Neural Substrates of Dopamine D2 Receptor Modulated Executive Functions in the Monkey Prefrontal Cortex

Adolescent oral oxycodone self-administration disrupts neurobehavioral and neurocognitive development

Nonmedical use of prescription opioids peaks during late adolescence, a developmental period associated with the maturation of higher-order cognitive processes. To date, however, how chronic adolescent oxycodone (OXY) self-administration alters neurobehavioral (i.e., locomotion, startle reactivity) and/or neurocognitive (i.e., preattentive processes, intrasession habituation, stimulus-reinforcement learning, sustained attention) function has not yet been systematically evaluated. Hence, the rationale was built for establishing the dose-dependency of adolescent OXY self-administration on the trajectory of neurobehavioral and neurocognitive development. From postnatal day (PD) 35 to PD 105, an age in rats that corresponds to the adolescent and young adult period in humans, male and female F344/N rats received access to either oral OXY (0, 2, 5, or 10 mg/kg) or water under a two-bottle choice experimental paradigm. Independent of biological sex or dose, rodents voluntarily escalated their OXY intake across ten weeks. A longitudinal experimental design revealed prominent OXY-induced impairments in neurobehavioral development, characterized by dose-dependent increases in locomotion and sex-dependent increases in startle reactivity. Systematic manipulation of the interstimulus interval in prepulse inhibition supports an OXY-induced impairment in preattentive processes. Despite the long-term cessation of OXY intake, rodents with a history of chronic adolescent oral OXY self-administration exhibited deficits in sustained attention; albeit no alterations in stimulus-reinforcement learning were observed. Taken together, adolescent oral OXY self-administration induces selective long-term alterations in neurobehavioral and neurocognitive development enjoining the implementation of safer prescribing guidelines for this population.

A neural modeling approach to study mechanisms underlying the heterogeneity of visual spatial frequency sensitivity in schizophrenia

Patients with schizophrenia exhibit abnormalities in spatial frequency sensitivity, and it is believed that these abnormalities indicate more widespread dysfunction and dysregulation of bottom-up processing. The early visual system, including the first-order Lateral Geniculate Nucleus of the thalamus (LGN) and the primary visual cortex (V1), are key contributors to spatial frequency sensitivity. Medicated and unmedicated patients with schizophrenia exhibit contrasting changes in spatial frequency sensitivity, thus making it a useful probe for examining potential effects of the disorder and antipsychotic medications in neural processing. We constructed a parameterized, rate-based neural model of on-center/off-surround neurons in the early visual system to investigate the impacts of changes to the excitatory and inhibitory receptive field subfields. By incorporating changes in both the excitatory and inhibitory subfields that are associated with pathophysiological findings in schizophrenia, the model successfully replicated perceptual data from behavioral/functional studies involving medicated and unmedicated patients. Among several plausible mechanisms, our results highlight the dampening of excitation and/or increase in the spread and strength of the inhibitory subfield in medicated patients and the contrasting decreased spread and strength of inhibition in unmedicated patients. Given that the model was successful at replicating results from perceptual data under a variety of conditions, these elements of the receptive field may be useful markers for the imbalances seen in patients with schizophrenia.

Locomotor Behavior and Memory Dysfunction Induced by 3-Nitropropionic Acid in Adult Zebrafish: Modulation of Dopaminergic Signaling

Huntington's disease (HD) is a progressive neurodegenerative disease characterized by neuropsychiatric disturbance, cognitive impairment, and locomotor dysfunction. In the early stage (chorea) of HD, expression of dopamine D2 receptors (D2R) is reduced, whereas dopamine (DA) levels are increased. Contrary, in the late stage (bradykinesia), DA levels and the expression of D2R and dopamine D1 receptors (D1R) are reduced. 3-Nitropropionic acid (3-NPA) is a toxin that may replicate HD behavioral phenotypes and biochemical aspects. This study assessed the neurotransmitter levels, dopamine receptor gene expression, and the effect of acute exposure to quinpirole (D2R agonist) and eticlopride (D2R antagonist) in an HD model induced by 3-NPA in adult zebrafish. Quinpirole and eticlopride were acutely applied by i.p. injection in adult zebrafish after chronic treatment of 3-NPA (60 mg/kg). 3-NPA treatment caused a reduction in DA, glutamate, and serotonin levels. Quinpirole reversed the bradykinesia and memory loss induced by 3-NPA. Together, these data showed that 3-NPA acts on the dopaminergic system and causes biochemical alterations similar to late-stage HD. These data reinforce the hypothesis that DA levels are linked with locomotor and memory deficits. Thus, these findings may suggest that the use of DA agonists could be a pharmacological strategy to improve the bradykinesia and memory deficits in the late-stage HD.

Dopamine receptor activation regulates reward expectancy signals during cognitive control in primate prefrontal neurons

Dopamine neurons respond to reward-predicting cues but also modulate information processing in the prefrontal cortex essential for cognitive control. Whether dopamine controls reward expectation signals in prefrontal cortex that motivate cognitive control is unknown. We trained two male macaques on a working memory task while varying the reward size earned for successful task completion. We recorded neurons in lateral prefrontal cortex while simultaneously stimulating dopamine D1 receptor (D1R) or D2 receptor (D2R) families using micro-iontophoresis. We show that many neurons predict reward size throughout the trial. D1R stimulation showed mixed effects following reward cues but decreased reward expectancy coding during the memory delay. By contrast, D2R stimulation increased reward expectancy coding in multiple task periods, including cueing and memory periods. Stimulation of either dopamine receptors increased the neurons' selective responses to reward size upon reward delivery. The differential modulation of reward expectancy by dopamine receptors suggests that dopamine regulates reward expectancy necessary for successful cognitive control.

Cymbopogon citratus Essential Oil: Extraction, GC-MS, Phytochemical Analysis, Antioxidant Activity, and In Silico Molecular Docking for Protein Targets Related to CNS

This study analyzed the chemical composition of Cymbopogon citratus essential oil from Puebla, México, assessed its antioxidant activity, and evaluated in silico protein-compound interactions related to central nervous system (CNS) physiology. GC-MS analysis identified myrcene (8.76%), Z-geranial (27.58%), and E-geranial (38.62%) as the main components, with 45 other compounds present, which depends on the region and growing conditions. DPPH and Folin-Ciocalteu assays using the leaves extract show a promising antioxidant effect (EC₅₀ = 48.5 µL EO/mL), reducing reactive oxygen species. The bioinformatic tool SwissTargetPrediction (STP) shows 10 proteins as potential targets associated with CNS physiology. Moreover, protein-protein interaction diagrams suggest that muscarinic and dopamine receptors are related to each other through a third party. Molecular docking reveals that Z-geranial has higher binding energy than M1 commercial blocker and blocks M2, but not M4 muscarinic acetylcholine receptors, whereas β-pinene and myrcene block M1, M2, and M4 receptors. These actions may positively affect cardiovascular activity, memory, Alzheimer's disease, and schizophrenia. This study highlights the significance of understanding natural product interactions with physiological systems to uncover potential therapeutic agents and advanced knowledge on their benefits for human health.

Neural substrates of cognitive impairment in a NMDAR hypofunction mouse model of schizophrenia and partial rescue by risperidone

N-methyl D-aspartate receptor (NMDAR) hypofunction is a pathophysiological mechanism relevant for schizophrenia. Acute administration of the NMDAR antagonist phencyclidine (PCP) induces psychosis in patients and animals while subchronic PCP (sPCP) produces cognitive dysfunction for weeks. We investigated the neural correlates of memory and auditory impairments in mice treated with sPCP and the rescuing abilities of the atypical antipsychotic drug risperidone administered daily for two weeks. We recorded neural activities in the medial prefrontal cortex (mPFC) and the dorsal hippocampus (dHPC) during memory acquisition, short-term, and long-term memory in the novel object recognition test and during auditory processing and mismatch negativity (MMN) and examined the effects of sPCP and sPCP followed by risperidone. We found that the information about the familiar object and its short-term storage were associated with mPFC→dHPC high gamma connectivity (phase slope index) whereas long-term memory retrieval depended on dHPC→mPFC theta connectivity. sPCP impaired short-term and long-term memories, which were associated with increased theta power in the mPFC, decreased gamma power and theta-gamma coupling in the dHPC, and disrupted mPFC-dHPC connectivity. Risperidone rescued the memory deficits and partly restored hippocampal desynchronization but did not ameliorate mPFC and circuit connectivity alterations. sPCP also impaired auditory processing and its neural correlates (evoked potentials and MMN) in the mPFC, which were also partly rescued by risperidone. Our study suggests that the mPFC and the dHPC disconnect during NMDAR hypofunction, possibly underlying cognitive impairment in schizophrenia, and that risperidone targets this circuit to ameliorate cognitive abilities in patients.

