Ventral striatum lesions enhance stimulus and response encoding in dorsal striatum

Shared and distinct neural activity during anticipation and outcome of win and loss: A meta-analysis of the monetary incentive delay task

Reward and punishment motivate decision making and behavioral changes. Numerous studies have examined regional activities during anticipation and outcome of win and loss in the monetary incentive delay task (MIDT). However, the great majority of studies reported findings of anticipation or outcome and of win or loss alone. It remains unclear how the neural correlates share and differentiate amongst these processes. We conducted an Activation Likelihood Estimation meta-analysis of 81 studies of the MIDT (5,864 subjects), including 24 published since the most recent meta-analysis, to identify and, with conjunction and subtraction, contrast regional responses to win anticipation, loss anticipation, win outcome, and loss outcome. Win and loss anticipation engaged a shared network of bilateral anterior insula (AI), striatum, thalamus, supplementary motor area (SMA), and precentral gyrus. Win and loss outcomes did not share regional activities. Win and loss outcome each engaged higher activity in medial orbitofrontal cortex (mOFC) and dorsal anterior cingulate cortex. Bilateral striatum and right occipital cortex responded to both anticipation and outcome of win, and right AI to both phases of loss. Win anticipation vs. outcome engaged higher activity in bilateral AI, striatum, SMA and precentral gyrus and right thalamus, and lower activity in bilateral mOFC and posterior cingulate cortex as well as right inferior frontal and angular gyri. Loss anticipation relative to outcome involved higher activity in bilateral striatum and left AI. These findings collectively suggest shared and distinct regional responses during monetary wins and losses. Delineating the neural correlates of these component processes may facilitate empirical research of motivated behaviors and dysfunctional approach and avoidance in psychopathology.

Aberrant prefrontal cortical-striatal functional connectivity in children with primary complex motor stereotypies

Motor stereotypies are rhythmic, repetitive, prolonged, predictable, and purposeless movements that stop with distraction. Although once believed to occur only in children with neurodevelopmental disorders such as autism, the presence and persistence of complex motor stereotypies (CMS) in otherwise typically developing children (primary CMS) has been well-established. Little, however, is known about the underlying pathophysiology of these unwanted actions. The aim of the present study was to use resting-state functional magnetic resonance imaging to evaluate functional connectivity within frontal-striatal circuits that are essential for goal-directed and habitual activity in children with primary complex motor stereotypies. Functional connectivity between prefrontal cortical and striatal regions, considered essential for developing goal-directed behaviors, was reduced in children with primary CMS compared to their typically developing peers. In contrast, functional connectivity between motor/premotor and striatal regions, critical for developing and regulating habitual behaviors, did not differ between groups. This documented alteration of prefrontal to striatal connectivity could provide the underlying mechanism for the presence and persistence of complex motor stereotypies in otherwise developmentally normal children.

Prior Cocaine Exposure Increases Firing to Immediate Reward While Attenuating Cue and Context Signals Related to Reward Value in the Insula

The insula contributes to behavioral control and is disrupted by substance abuse, yet we know little about the neural signals underlying these functions or how they are disrupted after chronic drug self-administration. Here, male and female rats self-administered either cocaine (experimental group) or sucrose (control) for 12 consecutive days. After a 1 month withdrawal period, we recorded from insula while rats performed a previously learned reward-guided decision-making task. Cocaine-exposed rats were more sensitive to value manipulations and were faster to respond. These behavioral changes were accompanied by elevated counts of neurons in the insula that increased firing to reward. These neurons also fired more strongly at the start of long-delay trials, when a more immediate reward would be expected, and fired less strongly in anticipation of the actual delivery of delayed rewards. Although reward-related firing to immediate reward was enhanced after cocaine self-administration, reward-predicting cue and context signals were attenuated. In addition to revealing novel firing patterns unique to insula, our data suggest changes in such neural activity likely contribute to impaired decision making observed after drug use.SIGNIFICANCE STATEMENT The insula plays a clear role in drug addiction and drug-induced impairments of decision making, yet there is little understanding of its underlying neural signals. We found that chronic cocaine self-administration reduces cue and context encoding in insula while enhancing signals related to immediate reward. These changes in neural activity likely contribute to impaired decision making and impulsivity observed after drug use.

