Relationship between the corticostriatal terminals from areas 9 and 46, and those from area 8A, dorsal and rostral premotor cortex and area 24c: an anatomical substrate for cognition to action

A shared neural network for emotional expression and perception: an anatomical study in the macaque monkey

Over the past two decades, the insula has been described as the sensory “interoceptive cortex”. As a consequence, human brain imaging studies have focused on its role in the sensory perception of emotions. However, evidence from neurophysiological studies in non-human primates have shown that the insula is also involved in generating emotional and communicative facial expressions. In particular, a recent study demonstrated that electrical stimulation of the mid-ventral sector of the insula evoked affiliative facial expressions. The present study aimed to describe the cortical connections of this “affiliative field”. To this aim, we identified the region with electrical stimulation and injected neural tracers to label incoming and outgoing projections. Our results show that the insular field underlying emotional expression is part of a network involving specific frontal, cingulate, temporal, and parietal areas, as well as the amygdala, the basal ganglia, and thalamus, indicating that this sector of the insula is a site of integration of motor, emotional, sensory and social information. Together with our previous functional studies, this result challenges the classic view of the insula as a multisensory area merely reflecting bodily and internal visceral states. In contrast, it supports an alternative perspective; that the emotional responses classically attributed to the insular cortex are endowed with an enactive component intrinsic to each social and emotional behavior.

Dysfunctional Activation and Brain Network Profiles in Youth with Obsessive-Compulsive Disorder: A Focus on the Dorsal Anterior Cingulate during Working Memory

Brain network dysfunction is emerging as a central biomarker of interest in psychiatry, in large part, because psychiatric conditions are increasingly seen as disconnection syndromes. Understanding dysfunctional brain network profiles in task-active states provides important information on network engagement in an experimental context. This in turn may be predictive of many of the cognitive and behavioral deficits associated with complex behavioral phenotypes. Here we investigated brain network profiles in youth with obsessive-compulsive disorder (OCD), contrasting them with a group of age-comparable controls. Network interactions were assessed during simple working memory: in particular, we focused on the modulation by the dorsal anterior cingulate cortex (dACC) of cortical, striatal, and thalamic regions. The focus on the dACC was motivated by its hypothesized role in the pathophysiology of OCD. However, its task-active network signatures have not been investigated before. Network interactions were modeled using psychophysiological interaction, a simple directional model of seed to target brain interactions. Our results indicate that OCD is characterized by significantly increased dACC modulation of cortical, striatal, and thalamic targets during working memory, and that this aberrant increase in OCD patients is maintained regardless of working memory demand. The results constitute compelling evidence of dysfunctional brain network interactions in OCD and suggest that these interactions may be related to a combination of network inefficiencies and dACC hyper-activity that has been associated with the phenotype.

The role of supplementary eye field in goal-directed behavior

The medial frontal cortex has been suggested to play a role in the control, monitoring, and selection of behavior. The supplementary eye field (SEF) is a cortical area within medial frontal cortex that is involved in the regulation of eye movements. Neurophysiological studies in the SEF of macaque monkeys have systematically investigated the role of SEF in various behavioral control and monitoring functions. Inhibitory control studies indicate that SEF neurons do not directly participate in the initiation of eye movements. Instead, recent value-based decision making studies suggest that the SEF participates in the control of eye movements by representing the context-dependent action values of all currently possible oculomotor behaviors. These action value signals in SEF would be useful in directing the activity distribution in more primary oculomotor areas, to guide decisions towards behaviorally optimal choices. SEF also does not participate in the fast, inhibitory control of eye movements in response to sudden changes in the task requirements. Instead, it participates in the long-term regulation of oculomotor excitability to adjust the speed-accuracy tradeoff. The context-dependent control signals found in SEF (including the action value signals) have to be learned and continuously adjusted in response to changes in the environment. This is likely the function of the large number of different response monitoring and evaluation signals in SEF. In conclusion, the overall function of SEF in goal-directed behavior seems to be the learning of context-dependent rules that allow predicting the likely consequences of different eye movements. This map of action value signals could be used so that eye movements are selected that best fulfill the current long-term goal of the agent.

Tricyclic antidepressant treatment evokes regional changes in neurotrophic factors over time within the intact and degenerating nigrostriatal system

In addition to alleviating depression, trophic responses produced by antidepressants may regulate neural plasticity in the diseased brain, which not only provides symptomatic benefit but also potentially slows the rate of disease progression in Parkinson's disease (PD). Recent in vitro and in vivo data provide evidence that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) may be key mediators of the therapeutic response to antidepressants. As such, we conducted a cross-sectional time-course study to determine whether antidepressant-mediated changes in neurotrophic factors occur in relevant brain regions in response to amitriptyline (AMI) treatment before and after intrastriatal 6-hydroxydopamine (6OHDA). Adult male Wistar rats were divided into seven cohorts and given daily injections (i.p.) of AMI (5mg/kg) or saline throughout the duration of the study. In parallel, various cohorts of intact or parkinsonian animals were sacrificed at specific time points to determine the impact of AMI treatment on trophic factor levels in the intact and degenerating nigrostriatal system. The left and right hemispheres of the substantia nigra, striatum, frontal cortex, piriform cortex, hippocampus, and anterior cingulate cortex were dissected, and BDNF and GDNF levels were measured with ELISA. Results show that chronic AMI treatment elicits effects in multiple brain regions and differentially regulates levels of BDNF and GDNF depending on the region. Additionally, AMI halts the progressive degeneration of dopamine (DA) neurons elicited by an intrastriatal 6-OHDA lesion. Taken together, these results suggest that AMI treatment elicits significant trophic changes important to DA neuron survival within both the intact and degenerating nigrostriatal system.

Comparative diffusion tractography of corticostriatal motor pathways reveals differences between humans and macaques

The primate corticobasal ganglia circuits are understood to be segregated into parallel anatomically and functionally distinct loops. Anatomical and physiological studies in macaque monkeys are summarized as showing that an oculomotor loop begins with projections from the frontal eye fields (FEF) to the caudate nucleus, and a motor loop begins with projections from the primary motor cortex (M1) to the putamen. However, recent functional and structural neuroimaging studies of the human corticostriatal system report evidence inconsistent with this organization. To obtain conclusive evidence, we directly compared the pattern of connectivity between cortical motor areas and the striatum in humans and macaques in vivo using probabilistic diffusion tractography. In macaques we found that FEF is connected with the head of the caudate and anterior putamen, and M1 is connected with more posterior sections of the caudate and putamen, corroborating neuroanatomical tract tracing findings. However, in humans FEF and M1 are connected to largely overlapping portions of posterior putamen and only a small portion of the caudate. These results demonstrate that the corticobasal connectivity for the oculomotor and primary motor loop is not entirely segregated for primates at a macroscopic level and that the description of the anatomical connectivity of corticostriatal motor systems in humans does not parallel that of macaques, perhaps because of an expansion of prefrontal projections to striatum in humans.

