Extinction of Cocaine Seeking Requires a Window of Infralimbic Pyramidal Neuron Activity after Unreinforced Lever Presses

A Prefrontal Cortex-Nucleus Accumbens Circuit Attenuates Cocaine-conditioned Place Preference Memories

The infralimbic (IL) subregion of the prefrontal cortex (PFC), via its descending projection to the nucleus accumbens (NAc), inhibits cue-induced drug seeking and reinstatement, but the underlying mechanisms are not fully understood. Here we show that the activity of IL layer 5 pyramidal neurons projecting to the NAc shell (IL-NAcSh neurons) suppresses cocaine-associated memories. Following repeated cocaine exposures in a conditioned place preference paradigm, IL-NAcSh neurons anatomically traced by fluorescent Retrobeads undergo prolonged decrease of membrane excitability, lasting for at least 15 days after cocaine withdrawal. This persistent IL-NAcSh neuron hypoexcitability is accompanied by an increase in the rheobase, an increase in the afterhyperpolarization potential, and a decrease in the membrane input resistance. This cocaine induced neuroadapation in intrinsic excitability is not observed in prelimibic cortex neurons projecting to the NAc core (PL-NAcCo neurons), a separate descending circuit thought to promote cue-triggered drug seeking. Chemogenetic restoration of IL-NAcSh neuron activity extinguishes both the acquisition and retention of cocaine conditioned place preference memories. Our results provide direct support for the notion that the IL-NAcSh circuit serves to extinct drug associated memories and restoring the drug impaired excitability of IL-NAcSh neurons has the potential to mitigate drug-cue association memories and drug seeking.

A Prefrontal Cortex-Nucleus Accumbens Circuit Attenuates Cocaine-conditioned Place Preference Memories

The infralimbic (IL) subregion of the prefrontal cortex (PFC), via its descending projection to the nucleus accumbens (NAc), inhibits cue-induced drug seeking and reinstatement, but the underlying mechanisms are not fully understood. Here we show that the intrinsic membrane excitability of IL layer 5 pyramidal neurons projecting to the NAc shell (IL-NAcSh neurons) suppresses cocaine-associated memories. Following repeated cocaine exposures in a conditioned place preference paradigm, IL-NAcSh neurons anatomically traced by fluorescent retrobeads undergo prolonged decrease of membrane excitability, lasting for at least 15 days after cocaine withdrawal. This persistent IL-NAcSh neuron hypoexcitability was accompanied by an increase in the rheobase, an increase in the afterhyperpolarization potential, and a decrease in the membrane input resistance. This cocaine induced neuroadapation in intrinsic excitability was not observed in prelimibic cortex neurons projecting to the NAc core (PL-NAcCo neurons), a separate descending circuit thought to promote cue-triggered drug seeking. Chemogenetic restoration of IL-NAcSh neuron activity extinguishes both the acquisition and retention of cocaine conditioned place preference memories. Our results provide direct support for the notion that the IL-NAcSh circuit serves to extinct drug associated memories and restoring the drug impaired excitability of IL-NAcSh neurons has the potential to mitigate drug-cue association memories and drug seeking.

The infralimbic, but not the prelimbic cortex is needed for a complex olfactory memory task

The medial prefrontal cortex (mPFC) plays a key role in memory and behavioral flexibility, and a growing body of evidence suggests that the prelimbic (PL) and infralimbic (IL) subregions contribute differently to these processes. Studies of fear conditioning and goal-directed learning suggest that the PL promotes behavioral responses and memory retrieval, while the IL inhibits them. Other studies have shown that the mPFC is engaged under conditions of high interference. This raises the possibility that the PL and IL play differing roles in resolving interference. To examine this, we first used chemogenetics (DREADDs) to suppress mPFC neuronal activity and tested subjects on a conditional discrimination task known to be sensitive to muscimol inactivation. After confirming the effectiveness of the DREADD procedures, we conducted a second experiment to examine the PL and IL roles in a high interference memory task. We trained rats on two consecutive sets of conflicting odor discrimination problems, A and B, followed by test sessions involving a mid-session switch between the problem sets. Controls repeatedly performed worse on Set A, suggesting that learning Set B inhibited the rats' ability to retrieve Set A memories (i.e. retroactive interference). PL inactivation rats performed similarly to controls. However, IL inactivation rats did not show this effect, suggesting that the IL plays a critical role in suppressing the retrieval of previously acquired memories that may interfere with retrieval of more recent memories. These results suggest that the IL plays a critical role in memory control processes needed for resolving interference.

The Infralimbic, but not the Prelimbic Cortex is needed for a Complex Olfactory Memory Task

The medial prefrontal cortex (mPFC) plays a key role in memory and behavioral flexibility, and a growing body of evidence suggests that the prelimbic (PL) and infralimbic (IL) subregions contribute differently to these processes. Studies of fear conditioning and goal-directed learning suggest that the PL promotes behavioral responses and memory retrieval, while the IL inhibits them. Other studies have shown that the mPFC is engaged under conditions of high interference. This raises the possibility that the PL and IL play differing roles in resolving interference. To examine this, we first used chemogenetics (DREADDs) to suppress mPFC neuronal activity and tested subjects on a conditional discrimination task known to be sensitive to muscimol inactivation. After confirming the effectiveness of the DREADD procedures, we conducted a second experiment to examine the PL and IL roles in a high interference memory task. We trained rats on two consecutive sets of conflicting odor discrimination problems, A and B, followed by test sessions involving a mid-session switch between the problem sets. Controls repeatedly performed worse on Set A, suggesting that learning Set B inhibited the rats' ability to retrieve Set A memories (i.e. retroactive interference). PL inactivation rats performed similarly to controls. However, IL inactivation rats did not show this effect, suggesting that the IL plays a critical role in suppressing the retrieval of previously acquired memories that may interfere with retrieval of more recent memories. These results suggest that the IL plays a critical role in memory control processes needed for resolving interference.

