Temporally limited role of substantia nigra-central amygdala connections in surprise-induced enhancement of learning

Whole-Brain Map of Long-Range Monosynaptic Inputs to Different Cell Types in the Amygdala of the Mouse

The amygdala, which is involved in various behaviors and emotions, is reported to connect with the whole brain. However, the long-range inputs of distinct cell types have not yet been defined. Here, we used a retrograde trans-synaptic rabies virus to generate a whole-brain map of inputs to the main cell types in the mouse amygdala. We identified 37 individual regions that projected to neurons expressing vesicular glutamate transporter 2, 78 regions to parvalbumin-expressing neurons, 104 regions to neurons expressing protein kinase C-δ, and 89 regions to somatostatin-expressing neurons. The amygdala received massive projections from the isocortex and striatum. Several nuclei, such as the caudate-putamen and the CA1 field of the hippocampus, exhibited input preferences to different cell types in the amygdala. Notably, we identified several novel input areas, including the substantia innominata and zona incerta. These findings provide anatomical evidence to help understand the precise connections and diverse functions of the amygdala.

An Integrative Way for Studying Neural Basis of Basic Emotions With fMRI

How emotions are represented in the nervous system is a crucial unsolved problem in the affective neuroscience. Many studies are striving to find the localization of basic emotions in the brain but failed. Thus, many psychologists suspect the specific neural loci for basic emotions, but instead, some proposed that there are specific neural structures for the core affects, such as arousal and hedonic value. The reason for this widespread difference might be that basic emotions used previously can be further divided into more “basic” emotions. Here we review brain imaging data and neuropsychological data, and try to address this question with an integrative model. In this model, we argue that basic emotions are not contrary to the dimensional studies of emotions (core affects). We propose that basic emotion should locate on the axis in the dimensions of emotion, and only represent one typical core affect (arousal or valence). Therefore, we propose four basic emotions: joy-on positive axis of hedonic dimension, sadness-on negative axis of hedonic dimension, fear, and anger-on the top of vertical dimensions. This new model about basic emotions and construction model of emotions is promising to improve and reformulate neurobiological models of basic emotions.

Abundant collateralization of temporal lobe projections to the accumbens, bed nucleus of stria terminalis, central amygdala and lateral septum

Behavioral flexibility is subserved in part by outputs from the cerebral cortex to telencephalic subcortical structures. In our earlier evaluation of the organization of the cortical-subcortical output system (Reynolds and Zahm, J Neurosci 25:11757-11767, 2005), retrograde double-labeling was evaluated in the prefrontal cortex following tracer injections into pairs of the following subcortical telencephalic structures: caudate-putamen, core and shell of the accumbens (Acb), bed nucleus of stria terminalis (BST) and central nucleus of the amygdala (CeA). The present study was done to assess patterns of retrograde labeling in the temporal lobe after similar paired tracer injections into most of the same telencephalic structures plus the lateral septum (LS). In contrast to the modest double-labeling observed in the prefrontal cortex in the previous study, up to 60-80 % of neurons in the basal and accessory basal amygdaloid nuclei and amygdalopiriform transition area exhibited double-labeling in the present study. The most abundant double-labeling was generated by paired injections into structures affiliated with the extended amygdala, including the CeA, BST and Acb shell. Injections pairing the Acb core with the BST or CeA produced significantly fewer double-labeled neurons. The ventral subiculum exhibited modest amounts of double-labeling associated with paired injections into the Acb, BST, CeA and LS. The results raise the issue of how an extraordinarily collateralized output from the temporal lobe may contribute to behavioral flexibility.

Opposite initialization to novel cues in dopamine signaling in ventral and posterior striatum in mice

Dopamine neurons are thought to encode novelty in addition to reward prediction error (the discrepancy between actual and predicted values). In this study, we compared dopamine activity across the striatum using fiber fluorometry in mice. During classical conditioning, we observed opposite dynamics in dopamine axon signals in the ventral striatum (‘VS dopamine’) and the posterior tail of the striatum (‘TS dopamine’). TS dopamine showed strong excitation to novel cues, whereas VS dopamine showed no responses to novel cues until they had been paired with a reward. TS dopamine cue responses decreased over time, depending on what the cue predicted. Additionally, TS dopamine showed excitation to several types of stimuli including rewarding, aversive, and neutral stimuli whereas VS dopamine showed excitation only to reward or reward-predicting cues. Together, these results demonstrate that dopamine novelty signals are localized in TS along with general salience signals, while VS dopamine reliably encodes reward prediction error.

