Tonically active neurons in the primate caudate nucleus and putamen differentially encode instructed motivational outcomes of action

Deficits in proactive avoidance and neural responses to drinking motives in problem drinkers

Physical pain and negative emotions represent two distinct drinking motives that contribute to harmful alcohol use. Proactive avoidance which can reduce problem drinking in response to these motives appears to be impaired in problem drinkers. However, proactive avoidance and its underlying neural deficits have not been assessed experimentally. How these deficits inter-relate with drinking motives to influence alcohol use also remains unclear. The current study leveraged neuroimaging data collected in forty-one problem and forty-one social drinkers who performed a probabilistic learning go/nogo task that involved proactive avoidance of painful outcomes. We characterized the regional brain responses to proactive avoidance and identified the neural correlates of drinking to avoid physical pain and negative emotions. Behavioral results confirmed problem drinkers' proactive avoidance deficits in learning rate and performance accuracy, both which were associated with greater alcohol use. Imaging findings in problem drinkers showed that negative emotions as a drinking motive predicted attenuated right insula activation during proactive avoidance. In contrast, physical pain motive predicted reduced right putamen response. These regions' activations as well as functional connectivity with the somatomotor cortex also demonstrated a negative relationship with drinking severity and positive relationship with proactive avoidance performance. Path modeling further delineated the pathways through which physical pain and negative emotions, along with alcohol use severity, influenced the neural and behavioral measures of proactive avoidance. Taken together, the current findings provide experimental evidence for proactive avoidance deficits in problem drinkers and establish the link between their neural underpinnings and alcohol misuse.

Synchronous Measurements of Extracellular Action Potentials and Neurochemical Activity with Carbon Fiber Electrodes in Nonhuman Primates

Measuring the dynamic relationship between neuromodulators, such as dopamine, and neuronal action potentials is imperative to understand how these fundamental modes of neural signaling interact to mediate behavior. Here, we developed methods to measure concurrently dopamine and extracellular action potentials (i.e., spikes) and applied these in a monkey performing a behavioral task. Standard fast-scan cyclic voltammetric (FSCV) electrochemical (EChem) and electrophysiological (EPhys) recording systems are combined and used to collect spike and dopamine signals, respectively, from an array of carbon fiber (CF) sensors implanted in the monkey striatum. FSCV requires the application of small voltages at the implanted sensors to measure redox currents generated from target molecules, such as dopamine. These applied voltages create artifacts at neighboring EPhys-measurement sensors, producing signals that may falsely be classified as physiological spikes. Therefore, simple automated temporal interpolation algorithms were designed to remove these artifacts and enable accurate spike extraction. We validated these methods using simulated artifacts and demonstrated an average spike recovery rate of 84.5%. This spike extraction was performed on data collected from concurrent EChem and EPhys recordings made in a task-performing monkey to discriminate cell-type specific striatal units. These identified units were shown to correlate to specific behavioral task parameters related to reward size and eye-movement direction. Synchronous measures of spike and dopamine signals displayed contrasting relations to the behavioral task parameters, as taken from our small set of representative data, suggesting a complex relationship between these two modes of neural signaling. Future application of our methods will help advance our understanding of the interactions between neuromodulator signaling and neuronal activity, to elucidate more detailed mechanisms of neural circuitry and plasticity mediating behaviors in health and in disease.

Reward expectation enhances action-related activity of nigral dopaminergic and two striatal output pathways

Neurons comprising nigrostriatal system play important roles in action selection. However, it remains unclear how this system integrates recent outcome information with current action (movement) and outcome (reward or no reward) information to achieve appropriate subsequent action. We examined how neuronal activity of substantia nigra pars compacta (SNc) and dorsal striatum reflects the level of reward expectation from recent outcomes in rats performing a reward-based choice task. Movement-related activity of direct and indirect pathway striatal projection neurons (dSPNs and iSPNs, respectively) were enhanced by reward expectation, similarly to the SNc dopaminergic neurons, in both medial and lateral nigrostriatal projections. Given the classical basal ganglia model wherein dopamine stimulates dSPNs and suppresses iSPNs through distinct dopamine receptors, dopamine might not be the primary driver of iSPN activity increasing following higher reward expectation. In contrast, outcome-related activity was affected by reward expectation in line with the classical model and reinforcement learning theory, suggesting purposive effects of reward expectation.

Topology of pain networks in patients with temporomandibular disorder and pain-free controls with and without concurrent experimental pain: A pilot study

Temporomandibular disorders (TMD) involve chronic pain in the masticatory muscles and jaw joints, but the mechanisms underlying the pain are heterogenous and vary across individuals. In some cases, structural, functional, and metabolic changes in the brain may underlie the condition. In the present study, we evaluated the functional connectivity between 86 regions of interest (ROIs), which were chosen based on previously reported neuroimaging studies of pain and differences in brain morphology identified in an initial surface-based morphometry analysis. Our main objectives were to investigate the topology of the network formed by these ROIs and how it differs between individuals with TMD and chronic pain (n = 16) and pain-free control participants (n = 12). In addition to a true resting state functional connectivity scan, we also measured functional connectivity during a 6-min application of a noxious cuff stimulus applied to the left leg. Our principal finding is individuals with TMD exhibit more suprathreshold correlations (higher nodal degree) among all ROIs but fewer "hub" nodes (i.e., decreased betweenness centrality) across conditions and across all pain pathways. These results suggest is this pain-related network of nodes may be "over-wired" in individuals with TMD and chronic pain compared to controls, both at rest and during experimental pain.

A neuronal prospect theory model in the brain reward circuitry

Prospect theory, arguably the most prominent theory of choice, is an obvious candidate for neural valuation models. How the activity of individual neurons, a possible computational unit, obeys prospect theory remains unknown. Here, we show, with theoretical accuracy equivalent to that of human neuroimaging studies, that single-neuron activity in four core reward-related cortical and subcortical regions represents the subjective valuation of risky gambles in monkeys. The activity of individual neurons in monkeys passively viewing a lottery reflects the desirability of probabilistic rewards parameterized as a multiplicative combination of utility and probability weighting functions, as in the prospect theory framework. The diverse patterns of valuation signals were not localized but distributed throughout most parts of the reward circuitry. A network model aggregating these signals reconstructed the risk preferences and subjective probability weighting revealed by the animals’ choices. Thus, distributed neural coding explains the computation of subjective valuations under risk.

It is unclear how the activity of individual neurons conform to prospect theory. Here, the authors demonstrate that the activity of single neurons in various reward-related regions in the monkey brain can be described as encoding a multiplicative combination of utility and probability weighting, and that this subjective valuation process is achieved via a distributed coding scheme.

An fMRI meta-analysis of the role of the striatum in everyday-life vs laboratory-developed habits

The dorsolateral striatum plays a critical role in the acquisition and expression of stimulus-response habits that are learned in experimental laboratories. Here, we use meta-analytic procedures to contrast the neural circuits activated by laboratory-acquired habits with those activated by stimulus-response behaviours acquired in everyday-life. We confirmed that newly learned habits rely more on the anterior putamen with activation extending into caudate and nucleus accumbens. Motor and associative components of everyday-life habits were identified. We found that motor-dominant stimulus-response associations developed outside the laboratory primarily engaged posterior dorsal putamen, supplementary motor area (SMA) and cerebellum. Importantly, associative components were also represented in the posterior putamen. Thus, common neural representations for both naturalistic and laboratory-based habits were found in the left posterior and right anterior putamen. These findings suggest a partial common striatal substrate for habitual actions that are performed predominantly by stimulus-response associations represented in the posterior striatum. The overlapping neural substrates for laboratory and everyday-life habits supports the use of both methods for the analysis of habitual behaviour.