Striatal shape abnormalities as novel neurodevelopmental endophenotypes in schizophrenia: a longitudinal study

There are varying, often conflicting, reports with respect to altered striatal volume and morphometry in the major psychoses due to the influences of antipsychotic medications on striatal volume. Thus, disassociating disease effects from those of medication become exceedingly difficult. For the first time, using a longitudinally studied sample of structural magnetic resonance images from patients with childhood onset schizophrenia (COS; neurobiologically contiguous with the adult onset form of schizophrenia), their nonpsychotic siblings (COSSIBs), and novel shape mapping algorithms that are volume independent, we report the familial contribution of striatal morphology in schizophrenia. The results of our volumetric analyses demonstrate age-related increases in overall striatal volumes specific only to COS. However, both COS and COSSIBs showed overlapping shape differences in the striatal head, which normalized in COSSIBs by late adolescence. These results mirror previous studies from our group, demonstrating cortical thickness deficits in COS and COSSIBs as these deficits normalize in COSSIBs in the same age range as our striatal findings. Finally, there is a single region of nonoverlapping outward displacement in the dorsal aspect of the caudate body, potentially indicative of a response to medication. Striatal shape may be considered complimentary to volume as an endophenotype, and, in some cases may provide information that is not detectable using standard volumetric techniques. Our striatal shape findings demonstrate the striking localization of abnormalities in striatal the head. The neuroanatomical localization of these findings suggest the presence of abnormalities in the striatal-prefrontal circuits in schizophrenia and resilience mechanisms in COSSIBs with age dependent normalization.

The place of dopamine in the cortico-basal ganglia circuit

The midbrain dopamine (DA) neurons play a central role in developing appropriate goal-directed behaviors, including the motivation and cognition to develop appropriate actions to obtain a specific outcome. Indeed, subpopulations of DA neurons have been associated with these different functions: the mesolimbic, mesocortical, and nigrostriatal pathways. The mesolimbic and nigrostriatal pathways are an integral part of the basal ganglia through its reciprocal connections to the ventral and dorsal striatum respectively. This chapter reviews the connections of the midbrain DA cells and their role in integrating information across limbic, cognitive and motor functions. Emphasis is placed on the interface between these functional domains within the striatum through corticostriatal connections, through the striato-nigro-striatal connection, and through the lateral habenula projection to the midbrain.

Neural substrates of impulsive decision making modulated by modafinil in alcohol-dependent patients

BACKGROUND

Impulsive decision making is a hallmark of frequently occurring addiction disorders including alcohol dependence (AD). Therefore, ameliorating impulsive decision making is a promising target for the treatment of AD. Previous studies have shown that modafinil enhances cognitive control functions in various psychiatric disorders. However, the effects of modafinil on delay discounting and its underlying neural correlates have not been investigated as yet. The aim of the current study was to investigate the effects of modafinil on neural correlates of impulsive decision making in abstinent AD patients and healthy control (HC) subjects.

METHOD

A randomized, double-blind, placebo-controlled, within-subjects cross-over study using functional magnetic resonance imaging (fMRI) was conducted in 14 AD patients and 16 HC subjects. All subjects participated in two fMRI sessions in which they either received a single dose of placebo or 200 mg of modafinil 2 h before the session. During fMRI, subjects completed a delay-discounting task to measure impulsive decision making.

RESULTS

Modafinil improved impulsive decision making in AD pateints, which was accompanied by enhanced recruitment of frontoparietal regions and reduced activation of the ventromedial prefrontal cortex. Moreover, modafinil-induced enhancement of functional connectivity between the superior frontal gyrus and ventral striatum was specifically associated with improvement in impulsive decision making.

CONCLUSIONS

These findings indicate that modafinil can improve impulsive decision making in AD patients through an enhanced coupling of prefrontal control regions and brain regions coding the subjective value of rewards. Therefore, the current study supports the implementation of modafinil in future clinical trials for AD.

Estimates of projection overlap and zones of convergence within frontal-striatal circuits

Frontal-striatal circuits underlie important decision processes, and pathology in these circuits is implicated in many psychiatric disorders. Studies have shown a topographic organization of cortical projections into the striatum. However, work has also shown that there is considerable overlap in the striatal projection zones of nearby cortical regions. To characterize this in detail, we quantified the complete striatal projection zones from 34 cortical injection locations in rhesus monkeys. We first fit a statistical model that showed that the projection zone of a cortical injection site could be predicted with considerable accuracy using a cross-validated model estimated on only the other injection sites. We then examined the fraction of overlap in striatal projection zones as a function of distance between cortical injection sites, and found that there was a highly regular relationship. Specifically, nearby cortical locations had as much as 80% overlap, and the amount of overlap decayed exponentially as a function of distance between the cortical injection sites. Finally, we found that some portions of the striatum received inputs from all the prefrontal regions, making these striatal zones candidates as information-processing hubs. Thus, the striatum is a site of convergence that allows integration of information spread across diverse prefrontal cortical areas.

