Excitotoxic lesions of the hippocampus leave sensory preconditioning intact: implications for models of hippocampal function

Excitotoxic lesions of the perirhinal cortex leave intact rats' gustatory sensory preconditioning

We report findings from two sensory preconditioning experiments in which rats consumed two flavoured solutions, each with two gustatory components (AX and BY), composed of sweet, bitter, salt, and acid elements. After this pre-exposure, rats were conditioned to X by pairing with lithium chloride. Standard sensory preconditioning was observed: Consumption of flavour A was less than that of B. We found that sensory preconditioning was maintained when X was added to A and B. Both experiments included one group of rats with lesions of the perirhinal cortex, which did not influence sensory preconditioning. We discuss our findings in the light of other sensory preconditioning procedures that involve the perirhinal cortex and conclude that differences in experimental variables invoke different mechanisms of sensory preconditioning, which vary in their requirement of the perirhinal cortex.

Dopamine D1 and D2 Receptors Are Important for Learning About Neutral-Valence Relationships in Sensory Preconditioning

Dopamine neurotransmission has been ascribed multiple functions with respect to both motivational and associative processes in reward-based learning, though these have proven difficult to tease apart. In order to better describe the role of dopamine in associative learning, this series of experiments examined the potential of dopamine D1- and D2-receptor antagonism (or combined antagonism) to influence the ability of rats to learn neutral valence stimulus-stimulus associations. Using a sensory preconditioning task, rats were first exposed to pairings of two neutral stimuli (S2-S1). Subsequently, S1 was paired with a mild foot-shock and resulting fear to both S1 (directly conditioned) and S2 (preconditioned) was examined. Initial experiments demonstrated the validity of the procedure in that measures of sensory preconditioning were shown to be contingent on pairings of the two sensory stimuli. Subsequent experiments indicated that systemic administration of dopamine D1- or D2-receptor antagonists attenuated learning when administered prior to S2-S1 pairings. However, the administration of a more generic D1R/D2R antagonist was without effect. These effects remained constant regardless of the affective valence of the conditioning environment and did not differ between male and female rats. The results are discussed in the context of recent suggestions that dopaminergic systems encode more than a simple reward prediction error, and provide potential avenues for future investigation.

A general model of hippocampal and dorsal striatal learning and decision making

Humans and other animals use multiple strategies for making decisions. Reinforcement-learning theory distinguishes between stimulus-response (model-free; MF) learning and deliberative (model-based; MB) planning. The spatial-navigation literature presents a parallel dichotomy between navigation strategies. In "response learning," associated with the dorsolateral striatum (DLS), decisions are anchored to an egocentric reference frame. In "place learning," associated with the hippocampus, decisions are anchored to an allocentric reference frame. Emerging evidence suggests that the contribution of hippocampus to place learning may also underlie its contribution to MB learning by representing relational structure in a cognitive map. Here, we introduce a computational model in which hippocampus subserves place and MB learning by learning a "successor representation" of relational structure between states; DLS implements model-free response learning by learning associations between actions and egocentric representations of landmarks; and action values from either system are weighted by the reliability of its predictions. We show that this model reproduces a range of seemingly disparate behavioral findings in spatial and nonspatial decision tasks and explains the effects of lesions to DLS and hippocampus on these tasks. Furthermore, modeling place cells as driven by boundaries explains the observation that, unlike navigation guided by landmarks, navigation guided by boundaries is robust to "blocking" by prior state-reward associations due to learned associations between place cells. Our model, originally shaped by detailed constraints in the spatial literature, successfully characterizes the hippocampal-striatal system as a general system for decision making via adaptive combination of stimulus-response learning and the use of a cognitive map.

Retrosplenial cortex and its role in cue-specific learning and memory

The retrosplenial cortex (RSC) contributes to spatial navigation, as well as contextual learning and memory. However, a growing body of research suggests that the RSC also contributes to learning and memory for discrete cues, such as auditory or visual stimuli. In this review, we summarize and assess the Pavlovian and instrumental conditioning experiments that have examined the role of the RSC in cue-specific learning and memory. We use the term cue-specific to refer to these putatively non-spatial conditioning paradigms that involve discrete cues. Although these paradigms emphasize behavior related to cue presentations, we note that cue-specific learning and memory always takes place against a background of contextual stimuli. We review multiple ways by which contexts can influence responding to discrete cues and suggest that RSC contributions to cue-specific learning and memory are intimately tied to contextual learning and memory. Indeed, although the RSC is involved in several forms of cue-specific learning and memory, we suggest that many of these can be linked to processing of contextual stimuli.