Subcortical Brain Morphometry Differences between Adults with Autism Spectrum Disorder and Schizophrenia

Autism spectrum disorder (ASD) and schizophrenia (SZ) are neuropsychiatric disorders that overlap in symptoms associated with social-cognitive impairment. Subcortical structures play a significant role in cognitive and social-emotional behaviors and their abnormalities are associated with neuropsychiatric conditions. This exploratory study utilized ABIDE II/COBRE MRI and corresponding phenotypic datasets to compare subcortical volumes of adults with ASD (n = 29), SZ (n = 51) and age and gender matched neurotypicals (NT). We examined the association between subcortical volumes and select behavioral measures to determine whether core symptomatology of disorders could be explained by subcortical association patterns. We observed volume differences in ASD (viz., left pallidum, left thalamus, left accumbens, right amygdala) but not in SZ compared to their respective NT controls, reflecting morphometric changes specific to one of the disorder groups. However, left hippocampus and amygdala volumes were implicated in both disorders. A disorder-specific negative correlation (r = −0.39, p = 0.038) was found between left-amygdala and scores on the Social Responsiveness Scale (SRS) Social-Cognition in ASD, and a positive association (r = 0.29, p = 0.039) between full scale IQ (FIQ) and right caudate in SZ. Significant correlations between behavior measures and subcortical volumes were observed in NT groups (ASD-NT range; r = −0.53 to −0.52, p = 0.002 to 0.004, SZ-NT range; r = −0.41 to −0.32, p = 0.007 to 0.021) that were non-significant in the disorder groups. The overlap of subcortical volumes implicated in ASD and SZ may reflect common neurological mechanisms. Furthermore, the difference in correlation patterns between disorder and NT groups may suggest dysfunctional connectivity with cascading effects unique to each disorder and a potential role for IQ in mediating behavior and brain circuits.

Visual Neuroscience Methods for Marmosets: Efficient Receptive Field Mapping and Head-Free Eye Tracking

The marmoset has emerged as a promising primate model system, in particular for visual neuroscience. Many common experimental paradigms rely on head fixation and an extended period of eye fixation during the presentation of salient visual stimuli. Both of these behavioral requirements can be challenging for marmosets. Here, we present two methodological developments, each addressing one of these difficulties. First, we show that it is possible to use a standard eye-tracking system without head fixation to assess visual behavior in the marmoset. Eye-tracking quality from head-free animals is sufficient to obtain precise psychometric functions from a visual acuity task. Second, we introduce a novel method for efficient receptive field (RF) mapping that does not rely on moving stimuli but uses fast flashing annuli and wedges. We present data recorded during head-fixation in areas V1 and V6 and show that RF locations are readily obtained within a short period of recording time. Thus, the methodological advancements presented in this work will contribute to establish the marmoset as a valuable model in neuroscience.

Neural Population Dynamics Underlying Expected Value Computation

Computation of expected values (i.e., probability × magnitude) seems to be a dynamic integrative process performed by the brain for efficient economic behavior. However, neural dynamics underlying this computation is largely unknown. Using lottery tasks in monkeys (Macaca mulatta, male; Macaca fuscata, female), we examined (1) whether four core reward-related brain regions detect and integrate probability and magnitude cued by numerical symbols and (2) whether these brain regions have distinct dynamics in the integrative process. Extraction of the mechanistic structure of neural population signals demonstrated that expected value signals simultaneously arose in the central orbitofrontal cortex (cOFC; medial part of area 13) and ventral striatum (VS). Moreover, these signals were incredibly stable compared with weak and/or fluctuating signals in the dorsal striatum and medial OFC. Temporal dynamics of these stable expected value signals were unambiguously distinct: sharp and gradual signal evolutions in the cOFC and VS, respectively. These intimate dynamics suggest that the cOFC and VS compute the expected values with unique time constants, as distinct, partially overlapping processes.

SIGNIFICANCE STATEMENT Our results differ from those of earlier studies suggesting that many reward-related regions in the brain signal probability and/or magnitude and provide a mechanistic structure for expected value computation employed in multiple neural populations. A central part of the orbitofrontal cortex (cOFC) and ventral striatum (VS) can simultaneously detect and integrate probability and magnitude into an expected value. Our empirical study on these neural population dynamics raises a possibility that the cOFC and VS cooperate on this computation with unique time constants as distinct, partially overlapping processes.

Tonically Active Neurons in the Monkey Dorsal Striatum Signal Outcome Feedback during Trial-and-error Search Behavior

An animal's choice behavior is shaped by the outcome feedback from selected actions in a trial-and-error approach. Tonically active neurons (TANs), presumed cholinergic interneurons in the striatum, are thought to be involved in the learning and performance of reward-directed behaviors, but it remains unclear how TANs are involved in shaping reward-directed choice behaviors based on the outcome feedback. To this end, we recorded activity of TANs from the dorsal striatum of two macaque monkeys (Macaca fuscata; 1 male, 1 female) while they performed a multi-step choice task to obtain multiple rewards. In this task, the monkeys first searched for a rewarding target from among three alternatives in a trial-and-error manner and then earned additional rewards by repeatedly choosing the rewarded target. We found that a considerable proportion of TANs selectively responded to either the reward or the no-reward outcome feedback during the trial-and-error search, but these feedback responses were not observed during repeat trials. Moreover, the feedback responses of TANs were similarly observed in any search trials, without distinctions regarding the predicted probability of rewards and the location of chosen targets. Unambiguously, TANs detected reward and no-reward feedback specifically when the monkeys performed trial-and-error searches, in which the monkeys were learning the value of the targets and adjusting their subsequent choice behavior based on the reward and no-reward feedback. These results suggest that striatal cholinergic interneurons signal outcome feedback specifically during search behavior, in circumstances where the choice outcomes cannot be predicted with certainty by the animals.

Bilateral responses of rat ventral striatum tonically active neurons to unilateral medial forebrain bundle stimulation

Unilateral medial forebrain bundle (MFB) stimulation is an extremely effective promoter of reinforcement learning irrespective of the conditioned cue's laterality. The effectiveness of unilateral MFB stimulation, which activates the mesolimbic pathway connecting the ventral tegmental area to the ventral striatum (vStr), is surprising considering that these fibers rarely cross to the contralateral hemisphere. Specifically, this type of biased fiber distribution entails the activation of brain structures that are primarily ipsilateral to the stimulated MFB, along with weak to negligible activation of the contralateral structures, thus impeding the formation of a cue-outcome association. To better understand the spread of activation of MFB stimulation across hemispheres, we studied whether unilateral MFB stimulation primarily activates the ipsilateral vStr or the vStr of both hemispheres. We simultaneously recorded neuronal activity in the vStr of both hemispheres in response to several sets of unilateral MFB stimulation in anesthetized and freely moving rats. Unilateral MFB stimulation evoked strong stimulus-dependent activation of vStr tonically active neurons (TANs), presumably the cholinergic interneurons, in both hemispheres. However, the TANs' activation patterns and responsiveness depended on whether the stimulus was delivered ipsilaterally or contralaterally to the recorded neuron. These findings indicate that unilateral MFB stimulation effectively activates the vStr in both hemispheres in a stimulus-dependent manner which may serve as neuronal substrate for the formation of cue-outcome associations during reinforcement learning.