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

The Nucleus Accumbens Core Is Necessary for Responding to Incentive But Not Instructive Stimuli

An abundant literature has highlighted the importance of the nucleus accumbens core (NAcC) in behavioral tasks dependent on external stimuli. Yet, some studies have also reported the absence of involvement of the NAcC in stimuli processing. We aimed at comparing, in male rats, the underlying neuronal determinants of incentive and instructive stimuli in the same task. We developed a variant of a GO/NOGO task that reveals important differences in these two types of stimuli. The incentive stimulus invites the rat to engage in the task sequence. Once the rat has decided to initiate a trial, it remains engaged in the task until the end of the trial. This task revealed the differential contribution of the NAcC to responding to different types of stimuli: responding to the incentive stimulus depended on NAcC AMPA/NMDA and dopamine D1 receptors, but the retrieval of the response associated with the instructive stimuli (lever pressing on GO, withholding on NOGO) did not. Our electrophysiological study showed that more NAcC neurons responded more strongly to the incentive than the instructive stimuli. Furthermore, when animals did not respond to the incentive stimulus, the induced excitation was suppressed for most projection neurons, whereas interneurons were strongly activated at a latency preceding that found in projection neurons. This work provides insight on the underlying neuronal processes explaining the preferential implication of the NAcC in deciding whether and when to engage in reward-seeking rather than to decide which action to perform.SIGNIFICANCE STATEMENT The nucleus accumbens core (NAcC) is essential to process information carried by reward-predicting stimuli. Yet, stimuli have distinct properties: incentive stimuli orient the attention toward reward-seeking, whereas instructive stimuli inform about the action to perform. Our study shows that, in male rats, NAcC perturbation with glutamate or dopamine antagonists impeded responses to the incentive but not to the instructive stimulus. NAcC neuronal recordings revealed a stronger representation of incentive than instructive stimuli. Furthermore, we found that interneurons are recruited when rats fail to respond to incentive stimuli. This work provides insight on the underlying neuronal processes explaining the preferential implication of the NAcC in deciding whether and when to engage in reward-seeking rather than to decide which action to perform.

Controversies Surrounding the Pathophysiology of Tics

Tics are sudden, rapid, recurrent, nonrhythmic motor movements or vocalizations (phonic productions) that are commonly present in children and are required symptoms for the diagnosis of Tourette syndrome. Despite their frequency, the underlying pathophysiology of tics/Tourette syndrome remains unknown. In this review, we discuss a variety of controversies surrounding the pathophysiology of tics, including the following: Are tics voluntary or involuntary? What is the role of the premonitory urge? Are tics due to excess excitatory or deficient inhibition? Is it time to adopt the contemporary version of the cortico-basal ganglia-thalamocortical (CBGTC) circuit? and Do we know the primary abnormal neurotransmitter in Tourette syndrome? Data from convergent clinical and animal model studies support complex interactions among the various CBGTC sites and neurotransmitters. Advances are being made; however, numerous pathophysiologic questions persist.

Previous cocaine self-administration disrupts reward expectancy encoding in ventral striatum

The nucleus accumbens core (NAc) is important for integrating and providing information to downstream areas about the timing and value of anticipated reward. Although NAc is one of the first brain regions to be affected by drugs of abuse, we still do not know how neural correlates related to reward expectancy are affected by previous cocaine self-administration. To address this issue, we recorded from single neurons in the NAc of rats that had previously self-administered cocaine or sucrose (control). Neural recordings were then taken while rats performed an odor-guided decision-making task in which we independently manipulated value of expected reward by changing the delay to or size of reward across a series of trial blocks. We found that previous cocaine self-administration made rats more impulsive, biasing choice behavior toward more immediate reward. Further, compared to controls, cocaine-exposed rats showed significantly fewer neurons in the NAc that were responsive during odor cues and reward delivery, and in the reward-responsive neurons that remained, diminished directional and value encoding was observed. Lastly, we found that after cocaine exposure, reward-related firing during longer delays was reduced compared to controls. These results demonstrate that prior cocaine self-administration alters reward-expectancy encoding in NAc, which could contribute to poor decision making observed after chronic cocaine use.

The correlation between striatal and cortical binding ratio of 11C-PiB-PET in amyloid-uptake-positive patients

PURPOSE

In subjects with amyloid deposition, striatal accumulation of ¹¹C-Pittsburgh compound B (PiB) demonstrated by positron emission tomography (PET) is related to the stage of Alzheimer's disease (AD). In this study, we investigated the correlation between striatal and cortical non-displaceable binding potential (BP_ND).