DOI:http://dx.doi.org/10.7554/eLife.21886.001

New experiences trigger a variety of responses in animals. We are surprised by, move towards, and often explore new objects. But how does the brain control these responses?

Dopamine is a molecule that controls many processes in the brain and plays critical roles in various mental disorders, diseases that affect movement, and addiction. Rewarding experiences (like a glass of cold water on a hot day) can trigger dopamine neurons and studies have also shown that dopamine neurons respond to new experiences. This suggested that novelty may be rewarding in itself, or that novelty may signal the potential for future reward. On the other hand, it may be that different groups of dopamine neurons play different roles in responding to new or rewarding experiences.

In 2015, it was reported that dopamine neurons connected to the rear part of an area in the brain called the striatum receive signals from different parts of the brain than most other dopamine neurons. The dopamine neurons connected to this “tail” of the striatum preferentially received inputs from regions involved in arousal rather than reward, suggesting that they may have a unique role and transmit a different type of information.

Now, Menegas et al. have shown that dopamine signals in different areas of the striatum separate reward from novelty and other signals in mice. The results demonstrate that new odors activate dopamine neurons projecting to the tail of the striatum, but that this activity fades as the novelty wears off (as the mice learn to associate the odor with a particular outcome). By contrast, dopamine neurons projecting to the front of the striatum do not respond to novelty, but rather become more active as mice learn which odors accompany rewards (only responding to odors that predict reward). The experiments also show that dopamine neurons in the tail of the striatum encode information about the importance of a stimulus.

Together, these findings indicate that some of the roles dopamine plays in the brain may not be related to reward, but are instead linked to the novelty and importance of the stimulus. The next challenge will be to find out how the separate reward and novelty signals in dopamine neurons relate to the animals’ behavior. This may help us to better understand dopamine-related psychiatric conditions, such as depression and addiction.

DOI:http://dx.doi.org/10.7554/eLife.21886.002

Consolidation of altered associability information by amygdala central nucleus

The surprising omission of a reinforcer can enhance the associability of the stimuli that were present when the reward prediction error was induced, so that they more readily enter into new associations in the future. Previous research from this laboratory identified brain circuit elements critical to the enhancement of stimulus associability by the omission of an expected event and to the subsequent expression of that altered associability in more rapid learning. These elements include the amygdala, the midbrain substantia nigra, the basal forebrain substantia innominata, the dorsolateral striatum, the secondary visual cortex, and the posterior parietal cortex. Here, we found that consolidation of a surprise-enhanced associability memory in a serial prediction task depends on processing in the amygdala central nucleus (CeA) after completion of sessions that included the surprising omission of an expected event. Post-surprise infusions of anisomycin, lidocaine, or muscimol prevented subsequent display of surprise-enhanced associability. Because previous studies indicated that CeA function is unnecessary for the expression of associability enhancements that were induced previously when CeA function was intact (Holland & Gallagher, 2006), we interpreted these results as indicating that post-surprise activity of CeA ("surprise replay") is necessary for the consolidation of altered associability memories elsewhere in the brain, such as the posterior parietal cortex (Schiffino et al., 2014a).

Secondary visual cortex is critical to the expression of surprise-induced enhancements in cue associability in rats

Considerable evidence indicates that reinforcement prediction error, the difference between the obtained and expected reinforcer values, modulates attention to potential cues for reinforcement. The surprising delivery or omission of a reinforcer enhances the associability of the stimuli that were present when the error was induced, so that they more readily enter into new associations in the future. Previous research from our laboratory identified brain circuit elements critical to the enhancement of stimulus associability by omission of an expected event and to the subsequent expression of that altered associability in more rapid learning. A key finding was that the rat posterior parietal cortex was essential during the encoding, consolidation and retrieval of associability memories that were altered by the surprising omission of an expected event in a serial prediction task. Here, we found that the function of adjacent secondary visual cortex was critical only to the expression of altered cue associability in that same task. This specialization of function is discussed in the context of broader cortical and subcortical networks for modulation of attention in associative learning, as well as recent anatomical investigations that suggest that the rodent posterior parietal cortex overlaps with and may subsume secondary visual cortex.

