Sodium concentration coding gives way to evaluative coding in cortex and amygdala

Typically, stimulus batteries used to characterize sensory neural coding span physical parameter spaces (e.g., concentration: from low to high). For awake animals, however, psychological variables (e.g., pleasantness/palatability) with complicated relationships to the physical often dominate neural responses. Here we pit physical and psychological axes against one another, presenting awake rats with a stimulus set including 4 NaCl concentrations (0.01, 0.1, 0.3, and 1.0 m) plus palatable (0.3 m sucrose) and aversive (0.001 m quinine) benchmarks, while recording the activity of neurons in two sites vital for NaCl taste processing, gustatory cortex (GC) and central amygdala (CeA). Since NaCl palatability (i.e., preference) follows a non-monotonic, "inverted-U-shaped" curve while concentration increases monotonically, this stimulus battery allowed us to test whether GC and CeA responses better reflect external or internal variables. As predicted, GC single-neuron and population responses reflected both parameters in separate response epochs: sodium concentration-related information appeared with the earliest taste-specific responses, giving way to palatability-related information, in an overlapping subset of neurons, several hundred milliseconds later. CeA single-neuron and population responses, meanwhile, contained only a brief period of concentration specificity, occurring just before palatability-related information emerged (simultaneously with, or slightly later than, in GC). Thus, cortex and amygdala both prominently reflect NaCl palatability late in their responses; CeA neurons largely respond to either palatable or aversive stimuli, while GC responses tend to reflect the entire palatability spectrum in a graded fashion.     

Amygdala-gustatory insular cortex connections and taste neophobia

To examine whether communication between the amygdala and gustatory insular cortex (GC) is required for normal performance of taste neophobia, three experiments were conducted. In Experiment 1, rats with asymmetric unilateral lesions of the basolateral amygdala (BLA) and the GC displayed elevated intake of a novel saccharin solution relative to control subjects. However, an attenuation of neophobia was not found following asymmetric unilateral lesions of the GC and medial amygdala (MeA; Experiment 2) or of the MeA and BLA (Experiment 3). This pattern of results indicates that the BLA and GC functionally interact during expression of taste neophobia and that the MeA functionally interacts with neither the BLA nor the GC. Research is needed to further characterize the nature of the involvement of the MeA in taste neophobia and to determine the function of the BLA-GC interaction during exposure to a new taste.     

Multisensory Processing of Gustatory Stimuli

The brain’s processing of gustatory stimuli is inherently multimodal, since at approximately the same time that intraoral stimuli activate receptors on taste cells, somatosensory information is concurrently conveyed to the central nervous system. We first present evidence that throughout the oral cavity, often a single chemical stimulus will concomitantly activate different receptors expressed on taste cells and somatosensory nerve terminals. We then argue that gustatory perception is intrinsically linked to concurrent somatosensory processing. Finally, we review evidence showing that central gustatory pathways are sites where multisensory integration occurs, with particular emphasis on somatosensory responses in the gustatory cortex.     

The effect of satiety on responses of gustatory neurons in the amygdala of alert cynomolgus macaques

An alert cynomolgus macaque was fed a sweet solution to satiety as the activity of a gustatory neuron in the amygdala was recorded to that solution and to four other taste stimuli. This experiment was conducted a total of 14 times in two monkeys. The responses of individual neurons to the satiety stimuli were suppressed by as little as 1%, and as much as 100% by the induction of satiety (mean suppression = 58%). Nine of the 14 cells responded to the satiety solution with excitation, and their responses were suppressed by a mean of 62% by satiety. Five neurons responded with inhibition, and their responses were suppressed by a mean of 50%. Responses to other taste stimuli, not associated with satiety, were affected to a lesser extent. The amygdala is a taste relay between the primary gustatory cortex, where satiety has no influence on responses to taste stimuli, and the lateral hypothalamic area where the effect of satiety is total. The data presented here indicate that the amygdala is a functional as well as anatomical intermediary between these two areas, and serves as a stage in the process through which sensory stimuli are imbued with motivational significance.     