Topographic distinction in long-term value signals between presumed dopamine neurons and presumed striatal projection neurons in behaving monkeys

Nigrostriatal dopamine (DA) projections are anatomically organized along the dorsolateral-ventromedial axis, conveying long-term value signals to the striatum for shaping actions toward multiple future rewards. The present study examines whether the topographic organization of long-term value signals are observed upon activity of presumed DA neurons and presumed striatal projection neurons (phasically active neurons, PANs), as predicted based on anatomical literature. Our results indicate that DA neurons in the dorsolateral midbrain encode long-term value signals on a short timescale, while ventromedial midbrain DA neurons encode such signals on a relatively longer timescale. Activity of the PANs in the dorsal striatum is more heterogeneous for encoding long-term values, although significant differences in long-term value signals were observed between the caudate nucleus and putamen. These findings suggest that topographic DA signals for long-term values are not simply transferred to striatal neurons, possibly due to the contribution of other projections to the striatum.

The neuroscience of unmet social needs

John Cacioppo has compared loneliness to hunger or thirst in that it signals that one needs to act and repair what is lacking. This paper reviews Cacioppo's and others' contributions to our understanding of neural mechanisms underlying social motivation in humans and in other social species. We focus particularly on the dopaminergic reward system and try to integrate evidence from animal models and human research. In rodents, objective social isolation leads to increased social motivation, mediated by the brains' mesolimbic dopamine system. In humans, social rejection can lead to either increased or decreased social motivation, and is associated with activity in the insular cortex; while chronic loneliness is typically associated with decreased social motivation but has been associated with altered dopaminergic responses in the striatum. This mixed pattern of cross-species similarities and differences may arise from the substantially different methods used to study unmet social needs across species, and suggests the need for more direct and deliberate cross-species comparative research in this critically important domain.

Insula and putamen centered functional connectivity networks reflect healthy agers' subjective experience of cognitive fatigue in multiple tasks

Cognitive fatigue (CF) impairs ability to perform daily activities, is a common complaint of aging and a symptom of multiple neurological conditions. However, knowledge of the neural basis of CF is limited. This is partially because CF is difficult to systematically modulate in brain imaging experiments. The most common approach has been to scan brain activity during effortful cognitive tasks. Consequently, neural correlates of CF tend to be task-specific and may vary across tasks. This makes it difficult to know how results generalize across studies and is outside the subjective experience of CF which tends to be similar in different tasks. It has been hypothesized that the subjective experience of CF might arise from domain general systems monitoring and acting on energy depletion in task specific circuits. Direct supporting neural evidence is lacking. By repeatedly scanning aging individuals undertaking four different tasks using functional Magnetic Resonance Imaging and referencing scans to detailed CF self-ratings taken before and after scanning, we sought task-general correlates of CF. We ran a data-driven representational similarity analysis, treating each brain region as a candidate CF functional connectivity hub, and correlating inter-participant differences in hub-based connectivity patterns with inter-participant differences in self-rated CF-profiles (a pattern of ratings across 18 questions). Both right insula and right putamen-based network connectivity patterns reflected CF across all tasks and could underpin subjective experience of CF.

Structural brain correlates of fatigue in older adults with and without Parkinson's disease

Fatigue is one of the most common and disabling nonmotor symptoms seen in Parkinson's disease (PD) and is also commonly seen in healthy older adults. Our understanding of the etiology of fatigue in older adults with or without PD is limited and it remains unclear whether fatigue in PD is specifically related to PD pathology. The objective of this study was thus to determine whether fatigue in PD was associated with structural changes in gray or white matter and explore whether these changes were similar in older adults without PD. Magnetic resonance imaging (T₁ weighted) and diffusion tensor imaging were performed in 60 patients with PD (17 females; age = 67.58 ± 5.51; disease duration = 5.67 ± 5.83 years) and 41 age- and sex- matched healthy controls. FSL image processing was used to measure gray matter volume, fractional anisotropy, and leukoariosis differences. Voxel-based morphometry confirmed gray matter loss across the dorsal striatum and insula in the PD patient cohort. PD patients with fatigue had reduced gray matter volume in dorsal striatum relative to PD patients without fatigue (P < 0.05 False Discovery Rate corrected). No significant fatigue-related structural atrophy was found in controls. There were no areas of significant fractional anisotropy differences between high and low fatigue subjects in either the PD or non-PD groups. Control participants with high fatigue, but not PD, showed significantly greater total leukoariosis volumes (p = 0.03). Fatigue in PD is associated with unique structural changes in the caudate and putamen suggesting fatigue in PD is primarily related to PD pathology, particularly in the dorsal striatum, and not simply a consequence of aging.

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Fatigue is a disabling symptom in Parkinson's disease (PD) and healthy older adults.

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We studied structural correlates of fatigue using MRI morphometry.

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PD patients with high fatigue had caudate atrophy.

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Healthy older adults with fatigue had increased burden of leukoariosis.

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Patterns of structural brain changes were distinct between PD and healthy group.

Identification of alterations associated with age in the clustering structure of functional brain networks

Initial studies using resting-state functional magnetic resonance imaging on the trajectories of the brain network from childhood to adulthood found evidence of functional integration and segregation over time. The comprehension of how healthy individuals’ functional integration and segregation occur is crucial to enhance our understanding of possible deviations that may lead to brain disorders. Recent approaches have focused on the framework wherein the functional brain network is organized into spatially distributed modules that have been associated with specific cognitive functions. Here, we tested the hypothesis that the clustering structure of brain networks evolves during development. To address this hypothesis, we defined a measure of how well a brain region is clustered (network fitness index), and developed a method to evaluate its association with age. Then, we applied this method to a functional magnetic resonance imaging data set composed of 397 males under 31 years of age collected as part of the Autism Brain Imaging Data Exchange Consortium. As results, we identified two brain regions for which the clustering change over time, namely, the left middle temporal gyrus and the left putamen. Since the network fitness index is associated with both integration and segregation, our finding suggests that the identified brain region plays a role in the development of brain systems.

Increased cognitive load enables unlearning in procedural category learning

Interventions for drug abuse and other maladaptive habitual behaviors may yield temporary success but are often fragile and relapse is common. This implies that current interventions do not erase or substantially modify the representations that support the underlying addictive behavior-that is, they do not cause true unlearning. One example of an intervention that fails to induce true unlearning comes from Crossley, Ashby, and Maddox (2013, Journal of Experimental Psychology: General), who reported that a sudden shift to random feedback did not cause unlearning of category knowledge obtained through procedural systems, and they also reported results suggesting that this failure is because random feedback is noncontingent on behavior. These results imply the existence of a mechanism that (a) estimates feedback contingency and (b) protects procedural learning from modification when feedback contingency is low (i.e., during random feedback). This article reports the results of an experiment in which increasing cognitive load via an explicit dual task during the random feedback period facilitated unlearning. This result is consistent with the hypothesis that the mechanism that protects procedural learning when feedback contingency is low depends on executive function. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Pauses in Striatal Cholinergic Interneurons: What is Revealed by Their Common Themes and Variations?