Dorsal hippocampus contributes to model-based planning

Planning can be defined as action selection that leverages an internal model of the outcomes likely to follow each possible action. Its neural mechanisms remain poorly understood. Here we adapt recent advances from human research for rats, presenting for the first time an animal task that produces many trials of planned behavior per session, making multitrial rodent experimental tools available to study planning. We use part of this toolkit to address a perennially controversial issue in planning: the role of the dorsal hippocampus. Although prospective hippocampal representations have been proposed to support planning, intact planning in animals with damaged hippocampi has been repeatedly observed. Combining formal algorithmic behavioral analysis with muscimol inactivation, we provide causal evidence directly linking dorsal hippocampus with planning behavior. Our results and methods open the door to new and more detailed investigations of the neural mechanisms of planning in the hippocampus and throughout the brain.

Preconditioning of Spatial and Auditory Cues: Roles of the Hippocampus, Frontal Cortex, and Cue-Directed Attention

Loss of function of the hippocampus or frontal cortex is associated with reduced performance on memory tasks, in which subjects are incidentally exposed to cues at specific places in the environment and are subsequently asked to recollect the location at which the cue was experienced. Here, we examined the roles of the rodent hippocampus and frontal cortex in cue-directed attention during encoding of memory for the location of a single incidentally experienced cue. During a spatial sensory preconditioning task, rats explored an elevated platform while an auditory cue was incidentally presented at one corner. The opposite corner acted as an unpaired control location. The rats demonstrated recollection of location by avoiding the paired corner after the auditory cue was in turn paired with shock. Damage to either the dorsal hippocampus or the frontal cortex impaired this memory ability. However, we also found that hippocampal lesions enhanced attention directed towards the cue during the encoding phase, while frontal cortical lesions reduced cue-directed attention. These results suggest that the deficit in spatial sensory preconditioning caused by frontal cortical damage may be mediated by inattention to the location of cues during the latent encoding phase, while deficits following hippocampal damage must be related to other mechanisms such as generation of neural plasticity.

Transitions in the temporal parameters of sensory preconditioning during infancy

Sensory preconditioning (SPC) is a form of latent learning in which preexposure to co-occurring neutral stimuli (S1 -S2 ) permits subsequent learning to be transferred from one stimulus (S1 ) to the other (S2 ). We examined whether human infants exhibit developmental transitions in the temporal parameters of SPC by manipulating the preexposure regimen. Infants received simultaneous or sequential preexposure to puppets S1 and S2 (Days 1-2); saw target actions modeled on S1 (Day 3); and were tested for deferred imitation with S2 (Day 4). Although 6-, 9-, and 12-month-olds associated the puppets, there was a shift in the effective regimen from simultaneous to sequential preexposure-similar to prior findings with rat pups (Experiment 1). Experiment 2 revealed that human infants potentially exhibit another transition in SPC at 15 and 18 months of age. We consider the roles of ontogenetic shifts in infants' ecological niche, selective attention, and unitization in developmental transitions in SPC.

Over the river, through the woods: cognitive maps in the hippocampus and orbitofrontal cortex

The hippocampus and the orbitofrontal cortex (OFC) both have important roles in cognitive processes such as learning, memory and decision making. Nevertheless, research on the OFC and hippocampus has proceeded largely independently, and little consideration has been given to the importance of interactions between these structures. Here, evidence is reviewed that the hippocampus and OFC encode parallel, but interactive, cognitive 'maps' that capture complex relationships between cues, actions, outcomes and other features of the environment. A better understanding of the interactions between the OFC and hippocampus is important for understanding the neural bases of flexible, goal-directed decision making.

