8.95, p < 0.05). These results suggest that testosterone impairs cognitive flexibility, and demonstrates potential for AAS abuse to impair cognitive function in humans.

Superior Place Learning of C57BL/6 vs. DBA/2 Mice Following Prior Cued Learning in the Water Maze Depends on Prefrontal Cortical Subregions

The participation of the prefrontal cortex (PFC), hippocampus, and dorsal striatum in switching the learning task from cued to place learning were examined in C57BL/6 and DBA/2 mice, by assessing changed levels of phosphorylated CREB (pCREB). Mice of both strains first received cued training in a water maze for 4 days (4 trials per day), and were then assigned to one of four groups, one with no place training, and three with different durations of place training (2, 4, or 8 days). Both strains showed equal performance in cued training. After the switch to place training, C57BL/6 mice with 2 or 4 days of training performed significantly better than DBA/2 mice, but their superiority disappeared during the second half of an 8 days-place training period. The pCREB levels of these mice were measured 30 min after place training and compared with those of mice that received only cued training. Changes in pCREB levels of C57BL/6 mice were greater in the hippocampal CA3, hippocampal dentate gyrus, orbitofrontal and medial PFC than those of DBA/2 mice, when mice of both received the switched place training for 2 days. We further investigated the roles of orbitofrontal and medial PFC among these brain regions showing strain differences, by destroying each region using selective neurotoxins. C57BL/6 mice with orbitofrontal lesions were slower to acquire the place learning and continued to use the cued search acquired during the cued training phase. These findings indicate that mouse orbitofrontal cortex (OFC) pCREB is associated with behavioral flexibility such as the ability to switch a learning task.

An Integrated Model of Action Selection: Distinct Modes of Cortical Control of Striatal Decision Making

Making decisions in environments with few choice options is easy. We select the action that results in the most valued outcome. Making decisions in more complex environments, where the same action can produce different outcomes in different conditions, is much harder. In such circumstances, we propose that accurate action selection relies on top-down control from the prelimbic and orbitofrontal cortices over striatal activity through distinct thalamostriatal circuits. We suggest that the prelimbic cortex exerts direct influence over medium spiny neurons in the dorsomedial striatum to represent the state space relevant to the current environment. Conversely, the orbitofrontal cortex is argued to track a subject's position within that state space, likely through modulation of cholinergic interneurons.

Beneficial and adverse effects of antipsychotic medication on cognitive flexibility are related to COMT genotype in first episode psychosis

This study evaluated the ability to flexibly shift cognitive set and to consistently maintain a new response preference using the Penn Conditional Exclusion Test (PCET). The relationship of performance errors with catechol-O-methyltransferase (COMT) rs4680 (Val158Met) genotype (Met carriers vs. Val homozygotes) on test performance before and after antipsychotic treatment in 32 first episode psychosis (FEP) patients was examined. After treatment, patients demonstrated a mixture of beneficial and adverse cognitive outcomes that varied in relation to COMT genotype. Met carriers showed decreased perseverative and regressive errors, reflecting improved cognitive flexibility and enhanced stability of behavioral preferences, respectively. In contrast, Val homozygotes exhibited an increase in regressive errors after treatment. These findings suggest that Val homozygotes may be vulnerable to adverse effects of antipsychotic medication on cognitive processes that maintain consistent adaptive response preferences, an ability linked to the striatum in rodent models.

From learning to action: the integration of dorsal striatal input and output pathways in instrumental conditioning

Considerable evidence suggests that the learning and performance of instrumental actions depend on activity in basal ganglia circuitry; however, these two functions have generally been considered independently. Whereas research investigating the associative mechanisms underlying instrumental conditioning has identified critical cortical and limbic input pathways to the dorsal striatum, the performance of instrumental actions has largely been attributed to activity in the dorsal striatal output pathways, with direct and indirect pathway projection neurons mediating action initiation, perseveration and cessation. Here, we discuss evidence that the dorsal striatal input and basal ganglia output pathways mediate the learning and performance of instrumental actions, respectively, with the dorsal striatum functioning as a transition point. From this perspective, the issue of how multiple striatal inputs are integrated at the level of the dorsal striatum and converted into relatively restricted outputs becomes one of critical significance for understanding how learning is translated into action. So too does the question of how learning signals are modulated by recent experience. We propose that this occurs through recurrent corticostriatothalamic feedback circuits that serve to integrate performance signals by updating ongoing action-related learning.