The Aversive Lens: Stress effects on the prefrontal-cingulate cortical pathways that regulate emotion

ARNSTEN, A.F.T., M.K.P. Joyce and A.C. Roberts. The Aversive Lens: Stress effects on the prefrontal-cingulate cortical pathways that regulate emotion. NEUROSCI BIOBEHAV REV XXX-XXX, 2022. The symptoms of major-depressive-disorder include psychic pain and anhedonia, i.e. seeing the world through an "aversive lens". The neurobiology underlying this shift in worldview is emerging. Here these data are reviewed, focusing on how activation of subgenual cingulate (BA25) induces an "aversive lens", and how higher prefrontal cortical (PFC) areas (BA46/10/32) provide top-down regulation of BA25 but are weakened by excessive dopamine and norepinephrine release during stress exposure, and dendritic spine loss with chronic stress exposure. These changes may generate an attractor state, which maintains the brain under the control of BA25, requiring medication or neuromodulatory treatments to return connectivity to a more flexible state. In line with this hypothesis, effective anti-depressant treatments reduce the activity of BA25 and restore top-down regulation by higher circuits, e.g. as seen with SSRI medications, ketamine, deep brain stimulation of BA25, or rTMS to strengthen dorsolateral PFC. This research has special relevance in an era of chronic stress caused by the COVID19 pandemic, political unrest and threat of climate change.

Processing of auditory information in forebrain regions after hearing loss in adulthood: Behavioral and electrophysiological studies in a rat model

Background

Hearing loss was proposed as a factor affecting development of cognitive impairment in elderly. Deficits cannot be explained primarily by dysfunctional neuronal networks within the central auditory system. We here tested the impact of hearing loss in adult rats on motor, social, and cognitive function. Furthermore, potential changes in the neuronal activity in the medial prefrontal cortex (mPFC) and the inferior colliculus (IC) were evaluated.

Materials and methods

In adult male Sprague Dawley rats hearing loss was induced under general anesthesia with intracochlear injection of neomycin. Sham-operated and naive rats served as controls. Postsurgical acoustically evoked auditory brainstem response (ABR)-measurements verified hearing loss after intracochlear neomycin-injection, respectively, intact hearing in sham-operated and naive controls. In intervals of 8 weeks and up to 12 months after surgery rats were tested for locomotor activity (open field) and coordination (Rotarod), for social interaction and preference, and for learning and memory (4-arms baited 8-arms radial maze test). In a final setting, electrophysiological recordings were performed in the mPFC and the IC.

Results

Locomotor activity did not differ between deaf and control rats, whereas motor coordination on the Rotarod was disturbed in deaf rats (P < 0.05). Learning the concept of the radial maze test was initially disturbed in deaf rats (P < 0.05), whereas retesting every 8 weeks did not show long-term memory deficits. Social interaction and preference was also not affected by hearing loss. Final electrophysiological recordings in anesthetized rats revealed reduced firing rates, enhanced irregular firing, and reduced oscillatory theta band activity (4–8 Hz) in the mPFC of deaf rats as compared to controls (P < 0.05). In the IC, reduced oscillatory theta (4–8 Hz) and gamma (30–100 Hz) band activity was found in deaf rats (P < 0.05).

Conclusion

Minor and transient behavioral deficits do not confirm direct impact of long-term hearing loss on cognitive function in rats. However, the altered neuronal activities in the mPFC and IC after hearing loss indicate effects on neuronal networks in and outside the central auditory system with potential consequences on cognitive function.

Different Music Training Modulates Theta Brain Oscillations Associated with Executive Function

Different music training involves different hand coordination levels and may have a significant influence on brain oscillation for the executive function. However, few research has focused on the plasticity of executive function and the brain oscillation modulated by different musical instrument training modules. In this study, we recruited 18 string musicians, 20 pianists, and 19 non-musicians to perform a bimanual key pressing task during EEG recording. Behavioral results revealed that pianists have the highest accuracy and the shortest response time, followed by string musicians and non-musicians (p < 0.05). Time-frequency analyses of EEG revealed that pianists generated significantly greater theta power than the other groups from 500 ms to 800 ms post-stimulus in mid-central, frontal brain areas, and motor control areas. Functional connectivity analyses found that the pianists showed significantly greater connectivity in the frontal-parietal area in theta band based on phase-locking value analysis, which suggests that piano training improves executive function and enhances the connectivity between prefrontal and mid-central regions. These findings contribute to a better understanding of the effects of different music training on executive function.

Reversible Photocontrol of Dopaminergic Transmission in Wild-Type Animals

Understanding the dopaminergic system is a priority in neurobiology and neuropharmacology. Dopamine receptors are involved in the modulation of fundamental physiological functions, and dysregulation of dopaminergic transmission is associated with major neurological disorders. However, the available tools to dissect the endogenous dopaminergic circuits have limited specificity, reversibility, resolution, or require genetic manipulation. Here, we introduce azodopa, a novel photoswitchable ligand that enables reversible spatiotemporal control of dopaminergic transmission. We demonstrate that azodopa activates D₁-like receptors in vitro in a light-dependent manner. Moreover, it enables reversibly photocontrolling zebrafish motility on a timescale of seconds and allows separating the retinal component of dopaminergic neurotransmission. Azodopa increases the overall neural activity in the cortex of anesthetized mice and displays illumination-dependent activity in individual cells. Azodopa is the first photoswitchable dopamine agonist with demonstrated efficacy in wild-type animals and opens the way to remotely controlling dopaminergic neurotransmission for fundamental and therapeutic purposes.

Prefrontal Dopaminergic Regulation of Cue-Guided Risky Decision-Making Performance in Rats

Risky decision-making is the decision made by individuals when they know the probability of each outcome. In order to survive in unpredictable environments, it is necessary for individuals to assess the probability of events occurring to an make appropriate decisions. There are few studies on the neural basis of risky decision-making behavior guided by external cues, which is related to the relative paucity of animal behavioral paradigms. Previous studies have shown that the prefrontal cortex (PFC) plays a key role in risk-based decision-making. The PFC receives projections from the dopamine (DA) system from the ventral tegmental area of the midbrain. The mesocorticolimbic DA system regulates the judgments of reward and value in decision-making. However, the specific receptor mechanism for prefrontal DA regulation of cue-guided risky decision-making behavior remains unclear. Here we established a cue-guided risky decision-making behavioral paradigm (RDM task) to detect the behavior of rats making decisions between a small certain reward and a large uncertain reward in a self-paced manner. The D1 receptor antagonist SCH-23390 (5 mM) or agonist SKF-82958 (5 mM), and the D2 receptor antagonist thioridazine hydrochloride (5 mM) or agonist MLS-1547 (5 mM) was injected into the mPFC, respectively, to investigate how the behavior in the RDM task was changed. The results showed that: (1) rats were able to master the operation of the cue-guided RDM task in a self-paced way; (2) a majority of rats were inclined to choose risk rather than a safe option when the reward expectations were equal; and (3) risk selection was reduced upon inhibition of D1 receptors or stimulation of D2 receptors, but increased upon stimulation of D1 receptors or inhibition of D2 receptors, suggesting that the RDM performance is regulated by D1 and D2 receptors in the mPFC. The present results suggest that DA receptors in the mPFC of rats are involved in regulating cue-guided RDM behavior, with differential involvement of D1 and D2 receptors in the regulation.

The contribution of executive functions to sex differences in animal cognition

Cognitive sex differences have been reported in several vertebrate species, mostly in spatial abilities. Here, I review evidence of sex differences in a family of general cognitive functions that control behaviour and cognition, i.e., executive functions such as cognitive flexibility and inhibitory control. Most of this evidence derives from studies in teleost fish. However, analysis of literature from other fields (e.g., biomedicine, genetic, ecology) concerning mammals and birds reveals that more than 40% of species investigated exhibit sex differences in executive functions. Among species, the direction and magnitude of these sex differences vary greatly, even within the same family, suggesting sex-specific selection due to species' reproductive systems and reproductive roles of males and females. Evidence also suggests that sex differences in executive functions might provide males and females highly differentiated cognitive phenotypes. To understand the evolution of cognitive sex differences in vertebrates, future research should consider executive functions.