Impaired spatial working memory after anterior thalamic lesions: recovery with cerebrolysin and enrichment

Lesions to the anterior thalamic nuclei (ATN) in rats produce robust spatial memory deficits that reflect their influence as part of an extended hippocampal system. Recovery of spatial working memory after ATN lesions was examined using a 30-day administration of the neurotrophin cerebrolysin and/or an enriched housing environment. As expected, ATN lesions in standard-housed rats given saline produced severely impaired reinforced spatial alternation when compared to standard-housed rats with sham lesions. Both cerebrolysin and enrichment substantially improved this working memory deficit, including accuracy on trials that required attention to distal cues for successful performance. The combination of cerebrolysin and enrichment was more effective than either treatment alone when the delay between successive runs in a trial was increased to 40 s. Compared to the intact rats, ATN lesions in standard-housed groups produced substantial reduction in c-Fos expression in the retrosplenial cortex, which remained low after cerebrolysin and enrichment treatments. Evidence that multiple treatment strategies restore some memory functions in the current lesion model reinforces the prospect for treatments in human diencephalic amnesia.

Toward a conceptualization of retrohippocampal contributions to learning and memory

A wealth of data supports the notion that the hippocampus binds objects and events together in place and time. In support of this function, a cortical circuit that includes the retrosplenial cortex (RSC) and various structures in the parahippocampal region is thought to provide the hippocampus with essential information regarding the physical and temporal context in which the object/event occurs. However, it remains unclear if and how individual components of this so-called 'where' circuit make unique contributions to processing context-related information. Here we focus on the RSC and the postrhinal cortex (POR; homologous with parahippocampal cortex (PHC) in primates), two of the most strongly interconnected components of the where pathway and the foci of an increasing amount of recent research. Much of the behavioral evidence to date suggests that RSC and POR/PHC work closely together as a functional unit. We begin by briefly reviewing studies that have investigated the involvement of RSC and POR/PHC in contextual and spatial learning, both of which involve learning associations and relationships between the individual stimuli that compose an environment (i.e., where information). However, we propose that potential differences have been overlooked because most studies to date have relied on behavioral paradigms and experimental approaches that are not well suited for distinguishing between different aspects of information processing. We then consider the anatomical differences between RSC and POR/PHC and emerging behavioral evidence that gives rise to a working model of how these regions may differentially contribute to hippocampal-dependent learning and memory. We then discuss experimental designs and behavioral methods that may be useful in testing the model. Finally, approaches are described that may be valuable in probing the nature of information processing and neuroplasticity in the myriad of local circuits that are nested within the where pathway.

Neural correlates of sensory preconditioning: a preliminary fMRI investigation

Sensory preconditioning (SPC; also known as behaviorally silent learning) consists of a combination of two neutral stimuli, none of which elicits an unconditional response. After one of them is later paired with an unconditional stimulus (US), the other neutral stimulus also yields a conditional response although it has never been paired with the US. In this study, an event-related functional magnetic resonance imaging (fMRI) paradigm was used to specify brain regions involved in SPC. The results demonstrated that SPC was associated with significant changes in activity of several regions, notably, the left amygdala, the left hippocampus, the bilateral thalamus, the bilateral medial globus pallidus, the bilateral cerebellum, the bilateral premotor cortex, and the bilateral middle frontal gyrus. This is a first effort to use fMRI to examine the effects of SPC on brain activation. Our data suggest that there is a distributed network of structures involved in SPC including both cortical and subcortical regions, therefore add to our understanding of the neural mechanisms underlying the ability to associative learning.

Differential involvement of the basolateral amygdala and orbitofrontal cortex in the formation of sensory-specific associations in conditioned flavor preference and magazine approach paradigms

Four experiments examined the roles of the basolateral amygdala and orbitofrontal cortex in the formation of sensory-specific associations in conditioned flavor preference and conditioned magazine approach paradigms using unconditioned stimulus (US) devaluation and selective Pavlovian-instrumental transfer procedures in Long Evans rats. Experiment 1 found that pre-training amygdala and orbitofrontal cortex lesions had no detectable effect on the formation or flexible use of sensory-specific flavor-nutrient associations in a US devaluation task, where flavor cues were paired either simultaneously or sequentially with nutrient rewards in water-deprived subjects. In Experiment 2, pre-training amygdala and orbitofrontal cortex lesions both attenuated outcome-specific Pavlovian-instrumental transfer. Experiment 3 indicated that amygdala lesions have no effect on the formation of sensory-specific flavor-nutrient associations in a US devaluation task in food-deprived subjects. Finally, Experiment 4 demonstrated that the outcomes used in Experiment 3 were sufficiently motivationally significant to support conditioned flavor preference. These findings suggest that, although both orbitofrontal cortex and amygdala lesions attenuate the acquisition of sensory-specific associations in magazine approach conditioning, neither lesion reduces the ability to appropriately respond to a flavor cue that was paired with a devalued outcome.