Reconsolidation and update of morphine-associated contextual memory in mice

Drug addiction can be viewed as a pathological memory that is constantly retrieved and reconsolidated. Since drug abuse takes place in different contexts, it could be considered that reconsolidation plays a role in memory updating. There is consistent evidence supporting the role of reconsolidation in the strength and maintenance of contextual memories induced by drugs of abuse. However, this role is not well established in memory update. The purpose of the current study was to assess the reconsolidation process over memory update. C57BL6 mice were subjected to a morphine-induced, conditioned place preference (CPP) paradigm. Based on CPP results, animals were divided into distinct experimental groups, according to the contextual characteristics of the re-exposure and a second CPP Test. Re-exposure in the original context was important for memory maintenance and re-exposure under discrete contextual changes resulted in memory updating, although original memory was maintained. Interestingly, cycloheximide, an inhibitor of protein synthesis, had different outcomes in our protocol. When the re-exposure was done under discrete contextual changes, cycloheximide treatment just after re-exposure blocked memory updating, without changes in memory maintenance. When re-exposure was done under the original context, only two subsequent cycloheximide injections (3 and 6h) disrupted later CPP expression. Considering the temporal window of protein synthesis in consolidation and reconsolidation, these findings suggest that re-exposure, according to the contextual characteristics in our protocol, could trigger both phenomena. Furthermore, when new information is present on retrieval, reconsolidation plays a pivotal role in memory updating.

Mini-review: Prediction errors, attention and associative learning

Most modern theories of associative learning emphasize a critical role for prediction error (PE, the difference between received and expected events). One class of theories, exemplified by the Rescorla-Wagner (1972) model, asserts that PE determines the effectiveness of the reinforcer or unconditioned stimulus (US): surprising reinforcers are more effective than expected ones. A second class, represented by the Pearce-Hall (1980) model, argues that PE determines the associability of conditioned stimuli (CSs), the rate at which they may enter into new learning: the surprising delivery or omission of a reinforcer enhances subsequent processing of the CSs that were present when PE was induced. In this mini-review we describe evidence, mostly from our laboratory, for PE-induced changes in the associability of both CSs and USs, and the brain systems involved in the coding, storage and retrieval of these altered associability values. This evidence favors a number of modifications to behavioral models of how PE influences event processing, and suggests the involvement of widespread brain systems in animals' responses to PE.

Dorsolateral striatum is critical for the expression of surprise-induced enhancements in cue associability

The dorsolateral striatum (DLS) is frequently implicated in sensory-motor integration, including the performance of sensory orienting responses (ORs) and learned stimulus-response habits. Our laboratory previously identified a role for the DLS in rats' performance of conditioned ORs to Pavlovian cues for food delivery. Here, we considered whether DLS is also critical to another aspect of attention in associative learning, the surprise-induced enhancement of cue associability. A large behavioral literature shows that a cue present when an expected event is omitted enters into new associations more rapidly when that cue is subsequently paired with food. Research from our laboratory has shown that both cue associability enhancements and conditioned ORs depend on the function of a circuit that includes the amygdala central nucleus and the substantia nigra pars compacta. In three experiments, we explored the involvement of DLS in surprise-induced associability enhancements, using a three-stage serial prediction task that permitted separation of DLS function in registering surprise (prediction error) and enhancing cue associability, and in using that increased associability to learn more rapidly about that cue later. The results showed that DLS is critical to the expression, but not the establishment, of the enhanced cue associability normally produced by surprise in this task. They extend the role of DLS and the amygdalo-nigro-striatal circuit underlying learned orienting to more subtle aspects of attention in associative learning, but are consistent with the general notion that DLS is more important in the expression of previously acquired tendencies than in their acquisition.