The representation of information about faces in the temporal and frontal lobes

Neurophysiological evidence is described showing that some neurons in the macaque inferior temporal visual cortex have responses that are invariant with respect to the position, size and view of faces and objects, and that these neurons show rapid processing and rapid learning. Which face or object is present is encoded using a distributed representation in which each neuron conveys independent information in its firing rate, with little information evident in the relative time of firing of different neurons. This ensemble encoding has the advantages of maximising the information in the representation useful for discrimination between stimuli using a simple weighted sum of the neuronal firing by the receiving neurons, generalisation and graceful degradation. These invariant representations are ideally suited to provide the inputs to brain regions such as the orbitofrontal cortex and amygdala that learn the reinforcement associations of an individual's face, for then the learning, and the appropriate social and emotional responses, generalise to other views of the same face. A theory is described of how such invariant representations may be produced in a hierarchically organised set of visual cortical areas with convergent connectivity. The theory proposes that neurons in these visual areas use a modified Hebb synaptic modification rule with a short-term memory trace to capture whatever can be captured at each stage that is invariant about objects as the objects change in retinal view, position, size and rotation. Another population of neurons in the cortex in the superior temporal sulcus encodes other aspects of faces such as face expression, eye gaze, face view and whether the head is moving. These neurons thus provide important additional inputs to parts of the brain such as the orbitofrontal cortex and amygdala that are involved in social communication and emotional behaviour. Outputs of these systems reach the amygdala, in which face-selective neurons are found, and also the orbitofrontal cortex, in which some neurons are tuned to face identity and others to face expression. In humans, activation of the orbitofrontal cortex is found when a change of face expression acts as a social signal that behaviour should change; and damage to the orbitofrontal cortex can impair face and voice expression identification, and also the reversal of emotional behaviour that normally occurs when reinforcers are reversed.     

Alterations of emotion, cognition and firing activity of the basolateral nucleus of the amygdala after partial bilateral lesions of the nigrostriatal pathway in rats

Although increasing evidence indicates that psychiatric symptoms are crucial characteristic of the early stage of Parkinson's disease (PD) and precede motor impairments, the neuronal firing activity of the basolateral nucleus of the amygdala (BLA) in the psychiatric symptom of PD and the involved mechanism are still unclear. In the present study, we examined the changes in emotional and cognitive tests not focused on motor fluency and firing activity of projection neurons in the BLA rats with 6-hydroxydopamine (6-OHDA) injected bilaterally into dorsal striatum, and the effects of apomorphine and the medial prefrontal cortex (mPFC) on these changes. Injection of 6-OHDA (10.5 μg) into the dorsal striatum produced 18-22% and 26-30% loss of tyrosine hydroxylase immunoreactive neurons in the ventral tegmental area and substantia nigra pars compacta of rats, respectively. The striatal lesions induced anxiety-like responses in the rats but did not result in depressive-like behavior or cognitive impairments. In the lesioned rats, the firing rate of BLA projection neurons decreased significantly compared with sham-operated rats, and the firing pattern of BLA projection neurons was not changed. No significant differences were observed either in behaviors or firing activity of BLA projection neurons by further ibotenic acid lesions of the mPFC in the lesioned rats. Systemic administration of cumulative apomorphine (10-160 μg/kg) inhibited the firing rate of BLA projection neurons in sham-operated, 6-OHDA-lesioned and combined 6-OHDA- and mPFC-lesioned rats, but the latter needed more apomorphine stimulation. These data suggest that the anxiety in early stage of PD is possibly related to the decrease in firing activity of BLA projection neurons, which may be regulated by the activation of dopamine receptor in the mPFC.     

Basolateral amygdala,nicotinic cholinergic receptors,and nicotine: Pharmacological effects and addiction in animal models and humans

The amygdala is involved in processing incoming information about rewarding stimuli and emotions that denote danger such as anxiety and fear. Bi‐directional neural connections between basolateral amygdala (BLA) and brain regions such as nucleus accumbens, prefrontal cortex, hippocampus, and hindbrain regions regulate motivation, cognition, and responses to stress. Altered local regulation of BLA excitability is pivotal to the behavioral disturbances characteristic of posttraumatic stress disorder, and relapse to drug use induced by stress. Herein, we review the physiological regulation of BLA by cholinergic inputs, emphasizing the role of BLA nicotinic receptors. We review BLA‐dependent effects of nicotine on cognition, motivated behaviors, and emotional states, including memory, taking and seeking drugs, and anxiety and fear in humans and animal models. The alterations in BLA activity observed in animal studies inform human behavioral and brain imaging research by enabling a more exact understanding of altered BLA function. Converging evidence indicates that cholinergic signaling from basal forebrain projections to local nicotinic receptors is an important physiological regulator of BLA and that nicotine alters BLA function. In essence, BLA is necessary for behavioral responses to stimuli that evoke anxiety and fear; reinstatement of cue‐induced drug seeking; responding to second‐order cues conditioned to abused drugs; reacquisition of amplified nicotine self‐administration due to chronic stress during abstinence; and to promote responding for natural reward.     