Systemic D1-R and D2-R antagonists in Non-Human Primates Differentially Impact Learning and Memory While Impairing Motivation and Motor Performance

Dopamine (DA) modulates cognition in part via differential activation of D1 and D2 receptors within the striatum and prefrontal cortex, yet evidence for cognitive impairments stemming from DA blockade or deficiency is inconsistent. Given the predominance of D1 over D2 receptors (R) in the prefrontal cortex of primates, D1-R blockade should more strongly influence frontal executive function (including working memory), while D2-R blockade should impair processes more strongly associated with the dorsal striatum (including cognitive flexibility, and learning). To test how systemic DA blockade disrupts cognition, we administered D1-R and D2-R like antagonists to healthy monkeys while they performed a series of cognitive tasks. Two selective DA receptor antagonist drugs (SCH-23390 hydrochloride: D1/D5-R antagonist; or Eticlopride hydrochloride: D2/D3-R antagonist) or placebo (0.9% saline) were systemically administered. Four tasks were used: (1) 'visually guided reaching', to test response time and accuracy, (2) 'reversal learning', to test association learning and attention, (3) 'self-ordered sequential search' to test spatial working memory, and (4) 'delayed match to sample' to test object working memory. Increased reach response times and decreased motivation to work for liquid reward was observed with both the D1/D5-R and D2/D3-R antagonists at the maximum dosages that still enabled task performance. The D2/D3-R antagonist impaired performance in the reversal learning task, while object and spatial working memory performance was not consistently affected in the tested tasks for either drug. These results are consistent with the theory that systemic D2/D3-R antagonists preferentially influence striatum processes (cognitive flexibility) while systemic D1/D5-R administration is less detrimental to frontal executive function.

Flexible versus Fixed Spatial Self-Ordered Response Sequencing: Effects of Inactivation and Neurochemical Modulation of Ventrolateral Prefrontal Cortex

Previously, studies using human neuroimaging and excitotoxic lesions in non-human primate have demonstrated an important role of ventrolateral prefrontal cortex (vlPFC) in higher order cognitive functions such as cognitive flexibility and the planning of behavioral sequences. In the present experiments, we tested effects on performance of temporary inactivation (using GABA receptor agonists) and dopamine (DA) D2 and 5-HT2A-receptor (R) blockade of vlPFC via local intracerebral infusions in the marmoset. We trained common marmosets to perform spatial self-ordered sequencing tasks in which one cohort of animals performed two and three response sequences on a continuously varying spatial array of response options on a touch-sensitive screen. Inactivation of vlPFC produced a marked disruption of accuracy of sequencing which also exhibited significant error perseveration. There were somewhat contrasting effects of D2 and 5-HT2A-R blockade, with the former producing error perseveration on incorrect trials, though not significantly impairing accuracy overall, and the latter significantly impairing accuracy but not error perseveration. A second cohort of marmosets were directly compared on performance of fixed versus variable spatial arrays. Inactivation of vlPFC again impaired self-ordered sequencing, but only with varying, and not fixed spatial arrays, the latter leading to the consistent use of fewer, preferred sequences. These findings add to evidence that vlPFC is implicated in goal-directed behavior that requires higher-order response heuristics that can be applied flexibly over different (variable), as compared with fixed stimulus exemplars. They also show that dopaminergic and serotonergic chemomodulation has distinctive effects on such performance.SIGNIFICANCE STATEMENT This investigation employing local intracerebral infusions to inactivate the lateral prefrontal cortex (PFC) of the New World marmoset reveals the important role of this region in self-ordered response sequencing in variable but not fixed spatial arrays. These novel findings emphasize the higher order functions of this region, contributing to cognitive flexibility and planning of goal directed behavior. The investigation also reports for the first time somewhat contrasting neuromodulatory deficits produced by infusions of dopamine (DA) D2 and 5-HT2A receptor (R) antagonists into the same region, of possible significance for understanding cognitive deficits produced by anti-psychotic drugs.

The DA-antagonist Tiapride affects context-related extinction learning in a predictive learning task, but not initial forming of associations, or renewal

Renewal describes the recovery of an extinguished response if the contexts of extinction and recall differ, highlighting the context dependency of extinction. Studies demonstrated dopaminergic (DA) signalling to be important for context-related extinction learning with and without a fear component. In a previous study in humans, administration of the dopamine D2/D3 antagonist tiapride prior to extinction impaired extinction learning in a novel, but not a familiar context, without affecting renewal. In a further study, context processing during initial acquisition of associations was shown to be related to renewal. In this human fMRI study we investigated the potential role of DA signalling during this initial conditioning for the learning process and for renewal. While tiapride, administered prior to the start of learning, did not affect initial acquisition and renewal, extinction learning in a novel context was impaired, associated with reduced BOLD activation in vmPFC, left iFG and ACC - regions mediating response inhibition and selection from competing options using contextual information. Thus, different timepoints of administration of tiapride (before initial conditioning or extinction) had largely similar effects upon extinction and renewal. In addition, retrieval of previously acquired associations was impaired, pointing towards weaker association forming during acquisition. Conceivably, effects of the DA blockade are associated with the challenge present in the respective task rather than the administration timepoint: the cognitive flexibility required for forming a new inhibitory association that includes a novel element clearly requires DA processing, while initial forming of associations, or of inhibitory associations without a new element, apparently rely less on the proper function of the DA system.

PET Imaging of Dopamine Neurotransmission During EEG Neurofeedback

Neurofeedback (NFB) is a brain-based training method that enables users to control their own cortical oscillations using real-time feedback from the electroencephalogram (EEG). Importantly, no investigations to date have directly explored the potential impact of NFB on the brain's key neuromodulatory systems. Our study's objective was to assess the capacity of NFB to induce dopamine release as revealed by positron emission tomography (PET). Thirty-two healthy volunteers were randomized to either EEG-neurofeedback (NFB) or EEG-electromyography (EMG), and scanned while performing self-regulation during a single session of dynamic PET brain imaging using the high affinity D2/3 receptor radiotracer, [18F]Fallypride. NFB and EMG groups down-regulated cortical alpha power and facial muscle tone, respectively. Task-induced effects on endogenous dopamine release were estimated in the frontal cortex, anterior cingulate cortex, and thalamus, using the linearized simplified reference region model (LSRRM), which accounts for time-dependent changes in radiotracer binding following task initiation. Contrary to our hypothesis of a differential effect for NFB vs. EMG training, significant dopamine release was observed in both training groups in the frontal and anterior cingulate cortex, but not in thalamus. Interestingly, a significant negative correlation was observed between dopamine release in frontal cortex and pre-to-post NFB change in spontaneous alpha power, suggesting that intra-individual changes in brain state (i.e., alpha power) could partly result from changes in neuromodulatory tone. Overall, our findings constitute the first direct investigation of neurofeedback's effect on the endogenous release of a key neuromodulator, demonstrating its feasibility and paving the way for future studies using this methodology.

Synaptic Properties and Plasticity Mechanisms of Invertebrate Tonic and Phasic Neurons

Defining neuronal cell types and their associated biophysical and synaptic diversity has become an important goal in neuroscience as a mechanism to create comprehensive brain cell atlases in the post-genomic age. Beyond broad classification such as neurotransmitter expression, interneuron vs. pyramidal, sensory or motor, the field is still in the early stages of understanding closely related cell types. In both vertebrate and invertebrate nervous systems, one well-described distinction related to firing characteristics and synaptic release properties are tonic and phasic neuronal subtypes. In vertebrates, these classes were defined based on sustained firing responses during stimulation (tonic) vs. transient responses that rapidly adapt (phasic). In crustaceans, the distinction expanded to include synaptic release properties, with tonic motoneurons displaying sustained firing and weaker synapses that undergo short-term facilitation to maintain muscle contraction and posture. In contrast, phasic motoneurons with stronger synapses showed rapid depression and were recruited for short bursts during fast locomotion. Tonic and phasic motoneurons with similarities to those in crustaceans have been characterized in Drosophila, allowing the genetic toolkit associated with this model to be used for dissecting the unique properties and plasticity mechanisms for these neuronal subtypes. This review outlines general properties of invertebrate tonic and phasic motoneurons and highlights recent advances that characterize distinct synaptic and plasticity pathways associated with two closely related glutamatergic neuronal cell types that drive invertebrate locomotion.