Amygdalo-striatal interaction in the enhancement of stimulus salience in associative learning

Function of the central nucleus of the amygdala (CeA) is critical to 2 aspects of attention in associative learning: the conditioning of orienting responses (ORs) to cues paired with food, and the enhancement of cue salience by the surprising omission of expected events. Such salience enhancements have been found to depend on interactions within a circuit that includes CeA, the substantia nigra pars compacta (SNc), the substantia innominata (SI), and the posterior parietal cortex (PPC). The acquisition and expression of conditioned ORs requires interactions among CeA, SNc, and the dorsal lateral striatum (DLS), but not SI or PPC. Here, we considered whether CeA-DLS interactions are also important in surprise-induced salience enhancements in a serial prediction task. Rats received unilateral lesions of CeA and DLS, either contralaterally, which disrupted interactions between those structures, or ipsilaterally, which produced comparable damage to each structure but permitted interactions between them in 1 hemisphere. Rats with ipsilateral lesions of CeA and DLS showed the salience enhancements normally observed in this task, but rats with contralateral lesions of those structures did not. Thus, convergence of information processing by CeA and DLS is essential for surprise-induced salience enhancements, as well as for conditioned ORs.

The basolateral amygdala is necessary for negative prediction errors to enhance cue salience, but not to produce conditioned inhibition

Behavioral evidence shows that prediction errors (PEs) not only drive associative learning, but also enhance the salience of predictive cues, making them better able to capture attention when they are next encountered. Research from our laboratory suggests that this latter consequence of PEs depends on a neural circuit that includes the amygdala. Lesions of the basolateral complex of the amygdala (BLA), for instance, selectively disrupt enhancements in cue processing that are normally induced by positive PEs without compromising simple excitatory learning. This result is consistent with electrophysiological evidence showing that BLA neurons track positive PEs. Interestingly, the same neurons also seem to track negative PEs, suggesting the possibility that the BLA might also use these errors to drive enhancements in cue processing. Here, we examined the role of the BLA in the processing (Experiment 1) and utilization (Experiment 2) of negative PEs in increasing cue salience in an unblocking procedure. Using FOS expression as an index of neural activity, Experiment 1 confirmed that BLA neurons track negative PEs with reinforcement downshifts. This tracking was evident both when these errors were generated by decreasing the concentration of a sucrose reinforcer (which encourages the development of conditioned inhibition) and when they were generated by decreasing the number of sucrose reinforcers (which encourages excitatory learning - unblocking - and allows the detection of enhancements in cue processing). Experiment 2 demonstrated that BLA lesions abolished enhancements in cue processing while sparing inhibitory learning. These results suggest a general role of the BLA in utilizing PEs, whatever their sign, for boosting cue processing.

Role of lateral hypothalamus in two aspects of attention in associative learning

Orexin (hypocretin) and melanin-concentrating hormone (MCH) neurons are unique to the lateral hypothalamic (LH) region, but project throughout the brain. These cell groups have been implicated in a variety of functions, including reward learning, responses to stimulants, and the modulation of attention, arousal and the sleep/wakefulness cycle. Here, we examined roles for LH in two aspects of attention in associative learning shown previously to depend on intact function in major targets of orexin and MCH neurons. In experiments 1 and 2, unilateral orexin-saporin lesions of LH impaired the acquisition of conditioned orienting responses (ORs) and bilaterally suppressed FOS expression in the amygdala central nucleus (CeA) normally observed in response to food cues that provoke conditioned ORs. Those cues also induced greater FOS expression than control cues in LH orexin neurons, but not in MCH neurons. In experiment 3, unilateral orexin-saporin lesions of LH eliminated the cue associability enhancements normally produced by the surprising omission of an expected event. The magnitude of that impairment was positively correlated with the amount of LH damage and with the loss of orexin neurons in particular, but not with the loss of MCH neurons. We suggest that the effects of the LH orexin-saporin lesions were mediated by their effect on information processing in the CeA, known to be critical to both behavioral phenomena examined here. The results imply close relations between LH motivational amplification functions and attention, and may inform our understanding of disorders in which motivational and attentional impairments co-occur.