Hunger Modulates the Responses to Gustatory Stimuli of Single Neurons in the Caudolateral Orbitofrontal Cortex of the Macaque Monkey

1. In order to determine whether the responsiveness of neurons in the caudolateral orbitofrontal cortex (a secondary cortical gustatory area) is influenced by hunger, the activity evoked by prototypical taste stimuli (glucose, NaCl, HCl, and quinine hydrochloride) and fruit juice was recorded in single neurons in this cortical area before, while, and after cynomolgous macaque monkeys were fed to satiety with glucose or fruit juice. 2. It was found that the responses of the neurons to the taste of the glucose decreased to zero while the monkey ate it to satiety during the course of which his behaviour turned from avid acceptance to active rejection. 3. This modulation of responsiveness of the gustatory responses of the neurons to satiety was not due to peripheral adaptation in the gustatory system or to altered efficacy of gustatory stimulation after satiety was reached, because modulation of neuronal responsiveness by satiety was not seen at earlier stages of the gustatory system, including the nucleus of the solitary tract, the frontal opercular taste cortex, and the insular taste cortex. 4. The decreases in the responsiveness of the neurons were relatively specific to the food with which the monkey had been fed to satiety. For example, in seven experiments in which the monkey was fed glucose solution, neuronal responsiveness decreased to the taste of the glucose but not to the taste of blackcurrant juice. Conversely, in two experiments in which the monkey was fed to satiety with fruit juice, the responses of the neurons decreased to fruit juice but not to glucose. 5. These and earlier findings lead to a proposed neurophysiological mechanism for sensory-specific satiety in which the information coded by single neurons in the gustatory system becomes more specific through the processing stages consisting of the nucleus of the solitary tract, the taste thalamus, and the frontal opercular and insular taste primary taste cortices, until neuronal responses become relatively specific for the food tasted in the caudolateral orbitofrontal cortex (secondary) taste area. Then sensory-specific satiety occurs because in this caudolateral orbitofrontal cortex taste area (but not earlier in the taste system) it is a property of the synapses that repeated stimulation results in a decreased neuronal response. 6. Evidence was obtained that gustatory processing involved in thirst also becomes interfaced to motivation in the caudolateral orbitofrontal cortex taste projection area, in that neuronal responses here to water were decreased to zero while water was drunk until satiety was produced.     

Cortical spatial aspects of optical intrinsic signals in response to sucrose and NaCl stimuli

To examine whether cortical taste neurons use spatial codes for discriminating taste information, we investigated the spatial aspects of optical intrinsic signal (OIS) responses in the gustatory insular cortex (GC) elicited by the administration of two essential tastants, sucrose and NaCl, on the tongue. OIS responses to sucrose appeared in the rostral part of the GC, whereas those to NaCl appeared in the central part of the GC. Local anesthetization of the tongue abolished OIS responses, and the administration of distilled water elicited no OIS response. Thus, taste information elicited by sucrose and NaCl from the peripheral sensory organs is segregated in the GC, suggesting that the information from two essential tastants is assembled as spatial codes in the primary cortical taste area through the process of taste quality perception.     

Electrophysiological study of the response of medial prefrontal cortex neurons to stimulation of the basolateral nucleus of the amygdala in the rat.

The neural connections from the basolateral nucleus of the amygdala (BLA) to the medial prefrontal cortex (MPC) in urethane-anesthetized rats were investigated. Extracellular recordings were made from 200 neurons with spontaneous firing in the MPC, and the BLA was electrically stimulated. The most frequent response to BLA stimulation was inhibition (63.5%). Excitatory responses were found in 17 units (8.5%), while 56 neurons (28%) did not change their spontaneous firing after BLA stimulation. Inhibitory responses showed a wide range of latencies, suggesting the coexistence of mono- and polysynaptic pathways. On the contrary, the excitatory responses seem to be mediated by a monosynaptic pathway. BLA projections to the MPC play a predominantly inhibitory role in the spontaneous activity of prefrontal neurons. This inhibition may modulate central motor systems and motivated behaviors.     