Dopamine Receptor Expression Among Local and Visual Cortex-Projecting Frontal Eye Field Neurons

Dopaminergic modulation of prefrontal cortex plays an important role in numerous cognitive processes, including attention. The frontal eye field (FEF) is modulated by dopamine and has an established role in visual attention, yet the underlying circuitry upon which dopamine acts is not known. We compared the expression of D1 and D2 dopamine receptors (D1Rs and D2Rs) across different classes of FEF neurons, including those projecting to dorsal or ventral extrastriate cortex. First, we found that both D1Rs and D2Rs are more prevalent on pyramidal neurons than on several classes of interneurons and are particularly prevalent on putatively long-range projecting pyramidals. Second, higher proportions of pyramidal neurons express D1Rs than D2Rs. Third, overall a higher proportion of inhibitory neurons expresses D2Rs than D1Rs. Fourth, among inhibitory interneurons, a significantly higher proportion of parvalbumin+ neurons expresses D2Rs than D1Rs, and a significantly higher proportion of calbindin+ neurons expresses D1Rs than D2Rs. Finally, compared with D2Rs, virtually all of the neurons with identified projections to both dorsal and ventral extrastriate visual cortex expressed D1Rs. Our results demonstrate that dopamine tends to act directly on the output of the FEF and that dopaminergic modulation of top-down projections to visual cortex is achieved predominately via D1Rs.

Vulnerable and resilient cognitive performance related to early life stress: The potential mediating role of dopaminergic receptors in the medial prefrontal cortex of adult mice

RATIONALE

Exposure to early life stress (ELS) is known to have pronounced effects on the prefrontal cortex (PFC). However, not all individuals exposed to ELS manifest the same neurobiological and cognitive phenotypes when adults. Dopamine signaling could be a key factor in understanding the effects of stress on PFC-related cognitive function.

OBJECTIVES

We aimed to investigate the differential effects of ELS on cognitive performance of adult mice and the dopaminergic receptors expression in the PFC.

METHODS

BALB/c males were exposed to the maternal separation (MS) procedure and their cognitive performance on the eight-arm radial maze (8-RAM) were assessed during adulthood. For molecular-level assessments, we performed mRNA expression analyses for dopamine receptors-DRD1, DRD2, DRD3-and Hers1 expression in the medial PFC.

RESULTS

While MS produced an overall impairment on 8-RAM, the stressed animals could be divided in two groups based on their performance: those with impaired cognitive performance (vulnerable to maternal separation, V-MS) and those without any impairment (resilient to maternal separation, R-MS). V-MS animals showed increased DRD1 and DRD2 expression in comparison with other groups. Errors on 8-RAM were also positively correlated with DRD1 and DRD2 mRNA expression.

CONCLUSIONS

Our findings suggest a potential role of the dopaminergic system in the programming mechanisms of cognitive vulnerability and resilience related to ELS.

Effects of Dopaminergic Drugs on Cognitive Control Processes Vary by Genotype

Dopamine (DA) has been implicated in modulating multiple cognitive control processes, including the robust maintenance of task sets and memoranda in the face of distractors (cognitive stability) and, conversely, the ability to switch task sets or update the contents of working memory when it is advantageous to do so (cognitive flexibility). In humans, the limited specificity of available pharmacological probes has posed a challenge for understanding the mechanisms by which DA, acting on multiple receptor families across the PFC and striatum, differentially influences these cognitive processes. Using a within-subject, placebo-controlled design, we contrasted the impact of two mechanistically distinct DA drugs, tolcapone (an inhibitor of catechol-O-methyltransferase [COMT], a catecholamine inactivator) and bromocriptine (a DA agonist with preferential affinity for the D2 receptor), on the maintenance and switching of task rules. Given previous work demonstrating that drug effects on behavior are dependent on baseline DA tone, participants were stratified according to genetic polymorphisms associated with cortical (COMT Val158Met) and striatal (Taq1A) DA system function. Our results were partially consistent with an inverted-U-shaped relationship between tolcapone and robust rule maintenance (interaction with COMT genotype) and between bromocriptine and cued rule switching (interaction with Taq1A genotype). However, when task instructions were ambiguous, a third relationship emerged to explain drug effects on spontaneous task switching (interaction of COMT genotype and bromocriptine). Together, this pattern of results suggests that the effects of DA drugs vary not only as a function of the DA system component upon which they act but also on subtle differences in task demands and context.

Latent-Profile Analysis Reveals Behavioral and Brain Correlates of Dopamine-Cognition Associations

Evidence suggests that associations between the neurotransmitter dopamine and cognition are nonmonotonic and open to modulation by various other factors. The functional implications of a given level of dopamine may therefore differ from person to person. By applying latent-profile analysis to a large (n = 181) sample of adults aged 64-68 years, we probabilistically identified 3 subgroups that explain the multivariate associations between dopamine D2/3R availability (probed with 11C-raclopride-PET, in cortical, striatal, and hippocampal regions) and cognitive performance (episodic memory, working memory, and perceptual speed). Generally, greater receptor availability was associated with better cognitive performance. However, we discovered a subgroup of individuals for which high availability, particularly in striatum, was associated with poor performance, especially for working memory. Relative to the rest of the sample, this subgroup also had lower education, higher body-mass index, and lower resting-state connectivity between caudate nucleus and dorsolateral prefrontal cortex. We conclude that a smaller subset of individuals induces a multivariate non-linear association between dopamine D2/3R availability and cognitive performance in this group of older adults, and discuss potential reasons for these differences that await further empirical scrutiny.

Neurocognitive Profiles of Older Adults with Working-Memory Dysfunction

Individuals differ in how they perceive, remember, and think. There is evidence for the existence of distinct subgroups that differ in cognitive performance within the older population. However, it is less clear how individual differences in cognition in old age are linked to differences in brain-based measures. We used latent-profile analysis on n-back working-memory (WM) performance to identify subgroups in a large sample of older adults (n = 181; age = 64–68 years). Our analysis identified one larger normal subgroup with higher performance (n = 113; 63%), and a second smaller subgroup (n = 55; 31%) with lower performance. The low-performing subgroup showed weaker load-dependent BOLD modulation and lower connectivity within the fronto-parietal network (FPN) as well as between FPN and striatum during n-back, along with lower FPN connectivity at rest. This group also exhibited lower FPN structural integrity, lower frontal dopamine D2 binding potential, inferior performance on offline WM tests, and a trend-level genetic predisposition for lower dopamine-system efficiency. By contrast, this group exhibited relatively intact episodic memory and associated brain measures (i.e., hippocampal volume, structural, and functional connectivity within the default-mode network). Collectively, these data provide converging evidence for the existence of a group of older adults with impaired WM functioning characterized by reduced cortico-striatal coupling and aberrant cortico-cortical integrity within FPN.

Serotonin 5-HT1A, 5-HT2A and dopamine D2 receptors strongly influence prefronto-hippocampal neural networks in alert mice: Contribution to the actions of risperidone

Atypical antipsychotic drugs (APDs) used to treat positive and negative symptoms in schizophrenia block serotonin receptors 5-HT_2AR and dopamine receptors D₂R and stimulate 5-HT_1AR directly or indirectly. However, the exact cellular mechanisms mediating their therapeutic actions remain unresolved. We recorded neural activity in the prefrontal cortex (PFC) and hippocampus (HPC) of freely-moving mice before and after acute administration of 5-HT_1AR, 5-HT_2AR and D₂R selective agonists and antagonists and atypical APD risperidone. We then investigated the contribution of the three receptors to the actions of risperidone on brain activity via statistical modeling and pharmacological reversal (risperidone + 5-HT_1AR antagonist WAY-100635, risperidone + 5-HT_2A/2CR agonist DOI, risperidone + D₂R agonist quinpirole). Risperidone, 5-HT_1AR agonism with 8-OH-DPAT, 5-HT_2AR antagonism with M100907, and D₂R antagonism with haloperidol reduced locomotor activity of mice that correlated with a suppression of neural spiking, power of theta and gamma oscillations in PFC and HPC, and reduction of PFC-HPC theta phase synchronization. By contrast, activation of 5-HT_2AR with DOI enhanced high-gamma oscillations in PFC and PFC-HPC high gamma functional connectivity, likely related to its hallucinogenic effects. Together, power changes, regression modeling and pharmacological reversals suggest an important role of 5-HT_1AR agonism and 5-HT_2AR antagonism in risperidone-induced alterations of delta, beta and gamma oscillations, while D₂R antagonism may contribute to risperidone-mediated changes in delta oscillations. This study provides novel insight into the neural mechanisms for widely prescribed psychiatric medication targeting the serotonin and dopamine systems in two regions involved in the pathophysiology of schizophrenia.