Hippocampal lesions can enhance discrimination learning despite normal sensitivity to interference from incidental information

Spatial properties of stimuli are sometimes encoded even when incidental to the demands of a particular learning task. Incidental encoding of spatial information may interfere with learning by (i) causing a failure to generalize learning between trials in which a cue is presented in different spatial locations and (ii) adding common spatial features to stimuli that predict different outcomes. Hippocampal lesions have been found to facilitate acquisition of certain tasks. This facilitation may occur because hippocampal lesions impair incidental encoding of spatial information that interferes with learning. To test this prediction mice with lesions of the hippocampus were trained on appetitive simple simultaneous discrimination tasks using inserts in the goal arms of a T-maze. It was found that hippocampal lesioned mice were facilitated at learning the discriminations, but they were sensitive to changes in spatial information in a manner that was similar to control mice. In a second experiment it was found that both control and hippocampal lesioned mice showed equivalent incidental encoding of egocentric spatial properties of the inserts, but both groups did not encode the allocentric information. These results demonstrate that mice show incidental encoding of egocentric spatial information that decreases the ability to solve simultaneous discrimination tasks. The normal egocentric spatial encoding in hippocampal lesioned mice contradicts theories of hippocampal function that suggest that the hippocampus is necessary for incidental learning per se, or is required for modulating stimulus representations based on the relevancy of information. The facilitated learning suggests that the hippocampal lesions can enhance learning of the same qualitative information as acquired by control mice. © 2011 Wiley Periodicals, Inc.

Involvement of retrosplenial cortex in forming associations between multiple sensory stimuli

The retrosplenial cortex (RSP) is highly interconnected with medial temporal lobe structures, yet relatively little is known about its specific contributions to learning and memory. One possibility is that RSP is involved in forming associations between multiple sensory stimuli. Indeed, damage to RSP disrupts learning about spatial or contextual cues and also impairs learning about co-occurring conditioned stimuli (CSs). Two experiments were conducted to test this notion more rigorously. In Experiment 1, rats were trained in a serial feature negative discrimination task consisting of reinforced presentations of a tone alone and nonreinforced serial presentations of a light followed by the tone. Thus, in contrast to prior studies, this paradigm involved serial presentation of conditioned stimuli (CS), rather than simultaneous presentation. Rats with damage to RSP failed to acquire the discrimination, indicating that RSP is required for forming associations between sensory stimuli regardless of whether they occur serially or simultaneously. In Experiment 2, a sensory preconditioning task was used to determine if RSP was necessary for forming associations between stimuli even in the absence of reinforcement. During the first phase of this procedure, one auditory stimulus was paired with a light while a second auditory stimulus was presented alone. In the next phase of training, the same light was paired with food. During the final phase of the procedure both auditory stimuli were presented alone during a single session. Control, but not RSP-lesioned rats, exhibited more food cup behavior following presentation of the auditory cue that was previously paired with light compared with the unpaired auditory stimulus, indicating that a stimulus-stimulus association was formed during the first phase of training. These results support the idea that RSP has a fundamental role in forming associations between environmental stimuli.

The entorhinal cortex, but not the dorsal hippocampus, is necessary for single-cue latent learning

Two experiments were conducted to examine the roles of the entorhinal cortex (EC), dorsal hippocampus (DH), and ventral hippocampus (VH) in a modified Latent Cue Preference (LCP) task. The modified LCP task utilized one visual cue in each compartment, compared to several multimodal cues used in a previous version. In the single-cue LCP task, water-replete rats drink water in one compartment of the LCP box on 1 day, and then have no water in a second compartment of the LCP box the following day (one training trial), for a total of three training trials. Rats are then water-deprived prior to a preference test, in which they are allowed to move freely between the two compartments with the water removed. Latent learning is demonstrated when water-deprived rats spend more time in the compartment that previously contained the water. Experiment 1 demonstrated that the single-cue LCP task results in the same irrelevant-incentive latent learning as the multicue LCP task. In addition, Experiment 1 replicated the finding that a compartment preference based on this latent learning requires a deprivation state during the preference test, while a compartment preference based on conditioning does not. Experiment 2 examined the effects of pretraining neurotoxin lesions of the EC, DH, and VH on this single-cue LCP task. Results showed that lesions of the EC and VH disrupted the irrelevant-incentive latent learning, while lesions of the DH did not. These results indicate that a latent learning task that involves one discrete compartment cue, rather than several compartmental cues, does not require the DH. Therefore, the EC appears to play a central role in single-cue latent learning in the LCP task.