Homeostatic regulation of memory systems and adaptive decisions

While it is clear that many brain areas process mnemonic information, understanding how their interactions result in continuously adaptive behaviors has been a challenge. A homeostatic-regulated prediction model of memory is presented that considers the existence of a single memory system that is based on a multilevel coordinated and integrated network (from cells to neural systems) that determines the extent to which events and outcomes occur as predicted. The “multiple memory systems of the brain” have in common output that signals errors in the prediction of events and/or their outcomes, although these signals differ in terms of what the error signal represents (e.g., hippocampus: context prediction errors vs. midbrain/striatum: reward prediction errors). The prefrontal cortex likely plays a pivotal role in the coordination of prediction analysis within and across prediction brain areas. By virtue of its widespread control and influence, and intrinsic working memory mechanisms. Thus, the prefrontal cortex supports the flexible processing needed to generate adaptive behaviors and predict future outcomes. It is proposed that prefrontal cortex continually and automatically produces adaptive responses according to homeostatic regulatory principles: prefrontal cortex may serve as a controller that is intrinsically driven to maintain in prediction areas an experience-dependent firing rate set point that ensures adaptive temporally and spatially resolved neural responses to future prediction errors. This same drive by prefrontal cortex may also restore set point firing rates after deviations (i.e. prediction errors) are detected. In this way, prefrontal cortex contributes to reducing uncertainty in prediction systems. An emergent outcome of this homeostatic view may be the flexible and adaptive control that prefrontal cortex is known to implement (i.e. working memory) in the most challenging of situations. Compromise to any of the prediction circuits should result in rigid and suboptimal decision making and memory as seen in addiction and neurological disease. © 2013 The Authors. Hippocampus Published by Wiley Periodicals, Inc.

Posterior parietal cortex is critical for the encoding, consolidation, and retrieval of a memory that guides attention for learning

Within most contemporary learning theories, reinforcement prediction error, the difference between the obtained and expected reinforcer value, critically influences associative learning. In some theories, this prediction error determines the momentary effectiveness of the reinforcer itself, such that the same physical event produces more learning when its presentation is surprising than when it is expected. In other theories, prediction error enhances attention to potential cues for that reinforcer by adjusting cue-specific associability parameters, biasing the processing of those stimuli so that they more readily enter into new associations in the future. A unique feature of these latter theories is that such alterations in stimulus associability must be represented in memory in an enduring fashion. Indeed, considerable data indicate that altered associability may be expressed days after its induction. Previous research from our laboratory identified brain circuit elements critical to the enhancement of stimulus associability by the omission of an expected event, and to the subsequent expression of that altered associability in more rapid learning. Here, for the first time, we identified a brain region, the posterior parietal cortex, as a potential site for a memorial representation of altered stimulus associability. In three experiments using rats and a serial prediction task, we found that intact posterior parietal cortex function was essential during the encoding, consolidation, and retrieval of an associability memory enhanced by surprising omissions. We discuss these new results in the context of our previous findings and additional plausible frontoparietal and subcortical networks.

Updating appetitive memory during reconsolidation window: critical role of cue-directed behavior and amygdala central nucleus

When presented with a light cue followed by food, some rats simply approach the foodcup (Nonorienters), while others first orient to the light in addition to displaying the food-cup approach behavior (Orienters). Cue-directed orienting may reflect enhanced attentional and/or emotional processing of the cue, suggesting divergent natures of cue-information processing in Orienters and Nonorienters. The current studies investigate how differences in cue processing might manifest in appetitive memory retrieval and updating using a paradigm developed to persistently attenuate fear responses (Retrieval-extinction paradigm; Monfils et al., 2009). First, we examined whether the retrieval-extinction paradigm could attenuate appetitive responses in Orienters and Nonorienters. Next, we investigated if the appetitive memory could be updated using reversal learning (fear conditioning) during the reconsolidation window (as opposed to repeated unreinforced trials, i.e., extinction). Both extinction and new fear learning given within the reconsolidation window were effective at persistently updating the initial appetitive memory in the Orienters, but not the Nonorienters. Since conditioned orienting is mediated by the amygdala central nucleus (CeA), our final experiment examined the CeA's role in the retrieval-extinction process. Bilateral CeA lesions interfered with the retrieval-extinction paradigm-did not prevent spontaneous recovery of food-cup approach. Together, our studies demonstrate the critical role of conditioned orienting behavior and the CeA in updating appetitive memory during the reconsolidation window.