Basolateral amygdala regulation of adult hippocampal neurogenesis and fear-related activation of newborn neurons

Impaired regulation of emotional memory is a feature of several affective disorders, including depression, anxiety and post-traumatic stress disorder. Such regulation occurs, in part, by interactions between the hippocampus and the basolateral amygdala (BLA). Recent studies have indicated that within the adult hippocampus, newborn neurons may contribute to support emotional memory, and that regulation of hippocampal neurogenesis is implicated in depressive disorders. How emotional information affects newborn neurons in adults is not clear. Given the role of the BLA in hippocampus-dependent emotional memory, we investigated whether hippocampal neurogenesis was sensitive to emotional stimuli from the BLA. We show that BLA lesions suppress adult neurogenesis, while lesions of the central nucleus of the amygdala do not. Similarly, we show that reducing BLA activity through viral vector-mediated overexpression of an outwardly rectifying potassium channel suppresses neurogenesis. We also show that BLA lesions prevent selective activation of immature newborn neurons in response to a fear-conditioning task. These results demonstrate that BLA activity regulates adult hippocampal neurogenesis and the fear context-specific activation of newborn neurons. Together, these findings denote functional implications for proliferation and recruitment of new neurons into emotional memory circuits.     

Convergent gustatory and viscerosensory processing in the human dorsal mid‐insula

The homeostatic regulation of feeding behavior requires an organism to be able to integrate information from its internal environment, including peripheral visceral signals about the body's current energy needs, with information from its external environment, such as the palatability of energy‐rich food stimuli. The insula, which serves as the brain's primary sensory cortex for representing both visceral signals from the body and taste signals from the mouth and tongue, is a likely candidate region in which this integration might occur. However, to date it has been unclear whether information from these two homeostatically critical faculties is merely co‐represented in the human insula, or actually integrated there. Recent functional neuroimaging evidence of a common substrate for visceral interoception and taste perception within the human dorsal mid‐insula suggests a model whereby a single population of neurons may integrate viscerosensory and gustatory signals. To test this model, we used fMRI‐Adaptation to identify whether insula regions that exhibit repetition suppression following repeated interoception trials would then also exhibit adapted responses to subsequent gustatory stimuli. Multiple mid and anterior regions of the insula exhibited adaptation to interoceptive trials specifically, but only the dorsal mid‐insula regions exhibited an adapted gustatory response following interoception. The discovery of this gustatory‐interoceptive convergence within the neurons of the human insula supports the existence of a heretofore‐undocumented neural pathway by which visceral signals from the periphery modulate the activity of brain regions involved in feeding behavior. Hum Brain Mapp 38:2150–2164, 2017. © 2017 Wiley Periodicals, Inc.     

Differential involvement of gustatory insular cortex and amygdala in the acquisition and retrieval of conditioned taste aversion in rats.

Lesion studies of the role of the gustatory insular cortex (GC) and amygdala (Am) in conditioned taste aversion (CTA) are confounded by the irreversibility of the intervention. Functional ablation methods allow more specific influencing of different phases of CTA acquisition and retrieval. Bilateral tetrodotoxin (TTX) blockade of GC (10 ng) or Am (3 ng) before or after saccharin drinking in rats with chronically implanted intracerebral cannulae showed that GC is indispensable for the initial processing of the taste stimulus but not for the association of the gustatory trace with the symptoms of LiCl poisoning. Gustatory signals can by-pass the blocked Am, the inactivation of which, however, impairs the gustatory trace-poisoning association. TTX injection into both GC and Am impairs CTA retrieval more than isolated blockade of either of these structures. It is argued that GC and Am implement processing of gustatory and visceral signals, respectively, but that formation and consolidation of the CTA engram proceeds outside forebrain, probably at the level of the brainstem.     