Striatal cholinergic interneurons, the so-called tonically active neurons (TANs), pause their firing in response to sensory cues and rewards during classical conditioning and instrumental tasks. The respective pause responses observed can demonstrate many commonalities, such as constant latency and duration, synchronous occurrence in a population of cells, and coincidence with phasic activities of midbrain dopamine neurons (DANs) that signal reward predictions and errors. Pauses can however also show divergent properties. Pause latencies and durations can differ in a given TAN between appetitive vs. aversive outcomes in classical conditioning, initial excitation can be present or absent, and a second pause can variably follow a rebound. Despite more than 20 years of study, the functions of these pause responses are still elusive. Our understanding of pause function is hindered by an incomplete understanding of how pauses are generated. In this mini-review article, we compare pause types, as well as current key hypotheses for inputs underlying pauses that include dopamine-induced inhibition through D₂-receptors, a GABA input from ventral tegmental area, and a prolonged afterhyperpolarization induced by excitatory input from the cortex or from the thalamus. We review how each of these mechanisms alone explains some but not all aspects of pause responses. These mechanisms might need to operate in specific but variable sets of sequences to generate a full range of pause responses. Alternatively, these mechanisms might operate in conjunction with an underlying control mechanism within cholinergic interneurons which could potentially provide a framework to generate the common themes and variations seen amongst pause responses.

The role of the intrinsic cholinergic system of the striatum: What have we learned from TAN recordings in behaving animals?

Cholinergic interneurons provide rich local innervation of the striatum and play an important role in controlling behavior, as evidenced by the variety of movement and psychiatric disorders linked to disrupted striatal cholinergic transmission. Much progress has been made in recent years regarding our understanding of how these interneurons contribute to the processing of information in the striatum. In particular, investigation of the activity of presumed striatal cholinergic interneurons, identified as tonically active neurons or TANs in behaving animals, has pointed to their role in the signaling and learning of the motivational relevance of environmental stimuli. Although the bulk of this work has been conducted in monkeys, several studies have also been carried out in behaving rats, but information remains rather disparate across studies and it is still questionable whether rodent TANs correspond to TANs described in monkeys. Consequently, our current understanding of the function of cholinergic transmission in the striatum is challenged by the rapidly growing, but often confusing literature on the relationship between TAN activity and specific behaviors. As regards the precise nature of the information conveyed by the cholinergic TANs, a recent influential view emphasized that these local circuit neurons may play a special role in the processing of contextual information that is important for reinforcement learning and selection of appropriate actions. This review provides a summary of recent progress in TAN physiology from which it is proposed that striatal cholinergic interneurons are crucial elements for flexible switching of behaviors under changing environmental conditions.

Differences between Dorsal and Ventral Striatum in the Sensitivity of Tonically Active Neurons to Rewarding Events

Within the striatum, cholinergic interneurons, electrophysiologically identified as tonically active neurons (TANs), represent a relatively homogeneous group in terms of their functional properties. They display typical pause in tonic firing in response to rewarding events which are of crucial importance for reinforcement learning. These responses are uniformly distributed throughout the dorsal striatum (i.e., motor and associative striatum), but it is unknown, at least in monkeys, whether differences in the modulation of TAN activity exist in the ventral striatum (i.e., limbic striatum), a region specialized for processing of motivational information. To address this issue, we examined the activity of dorsal and ventral TANs in two monkeys trained on a Pavlovian conditioning task in which a visual stimulus preceded the delivery of liquid reward by a fixed time interval. We found that the proportion of TANs responding to the stimulus predictive of reward did not vary significantly across regions (58%–80%), whereas the fraction of TANs responding to reward was higher in the limbic striatum (100%) compared to the motor (65%) and associative striatum (52%). By examining TAN modulation at the level of both the population and the individual neurons, we showed that the duration of pause responses to the stimulus and reward was longer in the ventral than in the dorsal striatal regions. Also, the magnitude of the pause was greater in ventral than dorsal striatum for the stimulus predictive of reward but not for the reward itself. We found similar region-specific differences in pause response duration to the stimulus when the timing of reward was less predictable (fixed replaced by variable time interval). Regional variations in the duration and magnitude of the pause response were transferred from the stimulus to reward when reward was delivered in the absence of any predictive stimulus. It therefore appears that ventral TANs exhibit stronger responses to rewarding stimuli, compared to dorsal TANs. The high proportion of responsive neurons, combined with particular response features, support the notion that the ventral TAN system can be driven by specific synaptic inputs arising from afferent sources distinct from those targeting the dorsal TAN system.

Cholinergic Interneurons Use Orbitofrontal Input to Track Beliefs about Current State

When conditions change, organisms need to learn about the changed conditions without interfering with what they already know. To do so, they can assign the new learning to a new "state" and the old learning to a previous state. This state assignment is fundamental to behavioral flexibility. Cholinergic interneurons (CINs) in the dorsomedial striatum (DMS) are necessary for associative information to be compartmentalized in this way, but the mechanism by which they do so is unknown. Here we addressed this question by recording putative CINs from the DMS in rats performing a task consisting of a series of trial blocks, or states, that required the recall and application of contradictory associative information. We found that individual CINs in the DMS represented the current state throughout each trial. These state correlates were not observed in dorsolateral striatal CINs recorded in the same rats. Notably, DMS CIN ensembles tracked rats' beliefs about the current state such that, when states were miscoded, rats tended to make suboptimal choices reflecting the miscoding. State information held by the DMS CINs also depended completely on the orbitofrontal cortex, an area that has been proposed to signal environmental states. These results suggest that CINs set the stage for recalling associative information relevant to the current environment by maintaining a real-time representation of the current state. Such a role has novel implications for understanding the neural basis of a variety of psychiatric diseases, such as addiction or anxiety disorders, in which patients generalize inappropriately (or fail to generalize) between different environments.

SIGNIFICANCE STATEMENT

Striatal cholinergic interneurons (CINs) are thought to be identical to tonically active neurons. These neurons have long been thought to have an important influence on striatal processing during reward-related learning. Recently, a more specific function for striatal CINs has been suggested, which is that they are necessary for striatal learning to be compartmentalized into different states as the state of the environment changes. Here we report that putative CINs appear to track rats' beliefs about which environmental state is current. We further show that this property of CINs depends on orbitofrontal cortex input and is correlated with choices made by rats. These findings could provide new insight into neuropsychiatric diseases that involve improper generalization between different contexts.

Frequency-dependent changes in the amplitude of low-frequency fluctuations in patients with Wilson's disease: a resting-state fMRI study

To investigate the frequency-dependent changes in the amplitude of low-frequency fluctuations (ALFF) in patients with Wilson's disease (WD). Resting-state function magnetic resonance imaging (R-fMRI) were employed to measure the amplitude of ALFF in 28 patients with WD and 27 matched normal controls. Slow-5 (0.01-0.027 Hz) and slow-4 (0.027-0.073 Hz) frequency bands were analyzed. Apart from the observation of atrophy in the cerebellum, basal ganglia, occipital gyrus, frontal gyrus, precentral gyrus, and paracentral lobule, we also found widespread differences in ALFF of the two bands in the medial frontal gyrus, inferior temporal gyrus, insula, basal ganglia, hippocampus/parahippocampal gyrus, and thalamus bilaterally. Compared to normal controls, WD patients had increased ALFF in the posterior lobe of the cerebellum, inferior temporal gyrus, brain stem, basal ganglia, and decreased ALFF in the anterior lobe of the cerebellum and medial frontal gyrus. Specifically, we observed that the ALFF abnormalities in the cerebellum and middle frontal gyrus were greater in the slow-5 than in the slow-4 band. Correlation analysis showed consistently positive correlations between urinary copper excretion (Cu), serum ceruloplasmin (CP) and ALFFs in the cerebellum. Our study suggests the accumulation of copper profoundly impaired intrinsic brain activity and the impairments seem to be frequency-dependent. These results provide further insights into the understanding of the pathophysiology of WD.