Macaque anterior cingulate cortex deactivation impairs performance and alters lateral prefrontal oscillatory activities in a rule-switching task

In primates, both the dorsal anterior cingulate cortex (dACC) and the dorsolateral prefrontal cortex (dlPFC) are key regions of the frontoparietal cognitive control network. To study the role of the dACC and its communication with the dlPFC in cognitive control, we recorded local field potentials (LFPs) from the dlPFC before and during the reversible deactivation of the dACC, in macaque monkeys engaging in uncued switches between 2 stimulus-response rules, namely prosaccade and antisaccade. Cryogenic dACC deactivation impaired response accuracy during maintenance of—but not the initial switching to—the cognitively demanding antisaccade rule, which coincided with a reduction in task-related theta activity and the correct-error (C-E) difference in dlPFC beta-band power. During both rule switching and maintenance, dACC deactivation prolonged the animals’ reaction time and reduced task-related alpha power in the dlPFC. Our findings support a role of the dACC in prefrontal oscillatory activities that are involved the maintenance of a new, challenging task rule.

Reversible deactivation of the dorsal anterior cingulate cortex — an area of the cognitive control network — impairs rule maintenance but not rule switching per se, and disrupts task-related oscillatory activities in the dorsolateral prefrontal cortex — another area of the same network.

D2 receptors and cognitive flexibility in marmosets: tri-phasic dose-response effects of intra-striatal quinpirole on serial reversal performance

Behavioral flexibility, which allows organisms to adapt their actions in response to environmental changes, is impaired in a number of neuropsychiatric conditions, including obsessive-compulsive disorder and addiction. Studies in human subjects and monkeys have reported correlations between individual differences in dopamine D2-type receptor (D2R) levels in the caudate nucleus and performance in a discrimination reversal task, in which established contingent relationships between abstract stimuli and rewards (or punishments) are reversed. Global genetic deletion of the D2R in mice disrupts reversal performance, indicating a likely causal role for this receptor in supporting flexible behaviors. To directly examine the specific role of caudate D2-type receptors in reversal performance, the D2/3/4R agonist quinpirole was infused via chronic indwelling cannulae into the medial caudate of male and female marmoset monkeys performing a touchscreen-based serial discrimination reversal task. Given prior evidence for dose-dependent effects of quinpirole and other dopaminergic drugs, a full dose-response curve was established. Individually, marmosets displayed marked differences in behavioral sensitivity to specific doses of intra-caudate quinpirole. Collectively, they exhibited a behaviorally specific bi-phasic deficit in reversal learning, being consistently impaired at both relatively low and high doses of quinpirole. However, intermediate doses of intra-caudate quinpirole produced significant improvement in reversal performance. These data support previous human and monkey neuroimaging studies by providing causal evidence of a U-shaped function describing how dopamine modulates cognitive flexibility in the primate striatum.

Dopamine and Cognitive Control in Prefrontal Cortex

Cognitive control, the ability to orchestrate behavior in accord with our goals, depends on the prefrontal cortex. These cognitive functions are heavily influenced by the neuromodulator dopamine. We review here recent insights exploring the influence of dopamine on neuronal response properties in prefrontal cortex (PFC) during ongoing behaviors in primates. This review suggests three major computational roles of dopamine in cognitive control: (i) gating sensory input, (ii) maintaining and manipulating working memory contents, and (iii) relaying motor commands. For each of these roles, we propose a neuronal microcircuit based on known mechanisms of action of dopamine in PFC, which are corroborated by computational network models. This conceptual approach accounts for the various roles of dopamine in prefrontal executive functioning.

Dopamine guides competition for cognitive control: Common effects of haloperidol on working memory and response conflict

Several lines of evidence suggest that dopamine modulates working memory (the ability to faithfully maintain and efficiently manipulate information over time) but its specific role has not been fully defined. Nor is it clear whether any effects of dopamine are specific to memory processes or whether they reflect more general cognitive mechanisms that extend beyond the working memory domain. Here, we examine the effect of haloperidol, principally a dopamine D₂ receptor antagonist, on the ability of humans to ignore distracting information or update working memory contents. We compare these effects to performance on an independent measure of cognitive control (response conflict) which has minimal memory requirements. Haloperidol did not selectively affect the ability to ignore or update, but instead reduced the overall quality of recall. In addition, it impaired the ability to overcome response conflict. The deleterious effect of haloperidol on response conflict was selectively associated with the negative effect of the drug on ignoring - but not updating - suggesting that dopamine affects protection of working memory contents and inhibition in response conflict through a common mechanism. These findings provide new insights into the role of dopamine D₂ receptors on human cognition. They suggest that D₂ receptor effects on protecting the memory contents from distraction might be related to a more general process that supports inhibitory control in contexts that do not require working memory.

Learning the meaning of new stimuli increases the cross-correlated activity of prefrontal neurons

The prefrontal cortex (PF) has a key role in learning rules and generating associations between stimuli and responses also called conditional motor learning. Previous studies in PF have examined conditional motor learning at the single cell level but not the correlation of discharges between neurons at the ensemble level. In the present study, we recorded from two rhesus monkeys in the dorsolateral and the mediolateral parts of the prefrontal cortex to address the role of correlated firing of simultaneously recorded pairs during conditional motor learning. We trained two rhesus monkeys to associate three stimuli with three response targets, such that each stimulus was mapped to only one response. We recorded the neuronal activity of the same neuron pairs during learning of new associations and with already learned associations. In these tasks after a period of fixation, a visual instruction stimulus appeared centrally and three potential response targets appeared in three positions: right, left, and up from center. We found a higher number of neuron pairs significantly correlated and higher cross-correlation coefficients during stimulus presentation in the new than in the familiar mapping task. These results demonstrate that learning affects the PF neural correlation structure.

Blockade of serotonin 5-HT2A receptors potentiates dopamine D2 activation-induced disruption of pup retrieval on an elevated plus maze, but has no effect on D2 blockade-induced one

Appetitive aspect of rat maternal behavior, such as pup retrieval, is motivationally driven and sensitive to dopamine disturbances. Activation or blockade of dopamine D₂ receptors causes a similar disruption of pup retrieval, which may also reflect an increase in maternal anxiety and/or a disruption of executive function. Recent work indicates that serotonin 5-HT_2A receptors also play an important role in rat maternal behavior. Given the well-known modulation of 5-HT_2A on the mesolimbic and mesocortical dopamine functions, the present study examined the extent to which blockade of 5-HT_2A receptors on dopamine D₂-mediated maternal effects using a pup retrieval on the elevated plus maze (EPM) test. Sprague-Dawley postpartum female rats were acutely injected with quinpirole (a D₂ agonist, 0.10 and 0.25 mg/kg, sc), or haloperidol (a D₂ antagonist, 0.1 or 0.2 mg/kg, sc), in combination of MDL100907 (a 5-HT_2A receptor antagonist, 1.0 mg/kg, sc, 30 min before quinpirole or haloperidol injection) or saline and tested at 30, 90 and 240 min after quinpirole or haloperidol injection on postpartum days 3 and 7. Quinpirole and haloperidol decreased the number of pup retrieved (an index of maternal motivation) and sequential retrieval score (an index of executive function), prolonged the pup retrieval latencies, reduced the percentage of time spent on the open arms (an index of maternal anxiety), and decreased the distance travelled on the maze in a dose-dependent and time-dependent fashion. MDL100907 treatment by itself had no effect on pup retrieval, but it exacerbated the quinpirole-induced disruption of pup retrieval, but had no effect on the haloperidol-induced one. These findings suggest a complex interactive effect between 5-HT_2A and D₂ receptors on one or several maternal processes (maternal motivation, anxiety and executive function), and support the idea that one molecular mechanism by which 5-HT_2A receptors mediate maternal behavior is through its modulation of D₂ receptors.