Vagus Nerve Stimulation (VNS) Modulates Synaptic Plasticity in the Infralimbic Cortex via Trk-B Receptor Activation to Reduce Drug-Seeking in Male Rats

Drugs of abuse cause changes in the prefrontal cortex (PFC) and associated regions that impair inhibitory control over drug-seeking. Breaking the contingencies between drug-associated cues and the delivery of the reward during extinction learning reduces relapse. Vagus nerve stimulation (VNS) has previously been shown to enhance extinction learning and reduce drug-seeking. Here we determined the effects of VNS-mediated release of brain-derived neurotrophic factor (BDNF) on extinction and cue-induced reinstatement in male rats trained to self-administer cocaine. Pairing 10 d of extinction training with VNS facilitated extinction and reduced drug-seeking behavior during reinstatement. Rats that received a single extinction session with VNS showed elevated BDNF levels in the medial PFC as determined via an enzyme-linked immunosorbent assay. Systemic blockade of tropomyosin receptor kinase B (TrkB) receptors during extinction, via the TrkB antagonist ANA-12, decreased the effects of VNS on extinction and reinstatement. Whole-cell recordings in brain slices showed that cocaine self-administration induced alterations in the ratio of AMPA and NMDA receptor-mediated currents in Layer 5 pyramidal neurons of the infralimbic cortex (IL). Pairing extinction with VNS reversed cocaine-induced changes in glutamatergic transmission by enhancing AMPAR currents, and this effect was blocked by ANA-12. Our study suggests that VNS consolidates the extinction of drug-seeking behavior by reversing drug-induced changes in synaptic AMPA receptors in the IL, and this effect is abolished by blocking TrkB receptors during extinction, highlighting a potential mechanism for the therapeutic effects of VNS in addiction.

Examining a punishment-related brain circuit with miniature fluorescence microscopes and deep learning

In humans experiencing substance use disorder (SUD), abstinence from drug use is often motivated by a desire to avoid some undesirable consequence of further use: health effects, legal ramifications, etc. This process can be experimentally modeled in rodents by training and subsequently punishing an operant response in a context-induced reinstatement procedure. Understanding the biobehavioral mechanisms underlying punishment learning is critical to understanding both abstinence and relapse in individuals with SUD. To date, most investigations into the neural mechanisms of context-induced reinstatement following punishment have utilized discrete loss-of-function manipulations that do not capture ongoing changes in neural circuitry related to punishment-induced behavior change. Here, we describe a two-pronged approach to analyzing the biobehavioral mechanisms of punishment learning using miniature fluorescence microscopes and deep learning algorithms. We review recent advancements in both techniques and consider a target neural circuit.

Infralimbic cortex plays a similar role in the punishment and extinction of instrumental behavior

Learning to stop responding is a fundamental process in instrumental learning. Animals may learn to stop responding under a variety of conditions that include punishment-where the response earns an aversive stimulus in addition to a reinforcer-and extinction-where a reinforced response now earns nothing at all. Recent research suggests that punishment and extinction may be related manifestations of a common retroactive interference process. In both paradigms, animals learn to stop performing a specific response in a specific context, suggesting direct inhibition of the response by the context. This process may depend on the infralimbic cortex (IL), which has been implicated in a variety of interference-based learning paradigms including extinction and habit learning. Despite the behavioral parallels between extinction and punishment, a corresponding role for IL in punishment has not been identified. Here we report that, in a simple arrangement where either punishment or extinction was conducted in a context that differed from the context in which the behavior was first acquired, IL inactivation reduced response suppression in the inhibitory context, but not responding when it "renewed" in the original context. In a more complex arrangement in which two responses were first trained in different contexts and then extinguished or punished in the opposite one, IL inactivation had no effect. The results advance our understanding of the effects of IL in retroactive interference and the behavioral mechanisms that can produce suppression of a response.

Vagus nerve stimulation (VNS) modulates synaptic plasticity in the rat infralimbic cortex via Trk-B receptor activation to reduce drug-seeking

Drugs of abuse cause changes in the prefrontal cortex (PFC) and associated regions that impair inhibitory control over drug-seeking. Breaking the contingencies between drug-associated cues and the delivery of the reward during extinction learning reduces relapse. Vagus nerve stimulation (VNS) has previously been shown to enhance extinction learning and reduce drug-seeking. Here we determined the effects of VNS-mediated release of brain-derived neurotrophic factor (BDNF) on extinction and cue-induced reinstatement in rats trained to self-administer cocaine. Pairing 10 days of extinction training with VNS facilitated extinction and reduced drug-seeking behavior during reinstatement. Rats that received a single extinction session with VNS showed elevated BDNF levels in the medial PFC as determined via an enzyme-linked immunosorbent assay (ELISA). Systemic blockade of Tropomyosin receptor kinase B (TrkB) receptors during extinction, via the TrkB antagonist ANA-12, decreased the effects of VNS on extinction and reinstatement. Whole-cell recordings in brain slices showed that cocaine self-administration induced alterations in the ratio of AMPA and NMDA receptor-mediated currents in layer 5 pyramidal neurons of the infralimbic cortex (IL). Pairing extinction with VNS reversed cocaine-induced changes in glutamatergic transmission by enhancing AMPAR currents, and this effect was blocked by ANA-12. Our study suggests that VNS consolidates extinction of drug-seeking behavior by reversing drug-induced changes in synaptic AMPA receptors in the IL, and this effect is abolished by blocking TrkB receptors during extinction, highlighting a potential mechanism for the therapeutic effects of VNS in addiction.

Still a "hidden island"? The rodent insular cortex in drug seeking, reward, and risk

The insular cortex (IC) is implicated in risky decision making and drug-seeking behaviors, in a manner dissociable from natural reward seeking. However, evidence from rodent studies of motivated behaviors suggests that the role of the IC is not always consistent across procedures. Moreover, there is evidence of dissociation of function between posterior (pIC) and anterior (aIC) subregions in these behaviors. Under which circumstances, and by which mechanisms, these IC subregions are recruited to regulate motivated behaviors remains unclear. Here, we discuss evidence of rodent pIC and aIC function across drug-related behaviors, natural reward seeking, and decision making under risk and highlight procedural differences that may account for seemingly conflicting findings. Although gaps in the literature persist, we hypothesize that IC activity is broadly important for selection of appropriate behaviors based on learned action-outcome contingencies and that associated risk is sufficient, but not necessary, to recruit the aIC in reward seeking without involving the pIC.

Theoretical Considerations for Optimizing the Use of Optogenetics with Complex Behavior

Optogenetic approaches have allowed researchers to address complex questions about behavior that were previously unanswerable. However, as optogenetic procedures involve a large parameter space across multiple dimensions, it is crucial to consider such parameters in conjunction with the behaviors under study. Here, we discuss strategies to optimize optogenetic approaches with complex behavior by identifying critical experimental design considerations, including frequency specificity, temporal precision, activity-controlled optogenetics, stimulation pattern, and cell-type specificity. We highlight potential limitations or theoretical considerations to be made when manipulating each of these factors of optogenetic experiments. This overview emphasizes the importance of optimizing optogenetic study design to enhance the conclusions that can be drawn about the neuroscience of behavior. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC.