Roles of centromedian parafascicular nuclei of thalamus and cholinergic interneurons in the dorsal striatum in associative learning of environmental events

The thalamus provides a massive input to the striatum, but despite accumulating evidence, the functions of this system remain unclear. It is known, however, that the centromedian (CM) and parafascicular (Pf) nuclei of the thalamus can strongly influence particular striatal neuron subtypes, notably including the cholinergic interneurons of the striatum (CINs), key regulators of striatal function. Here, we highlight the thalamostriatal system through the CM-Pf to striatal CINs. We consider how, by virtue of the direct synaptic connections of the CM and PF, their neural activity contributes to the activity of CINs and striatal projection neurons (SPNs). CM-Pf neurons are strongly activated at sudden changes in behavioral context, such as switches in action-outcome contingency or sequence of behavioral requirements, suggesting that their activity may represent change of context operationalized as associability. Striatal CINs, on the other hand, acquire and loose responses to external events associated with particular contexts. In light of this physiological evidence, we propose a hypothesis of the CM-Pf-CINs system, suggesting that it augments associative learning by generating an associability signal and promotes reinforcement learning guided by reward prediction error signals from dopamine-containing neurons. We discuss neuronal circuit and synaptic organizations based on in vivo/in vitro studies that we suppose to underlie our hypothesis. Possible implications of CM-Pf-CINs dysfunction (or degeneration) in brain diseases are also discussed by focusing on Parkinson's disease.

Hierarchical control of procedural and declarative category-learning systems

Substantial evidence suggests that human category learning is governed by the interaction of multiple qualitatively distinct neural systems. In this view, procedural memory is used to learn stimulus-response associations, and declarative memory is used to apply explicit rules and test hypotheses about category membership. However, much less is known about the interaction between these systems: how is control passed between systems as they interact to influence motor resources? Here, we used fMRI to elucidate the neural correlates of switching between procedural and declarative categorization systems. We identified a key region of the cerebellum (left Crus I) whose activity was bidirectionally modulated depending on switch direction. We also identified regions of the default mode network (DMN) that were selectively connected to left Crus I during switching. We propose that the cerebellum-in coordination with the DMN-serves a critical role in passing control between procedural and declarative memory systems.

Neuronal circuits and physiological roles of the basal ganglia in terms of transmitters, receptors and related disorders

The authors have reviewed recent research advances in basal ganglia circuitry and function, as well as in related disorders from multidisciplinary perspectives derived from the results of morphological, electrophysiological, behavioral, biochemical and molecular biological studies. Based on their expertise in their respective fields, as denoted in the text, the authors discuss five distinct research topics, as follows: (1) area-specific dopamine receptor expression of astrocytes in basal ganglia, (2) the role of physiologically released dopamine in the striatum, (3) control of behavioral flexibility by striatal cholinergic interneurons, (4) regulation of phosphorylation states of DARPP-32 by protein phosphatases and (5) physiological perspective on deep brain stimulation with optogenetics and closed-loop control for ameliorating parkinsonism.

Modulation of Tonically Active Neurons of the Monkey Striatum by Events Carrying Different Force and Reward Information

The role of basal ganglia in motivational processes has been under scrutiny in recent decades, with increasing evidence from clinical studies of cognitive and motivational deficits in patients with basal ganglia lesions. Tonically active neurons (TANs), the presumed striatal cholinergic interneurons, could be important actors in integrating and relaying motivational information arising from various modalities. Their multiphasic responses to rewards and to conditioned stimuli associated with reward conferred them a role in limbic processes. They are also modulated by a task's motor aspect. Recent studies suggest they are influenced by the context in which behavioral responses are expressed. To investigate the role of TANs in motor-limbic interaction processes, we recorded 169 TANs in the striatum of two monkeys performing a motivational task, in which they had to develop a variable force to receive different amounts of reward in response to visual stimuli. Our results reveal new features of TANs response properties. First, TANs usually responded either by a pause or an elevation of discharge rate to the visual cues and the reward, with few neurons combining both pause and rebound. Second, the elevations of discharge rate after the cues were most sensitive to the least valuable (high force or small reward) task conditions. Finally, the responses of TANs to the visual cues were time locked on the onset of the animal's movement. TANs' population and responses could thus play a role in signaling less attractive situations, those with either a high motor demand and/or small reward.

SIGNIFICANCE STATEMENT

Tonically active neurons (TANs) are known for their responses to unpredictable positive or negative events. However, here we show that TANs respond by a pause or an increase in their activity to all rewarding events in a task in which combined visual cues indicate to the monkeys the levels of force to produce and the upcoming reward. Unlike the pause, the increase in activity is modulated by task parameters and is most sensitive to the least attractive task conditions (high force and/or small reward). TANs' responses triggered by cue occurrence are also modulated by movement-related information (movement onset). We therefore propose here that TANs could play a role, via their action on striatal projections neurons, in maintaining high cost/low benefit ratio behaviors.

Characteristics of fast-spiking neurons in the striatum of behaving monkeys

Inhibitory interneurons are the fundamental constituents of neural circuits that organize network outputs. The striatum as part of the basal ganglia is involved in reward-directed behaviors. However, the role of the inhibitory interneurons in this process remains unclear, especially in behaving monkeys. We recorded the striatal single neuron activity while monkeys performed reward-directed hand or eye movements. Presumed parvalbumin-containing GABAergic interneurons (fast-spiking neurons, FSNs) were identified based on narrow spike shapes in three independent experiments, though they were a small population (4.2%, 42/997). We found that FSNs are characterized by high-frequency and less-bursty discharges, which are distinct from the basic firing properties of the presumed projection neurons (phasically active neurons, PANs). Besides, the encoded information regarding actions and outcomes was similar between FSNs and PANs in terms of proportion of neurons, but the discharge selectivity was higher in PANs than that of FSNs. The coding of actions and outcomes in FSNs and PANs was consistently observed under various behavioral contexts in distinct parts of the striatum (caudate nucleus, putamen, and anterior striatum). Our results suggest that FSNs may enhance the discharge selectivity of postsynaptic output neurons (PANs) in encoding crucial variables for a reward-directed behavior.

Expanding the role of striatal cholinergic interneurons and the midbrain dopamine system in appetitive instrumental conditioning

The basal ganglia are a collection of subcortical nuclei thought to underlie a wide variety of vertebrate behavior. Although a great deal is known about the functional and physiological properties of the basal ganglia, relatively few models have been formally developed that have been tested against both behavioral and physiological data. Our previous work (Ashby FG, Crossley MJ. J Cogn Neurosci 23: 1549-1566, 2011) showed that a model grounded in the neurobiology of the basal ganglia could account for basic single-neuron recording data, as well as behavioral phenomena such as fast reacquisition that constrain models of conditioning. In this article we show that this same model accounts for a variety of appetitive instrumental conditioning phenomena, including the partial reinforcement extinction (PRE) effect, rapid and slowed reacquisition following extinction, and renewal of previously extinguished instrumental responses by environmental context cues.