METHODS

Seventy-three subjects who complained of cognitive disturbance underwent dynamic PiB-PET studies and showed positive PiB accumulation were retrospectively selected. These subjects included 34 AD, 26 mild cognitive impairment, 2 frontotemporal lobar degeneration, 2 Parkinson's disease, 5 dementia with Lewy bodies, and 4 undefined diagnosis patients. Individual BP_ND images were produced from the dynamic data of the PiB-PET study, and voxel-based analyses were performed to estimate the correlations between striatal and other regional cortical BP_ND measures.

RESULTS

There were highly significant correlations between striatal and prefrontal BP_ND, with the highest correlation being demonstrated in left Brodmann area 11. We found that almost all of the high cortical BP_ND values correlated with striatal BP_ND values, with the exception of the occipital cortex with low correlation.

CONCLUSION

Our study demonstrated positive correlations in amyloid deposits between the striatum and other cortical areas with functional and anatomical links. The amyloid distribution in the brain is not random, but spreads following the functional and anatomical connections.

Neural Activity in Ventral Medial Prefrontal Cortex Is Modulated More Before Approach Than Avoidance During Reinforced and Extinction Trial Blocks

Ventromedial prefrontal cortex (vmPFC) is thought to provide regulatory control over Pavlovian fear responses and has recently been implicated in appetitive approach behavior, but much less is known about its role in contexts in which appetitive and aversive outcomes can be obtained and avoided, respectively. To address this issue, we recorded from single neurons in vmPFC while male rats performed our combined approach and avoidance task under reinforced and non-reinforced (extinction) conditions. Surprisingly, we found that cues predicting reward modulated cell firing in vmPFC more often and more robustly than cues preceding avoidable shock; in addition, firing of vmPFC neurons was both response (press or no-press) and outcome (reinforced or extinction) selective. These results suggest a complex role for vmPFC in regulating behavior and support its role in appetitive contexts during both reinforced and non-reinforced conditions.SIGNIFICANCE STATEMENT Selecting context-appropriate behaviors to gain reward or avoid punishment is critical for survival. Although the role of ventromedial prefrontal cortex (vmPFC) in mediating fear responses is well established, vmPFC has also been implicated in the regulation of reward-guided approach and extinction. Many studies have used indirect methods and simple behavioral procedures to study vmPFC, which leaves the literature incomplete. We recorded vmFPC neural activity during a complex cue-driven combined approach and avoidance task and during extinction. Surprisingly, we found very little vmPFC modulation to cues predicting avoidable shock, whereas cues predicting reward approach robustly modulated vmPFC firing in a response- and outcome-selective manner. This suggests a more complex role for vmPFC than current theories suggest, specifically regarding context-specific behavioral optimization.

Time, Not Size, Matters for Striatal Reward Predictions to Dopamine

Midbrain dopamine neurons encode reward prediction errors. In this issue of Neuron, Takahashi et al. (2016) show that the ventral striatum provides dopamine neurons with prediction information specific to the timing, but not the quantity, of reward, suggesting a surprisingly nuanced neural implementation of reward prediction errors.

Prior Cocaine Self-Administration Increases Response-Outcome Encoding That Is Divorced from Actions Selected in Dorsal Lateral Striatum

Dorsal lateral striatum (DLS) is a highly associative structure that encodes relationships among environmental stimuli, behavioral responses, and predicted outcomes. DLS is known to be disrupted after chronic drug abuse; however, it remains unclear what neural signals in DLS are altered. Current theory suggests that drug use enhances stimulus-response processing at the expense of response-outcome encoding, but this has mostly been tested in simple behavioral tasks. Here, we investigated what neural correlates in DLS are affected by previous cocaine exposure as rats performed a complex reward-guided decision-making task in which predicted reward value was independently manipulated by changing the delay to or size of reward associated with a response direction across a series of trial blocks. After cocaine self-administration, rats exhibited stronger biases toward higher-value reward and firing in DLS more strongly represented action-outcome contingencies independent from actions subsequently taken rather than outcomes predicted by selected actions (chosen-outcome contingencies) and associations between stimuli and actions (stimulus-response contingencies). These results suggest that cocaine self-administration strengthens action-outcome encoding in rats (as opposed to chosen-outcome or stimulus-response encoding), which abnormally biases behavior toward valued reward when there is a choice between two options during reward-guided decision-making.SIGNIFICANCE STATEMENT Current theories suggest that the impaired decision-making observed in individuals who chronically abuse drugs reflects a decrease in goal-directed behaviors and an increase in habitual behaviors governed by neural representations of response-outcome (R-O) and stimulus-response associations, respectively. We examined the impact that prior cocaine self-administration had on firing in dorsal lateral striatum (DLS), a brain area known to be involved in habit formation and affected by drugs of abuse, during performance of a complex reward-guided decision-making task. Surprisingly, we found that previous cocaine exposure enhanced R-O associations in DLS. This suggests that there may be more complex consequences of drug abuse than current theories have explored, especially when examining brain and behavior in the context of a complex two-choice decision-making task.