Layer- and Cell Type-Specific Response Properties of Gustatory Cortex Neurons in Awake Mice

Studies in visual, auditory, and somatosensory cortices have revealed that different cell types as well as neurons located in different laminae display distinct stimulus response profiles. The extent to which these layer and cell type-specific distinctions generalize to gustatory cortex (GC) remains unknown. In this study, we performed extracellular recordings in adult female mice to monitor the activity of putative pyramidal and inhibitory neurons located in deep and superficial layers of GC. Awake, head-restrained mice were trained to lick different tastants (sucrose, salt, citric acid, quinine, and water) from a lick spout. We found that deep layer neurons show higher baseline firing rates (FRs) in GC with deep-layer inhibitory neurons displaying highest FRs at baseline and following the stimulus. GC''s activity shows robust modulations before animals'' contact with tastants, and this phenomenon is most prevalent in deep-layer inhibitory neurons. Furthermore, we show that licking activity strongly shapes the spiking pattern of GC pyramidal neurons, eliciting phase-locked spiking across trials and tastants. We demonstrate that there is a greater percentage of taste-coding neurons in deep versus superficial layers with chemosensitive neurons across all categories showing similar breadth of tuning, but different decoding performance. Lastly, we provide evidence for functional convergence in GC, with neurons that can show prestimulus activity, licking-related rhythmicity and taste responses. Overall, our results demonstrate that baseline and stimulus-evoked firing profiles of GC neurons and their processing schemes change as a function of cortical layer and cell type in awake mice.SIGNIFICANCE STATEMENT Sensory cortical areas show a laminar structure, with each layer composed of distinct cell types embedded in different circuits. While studies in other primary sensory areas have elucidated that pyramidal and inhibitory neurons belonging to distinct layers show distinct response properties, whether and how response properties of gustatory cortex (GC) neurons change as a function of their laminar position and cell type remains uninvestigated. Here, we show that there are several notable differences in baseline, prestimulus, and stimulus-evoked response profiles of pyramidal and inhibitory neurons belonging to deep and superficial layers of GC.     

Gamma Oscillations in the Basolateral Amygdala: Localization,Microcircuitry, and Behavioral Correlates

The lateral (LA) and basolateral (BL) nuclei of the amygdala regulate emotional behaviors. Despite their dissimilar extrinsic connectivity, they are often combined, perhaps because their cellular composition is similar to that of the cerebral cortex, including excitatory principal cells reciprocally connected with fast-spiking interneurons (FSIs). In the cortex, this microcircuitry produces gamma oscillations that support information processing and behavior. We tested whether this was similarly the case in the rat (males) LA and BL using extracellular recordings, biophysical modeling, and behavioral conditioning. During periods of environmental assessment, both nuclei exhibited gamma oscillations that stopped upon initiation of active behaviors. Yet, BL exhibited more robust spontaneous gamma oscillations than LA. The greater propensity of BL to generate gamma resulted from several microcircuit differences, especially the proportion of FSIs and their interconnections with principal cells. Furthermore, gamma in BL but not LA regulated the efficacy of excitatory synaptic transmission between connected neurons. Together, these results suggest fundamental differences in how LA and BL operate. Most likely, gamma in LA is externally driven, whereas in BL it can also arise spontaneously to support ruminative processing and the evaluation of complex situations.SIGNIFICANCE STATEMENT The basolateral amygdala (BLA) participates in the production and regulation of emotional behaviors. It is thought to perform this using feedforward circuits that enhance stimuli that gain emotional significance and directs them to valence-appropriate downstream effectors. This perspective overlooks the fact that its microcircuitry is recurrent and potentially capable of generating oscillations in the gamma band (50–80 Hz), which synchronize spiking activity and modulate communication between neurons. This study found that BLA gamma supports both of these processes, is associated with periods of action selection and environmental assessment regardless of valence, and differs between BLA subnuclei in a manner consistent with their heretofore unknown microcircuit differences. Thus, it provides new mechanisms for BLA to support emotional behaviors.     

Neural correlates of evaluative compared with passive tasting

We used functional magnetic resonance imaging to test the hypothesis that the nature of the neural response to taste varies as a function of the task the subject is asked to perform. Subjects received sweet, sour, salty and tasteless solutions passively and while evaluating stimulus presence, pleasantness and identity. Within the insula and overlying operculum the location of maximal response to taste vs. tasteless varied as a function of task; however, the primary taste cortex (anterior dorsal insula/frontal operculum – AIFO), as well as a more ventral region of anterior insula, responded to taste vs. tasteless irrespective of task. Although the response here did not depend upon task, preferential connectivity between AIFO and the amygdala (bilaterally) was observed when subjects tasted passively compared with when they performed a task. This suggests that information transfer between AIFO and the amygdala is maximal during implicit processing of taste. In contrast, a region of the left lateral orbitofrontal cortex (OFC) responded preferentially to taste and to tasteless when subjects evaluated pleasantness, and was preferentially connected to earlier gustatory relays (caudomedial OFC and AIFO) when a taste was present. This suggests that processing in the lateral OFC organizes the retrieval of gustatory information from earlier relays in the service of computing perceived pleasantness. These findings show that neural encoding of taste varies as a function of task beyond that of the initial cortical representation.     