Dissociable functions of reward inference in the lateral prefrontal cortex and the striatum

In a complex and uncertain world, how do we select appropriate behavior? One possibility is that we choose actions that are highly reinforced by their probabilistic consequences (model-free processing). However, we may instead plan actions prior to their actual execution by predicting their consequences (model-based processing). It has been suggested that the brain contains multiple yet distinct systems involved in reward prediction. Several studies have tried to allocate model-free and model-based systems to the striatum and the lateral prefrontal cortex (LPFC), respectively. Although there is much support for this hypothesis, recent research has revealed discrepancies. To understand the nature of the reward prediction systems in the LPFC and the striatum, a series of single-unit recording experiments were conducted. LPFC neurons were found to infer the reward associated with the stimuli even when the monkeys had not yet learned the stimulus-reward (SR) associations directly. Striatal neurons seemed to predict the reward for each stimulus only after directly experiencing the SR contingency. However, the one exception was "Exclusive Or" situations in which striatal neurons could predict the reward without direct experience. Previous single-unit studies in monkeys have reported that neurons in the LPFC encode category information, and represent reward information specific to a group of stimuli. Here, as an extension of these, we review recent evidence that a group of LPFC neurons can predict reward specific to a category of visual stimuli defined by relevant behavioral responses. We suggest that the functional difference in reward prediction between the LPFC and the striatum is that while LPFC neurons can utilize abstract code, striatal neurons can code individual associations between stimuli and reward but cannot utilize abstract code.

Insula-Dorsal Anterior Cingulate Cortex Coupling is Associated with Enhanced Brain Reactivity to Smoking Cues

The insula plays a critical role in maintaining nicotine dependence and reactivity to smoking cues. More broadly, the insula and the dorsal anterior cingulate cortex (dACC) are key nodes of the salience network (SN), which integrates internal and extrapersonal information to guide behavior. Thus, insula-dACC interactions may be integral in processing salient information such as smoking cues that facilitate continued nicotine use. We evaluated functional magnetic resonance imaging (fMRI) data from nicotine-dependent participants during rest, and again when they viewed smoking-related images. Greater insula-dACC coupling at rest was significantly correlated with enhanced smoking cue-reactivity in brain areas associated with attention and motor preparation, including the visual cortex, right ventral lateral prefrontal cortex, and the dorsal striatum. In an independent cohort, we found that insula-dACC connectivity was stable over 1-h delay and was not influenced by changes in subjective craving or expired carbon monoxide, suggesting that connectivity strength between these regions may be a trait associated with heightened cue-reactivity. Finally, we also showed that insula reactivity to smoking cues correlates with a rise in cue-reactivity throughout the entire SN, indicating that the insula's role in smoking cue-reactivity is not functionally independent, and may actually represent the engagement of the entire SN. Collectively, these data provide a more network-level understanding of the insula's role in nicotine dependence and shows a relationship between inherent brain organization and smoking cue-reactivity.

Cholinergic interneurons in the dorsal and ventral striatum: anatomical and functional considerations in normal and diseased conditions

Striatal cholinergic interneurons (ChIs) are central for the processing and reinforcement of reward-related behaviors that are negatively affected in states of altered dopamine transmission, such as in Parkinson's disease or drug addiction. Nevertheless, the development of therapeutic interventions directed at ChIs has been hampered by our limited knowledge of the diverse anatomical and functional characteristics of these neurons in the dorsal and ventral striatum, combined with the lack of pharmacological tools to modulate specific cholinergic receptor subtypes. This review highlights some of the key morphological, synaptic, and functional differences between ChIs of different striatal regions and across species. It also provides an overview of our current knowledge of the cellular localization and function of cholinergic receptor subtypes. The future use of high-resolution anatomical and functional tools to study the synaptic microcircuitry of brain networks, along with the development of specific cholinergic receptor drugs, should help further elucidate the role of striatal ChIs and permit efficient targeting of cholinergic systems in various brain disorders, including Parkinson's disease and addiction.

Targeted ablation of cholinergic interneurons in the dorsolateral striatum produces behavioral manifestations of Tourette syndrome

Gilles de la Tourette syndrome (TS) is characterized by tics, which are transiently worsened by stress, acute administration of dopaminergic drugs, and by subtle deficits in motor coordination and sensorimotor gating. It represents the most severe end of a spectrum of tic disorders that, in aggregate, affect ∼ 5% of the population. Available treatments are frequently inadequate, and the pathophysiology is poorly understood. Postmortem studies have revealed a reduction in specific striatal interneurons, including the large cholinergic interneurons, in severe disease. We tested the hypothesis that this deficit is sufficient to produce aspects of the phenomenology of TS, using a strategy for targeted, specific cell ablation in mice. We achieved ∼ 50% ablation of the cholinergic interneurons of the striatum, recapitulating the deficit observed in patients postmortem, without any effect on GABAergic markers or on parvalbumin-expressing fast-spiking interneurons. Interneuron ablation in the dorsolateral striatum (DLS), corresponding roughly to the human putamen, led to tic-like stereotypies after either acute stress or d-amphetamine challenge; ablation in the dorsomedial striatum, in contrast, did not. DLS interneuron ablation also led to a deficit in coordination on the rotorod, but not to any abnormalities in prepulse inhibition, a measure of sensorimotor gating. These results support the causal sufficiency of cholinergic interneuron deficits in the DLS to produce some, but not all, of the characteristic symptoms of TS.

Serotoninergic and dopaminergic modulation of cortico-striatal circuit in executive and attention deficits induced by NMDA receptor hypofunction in the 5-choice serial reaction time task

Executive functions are an emerging propriety of neuronal processing in circuits encompassing frontal cortex and other cortical and subcortical brain regions such as basal ganglia and thalamus. Glutamate serves as the major neurotrasmitter in these circuits where glutamate receptors of NMDA type play key role. Serotonin and dopamine afferents are in position to modulate intrinsic glutamate neurotransmission along these circuits and in turn to optimize circuit performance for specific aspects of executive control over behavior. In this review, we focus on the 5-choice serial reaction time task which is able to provide various measures of attention and executive control over performance in rodents and the ability of prefrontocortical and striatal serotonin 5-HT_1A, 5-HT_2A, and 5-HT_2C as well as dopamine D₁- and D₂-like receptors to modulate different aspects of executive and attention disturbances induced by NMDA receptor hypofunction in the prefrontal cortex. These behavioral studies are integrated with findings from microdialysis studies. These studies illustrate the control of attention selectivity by serotonin 5-HT_1A, 5-HT_2A, 5-HT_2C, and dopamine D₁- but not D₂-like receptors and a distinct contribution of these cortical and striatal serotonin and dopamine receptors to the control of different aspects of executive control over performance such as impulsivity and compulsivity. An association between NMDA antagonist-induced increase in glutamate release in the prefrontal cortex and attention is suggested. Collectively, this review highlights the functional interaction of serotonin and dopamine with NMDA dependent glutamate neurotransmission in the cortico-striatal circuitry for specific cognitive demands and may shed some light on how dysregulation of neuronal processing in these circuits may be implicated in specific neuropsychiatric disorders.