Separate amygdala subregions signal surprise and predictiveness during associative fear learning in humans

It has recently been suggested that learning signals in the amygdala might be best characterized by attentional theories of associative learning [such as Pearce-Hall (PH)] and more recent hybrid variants that combine Rescorla-Wagner and PH learning models. In these models, unsigned prediction errors (PEs) determine the associability of a cue, which is used in turn to control learning of outcome expectations dynamically and reflects a function of the reliability of prior outcome predictions. Here, we employed an aversive Pavlovian reversal-learning task to investigate computational signals derived from such a hybrid model. Unlike previous accounts, our paradigm allowed for the separate assessment of associability at the time of cue presentation and PEs at the time of outcome. We combined this approach with high-resolution functional magnetic resonance imaging to understand how different subregions of the human amygdala contribute to associative learning. Signal changes in the corticomedial amygdala and in the midbrain represented unsigned PEs at the time of outcome showing increased responses irrespective of whether a shock was unexpectedly administered or omitted. In contrast, activity in basolateral amygdala regions correlated negatively with associability at the time of cue presentation. Thus, whereas the corticomedial amygdala and the midbrain reflected immediate surprise, the basolateral amygdala represented predictiveness and displayed increased responses when outcome predictions became more reliable. These results extend previous findings on PH-like mechanisms in the amygdala and provide unique insights into human amygdala circuits during associative learning.

Attention-related Pearce-Kaye-Hall signals in basolateral amygdala require the midbrain dopaminergic system

BACKGROUND

Neural activity in basolateral amygdala has recently been shown to reflect surprise or attention as predicted by the Pearce-Kaye-Hall model (PKH)--an influential model of associative learning. Theoretically, a PKH attentional signal originates in prediction errors of the kind associated with phasic firing of dopamine neurons. This requirement for prediction errors, coupled with projections from the midbrain dopamine system into basolateral amygdala, suggests that the PKH signal in amygdala may depend on dopaminergic input.

METHODS

To test this, we recorded single unit activity in basolateral amygdala in rats with 6-hydroxydopamine or sham lesions of the ipsilateral midbrain region. Neurons were recorded as the rats performed a task previously used to demonstrate both dopaminergic reward prediction errors and attentional signals in basolateral amygdala neurons.

RESULTS

We found that neurons recorded in sham lesioned rats exhibited the same attention-related PKH signal observed in previous studies. By contrast, neurons recorded in rats with ipsilateral 6-hydroxydopamine lesions failed to show attentional signaling.

CONCLUSIONS

These results indicate a linkage between the neural instantiations of the basolateral complex of the amygdala attentional signal and dopaminergic prediction errors. Such a linkage would have important implications for understanding both normal and aberrant learning and behavior, particularly in diseases thought to have a primary effect on dopamine systems, such as addiction and schizophrenia.

Role of amygdala central nucleus in feature negative discriminations

Consistent with a popular theory of associative learning, the Pearce-Hall (1980) model, the surprising omission of expected events enhances cue associability (the ease with which a cue may enter into new associations), across a wide variety of behavioral training procedures. Furthermore, previous experiments from this laboratory showed that these enhancements are absent in rats with impaired function of the amygdala central nucleus (CeA). A notable exception to these assertions is found in feature negative (FN) discrimination learning, in which a "target" stimulus is reinforced when it is presented alone but nonreinforced when it is presented in compound with another, "feature" stimulus. According to the Pearce-Hall model, reinforcer omission on compound trials should enhance the associability of the feature relative to control training conditions. However, prior experiments have shown no evidence that CeA lesions affect FN discrimination learning. Here we explored this apparent contradiction by evaluating the hypothesis that the surprising omission of an event confers enhanced associability on a cue only if that cue itself generates the disconfirmed prediction. Thus, in a FN discrimination, the surprising omission of the reinforcer on compound trials would enhance the associability of the target stimulus but not that of the feature. Our data confirmed this hypothesis and showed this enhancement to depend on intact CeA function, as in other procedures. The results are consistent with modern reformulations of both cue and reward processing theories that assign roles for both individual and aggregate error terms in associative learning.