Effects of striatal lesions on components of choice: Reward discrimination, preference, and relative valuation

The striatum is a key structure involved in reward processing and choice. Recently, we have developed a paradigm to explore how components of reward processing work together or independently during choice behavior. These components include reward discrimination, preference and relative valuation, and the goal of the present study was to determine how the striatum is involved in these dissociable components during this novel free choice paradigm. We tested choice utilizing two different outcome series with one being a more straightforward single-option discrimination anchored by a 0 reward outcome, and the other as a multi-option outcome discrimination of greater difficulty. We compared the free choice reward task to a sequential reward task and an extinction task. Striatal lesions impaired responding only in the free choice version with alterations in both appetitive and consummatory measures. Ventral striatal lesions had greater impact altering discrimination, preference and relative valuation in both the single and multi-option week studies. A major factor involved in these deficits was a significant aversion to the multi-option that contained a larger outcome option but with a longer delay to reward. Dorsal striatal lesions caused less impairment even leading to enhanced choice behavior compared to control animals during the more difficult multi-option free choice series. Overall, the results suggest that the context of action is crucial when linking striatal function to choice behavior and its diverse components. The implications include the idea that striatal involvement in decision-making is increased when responses are self-paced and diverse in a more naturalistic environment.

Temporal Specificity of Reward Prediction Errors Signaled by Putative Dopamine Neurons in Rat VTA Depends on Ventral Striatum

Dopamine neurons signal reward prediction errors. This requires accurate reward predictions. It has been suggested that the ventral striatum provides these predictions. Here we tested this hypothesis by recording from putative dopamine neurons in the VTA of rats performing a task in which prediction errors were induced by shifting reward timing or number. In controls, the neurons exhibited error signals in response to both manipulations. However, dopamine neurons in rats with ipsilateral ventral striatal lesions exhibited errors only to changes in number and failed to respond to changes in timing of reward. These results, supported by computational modeling, indicate that predictions about the temporal specificity and the number of expected reward are dissociable and that dopaminergic prediction-error signals rely on the ventral striatum for the former but not the latter.

The Neural Representation of Goal-Directed Actions and Outcomes in the Ventral Striatum's Olfactory Tubercle

The ventral striatum is critical for evaluating reward information and the initiation of goal-directed behaviors. The many cellular, afferent, and efferent similarities between the ventral striatum's nucleus accumbens and olfactory tubercle (OT) suggests the distributed involvement of neurons within the ventral striatopallidal complex in motivated behaviors. Although the nucleus accumbens has an established role in representing goal-directed actions and their outcomes, it is not known whether this function is localized within the nucleus accumbens or distributed also within the OT. Answering such a fundamental question will expand our understanding of the neural mechanisms underlying motivated behaviors. Here we address whether the OT encodes natural reinforcers and serves as a substrate for motivational information processing. In recordings from mice engaged in a novel water-motivated instrumental task, we report that OT neurons modulate their firing rate during initiation and progression of the instrumental licking behavior, with some activity being internally generated and preceding the first lick. We further found that as motivational drive decreases throughout a session, the activity of OT neurons is enhanced earlier relative to the behavioral action. Additionally, OT neurons discriminate the types and magnitudes of fluid reinforcers. Together, these data suggest that the processing of reward information and the orchestration of goal-directed behaviors is a global principle of the ventral striatum and have important implications for understanding the neural systems subserving addiction and mood disorders.