Encoding by synchronization in the primate striatum

Information is encoded in the nervous system through the discharge and synchronization of single neurons. The striatum, the input stage of the basal ganglia, is divided into three territories: the putamen, the caudate, and the ventral striatum, all of which converge onto the same motor pathway. This parallel organization suggests that there are multiple and competing systems in the basal ganglia network controlling behavior. To explore which mechanism(s) enables the different striatal domains to encode behavioral events and to control behavior, we compared the neural activity of phasically active neurons [medium spiny neurons (MSNs), presumed projection neurons] and tonically active neurons (presumed cholinergic interneurons) across striatal territories from monkeys during the performance of a well practiced task. Although neurons in all striatal territories displayed similar spontaneous discharge properties and similar temporal modulations of their discharge rates to the behavioral events, their correlation structure was profoundly different. The distributions of signal and noise correlation of pairs of putamen MSNs were strongly shifted toward positive correlations and these two measures were correlated. In contrast, MSN pairs in the caudate and ventral striatum displayed symmetrical, near-zero signal and noise correlation distributions. Furthermore, only putamen MSN pairs displayed different noise correlation dynamics to rewarding versus neutral/aversive cues. Similarly, the noise correlation between tonically active neuron pairs was stronger in the putamen than in the caudate. We suggest that the level of synchronization of the neuronal activity and its temporal dynamics differentiate the striatal territories and may thus account for the different roles that striatal domains play in behavioral control.

Parallel processing of environmental recognition and locomotion in the mouse striatum

Information processing in behaving animals has been the target of many studies in the striatum; however, its dynamics and complexity remain to a large extent unknown. Here, we chronically recorded neuronal populations in dorsal striatum as mice were exposed to a novel environment, a paradigm which enables the dissociation of locomotion and environmental recognition. The findings indicate that non-overlapping populations of striatal projection neurons-the medium spiny neurons-reliably encode locomotion and environmental identity, whereas two subpopulations of short-spike interneurons encode distinct information: the fast spiking interneurons preferentially encode locomotion whereas the second type of interneurons preferentially encodes environmental identity. The three neuronal subgroups used cell-type specific coding schemes. This study provides evidence for the existence of parallel processing circuits within the sensorimotor region of the striatum.

Complexity and competition in appetitive and aversive neural circuits

Decision-making often involves using sensory cues to predict possible rewarding or punishing reinforcement outcomes before selecting a course of action. Recent work has revealed complexity in how the brain learns to predict rewards and punishments. Analysis of neural signaling during and after learning in the amygdala and orbitofrontal cortex, two brain areas that process appetitive and aversive stimuli, reveals a dynamic relationship between appetitive and aversive circuits. Specifically, the relationship between signaling in appetitive and aversive circuits in these areas shifts as a function of learning. Furthermore, although appetitive and aversive circuits may often drive opposite behaviors – approaching or avoiding reinforcement depending upon its valence – these circuits can also drive similar behaviors, such as enhanced arousal or attention; these processes also may influence choice behavior. These data highlight the formidable challenges ahead in dissecting how appetitive and aversive neural circuits interact to produce a complex and nuanced range of behaviors.

Coding of the long-term value of multiple future rewards in the primate striatum

Decisions maximizing benefits involve a tradeoff between the quantity of a reward and the cost of elapsed time until an animal receives it. The estimation of long-term reward values is critical to attain the most desirable outcomes over a certain period of time. Reinforcement learning theories have established algorithms to estimate the long-term reward values of multiple future rewards in which the values of future rewards are discounted as a function of how many steps of choices are necessary to achieve them. Here, we report that presumed striatal projection neurons represent the long-term values of multiple future rewards estimated by a standard reinforcement learning model while monkeys are engaged in a series of trial-and-error choices and adaptive decisions for multiple rewards. We found that the magnitude of activity of a subset of neurons was positively correlated with the long-term reward values, and that of another subset of neurons was negatively correlated throughout the entire decision-making process in individual trials: from the start of the task trial, estimation of the values and their comparison among alternatives, choice execution, and evaluation of the received rewards. An idiosyncratic finding was that neurons showing negative correlations represented reward values in the near future (high discounting), while neurons showing positive correlations represented reward values not only in the near future, but also in the far future (low discounting). These findings provide a new insight that long-term value signals are embedded in two subsets of striatal neurons as high and low discounting of multiple future rewards.

Pause and rebound: sensory control of cholinergic signaling in the striatum

Cholinergic interneurons have emerged as one of the key players controlling network functions in the striatum. Extracellularly recorded cholinergic interneurons acquire characteristic responses to sensory stimuli during reward-related learning, including a pause and subsequent rebound in spiking. However, the precise underlying cellular mechanisms have remained elusive. Here, we review recent advances in our understanding of the regulation of cholinergic interneuron activity. We discuss evidence of mechanisms that have been proposed to underlie sensory responses, including antagonistic actions by dopamine, recurrent inhibition via local interneurons, and an intrinsically generated membrane hyperpolarization in response to excitatory inputs. The review highlights outstanding questions and concludes with a model of the sensory responses and their downstream effects through dynamic acetylcholine receptor activation.

Biology of Parkinson's disease: pathogenesis and pathophysiology of a multisystem neurodegenerative disorder

Parkinson's disease (PD) is the second most common movement disorder. The characteristic motor impairments - bradykinesia, rigidity, and resting tremor - result from degenerative loss of midbrain dopamine (DA) neurons in the substantia nigra, and are responsive to symptomatic treatment with dopaminergic medications and functional neurosurgery. PD is also the second most common neurodegenerative disorder. Viewed from this perspective, PD is a disorder of multiple functional systems, not simply the motor system, and of multiple neurotransmitter systems, not merely that of DA. The characteristic pathology - intraneuronal Lewy body inclusions and reduced numbers of surviving neurons - is similar in each of the targeted neuron groups, suggesting a common neurodegenerative process. Pathological and experimental studies indicate that oxidative stress, proteolytic stress, and inflammation figure prominently in the pathogenesis of PD. Yet, whether any of these mechanisms plays a causal role in human PD is unknown, because to date we have no proven neuroprotective therapies that slow or reverse disease progression in patients with PD. We are beginning to understand the pathophysiology of motor dysfunction in PD, but its etiopathogenesis as a neurodegenerative disorder remains poorly understood.

Variation in brain regions associated with fear and learning in contrasting climates

In environments where resources are difficult to obtain and enhanced cognitive capabilities might be adaptive, brain structures associated with cognitive traits may also be enhanced. In our previous studies, we documented a clear and significant relationship among environmental conditions, memory and hippocampal structure using ten populations of black-capped chickadees (Poecile atricapillus) over a large geographic range. In addition, focusing on just the two populations from the geographical extremes of our large-scale comparison, Alaska and Kansas, we found enhanced problem-solving capabilities and reduced neophobia in a captive-raised population of black-capped chickadees originating from the energetically demanding environment (Alaska) relative to conspecifics from the milder environment (Kansas). Here, we focused on three brain regions, the arcopallium (AP), the nucleus taeniae of the amygdala and the lateral striatum (LSt), that have been implicated to some extent in aspects of these behaviors in order to investigate whether potential differences in these brain areas may be associated with our previously detected differences in cognition. We compared the variation in neuron number and volumes of these regions between these populations, in both wild-caught birds and captive-raised individuals. Consistent with our behavioral observations, wild-caught birds from Kansas had a larger AP volume than their wild-caught conspecifics from Alaska, which possessed a higher density of neurons in the LSt. However, there were no other significant differences between populations in the wild-caught and captive-raised groups. Interestingly, individuals from the wild had larger LSt and AP volumes with more neurons than those raised in captivity. Overall, we provide some evidence that population-related differences in problem solving and neophobia may be associated with differences in volume and neuron numbers of our target brain regions. However, the relationship is not completely clear, and our study raises numerous questions about the relationship between the brain and behavior, especially in captive animals.