Function of basal ganglia in bridging cognitive and motor modules to perform an action

The basal ganglia (BG) are thought to be involved in the integration of multiple sources of information, and their dysfunction can lead to disorders such as Parkinson's disease (PD). PD patients show motor and cognitive dysfunction with specific impairments in the internal generation of motor actions and executive deficits, respectively. The role of the BG, then, would be to integrate information from several sources in order to make a decision on a resulting action adequate for the required task. Reanalyzing the data set from our previous study (Martinu et al., 2012), we investigated this hypothesis by applying a graph theory method to a series of fMRI data during the performance of self-initiated (SI) finger movement tasks obtained in healthy volunteers (HV) and early stage PD patients. Dorsally, connectivity strength between the medial prefrontal areas (mPFC) and cortical regions including the primary motor area (M1), the extrastriate visual cortex, and the associative cortex, was reduced in the PD patients. The connectivity strengths were positively correlated to activity in the striatum in both groups. Ventrally, all connectivity between the striatum, the thalamus, and the extrastriate visual cortex decreased in strength in the PD, as did the connectivity between the striatum and the ventrolateral PFC (VLPFC). Individual response time (RT) was negatively correlated to connectivity strength between the dorsolateral PFC (DLPFC) and the striatum and positively correlated to connectivity between the VLPFC and the striatum in the HV. These results indicate that the BG, with the mPFC and thalamus, are involved in integrating multiple sources of information from areas such as DLPFC, and VLPFC, connecting to M1, thereby determining a network that leads to the adequate decision and performance of the resulting action.

Brain mechanisms of acoustic communication in humans and nonhuman primates: An evolutionary perspective

Any account of “what is special about the human brain” (Passingham 2008) must specify the neural basis of our unique ability to produce speech and delineate how these remarkable motor capabilities could have emerged in our hominin ancestors. Clinical data suggest that the basal ganglia provide a platform for the integration of primate-general mechanisms of acoustic communication with the faculty of articulate speech in humans. Furthermore, neurobiological and paleoanthropological data point at a two-stage model of the phylogenetic evolution of this crucial prerequisite of spoken language: (i) monosynaptic refinement of the projections of motor cortex to the brainstem nuclei that steer laryngeal muscles, presumably, as part of a “phylogenetic trend” associated with increasing brain size during hominin evolution; (ii) subsequent vocal-laryngeal elaboration of cortico-basal ganglia circuitries, driven by human-specificFOXP2mutations.;>This concept implies vocal continuity of spoken language evolution at the motor level, elucidating the deep entrenchment of articulate speech into a “nonverbal matrix” (Ingold 1994), which is not accounted for by gestural-origin theories. Moreover, it provides a solution to the question for the adaptive value of the “first word” (Bickerton 2009) since even the earliest and most simple verbal utterances must have increased the versatility of vocal displays afforded by the preceding elaboration of monosynaptic corticobulbar tracts, giving rise to enhanced social cooperation and prestige. At the ontogenetic level, the proposed model assumes age-dependent interactions between the basal ganglia and their cortical targets, similar to vocal learning in some songbirds. In this view, the emergence of articulate speech builds on the “renaissance” of an ancient organizational principle and, hence, may represent an example of “evolutionary tinkering” (Jacob 1977).

Altered resting-state functional connectivity of striatal-thalamic circuit in bipolar disorder

Bipolar disorder is characterized by internally affective fluctuations. The abnormality of inherently mental state can be assessed using resting-state fMRI data without producing task-induced biases. In this study, we hypothesized that the resting-state connectivity related to the frontal, striatal, and thalamic regions, which were associated with mood regulations and cognitive functions, can be altered for bipolar disorder. We used the Pearson's correlation coefficients to estimate functional connectivity followed by the hierarchical modular analysis to categorize the resting-state functional regions of interest (ROIs). The selected functional connectivities associated with the striatal-thalamic circuit and default mode network (DMN) were compared between bipolar patients and healthy controls. Significantly decreased connectivity in the striatal-thalamic circuit and between the striatal regions and the middle and posterior cingulate cortex was observed in the bipolar patients. We also observed that the bipolar patients exhibited significantly increased connectivity between the thalamic regions and the parahippocampus. No significant changes of connectivity related to the frontal regions in the DMN were observed. The changed resting-state connectivity related to the striatal-thalamic circuit might be an inherent basis for the altered emotional and cognitive processing in the bipolar patients.

Brain tissue properties differentiate between motor and limbic basal ganglia circuits

Despite advances in understanding basic organizational principles of the human basal ganglia, accurate in vivo assessment of their anatomical properties is essential to improve early diagnosis in disorders with corticosubcortical pathology and optimize target planning in deep brain stimulation. Main goal of this study was the detailed topological characterization of limbic, associative, and motor subdivisions of the subthalamic nucleus (STN) in relation to corresponding corticosubcortical circuits. To this aim, we used magnetic resonance imaging and investigated independently anatomical connectivity via white matter tracts next to brain tissue properties. On the basis of probabilistic diffusion tractography we identified STN subregions with predominantly motor, associative, and limbic connectivity. We then computed for each of the nonoverlapping STN subregions the covariance between local brain tissue properties and the rest of the brain using high‐resolution maps of magnetization transfer (MT) saturation and longitudinal (R1) and transverse relaxation rate (R2*). The demonstrated spatial distribution pattern of covariance between brain tissue properties linked to myelin (R1 and MT) and iron (R2*) content clearly segregates between motor and limbic basal ganglia circuits. We interpret the demonstrated covariance pattern as evidence for shared tissue properties within a functional circuit, which is closely linked to its function. Our findings open new possibilities for investigation of changes in the established covariance pattern aiming at accurate diagnosis of basal ganglia disorders and prediction of treatment outcome. Hum Brain Mapp 35:5083–5092, 2014. © 2014 The Authors. Human Brain Mapping Published by Wiley Periodicals, Inc.

Representation of outcome risk and action in the anterior caudate nucleus

The anterior caudate nucleus is essential for goal-directed behavior because it links outcome information to actions. It is well known that caudate neurons provide a variety of reward-related and action signals. However, it is still unclear how the two signals are integrated. We investigated whether and how outcome risk modulates spatial representation. We recorded neural activity in the anterior caudate nucleus while monkeys made saccades to multiple spatial targets, each associated with either fixed (safe) or variable (risky) amount of reward. We report that individual neurons combined the outcome reward signal with spatial information about the direction of saccades. These signals could be reliably read out from the populations of neurons. Moreover, the prospect of a risky outcome improved the quality of spatial information. These results provide direct evidence that global spatial representation in the caudate is modulated by outcome, which can be important for flexible control of behavior, particularly during learning and habit formation, when outcomes vary.

