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Olfaction, Emtion & the Amygdala: arousal-dependent modulation of long-term autobiographical memory and its association with olfaction
Abstract
The sense of smell is set apart from other sensory modalities. Odours possess the capacity to trigger immediately strong emotional memories. Moreover, odorous stimuli provide a higher degree of memory retention than other sensory stimuli. Odour perception, even in its most elemental form - olfaction - already involves limbic structures. This early involvement is not paralleled in other sensory modalities. Bearing in mind the considerable connectivity with limbic structures, and the fact that an activation of the amygdala is capable of instantaneously evoking emotions and facilitating the encoding of memories, it is unsurprising that the sense of smell has its characteristic nature. The aim of this review is to analyse current understanding of higher olfactory information processing as it relates to the ability of odours to spontaneously cue highly vivid, affectively toned, and often very old autobiographical memories (episodes known anecdotally as Proust phenomena). Particular emphasis is placed on the diversity of functions attributed to the amygdala. Its role in modulating the encoding and retrieval of long-term memory is investigated with reference to lesion, electrophysiological, immediate early gene, and functional imaging studies in both rodents and humans. Additionally, the influence of hormonal modulation and the adrenergic system on emotional memory storage is outlined. I finish by proposing a schematic of some of the critical neural pathways that underlie the odour-associated encoding and retrieval of emotionally toned autobiographical memories.
... Generally, all stimuli derived from the environment initially undergo a sensorial filtering process in sensorial receptors, beginning with parareceptors [8], reaching synaptic relays, and leading to an integrative process that involves anatomical structures related to emotional memory [43], in which comparisons are made with older elements of memory [92]. As the stimulus inputs reach the striatum and cortical structures [43], a selection of the adequate survival strategy is often reached [34]. ...
... Generally, all stimuli derived from the environment initially undergo a sensorial filtering process in sensorial receptors, beginning with parareceptors [8], reaching synaptic relays, and leading to an integrative process that involves anatomical structures related to emotional memory [43], in which comparisons are made with older elements of memory [92]. As the stimulus inputs reach the striatum and cortical structures [43], a selection of the adequate survival strategy is often reached [34]. In turn, connections with motor areas and motoneurons activates skeletal muscles [43], and a motoric response may be observed. ...
... As the stimulus inputs reach the striatum and cortical structures [43], a selection of the adequate survival strategy is often reached [34]. In turn, connections with motor areas and motoneurons activates skeletal muscles [43], and a motoric response may be observed. Laboratory animals subjected to a stressful situation (e.g., odors from a predator) will emit only a few responses-attacking, freezing, or escaping-no more and no less. ...
Anxiety as an adaptive response is a natural emotion that occurs in response to danger and
prepares an organism to cope with the environment, playing a critical role in its survival.
Among the components of anxiety, the expression of fear may inform other members of the
group about the presence of imminent danger (i.e., an alarm cue). The environment is perceived
by a filtering process that involves sensorial receptors. While coping with a stressful
situation, an individual may simultaneously emit vocalizations, perform movements to escape,
freeze, and deliver to the environment chemicals called alarm pheromones. These cues
are recognized by the receptor-individual by specific sensory systems located in the legs and
antennae in insects and olfactory sensorial systems in other organisms. In mammals, the
sensorial information is integrated by anatomical and functional pathways, with the participation
of structures related to emotional memory, namely deep temporal lobe structures.
Some stimuli are perceived as relevant when they contain relevant meaning according to
previous experience and learning. The participation of ventral striatum and prefrontal cortex
connections then leads to the selection of an adequate strategy for survival. The perception
of these cues by other individuals in the group establishes intraspecies communication
and causes striking behavioral responses in the receptor subject, namely anxiety, but the
consequence is likely different. While the emitting subject may be in an emergency situation
that is perhaps devoid of a solution, the receptor subject may have the chance to cope with
the dangerous situation by employing efficacious strategies, depending on previous experience.
The aim of this chapter is to review the participation of such anatomical pathways,
their neurotransmission systems, and the resulting behavioral patterns.