The effects of basolateral amygdala lesions on unblocking

Prior reinforcement of a neutral stimulus often blocks subsequent conditioning of a new stimulus if a compound of the original and new cues is paired with the same reinforcer. However, if the value of the reinforcer is altered when the compound is presented, the new cue typically acquires conditioning, a result called unblocking. Blocking, unblocking, and related phenomena have been attributed to variations in processing of either the reinforcer, for example, the Rescorla-Wagner (1972) model, or cues, for example, the Pearce-Hall (1980) model. Here, we examined the effects of lesions of the basolateral amygdala on the occurrence of unblocking when the food reinforcer was increased in quantity at the time of introduction of the new cue. The lesions had no effects on unblocking in a simple design (Experiment 1), which did not distinguish between unblocking produced by variations in reward or cue processing. However, in a procedure that distinguished between unblocking due to direct conditioning by the added reinforcer, consistent with the Rescorla-Wagner (1972) model, and that due to increases in conditioning to the original reinforcer, consistent with the Pearce-Hall (1980) and other models of learning, the lesions prevented unblocking of the latter type. These results were discussed in the context of roles of the basolateral amygdala in coding and using reward prediction error information in associative learning.

Effects of reward timing information on cue associability are mediated by amygdala central nucleus

The central nucleus of the amygdala (CeA) has been implicated in a range of associative learning phenomena often attributed to changes in attentional processing of events. Experiments using a number of behavioral tasks have shown that rats with lesions of CeA fail to show the enhancements of stimulus associability that are normally induced by the surprising omission of expected events. By contrast, in other tasks, rats with lesions of CeA show normal enhancements of associability when events are presented unexpectedly. In this experiment, we examined the effects of CeA lesions on changes in cue associability in a reward timing task. In sham-lesioned rats, the associability of cues that were followed by stimuli that provided reward timing information was maintained at higher levels than that of cues that were followed by uninformative stimuli. Rats with lesions of CeA failed to show this advantage. These results indicate that the role of CeA in the modulation of associability is not limited to cases of event omission. (PsycINFO Database Record (c) 2011 APA, all rights reserved).

Inputs to the midbrain dopaminergic complex in the rat, with emphasis on extended amygdala-recipient sectors

The midbrain dopaminergic neuronal groups A8, A9, A10, and A10dc occupy, respectively, the retrorubral field (RRF), substantia nigra compacta (SNc), ventral tegmental area (VTA), and ventrolateral periaqueductal gray (PAGvl). Collectively, these structures give rise to a mixed dopaminergic and nondopaminergic projection system that essentially permits adaptive behavior. However, knowledge is incomplete regarding how the afferents of these structures are organized. Although the VTA is known to receive numerous afferents from cortex, basal forebrain, and brainstem and the SNc is widely perceived as receiving inputs mainly from the striatum, the afferents of the RRF and PAGvl have yet to be assessed comprehensively. This study was performed to provide an account of those connections and to seek a better understanding of how afferents might contribute to the functional interrelatedness of the VTA, SNc, RRF, and PAGvl. Ventral midbrain structures received injections of retrograde tracer, and the resulting retrogradely labeled structures were targeted with injections of anterogradely transported Phaseolus vulgaris leucoagglutinin. Whereas all injections of retrograde tracer into the VTA, SNc, RRF, or PAGvl produced labeling in many structures extending from the cortex to caudal brainstem, pronounced labeling of structures making up the central division of the extended amygdala occurred following injections that involved the RRF and PAGvl. The anterograde tracing supported this finding, and the combination of retrograde and anterograde labeling data also confirmed reports from other groups indicating that the SNc receives robust input from many of the same structures that innervate the VTA, RRF, and PAGvl.

Dissociations between medial prefrontal cortical subregions in the modulation of learning and action

The medial prefrontal cortex (mPFC) has been implicated in various attentional functions. This experiment examined the involvement of mPFC subregions in the allocation of attention in learning and action as a function of the predictive accuracy of cues. Rats with dorsal (encompassing anterior cingulate, prelimbic, and infralimbic cortices) or ventral (encompassing mainly infralimbic and dorsopeduncular cortices and tenia tecta) mPFC lesions were trained in a multiple-choice discrimination task in which operant nosepoke responses to some visual cues were consistently (100%) reinforced (CRF) with food, whereas responses to other visual cues were partially (50%) reinforced (PRF). In challenge tests designed to assess attention in the control of action, responding was directed more to CRF cues than to PRF cues in sham and dorsal mPFC-lesioned rats, but ventral mPFC-lesioned rats showed similar levels of responding to both CRF and PRF cues. Nevertheless, when given a choice between simultaneously presented CRF and PRF cues in a cue competition test, all groups responded more to CRF cues. In a subsequent Pavlovian overshadowing phase designed to assess attention in the acquisition of new learning, previously trained CRF cues overshadowed conditioning to novel auditory cues more than did PRF cues in dorsal mPFC-lesioned rats, whereas the opposite pattern was observed in sham and ventral mPFC-lesioned rats. These results suggest a dissociation within the mPFC in the use of reinforcement prediction information to allocate attention for new learning and for the control of action.