Dysfunction and Dysconnection in Cortical-Striatal Networks during Sustained Attention: Genetic Risk for Schizophrenia or Bipolar Disorder and its Impact on Brain Network Function

Abnormalities in the brain's attention network may represent early identifiable neurobiological impairments in individuals at increased risk for schizophrenia or bipolar disorder. Here, we provide evidence of dysfunctional regional and network function in adolescents at higher genetic risk for schizophrenia or bipolar disorder [henceforth higher risk (HGR)]. During fMRI, participants engaged in a sustained attention task with variable demands. The task alternated between attention (120 s), visual control (passive viewing; 120 s), and rest (20 s) epochs. Low and high demand attention conditions were created using the rapid presentation of two- or three-digit numbers. Subjects were required to detect repeated presentation of numbers. We demonstrate that the recruitment of cortical and striatal regions are disordered in HGR: relative to typical controls (TC), HGR showed lower recruitment of the dorsal prefrontal cortex, but higher recruitment of the superior parietal cortex. This imbalance was more dramatic in the basal ganglia. There, a group by task demand interaction was observed, such that increased attention demand led to increased engagement in TC, but disengagement in HGR. These activation studies were complemented by network analyses using dynamic causal modeling. Competing model architectures were assessed across a network of cortical-striatal regions, distinguished at a second level using random-effects Bayesian model selection. In the winning architecture, HGR were characterized by significant reductions in coupling across both frontal-striatal and frontal-parietal pathways. The effective connectivity analyses indicate emergent network dysconnection, consistent with findings in patients with schizophrenia. Emergent patterns of regional dysfunction and dysconnection in cortical-striatal pathways may provide functional biological signatures in the adolescent risk-state for psychiatric illness.

Computational models of basal-ganglia pathway functions: focus on functional neuroanatomy

Over the past 15 years, computational models have had a considerable impact on basal-ganglia research. Most of these models implement multiple distinct basal-ganglia pathways and assume them to fulfill different functions. As there is now a multitude of different models, it has become complex to keep track of their various, sometimes just marginally different assumptions on pathway functions. Moreover, it has become a challenge to oversee to what extent individual assumptions are corroborated or challenged by empirical data. Focusing on computational, but also considering non-computational models, we review influential concepts of pathway functions and show to what extent they are compatible with or contradict each other. Moreover, we outline how empirical evidence favors or challenges specific model assumptions and propose experiments that allow testing assumptions against each other.

Cognitive control over learning: creating, clustering, and generalizing task-set structure

Learning and executive functions such as task-switching share common neural substrates, notably prefrontal cortex and basal ganglia. Understanding how they interact requires studying how cognitive control facilitates learning but also how learning provides the (potentially hidden) structure, such as abstract rules or task-sets, needed for cognitive control. We investigate this question from 3 complementary angles. First, we develop a new context-task-set (C-TS) model, inspired by nonparametric Bayesian methods, specifying how the learner might infer hidden structure (hierarchical rules) and decide to reuse or create new structure in novel situations. Second, we develop a neurobiologically explicit network model to assess mechanisms of such structured learning in hierarchical frontal cortex and basal ganglia circuits. We systematically explore the link between these modeling levels across task demands. We find that the network provides an approximate implementation of high-level C-TS computations, with specific neural mechanisms modulating distinct C-TS parameters. Third, this synergism yields predictions about the nature of human optimal and suboptimal choices and response times during learning and task-switching. In particular, the models suggest that participants spontaneously build task-set structure into a learning problem when not cued to do so, which predicts positive and negative transfer in subsequent generalization tests. We provide experimental evidence for these predictions and show that C-TS provides a good quantitative fit to human sequences of choices. These findings implicate a strong tendency to interactively engage cognitive control and learning, resulting in structured abstract representations that afford generalization opportunities and, thus, potentially long-term rather than short-term optimality.

The role of the striatum in social behavior

Where and how does the brain code reward during social behavior? Almost all elements of the brain's reward circuit are modulated during social behavior. The striatum in particular is activated by rewards in social situations. However, its role in social behavior is still poorly understood. Here, we attempt to review its participation in social behaviors of different species ranging from voles to humans. Human fMRI experiments show that the striatum is reliably active in relation to others' rewards, to reward inequity and also while learning about social agents. Social contact and rearing conditions have long-lasting effects on behavior, striatal anatomy and physiology in rodents and primates. The striatum also plays a critical role in pair-bond formation and maintenance in monogamous voles. We review recent findings from single neuron recordings showing that the striatum contains cells that link own reward to self or others' actions. These signals might be used to solve the agency-credit assignment problem: the question of whose action was responsible for the reward. Activity in the striatum has been hypothesized to integrate actions with rewards. The picture that emerges from this review is that the striatum is a general-purpose subcortical region capable of integrating social information into coding of social action and reward.

Exploring the cognitive and motor functions of the basal ganglia: an integrative review of computational cognitive neuroscience models

Many computational models of the basal ganglia (BG) have been proposed over the past twenty-five years. While computational neuroscience models have focused on closely matching the neurobiology of the BG, computational cognitive neuroscience (CCN) models have focused on how the BG can be used to implement cognitive and motor functions. This review article focuses on CCN models of the BG and how they use the neuroanatomy of the BG to account for cognitive and motor functions such as categorization, instrumental conditioning, probabilistic learning, working memory, sequence learning, automaticity, reaching, handwriting, and eye saccades. A total of 19 BG models accounting for one or more of these functions are reviewed and compared. The review concludes with a discussion of the limitations of existing CCN models of the BG and prescriptions for future modeling, including the need for computational models of the BG that can simultaneously account for cognitive and motor functions, and the need for a more complete specification of the role of the BG in behavioral functions.

Relationship of resting brain hyperconnectivity and schizophrenia-like symptoms produced by the NMDA receptor antagonist ketamine in humans

N-methyl-D-aspartate glutamate receptor (NMDA-R) antagonists produce schizophrenia-like positive and negative symptoms in healthy human subjects. Preclinical research suggests that NMDA-R antagonists interfere with the function of gamma-aminobutyric acid (GABA) neurons and alter the brain oscillations. These changes have been hypothesized to contribute to psychosis. In this investigation, we evaluated the hypothesis that the NMDA-R antagonist ketamine produces alterations in cortical functional connectivity during rest that are related to symptoms. We administered ketamine to a primary sample of 22 subjects and to an additional, partially overlapping, sample of 12 subjects. Symptoms before and after the experimental session were rated with the Positive and Negative Syndrome Scale (PANSS). In the primary sample, functional connectivity was measured via functional magnetic resonance imaging almost immediately after infusion began. In the additional sample, this assessment was repeated after 45 min of continuous ketamine infusion. Global, enhanced functional connectivity was observed at both timepoints, and this hyperconnectivity was related to symptoms in a region-specific manner. This study supports the hypothesis that pathological increases in resting brain functional connectivity contribute to the emergence of positive and negative symptoms associated with schizophrenia.