Dopamine D2 Receptors Enhance Population Dynamics in Primate Prefrontal Working Memory Circuits

Working memory is associated with persistent activity in the prefrontal cortex (PFC). The neuromodulator dopamine, which is released by midbrain neurons projecting into the frontal lobe, influences PFC neurons and networks via the dopamine D1 (D1R) and the D2 receptor (D2R) families. Although behavioral, clinical and computational evidence suggest an involvement of D2Rs in working memory, a neuronal explanation is missing. We report an enhancement of persistent working memory responses of PFC neurons after iontophoretically stimulating D2Rs in monkeys memorizing the number of items in a display. D2R activation improved working memory representation at the population level and increased population dynamics during the transition from visual to mnemonic representations. Computational modeling suggests that D2Rs act by modulating interneuron-to-pyramidal signaling. By increasing the population's response dynamics, D2Rs might put PFC networks in a more flexible state and enhance the neurons' working memory coding, thereby controlling dynamic cognitive control.

Variations in Dysbindin-1 are associated with cognitive response to antipsychotic drug treatment

Antipsychotics are the most widely used medications for the treatment of schizophrenia spectrum disorders. While such drugs generally ameliorate positive symptoms, clinical responses are highly variable in terms of negative symptoms and cognitive impairments. However, predictors of individual responses have been elusive. Here, we report a pharmacogenetic interaction related to a core cognitive dysfunction in patients with schizophrenia. We show that genetic variations reducing dysbindin-1 expression can identify individuals whose executive functions respond better to antipsychotic drugs, both in humans and in mice. Multilevel ex vivo and in vivo analyses in postmortem human brains and genetically modified mice demonstrate that such interaction between antipsychotics and dysbindin-1 is mediated by an imbalance between the short and long isoforms of dopamine D2 receptors, leading to enhanced presynaptic D2 function within the prefrontal cortex. These findings reveal one of the pharmacodynamic mechanisms underlying individual cognitive response to treatment in patients with schizophrenia, suggesting a potential approach for improving the use of antipsychotic drugs.

A Schizophrenia-Related Deletion Leads to KCNQ2-Dependent Abnormal Dopaminergic Modulation of Prefrontal Cortical Interneuron Activity

Altered prefrontal cortex function is implicated in schizophrenia (SCZ) pathophysiology and could arise from imbalance between excitation and inhibition (E/I) in local circuits. It remains unclear whether and how such imbalances relate to genetic etiologies. We used a mouse model of the SCZ-predisposing 22q11.2 deletion (Df(16)A+/- mice) to evaluate how this genetic lesion affects the excitability of layer V prefrontal pyramidal neurons and its modulation by dopamine (DA). Df(16)A+/- mice have normal balance between E/I at baseline but are unable to maintain it upon dopaminergic challenge. Specifically, in wild-type mice, D1 receptor (D1R) activation enhances excitability of layer V prefrontal pyramidal neurons and D2 receptor (D2R) activation reduces it. Whereas the excitatory effect upon D1R activation is enhanced in Df(16)A+/- mice, the inhibitory effect upon D2R activation is reduced. The latter is partly due to the inability of mutant mice to activate GABAergic parvalbumin (PV)+ interneurons through D2Rs. We further demonstrate that reduced KCNQ2 channel function in PV+ interneurons in Df(16)A+/- mice renders them less capable of inhibiting pyramidal neurons upon D2 modulation. Thus, DA modulation of PV+ interneurons and control of E/I are altered in Df(16)A+/- mice with a higher excitation and lower inhibition during dopaminergic modulation.

Dopamine Receptors Influence Internally Generated Oscillations during Rule Processing in Primate Prefrontal Cortex

Neural oscillations in distinct frequency bands in the prefrontal cortex (pFC) are associated with specialized roles during cognitive control. How dopamine modulates oscillations to structure pFC functions remains unknown. We trained macaques to switch between two numerical rules and recorded local field potentials from pFC while applying dopamine receptor targeting drugs using microiontophoresis. We show that the D1 and D2 family receptors (D1Rs and D2Rs, respectively) specifically altered internally generated prefrontal oscillations, whereas sensory-evoked potentials remained unchanged. Blocking D1Rs or stimulating D2Rs increased low-frequency theta and alpha oscillations known to be involved in learning and memory. In contrast, only D1R inhibition enhanced high-frequency beta oscillations, whereas only D2R stimulation increased gamma oscillations linked to top–down and bottom–up attentional processing. These findings suggest that dopamine alters neural oscillations relevant for executive functioning through dissociable actions at the receptor level.

Improvement in cognitive abilities following cabergoline treatment in patients with a prolactin-secreting pituitary adenoma

Hyperprolactinaemia may affect sexual and reproductive functioning. However, recent studies suggest that increased prolactin levels may also have negative effects on cognition. We aimed to study whether the reduction in prolactin levels by cabergoline in patients with hyperprolactinaemia is followed by an improvement in cognitive tasks. We studied seven patients with hyperprolactinaemia caused by a prolactinoma that had an indication to start treatment with cabergoline. All patients were assessed twice (baseline and 6-12 months after cabergoline treatment) with a cognitive battery. Plasma prolactin levels were determined. We found a significant improvement in the speed of processing, working memory, visual learning and reasoning and problem-solving domains after cabergoline treatment. Improvements in speed of processing and reasoning and problem solving were greater in patients with baseline prolactin levels above the median. In summary, a reduction in prolactin levels by cabergoline in patients with hyperprolactinaemia is followed by an improvement in cognitive abilities. This finding suggests that prolactin may be involved in cognitive processes, although cabergoline could also have procognitive effects that are independent of prolactin changes. Further clinical trials are needed to confirm the potential cognitive-enhancement properties of cabergoline in patients with chronic hyperprolactinaemia.

Do TRPC channels support working memory? Comparing modulations of TRPC channels and working memory through G-protein coupled receptors and neuromodulators

Working memory is a crucial ability we use in daily life. However, the cellular mechanisms supporting working memory still remain largely unclear. A key component of working memory is persistent neural firing which is believed to serve short-term (hundreds of milliseconds up to tens of seconds) maintenance of necessary information. In this review, we will focus on the role of transient receptor potential canonical (TRPC) channels as a mechanism underlying persistent firing. Many years of in vitro work have been suggesting a crucial role of TRPC channels in working memory and temporal association tasks. If TRPC channels are indeed a central mechanism for working memory, manipulations which impair or facilitate working memory should have a similar effect on TRPC channel modulation. However, modulations of working memory and TRPC channels were never systematically compared, and it remains unanswered whether TRPC channels indeed contribute to working memory in vivo or not. In this article, we review the effects of G-protein coupled receptors (GPCR) and neuromodulators, including acetylcholine, noradrenalin, serotonin and dopamine, on working memory and TRPC channels. Based on comparisons, we argue that GPCR and downstream signaling pathways that activate TRPC, generally support working memory, while those that suppress TRPC channels impair it. However, depending on the channel types, areas, and systems tested, this is not the case in all studies. Further work to clarify involvement of specific TRPC channels in working memory tasks and how they are affected by neuromodulators is still necessary in the future.

Outcome Modulation Across Tasks in the Primate Dorsolateral Prefrontal Cortex

Animals need to learn and to adapt to new and changing environments so that appropriate actions that lead to desirable outcomes are acquired within each context. The prefrontal cortex (PF) is known to underlie such function that directly implies that the outcome of each response must be represented in the brain for behavioral policies update. However, whether such PF signal is context dependent or it is a general representation beyond the specificity of a context is still unclear. Here, we analyzed the activity of neurons in the dorsolateral PF (PFdl) recorded while two monkeys performed two perceptual magnitude discrimination tasks. Both tasks were well known by the monkeys and unexpected changes did not occur but the difficulty of the task varied from trial to trial and thus the monkeys made mistakes in a proportion of trials. We show a context-independent coding of the response outcome with neurons maintaining similar selectivity in both task contexts. Using a classification method of the neural activity, we also show that the trial outcome could be well predicted from the activity of the same neurons in the two contexts. Altogether, our results provide evidence of high degree of outcome generality in PFdl.