The basolateral amygdala is critical for the acquisition and extinction of associations between a neutral stimulus and a learned danger signal but not between two neutral stimuli

We studied the neural substrates of higher-order conditioned fear in rats. We first studied acquisition and extinction of second-order fear. One stimulus (S1) was paired with a footshock unconditioned stimulus (US), a second stimulus (S2) was paired with S1, and, finally, fear of S2 was extinguished by S2 alone exposures. Reversible inactivation of the basolateral amygdala (BLA) via muscimol, systemic injection of the NMDA receptor (NMDAr) antagonist MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate], or intra-amygdala infusion of the NMDAr NR2B subunit selective antagonist ifenprodil impaired both acquisition and extinction of fear to S2. We then studied acquisition and extinction of sensory preconditioned fear. S2 was first paired with S1, S1 was then paired with the US, and, finally, fear of S2 was extinguished by S2 alone exposures. Extinction of sensory preconditioned fear was impaired by a BLA infusion of muscimol or ifenprodil and by MK-801. Acquisition of the S2-S1 association and extinction of this association by S2 alone exposures before conditioning of S1 was impaired by MK-801 but not by a BLA infusion of muscimol. These results show that NMDAr activation in the BLA is critical for acquisition of second-order conditioned fear and for the extinction of both second-order and sensory preconditioned fear just as it is for acquisition and extinction of first-order conditioned fear. Acquisition and extinction of an association between two neutral stimuli also require NMDAr activation. However, the present results show that the acquisition and extinction of these associations do not require the BLA.

Entorhinal cortex and cognition

Understanding the function of the entorhinal cortex (EC) has been an important subject over the years, not least because of its cortical intermediary to and from the hippocampus proper, and because of electrophysiological advances which have started to reveal the physiology in behaving animals. Clearly, a lot more needs to be done but is clear to date that EC is not merely a throughput station providing all hippocampal subfields with sensory information, but that processing within EC contributes significantly to attention, conditioning, event and spatial cognition possibly by compressing representations that overlap in time. These are transmitted to the hippocampus, where they are differentiated again and returned to EC. Preliminary evidence for such a role, but also their possible pitfalls are summarised.

Multiple memory systems are unnecessary to account for infant memory development: an ecological model

How the memory of adults evolves from the memory abilities of infants is a central problem in cognitive development. The popular solution holds that the multiple memory systems of adults mature at different rates during infancy. The early-maturing system (implicit or nondeclarative memory) functions automatically from birth, whereas the late-maturing system (explicit or declarative memory) functions intentionally, with awareness, from late in the first year. Data are presented from research on deferred imitation, sensory preconditioning, potentiation, and context for which this solution cannot account and present an alternative model that eschews the need for multiple memory systems. The ecological model of infant memory development (N. E. Spear, 1984) holds that members of all species are perfectly adapted to their niche at each point in ontogeny and exhibit effective, evolutionarily selected solutions to whatever challenges each new niche poses. Because adults and infants occupy different niches, what they perceive, learn, and remember about the same event differs, but their raw capacity to learn and remember does not.

Structural learning and the hippocampus

It is argued that while the hippocampus is not vital for all classes of configural learning, it is vital for a specific subclass of configural tasks called "structural learning." The defining feature of structural learning is that in addition to binding stimulus elements to make unique arrays (as in all configural learning), the relationship of these elements to each other, be it spatial or temporal, is specified. Direct evidence supporting the proposal that the hippocampus is required for structural learning comes from recent lesion studies with rats. While rats with hippocampal lesions were impaired at relearning a set of spatial structural problems, they showed no impairment when relearning two configural tasks (transverse patterning and the biconditional discrimination), neither of which required structural learning. Other support comes from surveys of spatial and temporal learning by amnesic patients with hippocampal damage, and from imaging studies of both humans and rats. While these studies offer consistent support for the structural hypothesis, very few provide a rigorous test as the tasks can often be solved by other strategies. For this reason, the present review details the design features of future stringent tests of the structural hypothesis.