Activity of striatal neurons reflects social action and own reward

Social interactions provide agents with the opportunity to earn higher benefits than when acting alone and contribute to evolutionary stable strategies. A basic requirement for engaging in beneficial social interactions is to recognize the actor whose movement results in reward. Despite the recent interest in the neural basis of social interactions, the neurophysiological mechanisms identifying the actor in social reward situations are unknown. A brain structure well suited for exploring this issue is the striatum, which plays a role in movement, reward, and goal-directed behavior. In humans, the striatum is involved in social processes related to reward inequity, donations to charity, and observational learning. We studied the neurophysiology of social action for reward in rhesus monkeys performing a reward-giving task. The behavioral data showed that the animals distinguished between their own and the conspecific's reward and knew which individual acted. Striatal neurons coded primarily own reward but rarely other's reward. Importantly, the activations occurred preferentially, and in approximately similar fractions, when either the own or the conspecific's action was followed by own reward. Other striatal neurons showed social action coding without reward. Some of the social action coding disappeared when the conspecific's role was simulated by a computer, confirming a social rather than observational relationship. These findings demonstrate a role of striatal neurons in identifying the social actor and own reward in a social setting. These processes may provide basic building blocks underlying the brain's function in social interactions.

Neurons in the basal forebrain project to the cortex in a complex topographic organization that reflects corticocortical connectivity patterns: an experimental study based on retrograde tracing and 3D reconstruction

The most prominent feature of the Basal Forebrain (BF) is the collection of large cortically projecting neurons (basal nucleus of Meynert) that serve as the primary source of cholinergic input to the entire cortical mantle. Despite its broad involvement in cortical activation, attention, and memory, the functional details of the BF are not well understood due to the anatomical complexity of the region. This study tested the hypothesis that basalocortical connections reflect cortical connectivity patterns. Distinct retrograde tracers were deposited into various frontal and posterior cortical areas, and retrogradely labeled cholinergic and noncholinergic neurons were mapped in the BF. Concurrently, we mapped retrogradely labeled cells in posterior cortical areas that project to various frontal areas, and all cell populations were combined in the same coordinate system. Our studies suggest that the cholinergic and noncholinergic projections to the neocortex are not diffuse, but instead, are organized into segregated or overlapping pools of projection neurons. The extent of overlap between BF populations projecting to the cortex depends on the degree of connectivity between the cortical targets of these projection populations. We suggest that the organization of projections from the BF may enable parallel modulation of multiple groupings of interconnected yet nonadjacent cortical areas.

Role of the striatum in language: Syntactic and conceptual sequencing

The basal ganglia (BG) have long been associated with cognitive control, and it is widely accepted that they also subserve an indirect, control role in language. Nevertheless, it cannot be completely ruled out that the BG may be involved in language in some domain-specific manner. The present study aimed to investigate one type of cognitive control-sequencing, a function that has long been connected with the BG-and to test whether the BG could be specifically implicated in language. Participants were required to rearrange materials sequentially based on linguistic (syntactic or conceptual) or non-linguistic (order switching) rules, or to repeat a previously ordered sequence as a control task. Functional magnetic resonance imaging (fMRI) data revealed a strongly active left-lateralized corticostriatal network, encompassing the anterior striatum, dorsolaterial and ventrolateral prefrontal cortex and presupplementary motor area, while the participants were sequencing materials using linguistic vs. non-linguistic rules. This functional network has an anatomical basis and is strikingly similar to the well-known associative loop implicated in sensorimotor sequence learning. We concluded that the anterior striatum has extended its original sequencing role and worked in concert with frontal cortical regions to subserve the function of linguistic sequencing in a domain-specific manner.

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.

The relationship between antipsychotic D2 occupancy and change in frontal metabolism and working memory : A dual [(11)C]raclopride and [(18) F]FDG imaging study with aripiprazole

RATIONALE

The effects of aripiprazole on cognitive function are obscure, possibly due to the difficulty in disentangling the specific effects on cognitive function from effects secondary to the improvement of other schizophrenic symptoms. This prompts the necessity of using an intermediate biomarker relating the drug effect on the brain to change in cognitive function.

OBJECTIVES

To explore the effect of aripiprazole on cognitive function, we measured changes in frontal metabolism as an intermediate biomarker and sought to determine its relationship with D2 receptor occupancy and changes in working memory.

METHODS

Fifteen healthy male volunteers participated in the study. Serial positron emission tomography (PET) scans with [(11)C]raclopride and [(18) F]FDG were conducted 1 day before and 2 days after the administration of aripiprazole. The subjects performed the N-back task just after finishing the [(18) F]FDG scan.

RESULTS

The mean (±SD) D2 receptor occupancies were 22.2 ± 16.0 % in the 2 mg group, 35.5 ± 3.6 % in the 5 mg group, 63.2 ± 9.9 % in the 10 mg group and 72.8 ± 2.1 % in the 30 mg group. The frontal metabolism was significantly decreased after the administration of aripiprazole (t = 2.705, df = 14, p = 0.017). Greater striatal D2 receptor occupancy was related to greater decrease in frontal metabolism (r = -0.659, p = 0.010), and greater reduction in frontal metabolism was associated with longer reaction times (r = -0.597, p = 0.019) under the greatest task load.

CONCLUSIONS

Aripiprazole can affect cognitive function and alter frontal metabolic function. The changes in these functions are linked to greater D2 receptor occupancy. This suggests that it may be important to find the lowest effective dose of aripiprazole in order to prevent adverse cognitive effects.