Questioning Seasonality of Neuronal Plasticity in the Adult Avian Brain

To date, studies that reported seasonal patterns of adult neurogenesis and neuronal recruitment have correlated them to seasonal behaviors as the cause or as a consequence of neuronal changes. The aim of our study was to test this correlation, and to investigate whether there is a seasonal pattern of new neuronal recruitment that is not correlated to behavior. To do this, we used adult female zebra finches (songbirds that are not seasonal breeders), kept them under constant social, behavioral, and spatial environments, and compared neuronal recruitment in their brains during two seasons, under natural and laboratory conditions. Under natural conditions, no significant differences were found in the pattern of new neuronal recruitment across seasons. However, under artificial indoor conditions that imitated the natural conditions, higher neuronal recruitment occurred in late summer (August) compared to early spring (February). Moreover, our data indicate that "mixing" temperature and day length significantly reduces new neuronal recruitment, demonstrating the importance of the natural combination of temperature and day length. Taken together, our findings show, for the first time, that neuroplasticity changes under natural vs. artificial conditions, and demonstrate the importance of both laboratory and field experiments when looking at complex biological systems.

The dorsomedial striatum mediates Pavlovian appetitive conditioning and food consumption

The dorsomedial striatum (DMS) is an important sensorimotor region mediating the acquisition of goal-directed instrumental reward learning and behavioral flexibility. However, whether the DMS also regulates Pavlovian cue-food learning is less clear. The current study used excitotoxic lesions to determine whether the DMS is critical in Pavlovian appetitive learning and behavior, using discriminative conditioning and reversal paradigms. The results showed that DMS lesions transiently retarded cue-food learning and subsequent reversal of this learning. Rats with DMS lesions selectively attenuated responding to a food cue but not a control cue, early in training, suggesting the DMS is involved when initial associations are formed. Similarly, initial reversal learning was attenuated in rats with DMS lesions, which suggests impaired flexibility to adjust behavior when the cue meaning is reversed. We also examined the effect of DMS lesions on food intake during tests with access to a highly palatable food along with standard chow diet. Rats with DMS lesions showed an altered pattern of intake, with an initial reduction in high-fat diet followed by an increase in chow consumption. These results demonstrate that the DMS has a role in mediating cue-food learning and its subsequent reversal, as well as changes in food intake when a choice is provided. Together, these results demonstrate the DMS is involved in reward associative learning and reward consumption, when behavioral flexibility is needed to adjust responding or consumption to match the current value. (PsycINFO Database Record

Dopamine receptors mediate strategy abandoning via modulation of a specific prelimbic cortex-nucleus accumbens pathway in mice

The ability to abandon old strategies and adopt new ones is essential for survival in a constantly changing environment. While previous studies suggest the importance of the prefrontal cortex and some subcortical areas in the generation of strategy-switching flexibility, the fine neural circuitry and receptor mechanisms involved are not fully understood. In this study, we showed that optogenetic excitation and inhibition of the prelimbic cortex-nucleus accumbens (NAc) pathway in the mouse respectively enhances and suppresses strategy-switching ability in a cross-modal spatial-egocentric task. This ability is dependent on an intact dopaminergic tone in the NAc, as local dopamine denervation impaired the performance of the animal in the switching of tasks. In addition, based on a brain-slice preparation obtained from Drd2-EGFP BAC transgenic mice, we demonstrated direct innervation of D2 receptor-expressing medium spiny neurons (D2-MSNs) in the NAc by prelimbic cortical neurons, which is under the regulation by presynaptic dopamine receptors. While presynaptic D1-type receptor activation enhances the glutamatergic transmission from the prelimbic cortex to D2-MSNs, D2-type receptor activation suppresses this synaptic connection. Furthermore, manipulation of this pathway by optogenetic activation or administration of a D1-type agonist or a D2-type antagonist could restore impaired task-switching flexibility in mice with local NAc dopamine depletion; this restoration is consistent with the effects of knocking down the expression of specific dopamine receptors in the pathway. Our results point to a critical role of a specific prelimbic cortex-NAc subpathway in mediating strategy abandoning, allowing the switching from one strategy to another in problem solving.