Optogenetic stimulation of infralimbic cortex projections to the paraventricular thalamus attenuates context-induced renewal

Contexts associated with prior reinforcement can renew extinguished conditioned responding. The prelimbic (PL) and infralimbic (IL) cortices are thought to mediate the expression and suppression of conditioned responding, respectively. Evidence suggests that PL inputs to the paraventricular nucleus of the thalamus (PVT) drive the expression of cue-induced reinstatement of drug seeking and that IL inputs to the PVT mediate fear extinction retrieval. However, the role of these projections in renewal of appetitive Pavlovian conditioned responding is unknown. We trained male and female Long-Evans rats to associate a conditioned stimulus (CS; 10 s white noise) with delivery of a 10% sucrose unconditioned stimulus (US; .2 ml/CS) to a fluid port in a distinct context (Context A). We then extinguished responding by presenting the CS without the US in a different context (Context B). At test, rats were returned to Context A, and optogenetic stimulation was delivered to either the IL-to-PVT or PL-to-PVT pathway during CS presentations. Optically stimulating the IL-to-PVT, but not the PL-to-PVT pathway, attenuated ABA renewal of CS port entries, and this effect was similar in males and females. Further, rats self-administered optical stimulation of the IL-to-PVT but not the PL-to-PVT pathway suggesting that activation of the IL-to-PVT pathway is reinforcing. The effectiveness of optical stimulation parameters to activate neurons in the IL, PL and PVT was confirmed using Fos immunohistochemistry. These findings provide evidence for novel neural mechanisms in renewal of responding to a sucrose-predictive CS, as well as more generally in contextual processing and appetitive associative learning.

Neural correlates of recall and extinction in a rat model of appetitive Pavlovian conditioning

Extinction is a fundamental form of inhibitory learning that is important for adapting to changing environmental contingencies. While numerous studies have investigated the neural correlates of extinction using Pavlovian fear conditioning and appetitive operant reward-seeking procedures, less is known about the neural circuitry mediating the extinction of appetitive Pavlovian responding. Here, we aimed to generate an extensive brain activation map of extinction learning in a rat model of appetitive Pavlovian conditioning. Male Long-Evans rats were trained to associate a conditioned stimulus (CS; 20 s white noise) with the delivery of a 10% sucrose unconditioned stimulus (US; 0.3 ml/CS) to a fluid port. Control groups also received CS presentations, but sucrose was delivered either during the inter-trial interval or in the home-cage. After conditioning, 1 or 6 extinction sessions were conducted in which the CS was presented but sucrose was withheld. We performed Fos immunohistochemistry and network connectivity analyses on a set of cortical, striatal, thalamic, and amygdalar brain regions. Neural activity in the prelimbic cortex, ventral orbitofrontal cortex, nucleus accumbens core, and paraventricular nucleus of the thalamus was greater during recall relative to extinction. Conversely, prolonged extinction following 6 sessions induced increased neural activity in the infralimbic cortex, medial orbitofrontal cortex, and nucleus accumbens shell compared to home-cage controls. All these structures were similarly recruited during recall on the first extinction session. These findings provide novel evidence for the contribution of brain areas and neural networks that are differentially involved in the recall versus extinction of appetitive Pavlovian conditioned responding.

Infralimbic Projections to the Nucleus Accumbens Shell and Amygdala Regulate the Encoding of Cocaine Extinction Learning

Prior evidence indicates that the infralimbic cortex (IL) mediates the ongoing inhibition of cocaine seeking following self-administration and extinction training in rats, specifically through projections to the nucleus accumbens shell (NAshell). Our own data indicate that IL activity immediately following an unreinforced lever press is critical for encoding the extinction contingencies in such procedures. Whether extinction encoding requires activity in the IL exclusively or also activity in its outputs, such as those to the NAshell and amygdala, is unknown. To address this issue, we used a closed-loop optogenetic approach in female and male Sprague Dawley rats to silence IL-NAshell or IL-amygdala activity following an unreinforced lever press during extinction training. Optical illumination (20 s) was given either immediately after a lever press or following a 20 s delay. IL-NAshell inhibition immediately following an unreinforced lever press increased lever pressing during extinction training and impaired retention of extinction learning, as assessed during subsequent extinction sessions without optical inhibition. Likewise, IL-amygdala inhibition given in the same manner impaired extinction retention during sessions without inhibition. Control experiments indicate that critical encoding of extinction learning does not require activity in these pathways beyond the initial 20 s post-lever press period, as delayed IL-NAshell and IL-amygdala inhibition had no effect on extinction learning. These results suggest that a larger network extending from the IL to the NAshell and amygdala is involved in encoding extinction contingencies following cocaine self-administration.SIGNIFICANCE STATEMENT Infralimbic cortex (IL) activity following an unreinforced lever press during extinction learning encodes the extinction of cocaine-seeking behavior. However, the larger circuitry controlling such encoding has not been investigated. Using closed-loop optogenetic pathway targeting, we found that inhibition of IL projections to the nucleus accumbens shell and to the amygdala impaired the extinction of cocaine seeking. Importantly, these effects were only observed when activity was disrupted during the first 20 s post-lever press and not when given following a 20 s delay. These findings suggest that successful cocaine extinction encoding requires activity across a larger circuit beyond simply inputs to the IL.

Persistent increase of accumbens cocaine ensemble excitability induced by IRK downregulation after withdrawal mediates the incubation of cocaine craving

The incubation phenomenon, cue-induced drug craving progressively increasing over prolonged withdrawal, accounts for persistent relapse, leading to a dilemma in the treatment of cocaine addiction. The role of neuronal ensembles activated by initial cocaine experience in the incubation phenomenon was unclear. In this study, with cocaine self-administration (SA) models, we found that neuronal ensembles in the nucleus accumbens shell (NAcSh) showed increasing activation induced by cue-induced drug-seeking after 30-day withdrawal. Inhibition or activation of NAcSh cocaine-ensembles suppressed or promoted craving for cocaine, demonstrating a critical role of NAcSh cocaine-ensembles in incubation for cocaine craving. NAcSh cocaine-ensembles showed a specific increase of membrane excitability and a decrease of inward rectifying channels Kir_2.1 currents after 30-day withdrawal. Overexpression of Kir_2.1 in NAcSh cocaine-ensembles restored neuronal membrane excitability and suppressed cue-induced drug-seeking after 30-day withdrawal. Expression of dominant-negative Kir_2.1 in NAcSh cocaine-ensembles enhanced neuronal membrane excitability and accelerated incubation of cocaine craving. Our results provide a cellular mechanism that the downregulation of Kir_2.1 functions in NAcSh cocaine-ensembles induced by prolonged withdrawal mediates the enhancement of ensemble membrane excitability, leading to incubation of cocaine craving.