The rat prefrontostriatal system analyzed in 3D: evidence for multiple interacting functional units

Previous studies in monkeys disclosed a specific arrangement of corticostriatal projections. Prefrontal and premotor areas form dense projection fields surrounded by diffuse terminal areas extending outside the densely innervated region and overlapping with projections from other areas. In this study, the mode of prefrontostriatal innervation was analyzed in rats using a 3D approach. Following injections of tracers in defined cortical areas, 3D maps from individual cases were elaborated and combined into a global 3D map allowing us to define putative overlaps between projection territories. In addition to providing a detailed 3D mapping of the topographic representation of prefrontal cortical areas in the rat striatum, the results stress important similarities between the rodent and primate prefrontostriatal projections. They share the dual pattern of focal and diffuse corticostriatal projections. Moreover, besides segregated projections consistent with parallel processing, the interweaving of projection territories establishes specific patterns of overlaps spatially organized along the dorsoventral, mediolateral, and anteroposterior striatal axis. In particular, the extensive striatal projection fields from the prelimbic and anterior cingulate areas, which partly overlap the terminal fields from medial, orbital, and lateral prefrontal cortical areas, provide putative domains of convergence for integration between reward, cognitive, and motor processes.

Connectivity-based functional analysis of dopamine release in the striatum using diffusion-weighted MRI and positron emission tomography

The striatum acts in conjunction with the cortex to control and execute functions that are impaired by abnormal dopamine neurotransmission in disorders such as Parkinson's and schizophrenia. To date, in vivo quantification of striatal dopamine has been restricted to structure-based striatal subdivisions. Here, we present a multimodal imaging approach that quantifies the endogenous dopamine release following the administration of d-amphetamine in the functional subdivisions of the striatum of healthy humans with [(11)C]PHNO and [(11)C]Raclopride positron emission tomography ligands. Using connectivity-based (CB) parcellation, we subdivided the striatum into functional subregions based on striato-cortical anatomical connectivity information derived from diffusion magnetic resonance imaging (MRI) and probabilistic tractography. Our parcellation showed that the functional organization of the striatum was spatially coherent across individuals, congruent with primate data and previous diffusion MRI studies, with distinctive and overlapping networks. d-amphetamine induced the highest dopamine release in the limbic followed by the sensory, motor, and executive areas. The data suggest that the relative regional proportions of D2-like receptors are unlikely to be responsible for this regional dopamine release pattern. Notably, the homogeneity of dopamine release was significantly higher within the CB functional subdivisions in comparison with the structural subdivisions. These results support an association between local levels of dopamine release and cortical connectivity fingerprints.

The neuropathology of autism

Autism is a behaviorally defined neurodevelopmental disorder that affects over 1% of new births in the United States and about 2% of boys. The etiologies are unknown and they are genetically complex. There may be epigenetic effects, environmental influences, and other factors that contribute to the mechanisms and affected neural pathway(s). The underlying neuropathology of the disorder has been evolving in the literature to include specific brain areas in the cerebellum, limbic system, and cortex. Part(s) of structures appear to be affected most rather than the entire structure, for example, select nuclei of the amygdala, the fusiform face area, and so forth. Altered cortical organization characterized by more frequent and narrower minicolumns and early overgrowth of the frontal portion of the brain, affects connectivity. Abnormalities include cytoarchitectonic laminar differences, excess white matter neurons, decreased numbers of GABAergic cerebellar Purkinje cells, and other events that can be traced developmentally and cause anomalies in circuitry. Problems with neurotransmission are evident by recent receptor and binding site studies especially in the inhibitory GABA system likely contributing to an imbalance of excitatory/inhibitory transmission. As postmortem findings are related to core behavior symptoms, and technology improves, researchers are gaining a much better perspective of contributing factors to the disorder.

Neural activity in the macaque putamen associated with saccades and behavioral outcome

It is now widely accepted that the basal ganglia nuclei form segregated, parallel loops with neocortical areas. The prevalent view is that the putamen is part of the motor loop, which receives inputs from sensorimotor areas, whereas the caudate, which receives inputs from frontal cortical eye fields and projects via the substantia nigra pars reticulata to the superior colliculus, belongs to the oculomotor loop. Tracer studies in monkeys and functional neuroimaging studies in human subjects, however, also suggest a potential role for the putamen in oculomotor control. To investigate the role of the putamen in saccadic eye movements, we recorded single neuron activity in the caudal putamen of two rhesus monkeys while they alternated between short blocks of pro- and anti-saccades. In each trial, the instruction cue was provided after the onset of the peripheral stimulus, thus the monkeys could either generate an immediate response to the stimulus based on the internal representation of the rule from the previous trial, or alternatively, could await the visual rule-instruction cue to guide their saccadic response. We found that a subset of putamen neurons showed saccade-related activity, that the preparatory mode (internally- versus externally-cued) influenced the expression of task-selectivity in roughly one third of the task-modulated neurons, and further that a large proportion of neurons encoded the outcome of the saccade. These results suggest that the caudal putamen may be part of the neural network for goal-directed saccades, wherein the monitoring of saccadic eye movements, context and performance feedback may be processed together to ensure optimal behavioural performance and outcomes are achieved during ongoing behaviour.

Epidural cortical stimulation of the left dorsolateral prefrontal cortex for refractory major depressive disorder

BACKGROUND

A significant number of patients with major depressive disorder are unresponsive to conventional therapies. For these patients, neuromodulation approaches are being investigated.

OBJECTIVE

To determine whether epidural cortical stimulation at the left dorsolateral prefrontal cortex is safe and efficacious for major depressive disorder through a safety and feasibility study.

METHODS

Twelve patients were recruited in this randomized, single-blind, sham-controlled study with a 104-week follow-up period. The main outcome measures were Hamilton Depression Rating Scale-28 (HDRS), Montgomery-Asberg Depression Rating Scale (MADRS), Global Assessment of Function (GAF), and Quality of Life Enjoyment and Satisfaction (QLES) questionnaire. An electrode was implanted over Brodmann area 9/46 in the left hemisphere. The electrode provided long-term stimulation to this target via its connections to an implanted neurostimulator in the chest.

RESULTS

During the sham-controlled phase, there was no statistical difference between sham and active stimulation, although a trend toward efficacy was seen with the active stimulation group. In the open-label phase, we observed a significant improvement in outcome scores for the HDRS, MADRS, and GAF but not the QLES (HDRS: df = 7, F = 7.72, P < .001; MADRS: df = 7, F = 8.2, P < .001; GAF: df = 5, F = 16.87, P < .001; QLES: df = 5, F = 1.32, P > .2; repeated measures ANOVA). With regard to the HDRS, 6 patients had ≥ 40% improvement, 5 patients had ≥ 50% improvement, and 4 subjects achieved remission (HDRS < 10) at some point during the study.