SIGNIFICANCE STATEMENT

Goal-directed behaviors are widespread among animals and underlie complex behaviors ranging from food intake, social behavior, and even pathological conditions, such as gambling and drug addiction. The ventral striatum is a neural system critical for evaluating reward information and the initiation of goal-directed behaviors. Here we show that neurons in the olfactory tubercle subregion of the ventral striatum robustly encode the onset and progression of motivated behaviors, and discriminate the type and magnitude of a reward. Our findings are novel in showing that olfactory tubercle neurons participate in such coding schemes and are in accordance with the principle that ventral striatum substructures may cooperate to guide motivated behaviors.

Neural correlates of rules and conflict in medial prefrontal cortex during decision and feedback epochs

The ability to properly adjust behavioral responses to cues in a changing environment is crucial for survival. Activity in the medial Prefrontal Cortex (mPFC) is thought to both represent rules to guide behavior as well as detect and resolve conflicts between rules in changing contingencies. However, while lesion and pharmacological studies have supported a crucial role for mPFC in this type of set-shifting, an understanding of how mPFC represents current rules or detects and resolves conflict between different rules is unclear. Here, we directly address the role of rat mPFC in shifting rule based behavioral strategies using a novel behavioral task designed to tease apart neural signatures of rules, conflict and direction. We demonstrate that activity of single neurons in rat mPFC represent distinct rules. Further, we show increased firing on high conflict trials in a separate population of mPFC neurons. Reduced firing in both populations of neurons was associated with poor performance. Moreover, activity in both populations increased and decreased firing during the outcome epoch when reward was and was not delivered on correct and incorrect trials, respectively. In addition, outcome firing was modulated by the current rule and the degree of conflict associated with the previous decision. These results promote a greater understanding of the role that mPFC plays in switching between rules, signaling both rule and conflict to promote improved behavioral performance.

Rule encoding in dorsal striatum impacts action selection

Cognitive flexibility is a hallmark of prefrontal cortical (PFC) function yet little is known about downstream area involvement. The medial dorsal striatum (mDS) receives major projections from the PFC and is uniquely situated to perform the integration of responses with rule information. In this study, we use a novel rule shifting task in rats that mirrors non-human primate and human studies in its temporal precision and counterbalanced responses. We record activity from single neurons in the mDS while rats switch between different rules for reward. Additionally, we pharmacologically inactivate mDS by infusion of a baclofen/muscimol cocktail. Inactivation of mDS impaired the ability to shift to a new rule and increased the number of regressive errors. While recording in mDS, we identified neurons modulated by direction whose activity reflected the conflict between competing rule information. We show that a subset of these neurons was also rule selective, and that the conflict between competing rule cues was resolved as behavioural performance improved. Other neurons were modulated by rule, but not direction. These neurons became selective before behavioural performance accurately reflected the current rule. These data provide an additional locus for investigating the mechanisms underlying behavioural flexibility. Converging lines of evidence from multiple human psychiatric disorders have implicated dorsal striatum as an important and understudied neural substrate of flexible cognition. Our data confirm the importance of mDS, and suggest a mechanism by which mDS mediates abstract cognition functions.

Orbitofrontal lesions eliminate signalling of biological significance in cue-responsive ventral striatal neurons

The ventral striatum has long been proposed as an integrator of biologically significant associative information to drive actions. While inputs from the amygdala and hippocampus have been much studied, the role of prominent inputs from orbitofrontal cortex (OFC) are less well understood. Here we recorded single unit activity from ventral striatum core in rats with sham or ipsilateral neurotoxic lesions of lateral OFC, as they performed an odor-guided spatial choice task. Consistent with prior reports, we found that spiking activity recorded in sham rats during cue sampling was related to both reward magnitude and reward identity, with higher firing rates observed for cues that predicted more reward. Lesioned rats also showed differential activity to the cues, but this activity was unbiased towards larger rewards. These data support a role for OFC in shaping activity in the ventral striatum to represent the biological significance of associative information in the environment.

From ventral-medial to dorsal-lateral striatum: neural correlates of reward-guided decision-making

The striatum is critical for reward-guided and habitual behavior. Anatomical and interference studies suggest a functional heterogeneity within striatum. Medial regions, such as nucleus accumbens core and dorsal medial striatum play roles in goal-directed behavior, while dorsal lateral striatum is critical for control of habitual action. Subdivisions of striatum are topographically connected with different cortical and subcortical structures forming channels that carry information related to limbic, associative, and sensorimotor functions. Here, we describe data showing that as one progresses from ventral-medial to dorsal-lateral striatum, there is a shift from more prominent value encoding to activity more closely related to associative and motor aspects of decision-making. In addition, we will describe data suggesting that striatal circuits work in parallel to control behavior and that regions within striatum can compensate for each other when functions are disrupted.