The roles of rat medial prefrontal and orbitofrontal cortices in relapse to cocaine-seeking: A comparison across methods for identifying neurocircuits

A large body of research supports the notion that regions of the rodent frontal cortex regulate reinstatement of cocaine seeking after cessation of intravenous cocaine self-administration. However, earlier studies identifying the roles of medial (mPFC) and orbital prefrontal cortices (OFC) in reinstatement relied on pharmacological inactivation methods, which indiscriminately inhibited cells within a target region. Here, we first review the anatomical borders and pathways of the rat mPFC and OFC. Next, we compare and contrast findings from more recent cocaine seeking and reinstatement studies that used chemogenetics, optogenetics, or advanced tracing to manipulate specific local cell types or input/output projections of the mPFC and OFC subregions. We found that these studies largely corroborated the roles for mPFC subregions as ascribed by pharmacological inactivation studies. Namely, the prelimbic cortex generally drives cocaine seeking behaviors while the infralimbic cortex is recruited to inhibit cocaine seeking by extinction training but may contribute to seeking after prolonged abstinence. While the OFC remains understudied, we suggest it should not be overlooked, and, as with prelimbic and infralimbic cortices, we identify specific pathways of interest for future studies.

The rodent medial prefrontal cortex and associated circuits in orchestrating adaptive behavior under variable demands

Emerging evidence implicates rodent medial prefrontal cortex (mPFC) in tasks requiring adaptation of behavior to changing information from external and internal sources. However, the computations within mPFC and subsequent outputs that determine behavior are incompletely understood. We review the involvement of mPFC subregions, and their projections to the striatum and amygdala in two broad types of tasks in rodents: 1) appetitive and aversive Pavlovian and operant conditioning tasks that engage mPFC-striatum and mPFC-amygdala circuits, and 2) foraging-based tasks that require decision making to optimize reward. We find support for region-specific function of the mPFC, with dorsal mPFC and its projections to the dorsomedial striatum supporting action control with higher cognitive demands, and ventral mPFC engagement in translating affective signals into behavior via discrete projections to the ventral striatum and amygdala. However, we also propose that defined mPFC subdivisions operate as a functional continuum rather than segregated functional units, with crosstalk that allows distinct subregion-specific inputs (e.g., internal, affective) to influence adaptive behavior supported by other subregions.

Corticostriatal Suppression of Appetitive Pavlovian Conditioned Responding

The capacity to suppress learned responses is essential for animals to adapt in dynamic environments. Extinction is a process by which animals learn to suppress conditioned responding when an expected outcome is omitted. The infralimbic (IL) cortex to nucleus accumbens shell (NAcS) neural circuit is implicated in suppressing conditioned responding after extinction, especially in the context of operant cocaine-seeking behavior. However, the role of the IL-to-NAcS neural circuit in the extinction of responding to appetitive Pavlovian cues is unknown, and the psychological mechanisms involved in response suppression following extinction are unclear. We trained male Long Evans rats to associate a 10 s auditory conditioned stimulus (CS; 14 trials per session) with a sucrose unconditioned stimulus (US; 0.2 ml per CS) in a specific context, and then following extinction in a different context, precipitated a renewal of CS responding by presenting the CS alone in the original Pavlovian conditioning context. Unilateral, optogenetic stimulation of the IL-to-NAcS circuit selectively during CS trials suppressed renewal. In a separate experiment, IL-to-NAcS stimulation suppressed CS responding regardless of prior extinction and impaired extinction retrieval. Finally, IL-to-NAcS stimulation during the CS did not suppress the acquisition of Pavlovian conditioning but was required for the subsequent expression of CS responding. These results are consistent with multiple studies showing that the IL-to-NAcS neural circuit is involved in the suppression of operant cocaine-seeking, extending these findings to appetitive Pavlovian cues. The suppression of appetitive Pavlovian responding following IL-to-NAcS circuit stimulation, however, does not appear to be an extinction-dependent process.SIGNIFICANCE STATEMENT Extinction is a form of inhibitory learning through which animals learn to suppress conditioned responding in the face of nonreinforcement. We investigated the role of the IL cortex inputs to the NAcS in the extinction of responding to appetitive Pavlovian cues and the psychological mechanisms involved in response suppression following extinction. Using in vivo optogenetics, we found that stimulating the IL-to-NAcS neural circuit suppressed context-induced renewal of conditioned responding after extinction. In a separate experiment, stimulating the IL-to-NAcS circuit suppressed conditioned responding in an extinction-independent manner. These findings can be used by future research aimed at understanding how corticostriatal circuits contribute to behavioral flexibility and mental disorders that involve the suppression of learned behaviors.

When the front fails, the rear wins. Cerebellar correlates of prefrontal dysfunction in cocaine-induced memory in male rats

Reciprocal pathways connecting the cerebellum to the prefrontal cortex provide a biological and functional substrate to modulate cognitive functions. Dysfunction of both medial prefrontal cortex (mPFC) and cerebellum underlie the phenotypes of several neuropsychiatric disorders that exhibit comorbidity with substance use disorder (SUD). In people with SUD, cue-action-reward associations appears to be particularly strong and salient, acting as powerful motivational triggers for craving and relapse. Studies of cue reactivity in human with SUD have shown cerebellar activations when drug-related cues are presented. Our preclinical research showed that cocaine-induced conditioned preference increases neural activity and upregulates perineuronal nets (PNNs) around Golgi interneurons in the posterior cerebellar cortex. In the present investigation, we aimed at evaluating cerebellar signatures of conditioned preference for cocaine when drug learning is established under mPFC impairment. We used lidocaine to temporarily inactivate in male rats either the Prelimbic (PL) or the Infralimbic (IL) cortices during cocaine-induced conditioning. The inactivation of the IL, but not the PL, encouraged the acquisition of preference for cocaine-related cues, increased posterior cerebellar cortex activity, and upregulated the expression of PNNs around Golgi interneurons. Moreover, IL impairment not only increased vGluT2- and vGAT-related activity around Golgi cells but also regulated PNNs differently on subpopulations of Golgi cells, increasing the number of neurogranin+ PNN-expressing Golgi cells. Our findings suggest that IL dysfunction may facilitate the acquisition of cocaine-induced memory and cerebellar drug-related learning hallmarks. Overall, IL perturbation during cocaine-induced Pavlovian learning increased cerebellar activity and drug effects. Importantly, cerebellum involvement requires a contingent experience with the drug, and it is not the effect of a mere inactivation of IL cortex.