CONCLUSION

Epidural cortical stimulation of the left dorsolateral prefrontal cortex appears to be a safe and potentially efficacious neuromodulation approach for treatment-refractory major depressive disorder.

The organization of the human striatum estimated by intrinsic functional connectivity

The striatum is connected to the cerebral cortex through multiple anatomical loops that process sensory, limbic, and heteromodal information. Tract-tracing studies in the monkey reveal that these corticostriatal connections form stereotyped patterns in the striatum. Here the organization of the striatum was explored in the human with resting-state functional connectivity MRI (fcMRI). Data from 1,000 subjects were registered with nonlinear deformation of the striatum in combination with surface-based alignment of the cerebral cortex. fcMRI maps derived from seed regions placed in the foot and tongue representations of the motor cortex yielded the expected inverted somatotopy in the putamen. fcMRI maps derived from the supplementary motor area were located medially to the primary motor representation, also consistent with anatomical studies. The topography of the complete striatum was estimated and replicated by assigning each voxel in the striatum to its most strongly correlated cortical network in two independent groups of 500 subjects. The results revealed at least five cortical zones in the striatum linked to sensorimotor, premotor, limbic, and two association networks with a topography globally consistent with monkey anatomical studies. The majority of the human striatum was coupled to cortical association networks. Examining these association networks further revealed details that fractionated the five major networks. The resulting estimates of striatal organization provide a reference for exploring how the striatum contributes to processing motor, limbic, and heteromodal information through multiple large-scale corticostriatal circuits.

Supplementary eye field encodes reward prediction error

The outcomes of many decisions are uncertain and therefore need to be evaluated. We studied this evaluation process by recording neuronal activity in the supplementary eye field (SEF) during an oculomotor gambling task. While the monkeys awaited the outcome, SEF neurons represented attributes of the chosen option, namely, its expected value and the uncertainty of this value signal. After the gamble result was revealed, a number of neurons reflected the actual reward outcome. Other neurons evaluated the outcome by encoding the difference between the reward expectation represented during the delay period and the actual reward amount (i.e., the reward prediction error). Thus, SEF encodes not only reward prediction error but also all the components necessary for its computation: the expected and the actual outcome. This suggests that SEF might actively evaluate value-based decisions in the oculomotor domain, independent of other brain regions.

Mechanisms of hierarchical reinforcement learning in corticostriatal circuits 1: computational analysis

Growing evidence suggests that the prefrontal cortex (PFC) is organized hierarchically, with more anterior regions having increasingly abstract representations. How does this organization support hierarchical cognitive control and the rapid discovery of abstract action rules? We present computational models at different levels of description. A neural circuit model simulates interacting corticostriatal circuits organized hierarchically. In each circuit, the basal ganglia gate frontal actions, with some striatal units gating the inputs to PFC and others gating the outputs to influence response selection. Learning at all of these levels is accomplished via dopaminergic reward prediction error signals in each corticostriatal circuit. This functionality allows the system to exhibit conditional if-then hypothesis testing and to learn rapidly in environments with hierarchical structure. We also develop a hybrid Bayesian-reinforcement learning mixture of experts (MoE) model, which can estimate the most likely hypothesis state of individual participants based on their observed sequence of choices and rewards. This model yields accurate probabilistic estimates about which hypotheses are attended by manipulating attentional states in the generative neural model and recovering them with the MoE model. This 2-pronged modeling approach leads to multiple quantitative predictions that are tested with functional magnetic resonance imaging in the companion paper.

The neural correlates of performance in adolescents at risk for schizophrenia: inefficiently increased cortico-striatal responses measured with fMRI

BACKGROUND

fMRI studies indicate that schizophrenia patients and their adult relatives require greater prefrontal activation to maintain performance at levels equal to controls, but studies have not established if this pattern of inefficiency is observed in child and adolescent offspring of schizophrenia patients (SCZ-Off).

METHODS

Using a task with visual working memory demands, we investigated activation in cortico-striatal networks and dorsal prefrontal modulation of regions underlying visual working memory in a group of SCZ-Off (n = 19) and controls with no family history of psychosis (n = 25 subjects) using an event-related design. Trials were divided based on memory performance (correct vs. incorrect) to specifically identify the neural correlates of correct working memory performance.

RESULTS

Whereas groups did not differ in terms of behavioral accuracy, SCZ-Off demonstrated significantly increased fMRI-measured activation in dorsal prefrontal cortex and the caudate nucleus during correct, relative to incorrect memory performance. Whereas activation in SCZ-Off was high and independent of performance in each region, in controls the fMRI response was related to behavioral proficiency in the caudate. Further, exploratory analyses indicated that this inefficiency in the dorsal prefrontal cortex response increased with age in SCZ-Off (but in no other regions or group). Finally, these differences were not based in differences in dorsal prefrontal modulation of other regions during successful performance.

DISCUSSION

These results are consistent with observed patterns in adult patients and first-degree relatives. Inefficient fronto-striatal responses during working memory may characterize the schizophrenia diathesis and may reflect the effects of the illness and vulnerability for the illness.

Task-specific effects of tDCS-induced cortical excitability changes on cognitive and motor sequence set shifting performance

In this study, we tested the effects of transcranial Direct Current Stimulation (tDCS) on two set shifting tasks. Set shifting ability is defined as the capacity to switch between mental sets or actions and requires the activation of a distributed neural network. Thirty healthy subjects (fifteen per site) received anodal, cathodal and sham stimulation of the dorsolateral prefrontal cortex (DLPFC) or the primary motor cortex (M1). We measured set shifting in both cognitive and motor tasks. The results show that both anodal and cathodal single session tDCS can modulate cognitive and motor tasks. However, an interaction was found between task and type of stimulation as anodal tDCS of DLPFC and M1 was found to increase performance in the cognitive task, while cathodal tDCS of DLPFC and M1 had the opposite effect on the motor task. Additionally, tDCS effects seem to be most evident on the speed of changing sets, rather than on reducing the number of errors or increasing the efficacy of irrelevant set filtering.