Neurophysiology of Reward-Guided Behavior: Correlates Related to Predictions, Value, Motivation, Errors, Attention, and Action

Many brain areas are activated by the possibility and receipt of reward. Are all of these brain areas reporting the same information about reward? Or are these signals related to other functions that accompany reward-guided learning and decision-making? Through carefully controlled behavioral studies, it has been shown that reward-related activity can represent reward expectations related to future outcomes, errors in those expectations, motivation, and signals related to goal- and habit-driven behaviors. These dissociations have been accomplished by manipulating the predictability of positively and negatively valued events. Here, we review single neuron recordings in behaving animals that have addressed this issue. We describe data showing that several brain areas, including orbitofrontal cortex, anterior cingulate, and basolateral amygdala signal reward prediction. In addition, anterior cingulate, basolateral amygdala, and dopamine neurons also signal errors in reward prediction, but in different ways. For these areas, we will describe how unexpected manipulations of positive and negative value can dissociate signed from unsigned reward prediction errors. All of these signals feed into striatum to modify signals that motivate behavior in ventral striatum and guide responding via associative encoding in dorsolateral striatum.

Brain network function during shifts in learning strategies in portal hypertension animals

Patients with minimal hepatic encephalopathy exhibit early impairments in their ability to shift attentional set. We employed a task-switching protocol to evaluate brain network changes. Strategy switching requires the modification of both the relevant stimulus dimension and the required memory system. Rats were trained in an allocentric (A) and a cue-guided (C) task using a four-arm maze. To examine priming, we changed the order in which the tasks were presented. Five groups of animals were used: a SHAM (sham-operated) A-C group (n=10), a SHAM C-A group (n=8), a PH (portal hypertension) A-C group (n=8), PH C-A group (n=8), and a naïve group (n=10). The triple portal vein ligation method was used to create an animal model of the early evolutive phase of PH. The animals were tested in the four-arm radial water maze in a single 10-trial session each day for six days (three days for the allocentric task and three days for the cue-guided task). The metabolic activities of the brains were studied with cytochrome oxidase histochemistry, and brain network changes were assessed with principal component analysis. The behavioural results revealed significant increases in the numbers of correct choices across training days in all groups studied, and facilitation of the acquisition of the second task was present in the C-A groups. Moreover, different brain network activities were found; in the experimental groups, the performance of A-C switch involved the prefrontal cortex, and the key structures involved in the C-A switch in the other groups were the dentate gyrus of the dorsal hippocampus and the basolateral and central amygdala. These networks have a common nucleus of structures (i.e., the parietal cortex and the dorsal and ventral striatum), whereas other structures were specifically involved in each type of strategy, suggesting that these regions are part of both circuits and may interact with one another during learning.

Impact of appetitive and aversive outcomes on brain responses: linking the animal and human literatures

Decision-making is motivated by the possibility of obtaining reward and/or avoiding punishment. Though many have investigated behavior associated with appetitive or aversive outcomes, few have examined behaviors that rely on both. Fewer still have addressed questions related to how anticipated appetitive and aversive outcomes interact to alter neural signals related to expected value, motivation, and salience. Here we review recent rodent, monkey, and human research that address these issues. Further development of this area will be fundamental to understanding the etiology behind human psychiatric diseases and cultivating more effective treatments.

Nucleus accumbens core lesions enhance two-way active avoidance

The majority of work examining the nucleus accumbens core (NAc) has focused on functions pertaining to behaviors guided by appetitive outcomes. These studies have pointed to the NAc as being critical for motivating behavior toward desirable outcomes. For example, we have recently shown that lesions of the NAc impaired performance on a reward-guided decision-making task that required rats to choose between differently valued rewards. Unfortunately, much less is known about the role that the NAc plays in motivating behavior when aversive outcomes are predicted. To address this issue we asked if NAc lesions impact performance on a two-way active avoidance task in which rats must learn to shuttle back and forth in a behavioral training box in order to avoid a footshock predicted by an auditory tone. Although bilateral NAc lesions initially impaired reward-guided decision-making, we found that the same lesions improved acquisition and retention of two-way active avoidance.