Theta oscillations in rat infralimbic cortex are associated with the inhibition of cocaine seeking during extinction

Infralimbic cortical (IL) manipulations indicate that this region mediates extinction learning and suppresses cocaine seeking following cocaine self‐administration. However, little work has recorded IL activity during the inhibition of cocaine seeking due to the difficulty of determining precisely when cocaine‐seeking behaviour is inhibited within a cocaine‐seeking session. The present study used in vivo electrophysiology to examine IL activity across extinction as well as during cocaine self‐administration and reinstatement. Sprague–Dawley rats underwent 6‐h access cocaine self‐administration in which the response lever was available during discrete signalled trials, a procedure which allowed for the comparison between epochs of cocaine seeking versus the inhibition thereof. Subsequently, rats underwent extinction and cocaine‐primed reinstatement using the same procedure. Results indicate that theta rhythms (4–10 Hz) dominated IL local‐field potential (LFP) activity during all experimental stages. During extinction, theta power fluctuated significantly surrounding the lever press and was lower when rats engaged in cocaine seeking versus when they withheld from doing so. These patterns of oscillatory activity differed from self‐administration and reinstatement stages. Single‐unit analyses indicate heterogeneity of IL unit responses, supporting the idea that multiple neuronal subpopulations exist within the IL and promote the expression of different and even opposing cocaine‐seeking behaviours. Together, these results are consistent with the idea that aggregate synaptic and single‐unit activity in the IL represent the engagement of the IL in action monitoring to promote adaptive behaviour in accordance with task contingencies and reveal critical insights into the relationship between IL activity and the inhibition of cocaine seeking.

Infralimbic cortex functioning across motivated behaviors: Can the differences be reconciled?

The rodent infralimbic cortex (IL) is implicated in higher order executive functions such as reward seeking and flexible decision making. However, the precise nature of its role in these processes is unclear. Early evidence indicated that the IL promotes the extinction and ongoing inhibition of fear conditioning and cocaine seeking. However, evidence spanning other behavioral domains, such as natural reward seeking and habit-based learning, suggests a more nuanced understanding of IL function. As techniques have advanced and more studies have examined IL function, identifying a unifying explanation for its behavioral function has become increasingly difficult. Here, we discuss evidence of IL function across motivated behaviors, including associative learning, drug seeking, natural reward seeking, and goal-directed versus habit-based behaviors, and emphasize how context-specific encoding and heterogeneous IL neuronal populations may underlie seemingly conflicting findings in the literature. Together, the evidence suggests that a major IL function is to facilitate the encoding and updating of contingencies between cues and behaviors to guide subsequent behaviors.

Elevated fear responses to threatening cues in rats with early life stress is associated with greater excitability and loss of gamma oscillations in ventral-medial prefrontal cortex

Stress experienced early in development can have profound influences on developmental trajectories and ultimately behaviors in adulthood. Potent stressors during brain maturation can profoundly disrupt prefrontal cortical areas in particular, which can set the stage for prefrontal-dependent alterations in fear regulation and risk of drug abuse in adulthood. Despite these observations, few studies have investigated in vivo signaling in prefrontal signals in animals with a history of early life stress (ELS). Here, rats with ELS experienced during the first post-natal week were then tested on a conditioned suppression paradigm during adulthood. During conditioned suppression, electrophysiological recordings were made in the ventral medial prefrontal cortex (vmPFC) during presentations of a fear-associated cue that resolved both single-unit activity and local field potentials (LFPs). Relative to unstressed controls, ELS-experienced rats showed greater fear-related suppression of lever pressing. During presentations of the fear-associated cue (CS+), neurons in the vmPFC of ELS animals showed a significant increase in the probability of excitatory encoding relative to controls, and excitatory phasic responses in the ELS animals were reliably of higher magnitude than Controls. In contrast, vmPFC neurons in ELS subjects better discriminated between the shock-associated CS+ and the neutral ("safe") CS- cue than Controls. LFPs recorded in the same locations revealed that high gamma band (65-95 Hz) oscillations were strongly potentiated in Controls during presentation of the fear-associated CS+ cue, but this potentiation was abolished in ELS subjects. Notably, no other LFP spectra differed between ELS and Controls for either the CS+ or CS-. Collectively, these data suggest that ELS experience alters the neurobehavioral functions of PFC in adulthood that are critical for processing fear regulation. As such, these alterations may also provide insight into increased susceptibility to other PFC-dependent processes such as risk-based choice, motivation, and regulation of drug use and relapse in ELS populations.

The Paradoxical Effect Hypothesis of Abused Drugs in a Rat Model of Chronic Morphine Administration

A growing body of studies has recently shown that abused drugs could simultaneously induce the paradoxical effect in reward and aversion to influence drug addiction. However, whether morphine induces reward and aversion, and which neural substrates are involved in morphine’s reward and aversion remains unclear. The present study first examined which doses of morphine can simultaneously produce reward in conditioned place preference (CPP) and aversion in conditioned taste aversion (CTA) in rats. Furthermore, the aversive dose of morphine was determined. Moreover, using the aversive dose of 10 mg/kg morphine tested plasma corticosterone (CORT) levels and examined which neural substrates were involved in the aversive morphine-induced CTA on conditioning, extinction, and reinstatement. Further, we analyzed c-Fos and p-ERK expression to demonstrate the paradoxical effect—reward and aversion and nonhomeostasis or disturbance by morphine-induced CTA. The results showed that a dose of more than 20 mg/kg morphine simultaneously induced reward in CPP and aversion in CTA. A dose of 10 mg/kg morphine only induced the aversive CTA, and it produced higher plasma CORT levels in conditioning and reacquisition but not extinction. High plasma CORT secretions by 10 mg/kg morphine-induced CTA most likely resulted from stress-related aversion but were not a rewarding property of morphine. For assessments of c-Fos and p-ERK expression, the cingulate cortex 1 (Cg1), prelimbic cortex (PrL), infralimbic cortex (IL), basolateral amygdala (BLA), nucleus accumbens (NAc), and dentate gyrus (DG) were involved in the morphine-induced CTA, and resulted from the aversive effect of morphine on conditioning and reinstatement. The c-Fos data showed fewer neural substrates (e.g., PrL, IL, and LH) on extinction to be hyperactive. In the context of previous drug addiction data, the evidence suggests that morphine injections may induce hyperactivity in many neural substrates, which mediate reward and/or aversion due to disturbance and nonhomeostasis in the brain. The results support the paradoxical effect hypothesis of abused drugs. Insight from the findings could be used in the clinical treatment of drug addiction.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Ethanol Alters Variability, But Not Rate, of Firing in Medial Prefrontal Cortex Neurons of Awake-Behaving Rats