Hypo-activation in the executive core of the sustained attention network in adolescent offspring of schizophrenia patients mediated by premorbid functional deficits

Adolescent offspring of schizophrenia patients (SCZ-Off) are vulnerable to psychiatric disorders. Assessing relationships between clinical and biological measures (such as functional magnetic resonance imaging, fMRI) may elucidate pathways of vulnerability in this group. Here we assessed the relationship between clinically assessed premorbid function, and cortico-striatal activity during sustained attention in controls (HC: with no family history of psychosis) and SCZ-Off. Subjects (n=39) were assessed using the Structured Interview for Prodromal Syndromes and the Scale of Prodromal Symptoms. Based on the Global Assessment of Functioning (GAF) score, SCZ-Off were cleaved into "high" or "low" clinically functioning sub-groups (SCZ-Off(HF), SCZ-Off(LF) respectively). During fMRI, subjects participated in a modified continuous performance task (CPT-IP). fMRI was conducted on a Bruker MedSpec 4T system (345 EPI scans; TR=2s; 24 slices; 3.8×3.8×4mm). Results show SCZ-Off(LF) evinced less activation than both HC and SCZ-Off(HF) in the executive core of the brain's attentional system (anterior cingulate, dorsal prefrontal cortex and caudate), but not visuo-spatial regions such as primary visual or superior parietal cortex. Differences were independent of behavioral performance, and reduction in activity was related to GAF score in a dose-dependent manner. Assessing the relationship between clinical measures and brain activity in domains such as attention provides a window into mechanisms of vulnerability in the developing adolescent brain.

Differential roles of caudate nucleus and putamen during instrumental learning

The dorsal striatum is crucial for the acquisition and consolidation of instrumental behaviour, but the underlying computations and internal dynamics remain elusive. To address this issue, we combined a model of key computations supporting decision-making during instrumental learning with human behavioural and functional magnetic resonance imaging (fMRI) data. The results showed that the associative and sensorimotor dorsal striatum host complementary computations that, we suggest, may differentially support goal-directed and habitual processes. The anterior caudate nucleus integrates information about performance and cognitive control demands, whereas the putamen tracks how likely the conditioning stimuli lead to correct response. Contrary to current models, the putamen is recruited during initial acquisition. As the exploratory phase proceeds, the relative contribution of the caudate nucleus becomes dominant over the putamen. During early consolidation, caudate nucleus and putamen settle to asymptotic values and share control. We then investigated how dorsal striatal computations may affect decision-making. We found that portion of reaction times' variance parallels the combined cost associated with the dorsal striatal computations. Overall, our findings provide a deeper insight into the functional heterogeneity within the dorsal striatum and suggest that the dynamic interplay between caudate nucleus and putamen, rather than their serial recruitment, underlies the acquisition and early consolidation of instrumental behaviours.

The contribution of the putamen to sensory aspects of pain: insights from structural connectivity and brain lesions

Cerebral cortical activity is heavily influenced by interactions with the basal ganglia. These interactions occur via cortico-basal ganglia-thalamo-cortical loops. The putamen is one of the major sites of cortical input into basal ganglia loops and is frequently activated during pain. This activity has been typically associated with the processing of pain-related motor responses. However, the potential contribution of putamen to the processing of sensory aspects of pain remains poorly characterized. In order to more directly determine if the putamen can contribute to sensory aspects of pain, nine individuals with lesions involving the putamen underwent both psychophysical and functional imaging assessment of perceived pain and pain-related brain activation. These individuals exhibited intact tactile thresholds, but reduced heat pain sensitivity and widespread reductions in pain-related cortical activity in comparison with 14 age-matched healthy subjects. Using magnetic resonance imaging to assess structural connectivity in healthy subjects, we show that portions of the putamen activated during pain are connected not only with cortical regions involved in sensory-motor processing, but also regions involved in attention, memory and affect. Such a framework may allow cognitive information to flow from these brain areas to the putamen where it may be used to influence how nociceptive information is processed. Taken together, these findings indicate that the putamen and the basal ganglia may contribute importantly to the shaping of an individual subjective sensory experience by utilizing internal cognitive information to influence activity of large areas of the cerebral cortex.

Computational models of motivated action selection in corticostriatal circuits

Computational models of the basal ganglia have matured and received increasing attention over the last decade. This article reviews some of the theoretical advances offered by these models, focusing on motor and cognitive action selection, learning, and the interaction between multiple corticostriatal circuits in selection and learning.

Development of repetitive behavior in a mouse model: roles of indirect and striosomal basal ganglia pathways

Restricted repetitive behaviors (stereotypy, compulsions, rituals) are diagnostic for autism spectrum disorder and common in related neurodevelopmental disorders. Despite their prevalence in clinical populations, underlying mechanisms associated with the development of these behaviors remain poorly understood. We examined the role of the indirect basal ganglia pathway in the development of stereotypy using deer mice. We measured neuronal metabolic activity in the subthalamic nucleus (STN) and other relevant brain regions using cytochrome oxidase (CO) histochemistry at three developmental time-points. Although no differences were observed in STN across development, significant differences were found when mice were grouped by developmental trajectory. At 6 weeks post-weaning, significantly lower CO activity in STN was found in those trajectory groups that developed high levels of repetitive behavior versus the trajectory group that did not, suggesting the development of stereotypy is associated with decreased indirect basal ganglia pathway activity. In addition, we tested the hypothesis that preferential activation of striatal striosomes relative to surrounding matrix would be associated with the development of stereotypy. No differences in the relative activation of these striatal compartments were observed across development or among trajectory groups. Our results point to dynamic changes in the indirect pathway associated with the development of repetitive behavior and extends our prior work linking reduced indirect pathway activation to stereotypy in adult deer mice.

Caudate encodes multiple computations for perceptual decisions

Perceptual decision making is a complex process that requires multiple computations, including the accumulation of sensory evidence and an ongoing evaluation of the accumulation process to use for prediction and adjustment. Implementing these computations likely involves interactions among many brain regions. For perceptual decisions linked to oculomotor actions, neural correlates of sensory evidence accumulation have been identified in several cortical areas, including the frontal eye field and lateral intraparietal area, and one of their direct, subcortical targets, the superior colliculus. These structures are also connected indirectly, via the basal ganglia. The basal ganglia pathway has been theorized to contribute to perceptual decision making, but the nature of this contribution has yet to be examined directly. Here we show that in monkeys performing a reaction-time visual motion direction-discrimination task, neurons in a primary input structure of the basal ganglia, the caudate nucleus, encode three aspects of decision making: evidence accumulation, evaluation, and choice biases. These results indicate that the basal ganglia pathway can provide important signals to influence and assess perceptual decisions that guide oculomotor behavior.