Neural circuits mediating latent learning and conditioning for salt in the rat

Male Long-Evans rats alternately drank a salt solution in one distinctive compartment of a conditioned cue preference (CCP) apparatus and water in a different compartment over 8 days (training trials) and were then given a choice between the two compartments with no solutions present (test trial). Rats that were water deprived during training, then salt+water deprived during testing, spent more time in their salt-paired compartments, a salt latent cue preference (LCP). Rats that were water-only deprived during training and testing spent more time in their water-paired compartments, a water CCP. Rats that were salt+water deprived during both training and testing spent more time in their salt-paired compartments, a salt CCP. Bilateral, pre-training lesions of the lateral amygdala impaired the water and salt CCPs but not the salt LCP, reflecting the role of the amygdala in Pavlovian conditioning. Lesions of the dorsal or ventral hippocampus impaired the salt LCP and the water and salt CCPs, possibly reflecting the role of the hippocampus in contextual learning. Lesions of the fimbria-fornix impaired the water and salt CCPs but not the salt LCP, while lesions of the entorhinal cortex impaired the salt LCP but not the CCPs. This suggests that the LCP depends on a circuit that includes dorsal and ventral hippocampus and entorhinal cortex, a major conduit of sensory information from the cortex. In contrast, the CCPs depend on the amygdala and a circuit that includes the hippocampus and fimbria-fornix, possibly as a conduit of motivational information from subcortical structures.

Dorsal hippocampus function in learning and expressing a spatial discrimination

Learning to discriminate between spatial locations defined by two adjacent arms of a radial maze in the conditioned cue preference paradigm requires two kinds of information: latent spatial learning when the rats explore the maze with no food available, and learning about food availability in two spatial locations when the rats are then confined in one arm with food and the other with no food. Previous research showed that a functional dorsal hippocampus is not required for latent learning. The present experiments show that it is required for learning about food availability, and during retrieval of both types of information.

Changes in immediate early gene expression in the rat brain after unilateral lesions of the hippocampus

Activity of the immediate early genes c-fos and zif268 was compared across hemispheres in rats with unilateral, excitotoxic lesions of the hippocampus (dentate gyrus and CA fields 1-4). Counts of the protein products of these genes were made shortly after rats performed a test of spatial working memory in the radial-arm maze, a task that is sensitive to bilateral lesions of the hippocampus. Unilateral hippocampal lesions produced evidence of widespread hypoactivity. Significant reductions in immediate early gene counts were observed within all three anterior thalamic nuclei, as well as the entorhinal, perirhinal, and postrhinal cortices, and much of the subicular complex. In contrast, no observable changes were detected in the anterior cingulate, infralimbic or prelimbic cortices, as well as several amygdala nuclei, even though many of these regions receive projections from the subiculum. Instead, the immediate early gene changes were closely linked to sites that are thought to be required for successful task performance, with both immediate early genes giving similar patterns of results. The findings support the notion that the anterior thalamic nuclei, hippocampus, and parahippocampal cortices form the key components of an interdependent neuronal network involved in spatial mnemonic processing.

Excitotoxic Lesions of the Entorhinal Cortex Leave Gustatory Within-Event Learning Intact

The ability of rats with ibotenate lesions of the entorhinal cortex to form memories for events was assessed by using a gustatory within-event learning procedure. Rats first received exposure to 2 events, AX and BY, each composed of a pair of flavors. Following this exposure period, Flavor X alone was paired with the delivery of lithium chloride. Lesioned and control rats showed a greater aversion to A than to B and to AX than to BX. These results challenge theories that suppose that the entorhinal cortex plays a general role in forming representations of patterns of stimulation.

Sensory preconditioning in rats with lesions of the anterior thalamic nuclei: evidence for intact nonspatial 'relational' processing

Rats with neurotoxic lesions centered in the anterior thalamic nuclei were trained in two versions of a nonspatial, sensory preconditioning procedure. In both versions, two stimulus compounds (AX and BY) were first presented and then X, but not Y, was paired with an aversive unconditioned stimulus. This procedure resulted in greater conditioned responding to A than B. Anterior thalamic lesions had no apparent effect on these two examples of sensory preconditioning, nor did they affect fear conditioning or conditioned taste aversion. In contrast, the same lesions led to a severe deficit on a test of spatial memory. These results help to refine our understanding of the contribution of the anterior thalamic nuclei to spatial memory.