BACKGROUND

The medial prefrontal cortex (mPFC) is a brain region involved in the evaluation and selection of motivationally relevant outcomes. Neural activity in mPFC is altered following acute ethanol (EtOH) use and, in rodent models, doses as low as 0.75 g/kg yield cognitive deficits. Deficits in decision making following acute EtOH are thought to be mediated, at least in part, by decreases in mPFC firing rates (FRs). However, the data leading to this conclusion have been generated exclusively in anesthetized rodents. The present study characterizes the effects of acute EtOH injections on mPFC neural activity in awake-behaving rodents.

METHODS

Awake-behaving and anesthetized in vivo electrophysiological recordings were performed. We utilized 3 groups: the first received 2 saline injections, the second received a saline injection followed by 1.0 g/kg EtOH, and the last received saline followed by 2 g/kg EtOH. One week later, an anesthetized recording occurred where a saline injection was followed by an injection of 1.0 g/kg EtOH.

RESULTS

The anesthetized condition showed robust decreases in neural activity and differences in up-down states (UDS) dynamics. In the awake-behaving condition, FRs were grouped according to behavioral state: moving, not-moving, and sleep. The differences in median FRs were found for each treatment and behavioral state combination. A FR decrease was only found in the 2.0 g/kg EtOH treatment during not-moving states. However, robust decreases in FR variability were found across behavioral state in both the 1.0 and 2.0 g/kg EtOH treatment. Sleep was separately analyzed. EtOH modulated the UDS during sleep producing decreases in FRs.

CONCLUSIONS

In conclusion, the changes in neural activity following EtOH administration in anesthetized animals are not conserved in awake-behaving animals. The most prominent difference following EtOH was a decrease in FR variability suggesting that acute EtOH may be affecting decision making via this mechanism.

Cocaine- and stress-primed reinstatement of drug-associated memories elicit differential behavioral and frontostriatal circuit activity patterns via recruitment of L-type Ca2+ channels

Cocaine-associated memories are critical drivers of relapse in cocaine-dependent individuals that can be evoked by exposure to cocaine or stress. Whether these environmental stimuli recruit similar molecular and circuit-level mechanisms to promote relapse remains largely unknown. Here, using cocaine- and stress-primed reinstatement of cocaine conditioned place preference to model drug-associated memories, we find that cocaine drives reinstatement by increasing the duration that mice spend in the previously cocaine-paired context whereas stress increases the number of entries into this context. Importantly, both forms of reinstatement require Ca_v1.2 L-type Ca²⁺ channels (LTCCs) in cells of the prelimbic cortex that project to the nucleus accumbens core (PrL→NAcC). Utilizing fiber photometry to measure circuit activity in vivo in conjunction with the LTCC blocker, isradipine, we find that LTCCs drive differential recruitment of the PrL→ NAcC pathway during cocaine- and stress-primed reinstatement. While cocaine selectively activates PrL→NAcC cells prior to entry into the cocaine-paired chamber, a measure that is predictive of duration in that chamber, stress increases persistent activity of this projection, which correlates with entries into the cocaine-paired chamber. Using projection-specific chemogenetic manipulations, we show that PrL→NAcC activity is required for both cocaine- and stress-primed reinstatement, and that activation of this projection in Ca_v1.2-deficient mice restores reinstatement. These data indicate that LTCCs are a common mediator of cocaine- and stress-primed reinstatement. However, they engage different patterns of behavior and PrL→NAcC projection activity depending on the environmental stimuli. These findings establish a framework to further study how different environmental experiences can drive relapse, and supports further exploration of isradipine, an FDA-approved LTCC blocker, as a potential therapeutic for the prevention of relapse in cocaine-dependent individuals.

Activation of Infralimbic to Nucleus Accumbens Shell Pathway Suppresses Conditioned Aversion in Male But Not Female Rats

Hedonic processing plays an integral role in directing appropriate behavior, but disrupted hedonic processing is associated with psychiatric disorders such as depression. The infralimbic cortex (IL) is a key structure in affective processing in rodents and activation of its human homolog, the ventromedial prefrontal cortex, has been implicated in suppressing aversive states. Here, we tested whether optogenetic activation of glutamatergic projections from the IL to the nucleus accumbens shell (NAcSh) suppresses the aversive impact of sucrose devalued using the conditioned taste aversion paradigm in males and female rats. In naive rats, no significant differences in appetitive or aversive taste reactivity (TR) to sucrose was observed indicating that initial sucrose palatability was equivalent across sex. However, we found that optical activation of the IL-NAcSh pathway during intraoral infusion of devalued sucrose inhibited aversive TR in male but not female rats. Interestingly, when allowed to freely ingest water and sucrose in a two-bottle test both males and females with a history of IL-NAcSh stimulation exhibited greater preference for sucrose. Optical pathway activation failed to alter TR to innately bitter quinine in either sex. Finally, both sexes lever pressed to self-stimulate the IL-NAcSh pathway. These results indicate that the IL-NAcSh pathway plays an important role in suppressing learned aversive states selectively in males but spares hedonic processing of innately aversive tastants. Further, pathway activation is reinforcing in both sexes, indicating that suppression of conditioned aversive TR can be dissociable from the effects of unconditioned rewarding properties of IL-NAcSh pathway activation.SIGNIFICANCE STATEMENT Negative emotional states contribute to psychiatric disorders including depression and substance use disorders. In this study, we examined whether brain circuitry previously implicated in suppressing negative emotional states in humans can inhibit learned aversion in male and female rats. We found that optical activation of the infralimbic to nucleus accumbens shell pathway attenuates learned aversive responses in male but not female rats, indicating an important sex difference in the function of this brain pathway. Furthermore, we found that pathway stimulation was reinforcing in both sexes. Collectively, these findings support the role of the infralimbic cortex and its projection to the nucleus accumbens shell in suppressing learned negative emotional states and highlight an important sex-specific function of this pathway.