Ketamine Alters Lateral Prefrontal Oscillations in a Rule-Based Working Memory Task

Acute administration of N-methyl-D-aspartate receptor (NMDAR) antagonists in healthy humans and animals produces working memory deficits similar to those observed in schizophrenia. However, it is unclear whether they also lead to altered low-frequency (≤60 Hz) neural oscillatory activities similar to those associated with schizophrenia during working memory processes. Here, we recorded local field potentials (LFPs) and single-unit activity from the lateral prefrontal cortex (LPFC) of three male rhesus macaque monkeys while they performed a rule-based prosaccade and antisaccade working memory task both before and after systemic injections of a subanesthetic dose (≤0.7 mg/kg) of ketamine. Accompanying working-memory impairment, ketamine enhanced the low-gamma-band (30-60 Hz) and dampened the beta-band (13-30 Hz) oscillatory activities in the LPFC during both delay periods and intertrial intervals. It also increased task-related alpha-band activities, likely reflecting compromised attention. Beta-band oscillations may be especially relevant to working memory processes because stronger beta power weakly but significantly predicted shorter saccadic reaction time. Also in beta band, ketamine reduced the performance-related oscillation as well as the rule information encoded in the spectral power. Ketamine also reduced rule information in the spike field phase consistency in almost all frequencies up to 60 Hz. Our findings support NMDAR antagonists in nonhuman primates as a meaningful model for altered neural oscillations and synchrony, which reflect a disorganized network underlying the working memory deficits in schizophrenia.SIGNIFICANCE STATEMENT Low doses of ketamine, an NMDAR blocker, produce working memory deficits similar to those observed in schizophrenia. In the lateral prefrontal cortex, a key brain region for working memory, we found that ketamine altered neural oscillatory activities in similar ways that differentiate schizophrenic patients and healthy subjects during both task and nontask periods. Ketamine induced stronger gamma (30-60 Hz) and weaker beta (13-30 Hz) oscillations, reflecting local hyperactivity and reduced long-range communications. Furthermore, ketamine reduced performance-related oscillatory activities, as well as the rule information encoded in the oscillations and in the synchrony between single-cell activities and oscillations. The ketamine model helps link the molecular and cellular basis of neural oscillatory changes to the working memory deficit in schizophrenia.

Neuromodulatory Systems and Their Interactions: A Review of Models, Theories, and Experiments

Neuromodulatory systems, including the noradrenergic, serotonergic, dopaminergic, and cholinergic systems, track environmental signals, such as risks, rewards, novelty, effort, and social cooperation. These systems provide a foundation for cognitive function in higher organisms; attention, emotion, goal-directed behavior, and decision-making derive from the interaction between the neuromodulatory systems and brain areas, such as the amygdala, frontal cortex, hippocampus, and sensory cortices. Given their strong influence on behavior and cognition, these systems also play a key role in disease states and are the primary target of many current treatment strategies. The fact that these systems interact with each other either directly or indirectly, however, makes it difficult to understand how a failure in one or more systems can lead to a particular symptom or pathology. In this review, we explore experimental evidence, as well as focus on computational and theoretical models of neuromodulation. Better understanding of neuromodulatory systems may lead to the development of novel treatment strategies for a number of brain disorders.

Human subthalamic nucleus activity during non-motor decision making

Recent studies have implicated the subthalamic nucleus (STN) in decisions that involve inhibiting movements. Many of the decisions that we make in our daily lives, however, do not involve any motor actions. We studied non-motor decision making by recording intraoperative STN and prefrontal cortex (PFC) electrophysiology as participants perform a novel task that required them to decide whether to encode items into working memory. During all encoding trials, beta band (15-30 Hz) activity decreased in the STN and PFC, and this decrease was progressively enhanced as more items were stored into working memory. Crucially, the STN and lateral PFC beta decrease was significantly attenuated during the trials in which participants were instructed not to encode the presented stimulus. These changes were associated with increase lateral PFC-STN coherence and altered STN neuronal spiking. Our results shed light on why states of altered basal ganglia activity disrupt both motor function and cognition.

Dopamine terminals from the ventral tegmental area gate intrinsic inhibition in the prefrontal cortex

Spike frequency adaptation (SFA or accommodation) and calcium‐activated potassium channels that underlie after‐hyperpolarization potentials (AHP) regulate repetitive firing of neurons. Precisely how neuromodulators such as dopamine from the ventral tegmental area (VTA) regulate SFA and AHP (together referred to as intrinsic inhibition) in the prefrontal cortex (PFC) remains unclear. Using whole cell electrophysiology, we measured intrinsic inhibition in prelimbic (PL) layer 5 pyramidal cells of male adult rats. Results demonstrate that bath application of dopamine reduced intrinsic inhibition (EC₅₀: 25.0 μmol/L). This dopamine action was facilitated by coapplication of cocaine (1 μmol/L), a blocker of dopamine reuptake. To evaluate VTA dopamine terminals in PFC slices, we transfected VTA dopamine cells of TH::Cre rats in vivo with Cre‐dependent AAVs to express channelrhodopsin‐2 (ChR2) or designer receptors exclusively activated by designer drugs (DREADDS). In PFC slices from these animals, stimulation of VTA terminals with either blue light to activate ChR2 or bath application of clozapine‐N‐oxide (CNO) to activate Gq‐DREADDs produced a similar reduction in intrinsic inhibition in PL neurons. Electrophysiological recordings from cells expressing retrograde fluorescent tracers showed that this plasticity occurs in PL neurons projecting to the accumbens core. Collectively, these data highlight an ability of VTA terminals to gate intrinsic inhibition in the PFC, and under appropriate circumstances, enhance PL neuronal firing. These cellular actions of dopamine may be important for dopamine‐dependent behaviors involving cocaine and cue‐reward associations within cortical–striatal circuits.

Neuromodulation of Prefrontal Cortex in Non-Human Primates by Dopaminergic Receptors during Rule-Guided Flexible Behavior and Cognitive Control

The prefrontal cortex (PFC) is indispensable for several higher-order cognitive and executive capacities of primates, including representation of salient stimuli in working memory (WM), maintenance of cognitive task set, inhibition of inappropriate responses and rule-guided flexible behavior. PFC networks are subject to robust neuromodulation from ascending catecholaminergic systems. Disruption of these systems in PFC has been implicated in cognitive deficits associated with several neuropsychiatric disorders. Over the past four decades, a considerable body of work has examined the influence of dopamine on macaque PFC activity representing spatial WM. There has also been burgeoning interest in neuromodulation of PFC circuits involved in other cognitive functions of PFC, including representation of rules to guide flexible behavior. Here, we review recent neuropharmacological investigations conducted in our laboratory and others of the role of PFC dopamine receptors in regulating rule-guided behavior in non-human primates. Employing iontophoresis, we examined the effects of local manipulation of dopaminergic subtypes on neuronal activity during performance of rule-guided pro- and antisaccades, an experimental paradigm sensitive to PFC integrity, wherein deficits in performance are reliably observed in many neuropsychiatric disorders. We found dissociable effects of dopamine receptors on neuronal activity for rule representation and oculomotor responses and discuss these findings in the context of prior studies that have examined the role of dopamine in spatial delayed response tasks, attention, target selection, abstract rules, visuomotor learning and reward. The findings we describe here highlight the common features, as well as heterogeneity and context dependence of dopaminergic neuromodulation in regulating the efficacy of cognitive functions of PFC in health and disease.

Circuit Mechanisms of Sensorimotor Learning

The relationship between the brain and the environment is flexible, forming the foundation for our ability to learn. Here we review the current state of our understanding of the modifications in the sensorimotor pathway related to sensorimotor learning. We divide the process into three hierarchical levels with distinct goals: (1) sensory perceptual learning, (2) sensorimotor associative learning, and (3) motor skill learning. Perceptual learning optimizes the representations of important sensory stimuli. Associative learning and the initial phase of motor skill learning are ensured by feedback-based mechanisms that permit trial-and-error learning. The later phase of motor skill learning may primarily involve feedback-independent mechanisms operating under the classic Hebbian rule. With these changes under distinct constraints and mechanisms, sensorimotor learning establishes dedicated circuitry for the reproduction of stereotyped neural activity patterns and behavior.