Opioid modulation of taste responses in the nucleus of the solitary tract

Gustatory processing within the medulla is modulated by a number of physiologic and experiential factors. Several neurotransmitters, including excitatory amino acids, GABA, and substance P, are involved in synaptic processing within the rostral portion of the nucleus of the solitary tract (NST). Endogenous opiates have been implicated in the regulation of feeding behavior and in taste palatability and gustatory responses in the parabrachial nuclei are reduced by systemic morphine. In the present experiments, extracellular recording of neuronal activity within the NST in response to taste input was combined with local microinjection of met-enkephalin (Met-ENK) and naltrexone (NLTX) to determine the effect of these agents on gustatory activity. The anterior tongue was stimulated with anodal current pulses to determine the time course of drug action (n=85 cells) and with prototypical taste stimuli (0.032 M sucrose, NaCl, and quinine hydrochloride, and 0.0032 M citric acid) to investigate the effects of these opioid compounds on taste-evoked responses (n=80 cells). Among these 165 taste-responsive neurons in the NST, the activity of 39 (23.6%) was suppressed by Met-ENK. These effects were dose-dependent and blockable by NLTX, which alone was without effect, suggesting that opiates do not maintain a tonic inhibitory influence. Immunohistochemical experiments demonstrated both micro - and delta-opioid receptors within the gustatory portion of the NST; previous studies had shown numerous fiber terminals containing Met-ENK. These data suggest that endogenous opiates play an inhibitory role in gustatory processing within the medulla.     

Neurons in the amygdala of the monkey with responses selective for faces

To investigate the functions of the amygdala in visual information processing and in emotional and social responses, recordings were made from single neurons in the amygdala of the monkey. A population of neurons (40 of more than 1000 recorded in 4 monkeys) was investigated which responded primarily to faces. These neurons typically (1) responded to some human or monkey faces, which were presented to the monkey through a large aperture shutter so that response latencies could be measured, or were simply shown to the monkey, (2) responded to 2-dimensional representations of these faces, as well as to real 3-dimensional faces, (3) had no responses or only small (less than half maximum) responses to gratings, simple geometrical, other complex 3-D stimuli, or to arousing and aversive stimuli, (4) had response latencies of 110-200 ms, (5) were located in the basal accessory nucleus of the amygdala, (6) responded differently to different faces, as shown by measures of d', and could thus over a population of such neurons code information useful for making different responses to different individuals, (7) could in some cases (9/11 tested) respond to parts of faces, and (8) in a few cases (4/19 tested) responded more to a face which produced an emotional response. A comparison made in three monkeys of the responses of these neurons with the responses of 77 neurons with face-selective responses recorded in the cortex of the superior temporal sulcus (STS) showed that the amygdaloid neurons had longer response latencies (110-200 compared to 90-140 ms), and were in some respects more selective in their responses to different faces. It is suggested that the deficits in social and emotional behavior produced by amygdala lesions could be due in part to damage to a neuronal system specialized in utilizing information from faces so that appropriate social and emotional responses can be made to different individuals.     

Blockade of noradrenergic receptors in the basolateral amygdala impairs taste memory

In conditioned taste aversion (CTA), a subject learns to associate a novel taste (conditioned stimulus, CS) with visceral malaise (unconditioned stimulus, US). Considerable evidence indicates that the noradrenergic system in the amygdala plays an important role in memory consolidation for emotionally arousing experiences. The specific aim of the present set of experiments was to determine the involvement of noradrenergic activity in the basolateral amygdala (BLA) during the US presentation and consolidation of CTA as well as during the consolidation of a nonaversive/incidental gustatory memory. Selective bilateral microinfusions of the beta-adrenergic antagonist propranolol administered into the BLA immediately before intraperitoneal (i.p.) lithium chloride (LiCl) injections disrupted CTA memory. Additionally, propranolol infused into the BLA immediately after a pre-exposure to the saccharin (CS) significantly attenuated latent inhibition. The present findings indicating that alterations in noradrenergic function in the BLA affect taste memory formation, provide additional evidence that the BLA plays a critical role in modulating the consolidation of memory and that the influence is mediated by interactions with other brain regions that support memory for different kinds of experiences.