The role of the ventromedial prefrontal cortex and context in regulating fear learning and extinction

An organism's ability to learn about and respond to stimuli in its environment is crucial for survival, which can involve learning simple associations such as learning what stimuli predict danger. However, individuals must also be able to use contextual information to adapt to changing environmental demands. While the circuitry that supports fear conditioning has been extensively studied, the circuitry that allows individuals to regulate fear under different circumstance is less well understood. A view of ventromedial prefrontal cortex (vmPFC) function has emerged wherein the prelimbic region of the vmPFC supports fear expression, while the infralimbic region supports fear inhibition. However, despite a rich literature exploring the role of these regions in appetitive learning and memory suggesting a more nuanced function, there has been little integration of this literature with studies of the vmPFC in fear learning. In this review, we argue that the function of the vmPFC in fear learning is not restricted to fear inhibition versus expression per se. Instead, the vmPFC uses contextual information to guide behavior, particularly in situations of ambiguity or conflict.

Overexpression of ASIC1A in the nucleus accumbens of rats potentiates cocaine-seeking behavior

Acid-sensing ion channels (ASICs) are abundantly expressed in the nucleus accumbens core (NAcore), a region of the mesolimbocortical system that has an established role in regulating drug-seeking behavior. Previous work shows that a single dose of cocaine reduced the AMPA-to-NMDA ratio in Asic1a-/- mice, an effect observed after withdrawal in wild-type mice, whereas ASIC1A overexpression in the NAcore of rats decreases cocaine self-administration. However, whether ASIC1A overexpression in the NAcore alters measures of drug-seeking behavior after the self-administration period is unknown. To examine this issue, the ASIC1A subunit was overexpressed in male Sprague-Dawley rats by injecting them with adeno-associated virus, targeted at the NAcore, after completion of 2 weeks of cocaine or food self-administration. After 21 days of homecage abstinence, rats underwent a cue-/context-driven drug/food-seeking test, followed by extinction training and then drug/food-primed, cued, and cued + drug/food-primed reinstatement tests. The results indicate that ASIC1A overexpression in the NAcore enhanced cue-/context-driven cocaine seeking, cocaine-primed reinstatement, and cued + cocaine-primed reinstatement but had no effect on food-seeking behavior, indicating a selective effect for ASIC1A in the processes underlying extinction and cocaine-seeking behavior.

Dorsomedial prefrontal cortex neurons encode nicotine-cue associations

The role of medial prefrontal cortex (mPFC) in regulating nicotine taking and seeking remains largely unexplored. In this study we took advantage of the high time-resolution of optogenetic intervention by decreasing (Arch3.0) or increasing (ChR2) the activity of neurons in the dorsal and ventral mPFC during 5-s nicotine cue presentations in order to evaluate their contribution to cued nicotine seeking and taking. Wistar rats were trained to self-administer intravenous nicotine in 1 h self-administration sessions twice a day for a minimum of 10 days. Subsequently, dmPFC or vmPFC neuronal activity was modulated during or following presentation of the 5-s nicotine cue, both under extinction and self-administration conditions. We also used in vivo electrophysiology to record the activity of dmPFC neurons during nicotine self-administration and extinction tests. We show that optogenetic inhibition of dmPFC neurons during, but not following, response-contingent presentations of the nicotine cue increased nicotine seeking. We found no effect on nicotine self-administration or on food seeking in an extinction test. We also show that this effect is specific to dmPFC, because optogenetic inhibition of vmPFC had no effect on nicotine seeking and taking. In vivo recordings revealed that dmPFC network neuronal activity was modulated more strongly following nicotine cue presentation in extinction, compared to following nicotine self-administration. Our results strongly suggest that a population of neurons within the dmPFC is involved in encoding the incentive value of nicotine-associated cues.

Differential Effects of Dorsal and Ventral Medial Prefrontal Cortex Inactivation during Natural Reward Seeking, Extinction, and Cue-Induced Reinstatement

Rodent dorsal medial prefrontal cortex (mPFC), typically prelimbic cortex, is often described as promoting actions such as reward seeking, whereas ventral mPFC, typically infralimbic cortex, is thought to promote response inhibition. However, both dorsal and ventral mPFC are necessary for both expression and suppression of different behaviors, and each region may contribute to different functions depending on the specifics of the behavior tested. To better understand the roles of dorsal and ventral mPFC in motivated behavior we pharmacologically inactivated each area during operant fixed ratio 1 (FR1) seeking for a natural reward (sucrose), extinction, cue-induced reinstatement, and progressive ratio (PR) sucrose seeking in male Long–Evans rats. Bilateral inactivation of dorsal mPFC, but not ventral mPFC increased reward seeking during FR1. Inactivation of both dorsal and ventral mPFC decreased seeking during extinction. Bilateral inactivation of ventral mPFC, but not dorsal mPFC decreased reward seeking during cue-induced reinstatement. No effect of inactivation was found during PR. Our data contrast sharply with observations seen during drug seeking and fear conditioning, indicating that previously established roles of dorsal mPFC = going versus ventral mPFC = stopping are not applicable to all motivated behaviors and/or outcomes. Our results indicate that dichotomous functions of dorsal versus ventral mPFC, if they exist, may align better with other models, or may require the development of a new framework in which these multifaceted brain areas play different roles in action control depending on the behavioral context in which they are engaged.

Anti-relapse neurons in the infralimbic cortex of rats drive relapse-suppression by drug omission cues

Drug addiction is a chronic relapsing disorder of compulsive drug use. Studies of the neurobehavioral factors that promote drug relapse have yet to produce an effective treatment. Here we take a different approach and examine the factors that suppress-rather than promote-relapse. Adapting Pavlovian procedures to suppress operant drug response, we determined the anti-relapse action of environmental cues that signal drug omission (unavailability) in rats. Under laboratory conditions linked to compulsive drug use and heightened relapse risk, drug omission cues suppressed three major modes of relapse-promotion (drug-predictive cues, stress, and drug exposure) for cocaine and alcohol. This relapse-suppression is, in part, driven by omission cue-reactive neurons, which constitute small subsets of glutamatergic and GABAergic cells, in the infralimbic cortex. Future studies of such neural activity-based cellular units (neuronal ensembles/memory engram cells) for relapse-suppression can be used to identify alternate targets for addiction medicine through functional characterization of anti-relapse mechanisms.