Tonic or Phasic Stimulation of Dopaminergic Projections to Prefrontal Cortex Causes Mice to Maintain or Deviate from Previously Learned Behavioral Strategies

Dopamine neurons in the ventral tegmental area (VTA) encode reward prediction errors and can drive reinforcement learning through their projections to striatum, but much less is known about their projections to prefrontal cortex (PFC). Here, we studied these projections and observed phasic VTA-PFC fiber photometry signals after the delivery of rewards. Next, we studied how optogenetic stimulation of these projections affects behavior using conditioned place preference and a task in which mice learn associations between cues and food rewards and then use those associations to make choices. Neither phasic nor tonic stimulation of dopaminergic VTA-PFC projections elicited place preference. Furthermore, substituting phasic VTA-PFC stimulation for food rewards was not sufficient to reinforce new cue-reward associations nor maintain previously learned ones. However, the same patterns of stimulation that failed to reinforce place preference or cue-reward associations were able to modify behavior in other ways. First, continuous tonic stimulation maintained previously learned cue-reward associations even after they ceased being valid. Second, delivering phasic stimulation either continuously or after choices not previously associated with reward induced mice to make choices that deviated from previously learned associations. In summary, despite the fact that dopaminergic VTA-PFC projections exhibit phasic increases in activity that are time locked to the delivery of rewards, phasic activation of these projections does not necessarily reinforce specific actions. Rather, dopaminergic VTA-PFC activity can control whether mice maintain or deviate from previously learned cue-reward associations.SIGNIFICANCE STATEMENT Dopaminergic inputs from ventral tegmental area (VTA) to striatum encode reward prediction errors and reinforce specific actions; however, it is currently unknown whether dopaminergic inputs to prefrontal cortex (PFC) play similar or distinct roles. Here, we used bulk Ca²⁺ imaging to show that unexpected rewards or reward-predicting cues elicit phasic increases in the activity of dopaminergic VTA-PFC fibers. However, in multiple behavioral paradigms, we failed to observe reinforcing effects after stimulation of these fibers. In these same experiments, we did find that tonic or phasic patterns of stimulation caused mice to maintain or deviate from previously learned cue-reward associations, respectively. Therefore, although they may exhibit similar patterns of activity, dopaminergic inputs to striatum and PFC can elicit divergent behavioral effects.

Prefrontal Dopamine D1 and D2 Receptors Regulate Dissociable Aspects of Decision Making via Distinct Ventral Striatal and Amygdalar Circuits

Mesocortical dopamine (DA) regulates a variety of cognitive functions via actions on D1 and/or D2 receptors. For example, risk/reward decision making is modulated differentially by these two receptors within the prefrontal cortex (PFC), with D2 receptors enabling flexible decision making and D1 receptors promoting persistence in choice biases. However, it is unclear how DA mediates opposing patterns of behavior by acting on different receptors within the same terminal region. We explored the possibility that DA may act on separate networks of PFC neurons that are modulated by D1 or D2 receptors and in turn interface with divergent downstream structures such as the basolateral amygdala (BLA) or nucleus accumbens (NAc). Decision making was assessed using a probabilistic discounting task in which well trained male rats chose between small/certain or large/risky rewards, with the odds of obtaining the larger reward changing systematically within a session. Selective disruption of D1 or D2 modulation of separate PFC output pathways was achieved using unilateral intra-PFC infusions of DA antagonists combined with contralateral inactivation of the BLA or NAc. Disrupting D2 (but not D1) modulation of PFC→BLA circuitry impaired adjustments in decision biases in response to changes in reward probabilities. In contrast, disrupting D1 modulation of PFC→NAc networks reduced risky choice, attenuating reward sensitivity and increasing sensitivity to reward omissions. These findings reveal that mesocortical DA can facilitate dissociable components of reward seeking and action selection by acting on different functional networks of PFC neurons that can be distinguished by the subcortical projection targets with which they interface.SIGNIFICANCE STATEMENT Prefrontal cortical dopamine regulates a variety of executive functions governed by the frontal lobes via actions on D1 and D2 receptors. These receptors can in some instances mediate different patterns of behavior, but the mechanisms underlying these dissociable actions are unclear. Using a selective disconnection approach, we reveal that D1 and D2 receptors can facilitate diverse aspects of decision making by acting on separate networks of prefrontal neurons that interface with distinct striatal or amygdalar targets. These findings reveal an additional level of complexity in how mesocortical DA regulates different forms of cognition via actions on different receptors, highlighting how it may act upon distinct cortical microcircuits to drive different patterns of behavior.

Role of Anterior Cingulate Cortex in Instrumental Learning: Blockade of Dopamine D1 Receptors Suppresses Overt but Not Covert Learning

HIGHLIGHTS

Blockade of dopamine D1 receptors in ACC suppressed instrumental learning when overt responding was required.

Covert learning through observation was not impaired.

After treatment with a dopamine antagonist, instrumental learning recovered but not the rat's pretreatment level of effort tolerance.

ACC dopamine is not necessary for acquisition of task-relevant cues during learning, but regulates energy expenditure and effort based decision.

Dopamine activity in anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, including learning and effort based decision making. To dissociate learning from physical effort, we studied both observational (covert) learning, and trial-and-error (overt) learning. If ACC dopamine activity is required for task acquisition, its blockade should impair both overt and covert learning. If dopamine is not required for task acquisition, but solely for regulating the willingness to expend effort for reward, i.e., effort tolerance, blockade should impair overt learning but spare covert learning. Rats learned to push a lever for food rewards either with or without prior observation of an expert conspecific performing the same task. Before daily testing sessions, the rats received bilateral ACC microinfusions of SCH23390, a dopamine D1 receptor antagonist, or saline-control infusions. We found that dopamine blockade suppressed overt responding selectively, leaving covert task acquisition through observational learning intact. In subsequent testing sessions without dopamine blockade, rats recovered their overt-learning capacity but not their pre-treatment level of effort tolerance. These results suggest that ACC dopamine is not required for the acquisition of conditioned behaviors and that apparent learning impairments could instead reflect a reduced level of willingness to expend effort due to cortical dopamine blockade.

Current Concepts on the Physiopathological Relevance of Dopaminergic Receptors

Dopamine (DA) is a key neurotransmitter modulating essential functions of the central nervous system (CNS), like voluntary movement, reward, several cognitive functions and goal-oriented behaviors. The factual relevance of DAergic transmission can be well appreciated by considering that its dysfunction is recognized as a core alteration in several devastating neurological and psychiatric disorders, including Parkinson’s disease (PD) and associated movement disorders, as well as, schizophrenia, bipolar disorder, attention deficit hyperactivity disorder (ADHD) and addiction. Here we present an overview of the current knowledge on the involvement of DAergic receptors in the regulation of key physiological brain activities, and the consequences of their dysfunctions in brain disorders such as PD, schizophrenia and addiction.

Prefrontal Markers and Cognitive Performance Are Dissociated during Progressive Dopamine Lesion

Dopamine is thought to directly influence the neurophysiological mechanisms of both performance monitoring and cognitive control-two processes that are critically linked in the production of adapted behaviour. Changing dopamine levels are also thought to induce cognitive changes in several neurological and psychiatric conditions. But the working model of this system as a whole remains untested. Specifically, although many researchers assume that changing dopamine levels modify neurophysiological mechanisms and their markers in frontal cortex, and that this in turn leads to cognitive changes, this causal chain needs to be verified. Using longitudinal recordings of frontal neurophysiological markers over many months during progressive dopaminergic lesion in non-human primates, we provide data that fail to support a simple interaction between dopamine, frontal function, and cognition. Feedback potentials, which are performance-monitoring signals sometimes thought to drive successful control, ceased to differentiate feedback valence at the end of the lesion, just before clinical motor threshold. In contrast, cognitive control performance and beta oscillatory markers of cognitive control were unimpaired by the lesion. The differing dynamics of these measures throughout a dopamine lesion suggests they are not all driven by dopamine in the same way. These dynamics also demonstrate that a complex non-linear set of mechanisms is engaged in the brain in response to a progressive dopamine lesion. These results question the direct causal chain from dopamine to frontal physiology and on to cognition. They imply that biomarkers of cognitive functions are not directly predictive of dopamine loss.

Targeting Prefrontal Cortical Systems for Drug Development: Potential Therapies for Cognitive Disorders

Medications to treat cognitive disorders are increasingly needed, yet researchers have had few successes in this challenging arena. Cognitive abilities in primates arise from highly evolved N-methyl-d-aspartate (NMDA) receptor circuits in layer III of the dorsolateral prefrontal cortex. These circuits have unique modulatory needs that can differ from the layer V neurons that predominate in rodents, but they offer multiple therapeutic targets. Cognitive improvement often requires low doses that enhance the pattern of information held in working memory, whereas higher doses can produce nonspecific changes that obscure information. Identifying appropriate doses for clinical trials may be helped by assessments in monkeys and by flexible, individualized dose designs. The use of guanfacine (Intuniv) for prefrontal cortical disorders was based on research in monkeys, supporting this approach. Coupling our knowledge of higher primate circuits with the powerful methods now available in drug design will help create effective treatments for cognitive disorders.