The adenosine A2A receptor agonist, CGS 21680, attenuates a probabilistic reversal learning deficit and elevated grooming behavior in BTBR mice

Restricted interests and repetitive behaviors (RRBs) are a defining feature of autism spectrum disorder (ASD). To date there are limited options for treating this core symptomology. Treatments that stimulate adenosine A_2A receptors may represent a promising approach for reducing RRBs in ASD. This is because A_2A receptors are expressed on striatal neurons of the basal ganglia indirect pathway. Under activation of this pathway has been associated with RRBs while activation of A_2A receptors leads to increased activity of the indirect basal ganglia pathway. The present studies investigated whether acute, systemic treatment with CGS21680, an A_2A receptor agonist attenuates elevated self-grooming and a probabilistic reversal learning deficit in the BTBR T+ Itpr3^tf /J (BTBR) mouse model of idiopathic autism. The effects of this treatment were also investigated in C57BL/6J (B6) mice as a comparison strain. Using a spatial reversal learning test with 80/20 probabilistic feedback, comparable to one in which ASD individuals exhibit deficits, CGS 21680 (0.005 and 0.01mg/kg) attenuated a reversal learning deficit in BTBR mice. Enhancement in probabilistic reversal learning performance resulted from CGS 21680 improving the consistent maintenance of new adaptive behavioral choice patterns after reversal. CGS 21680 at 0.01 mg, but not 0.005 mg, also reduced self-grooming behavior in BTBR mice. CGS 21680 did not affect self-grooming or reversal learning in B6 mice. These findings demonstrate that A_2A receptor agonists may be a promising receptor target in the treatment of RRBs in ASD. Autism Res 2018, 11: 223-233. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

The present experiments determined whether the drug, CGS 21680, that facilitates activation of adenosine A_2A receptors in the brain, would reduce repetitive and inflexible behaviors in the BTBR mouse model of idiopathic autism. CGS 21680 treatment in BTBR mice reduced repetitive and inflexible behaviors. In the control C57BL/6J (B6) mouse strain, CGS 21680 did not affect performance. These findings suggest that stimulation of brain adenosine A_2A receptors may be a promising therapeutic strategy in ASD.

Alterations in brain activation in response to prolonged morphine withdrawal-induced behavioral inflexibility in rats

RATIONALE

The inability to stop a repetitive maladaptive behavior is a main problem in addictive disorders. Neuroadaptations that are associated with behavioral inflexibility may be involved in compulsive drug use.

OBJECTIVES

The aim of the present study was to investigate the pattern of behavioral inflexibility during morphine withdrawal and map brain activation that is linked to alterations in flexibility.

METHODS

We first analyzed the effects of chronic morphine exposure on reversal learning after 2-week (short-term) and 6-week (prolonged) morphine withdrawal. We then compared the level of neuronal activation using cFos immunohistochemistry in 15 brain areas between rats that underwent morphine withdrawal and saline-control rats after a test of reversal learning.

RESULTS

Only prolonged morphine withdrawal impaired reversal learning. Rats that exhibited impairments in reversal learning presented a significant decrease in cFos expression in the orbitofrontal cortex (OFC), including the medial, lateral, and ventral OFC. cFos expression significantly increased in the dorsomedial striatum and major subregions of the medial prefrontal cortex (mPFC) in the morphine group. Rats that underwent prolonged morphine withdrawal exhibited no significant changes in cFos expression in the dorsolateral striatum, nucleus accumbens, amygdala, paraventricular thalamic nucleus, or motor cortex. The rats that underwent short-term withdrawal did not present any changes in cFos expression in any of these brain regions.

CONCLUSION

Altogether, these data suggest that alterations in the function of the frontal cortex and its striatal connections during the late morphine withdrawal phase may underlie the disruption of inhibitory control in opioid dependence.