Dorsal Striatal Circuits for Habits, Compulsions and Addictions

Here, we review the neural circuit bases of habits, compulsions, and addictions, behaviors which are all characterized by relatively automatic action performance. We discuss relevant studies, primarily from the rodent literature, and describe how major headway has been made in identifying the brain regions and neural cell types whose activity is modulated during the acquisition and performance of these automated behaviors. The dorsal striatum and cortical inputs to this structure have emerged as key players in the wider basal ganglia circuitry encoding behavioral automaticity, and changes in the activity of different neuronal cell-types in these brain regions have been shown to co-occur with the formation of automatic behaviors. We highlight how disordered functioning of these neural circuits can result in neuropsychiatric disorders, such as obsessive-compulsive disorder (OCD) and drug addiction. Finally, we discuss how the next phase of research in the field may benefit from integration of approaches for access to cells based on their genetic makeup, activity, connectivity and precise anatomical location.

Increased Cocaine Motivation Is Associated with Degraded Spatial and Temporal Representations in IL-NAc Neurons

Craving for cocaine progressively increases in cocaine users during drug-free periods, contributing to relapse. The projection from the infralimbic cortex to the nucleus accumbens shell (IL-NAc) is thought to inhibit cocaine seeking. However, it is not known whether and how IL-NAc neurons contribute to the increased motivation associated with a drug-free period. We first performed cellular resolution imaging of IL-NAc neurons in rats during a drug-seeking test. This revealed neurons with spatial selectivity within the cocaine-associated context, a decrease in activity around the time of cocaine seeking, and an inverse relationship between cocaine-seeking activity and subsequent cocaine motivation. All these properties were reduced by a drug-free period. Next, we transiently activated this projection, which resulted in reduced drug seeking, regardless of the drug-free period. Taken together, this suggests that altered IL-NAc activity after a drug-free period may enhance cocaine motivation without fundamentally altering the projection's ability to inhibit drug seeking.

Attenuation of cocaine seeking in rats via enhancement of infralimbic cortical activity using stable step-function opsins

RATIONALE

The infralimbic cortex (IL) and its downstream projection target the nucleus accumbens shell (NAshell) mediate the active suppression of cocaine-seeking behavior. Although an optogenetic approach would be beneficial for stimulating the IL and its efferents to study their role during reinstatement of cocaine seeking, the use of channelrhodopsin introduces significant difficulties, as optimal stimulation parameters are not known.

OBJECTIVES

The present experiments utilized a stable step-function opsin (SSFO) to potentiate endogenous activity in the IL and in IL terminals in the NAshell during cocaine-seeking tests to determine how these manipulations affect cocaine-seeking behaviors.

METHODS

Rats first underwent 6-h access cocaine self-administration followed by 21-27 days in the homecage. Rats then underwent cue-induced and cocaine-primed drug-seeking tests during which the optogenetic manipulation was given. The same rats then underwent extinction training, followed by cue-induced and cocaine-primed reinstatements.

RESULTS

Potentiation of endogenous IL activity did not significantly alter cue-induced or cocaine-primed drug seeking following the homecage period. However, following extinction training, enhancement of endogenous IL activity attenuated cue-induced reinstatement by 35% and cocaine-primed reinstatement by 53%. Stimulation of IL terminals in the NAshell did not consistently alter cocaine-seeking behavior.

CONCLUSION

These results suggest the utility of an SSFO-based approach for enhancing activity in a structure without driving specific patterns of neuronal firing. However, the utility of an SSFO-based approach for axon terminal stimulation remains unclear. Moreover, these results suggest that the ability of the IL to reduce cocaine seeking depends, at least in part, on rats first having undergone extinction training.

Altering gain of the infralimbic-to-accumbens shell circuit alters economically dissociable decision-making algorithms

The nucleus accumbens shell (NAcSh) is involved in reward valuation. Excitatory projections from infralimbic cortex (IL) to NAcSh undergo synaptic remodeling in rodent models of addiction and enable the extinction of disadvantageous behaviors. However, how the strength of synaptic transmission of the IL-NAcSh circuit affects decision-making information processing and reward valuation remains unknown, particularly because these processes can conflict within a given trial and particularly given recent data suggesting that decisions arise from separable information-processing algorithms. The approach of many neuromodulation studies is to disrupt information flow during on-going behaviors; however, this limits the interpretation of endogenous encoding of computational processes. Furthermore, many studies are limited by the use of simple behavioral tests of value which are unable to dissociate neurally distinct decision-making algorithms. We optogenetically altered the strength of synaptic transmission between glutamatergic IL-NAcSh projections in mice trained on a neuroeconomic task capable of separating multiple valuation processes. We found that induction of long-term depression in these synapses produced lasting changes in foraging processes without disrupting deliberative processes. Mice displayed inflated reevaluations to stay when deciding whether to abandon continued reward-seeking investments but displayed no changes during initial commitment decisions. We also developed an ensemble-level measure of circuit-specific plasticity that revealed individual differences in foraging valuation tendencies. Our results demonstrate that alterations in projection-specific synaptic strength between the IL and the NAcSh are capable of augmenting self-control economic valuations within a particular decision-making modality and suggest that the valuation mechanisms for these multiple decision-making modalities arise from different circuits.

Neural systems mediating the inhibition of cocaine-seeking behaviors

Over the past decades, research has targeted the neurobiology regulating cocaine-seeking behaviors, largely in the hopes of identifying potential targets for the treatment of cocaine addiction. Although much of this work has focused on those systems driving cocaine seeking, recently, studies examining the inhibition of cocaine-related behaviors have made significant progress in uncovering the neural systems that attenuate cocaine seeking. Such systems include the infralimbic cortex, nucleus accumbens shell, and hypothalamus. Research in this field has focused largely on the infralimbic cortex, as activity in this region appears to attenuate cocaine seeking during reinstatement and contribute to extinction learning. However, an overarching theory of function for this region that includes its role in other types of reward seeking and learning remains to be determined. Furthermore, the precise relationship between other regions involved in attenuating cocaine-seeking behavior and the infralimbic cortex remains unclear. Recent advances in the use of viral vectors combined with optogenetics, chemogenetics, and other approaches have greatly affected our capacity to investigate those systems inhibiting behavior dependent on cocaine-associated memories. This review will present current understanding regarding the neurobiology underlying the inhibition of such behaviors, especially focusing on the extinction of such memories, and explore how viral-vector targeting of specific brain circuits has begun to alter, and will continue to enrich, our knowledge regarding this issue.