Neural correlates of variations in event processing during learning in central nucleus of amygdala

Attention or variations in event processing help drive learning. Lesion studies have implicated the central nucleus of the amygdala (CeA) in this process, particularly when expected rewards are omitted. However, lesion studies cannot specify how information processing in CeA supports such learning. To address these questions, we recorded CeA neurons in rats performing a task in which rewards were delivered or omitted unexpectedly. We found that activity in CeA neurons increased selectively at the time of omission and declined again with learning. Increased firing correlated with CeA-inactivation sensitive measures of attention. Notably CeA neurons did not fire to the cues or in response to unexpected rewards. These results indicate that CeA contributes to learning in response to reward omission due to a specific role in signaling actual omission rather than a more general involvement in signaling expectancies, errors, or reward value.

The central amygdala projection to the substantia nigra reflects prediction error information in appetitive conditioning

The central amygdala nucleus (CeA) plays a critical role in cognitive processes beyond fear conditioning. For example, intact CeA function is essential for enhancing attention to conditioned stimuli (CSs). Furthermore, this enhanced attention depends on the CeA's connections to the nigrostriatal system. In the current study, we examined the role of the CeA's connections to two midbrain dopamine regions, the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), in processing CS information when predictions of reward or nonreward were confirmed or disconfirmed. Initially, two different retrograde tracers were injected into the SNc and the VTA of rats, to label CeA cells. Different groups of rats then received a visual CS either paired or unpaired with food. Finally, Fos induction was assessed after a test session in which rats were exposed to the visual CS alone or paired with food. Colabeling of Fos and the retrograde tracer(s) showed that CeA neurons projecting to the SNc, but not to the VTA, were engaged in processing CS information when the training and testing conditions differed. These results suggest that the CeA-nigral pathway represents prediction error information during appetitive conditioning.

Inactivation of the central but not the basolateral nucleus of the amygdala disrupts learning in response to overexpectation of reward

The amygdala is critical for associating predictive cues with primary rewarding and aversive outcomes. This is particularly evident in tasks in which information about expected outcomes is required for normal responding. Here we used a pavlovian overexpectation task to test whether outcome signaling by amygdala might also be necessary for changing those representations in the face of unexpected outcomes. Rats were trained to associate several different cues with a food reward. After learning, two of the cues were presented together, in compound, followed by the same reward. Before each compound training session, rats received infusions of 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide or saline into either the basolateral (ABL) or central nucleus (CeN) of amygdala. We found that infusions into CeN abolished the normal decline in responding to the compounded cue in a later probe test, whereas infusions into ABL had no effect. These results are inconsistent with the proposal that signaling of information about expected outcomes by ABL contributes to learning, at least in this setting, and instead implicate the CeN in this process, perhaps attributable to the hypothesized involvement of this area in attention and variations in stimulus processing.

Categories of Novelty and States of Uncertainty

The concept of novelty has acquired a large number of diverse referents over the past quarter-century as a result of new methods that permit measurement of a variety of biological and behavioral reactions to novel incentives in both humans and animals. As a result, the term has acquired varied meanings. This analysis of novelty makes four claims. First, the specific state of uncertainty that a novel event creates depends on its origin. Second, unexpected events that alter the immediate stimulus surround (called stimulus novelty) should be distinguished from those that are inconsistent with an agent's long term knowledge (called conceptual novelty). Third, the critical features that render an event novel can vary with the agent's intention to classify or to act on an object and the balance between these two frames changes with development. Finally, the state of uncertainty created when an agent must choose one response from two or more alternatives differs from the states provoked by stimulus and conceptual novelty.