Dorsal-striatal 5-HT₂A and 5-HT₂C receptors control impulsivity and perseverative responding in the 5-choice serial reaction time task

RATIONAL

Prefrontal cortex (PFC) and dorsal striatum are part of the neural circuit critical for executive attention. The relationship between 5-HT and aspects of attention and executive control is complex depending on experimental conditions and the level of activation of different 5-HT receptors within the nuclei of corticostriatal circuitry.

OBJECTIVE

The present study investigated which 5-HT(2A) and 5-HT(2C) receptors in the dorsomedial-striatum (dm-STR) contribute to executive attention deficit induced by blockade of NMDA receptors in the PFC.

MATERIALS AND RESULTS

Executive attention was assessed by the five-choice serial reaction time task (5-CSRTT), which provides indices of attention (accuracy) and those of executive control over performance such as premature (an index of impulsivity) and perseverative responding. The effects of targeted infusion in dm-STR of 100 and 300 ng/μl doses of the selective 5-HT(2A) antagonist M100907 and 1 and 3 μg/μl doses of 5-HT(2C) agonist Ro60-0175 was examined in animals injected with 50 ng/μl dose of a competitive NMDA receptor antagonist 3-(R)-2-carboxypiperazin-4-phosphonic acid (CPP) in the mPFC. Blockade of NMDA receptors impaired accuracy as well as executive control as shown by increased premature and perseverative responding. The CPP-induced premature and perseverative over-responding were dose-dependently prevented by both M100907 and Ro60-0175. Both drugs partially removed the CPP-induced accuracy deficit but only at the highest dose tested.

CONCLUSIONS

It is suggested that in the dorsal striatum, 5-HT by an action on 5-HT(2A) and 5-HT(2C) receptors may integrate the glutamate corticostriatal inputs critical for different aspects of the 5-CSRT task performance.

Putative cholinergic interneurons in the ventral and dorsal regions of the striatum have distinct roles in a two choice alternative association task

The striatum consists of GABAergic projection neurons and various types of interneurons. Despite their relative scarcity, these interneurons play a key role in information processing in the striatum. One such class of interneurons is the cholinergic tonically active neurons (TANs). In the dorsal striatum, TANs are traditionally considered to be responsive to events of motivational significance. However, in recent years, studies have suggested that TANs are not exclusively related to reward and reward-predicting stimuli, but may contribute to other processes, including responses to aversive stimuli, detecting the spatial location of stimuli and generating movement. Currently there is little data concerning TAN activity in the ventral striatum (VS) of behaving animals. Here, we simultaneously recorded neurons in the ventral and the dorsolateral (DLS) regions of the striatum while animals performed a two choice alternative association task. Our data show that a large percentage of the putative TANs in both regions responded around movement initiation and execution. The majority of these neurons exhibited directional selectivity which was stronger in DLS relative to VS. In addition, the preferred directions in VS were mostly contralateral to the recording site whereas the observed preferred directions in DLS were equally distributed contralaterally and ipsilaterally to the recording site. The most interesting difference between DLS and VS was that DLS TANs maintained activity alterations throughout the movement whereas TANs in VS exhibited short-lasting phasic activity alterations that were maintained throughout the movement by different neurons. Our findings suggest that coding of movement by TANs in both regions overlaps to some degree, yet the differences in response patterns support the notion that the TANs in DLS participate in the motor loop whereas TANs in VS convey event-related information such as movement initiation, movement direction, and end of movement.

The role of striatal tonically active neurons in reward prediction error signaling during instrumental task performance

The detection of differences between predictions and actual outcomes is important for associative learning and for selecting actions according to their potential future reward. There are reports that tonically active neurons (TANs) in the primate striatum may carry information about errors in the prediction of rewards. However, this property seems to be expressed in classical conditioning tasks but not during performance of an instrumental task. To address this issue, we recorded the activity of TANs in the putamen of two monkeys performing an instrumental task in which probabilistic rewarding outcomes were contingent on an action in block-design experiments. Behavioral evidence suggests that animals adjusted their performance according to the level of probability for reward on each trial block. We found that the TAN response to reward was stronger as the reward probability decreased; this effect was especially prominent on the late component of the pause-rebound pattern of typical response seen in these neurons. The responsiveness to reward omission was also increased with increasing reward probability, whereas there were no detectable effects on responses to the stimulus that triggered the movement. Overall, the modulation of TAN responses by reward probability appeared relatively weak compared with that observed previously in a probabilistic classical conditioning task using the same block design. These data indicate that instrumental conditioning was less effective at demonstrating prediction error signaling in TANs. We conclude that the sensitivity of the TAN system to reward probability depends on the specific learning situation in which animals experienced the stimulus-reward associations.

Inactivation of the putamen selectively impairs reward history-based action selection

Behavioral decisions and actions are directed to achieve specific goals and to obtain rewards and escape punishments. Previous studies involving the recording of neuronal activity suggest the involvement of the cerebral cortex, basal ganglia, and midbrain dopamine system in these processes. The value signal of the action options is represented in the striatum, updated by reward prediction errors, and used for selecting higher-value actions. However, it remains unclear whether dysfunction of the striatum leads to impairment of value-based action selection. The present study examined the effect of inactivation of the putamen via local injection of the GABA(A) receptor agonist muscimol in monkeys engaged in a manual reward-based multi-step choice task. The monkeys first searched a reward target from three alternatives, based on the previous one or two choices and their outcomes, and obtained a large reward; they then earned an additional reward by choosing the last rewarded target. Inactivation of the putamen impaired the ability of monkeys to make optimal choices during third trial in which they were required to choose a target different from those selected in the two previous trials by updating the values of the three options. The monkeys normally changed options if the last choice resulted in small reward (lose-shift) and stayed with the last choice if it resulted in large reward (win-stay). Task start time and movement time during individual trials became longer after putamen inactivation. But monkeys could control the motivation level depending on the reward value of individual trial types before and after putamen inactivation. These results support a view that the putamen is involved selectively and critically in neuronal circuits for reward history-based action selection.

Dopamine in motivational control: rewarding, aversive, and alerting

Midbrain dopamine neurons are well known for their strong responses to rewards and their critical role in positive motivation. It has become increasingly clear, however, that dopamine neurons also transmit signals related to salient but nonrewarding experiences such as aversive and alerting events. Here we review recent advances in understanding the reward and nonreward functions of dopamine. Based on this data, we propose that dopamine neurons come in multiple types that are connected with distinct brain networks and have distinct roles in motivational control. Some dopamine neurons encode motivational value, supporting brain networks for seeking, evaluation, and value learning. Others encode motivational salience, supporting brain networks for orienting, cognition, and general motivation. Both types of dopamine neurons are augmented by an alerting signal involved in rapid detection of potentially important sensory cues. We hypothesize that these dopaminergic pathways for value, salience, and alerting cooperate to support adaptive behavior.