... Los olores que se encuentran en el ambiente en un determinado contexto pueden ser codi cados paralelamente con detalles del acontecimiento y ser usados consecuentemente como señales en la recuperación de esos detalles [37]. La notable e cacia de los olores como estímulo para permitir la recuperación de la memoria se atribuye a la relación entre una activación emocional y la información asociada con tales reacciones afectivas. ...
... La notable e cacia de los olores como estímulo para permitir la recuperación de la memoria se atribuye a la relación entre una activación emocional y la información asociada con tales reacciones afectivas. Dicha relación parece estar mediada por el núcleo basolateral de la amígdala, el cual juega un papel central en la modulación de la consolidación de memorias de largo plazo de experiencias emocionales [38], lo cual podría deberse a la vía directa entre el sistema olfativo y la amígdala lo que permite asociar memorias emocionales directamente con el estímulo olfativo más que con cualquier otra modalidad sensorial [37]. Así, la memoria emocional permite que un individuo reconozca señales de su entorno y las asocie con experiencias pasadas, como un elemento de juicio para responder a su entorno, es así como se establece la relación de estrategias adecuadas y correctas de afrontamiento, pero también de rechazo o aproximación [39]. ...
Se consideran al menos dos características de las emociones: 1) En una de ellas se llega a un punto de equilibrio, las emociones van de lo positivo (feliz o seguro) a lo negativo (miedo o enojo). Estas fluctuaciones normales conllevan pautas conductuales que les caracterizan. Por ejemplo, en los estados emocionales positivos, hay una tendencia hacia la atracción o acercamiento, una mayor interacción social. En cambio, los estados emocionales negativos están asociados con la aversión, la defensa, el escape y la evitación. 2) Una segunda característica de la emoción es el alertamiento, para llevar al sujeto que la experimenta desde la tranquilidad relativa hasta altos niveles de actividad locomotriz; ya en un extremo, pueden llevar al individuo a patrones de afrontamiento pasivos donde se da el congelamiento, es decir, se detiene la emisión de cualquier
conducta; o por el contrario, afrontamientos proactivos que llevan a tomar acciones para poner distancia con la situación aversiva que desencadeno la emoción, por ejemplo huyendo. En cualquiera que sea la circunstancia, la emoción puede tener utilidad para el individuo, por ejemplo, cuando se pone a salvo; o condenarle a ser presa indefensa, mediante el congelamiento. En el primer caso, la emoción (miedo, por ejemplo) lleva al individuo a huir y quizá salvarse; en el segundo caso, la emoción (y nuevamente, miedo) le paraliza y le vuelve completamente vulnerable y en no pocos casos, en una actitud sumisa. Habrá que observar que en ambas situaciones, la emoción es la misma, el miedo, pero la pauta conductual elegida, puede o no, ser útil y preservar, o no, la integridad del individuo. Es por ello (ver más adelante) que se ha acunado el concepto de memoria emocional. Así, las emociones juegan un papel fundamental en la vida cotidiana de los individuos, permitiéndoles enfrentar situaciones habituales y aun novedosas para adaptarse al entorno en el cual se desarrollan. En el presente trabajo se revisaran algunos conceptos como el estrés, el miedo y dos de sus acompañantes habituales, la ansiedad y la depresión, sus bases neurobiológicas y tratamientos, así como sus métodos de estudio. Resaltando que los factores estresantes y el estrés producido en los animales, incluyendo al ser humano, son predisponentes cruciales de las alteraciones emocionales en los individuos.
... However, the participant can also be adapted to the environment by modulating the participant. Such modulation can be done with the help of visual, audial or even olfactory stimulation (Hughes, 2004;Weinbach et al., 2015). This research takes several relevant steps in the direction of such a system since it shows that PMWL can be classified accurately using multiple modalities. ...
A lot of research has been done on the detection of mental workload (MWL) using various bio-signals. Recently, deep learning has allowed for novel methods and results. A plethora of measurement modalities have proven to be valuable in this task, yet studies currently often only use a single modality to classify MWL. The goal of this research was to classify perceived mental workload (PMWL) using a deep neural network (DNN) that flexibly makes use of multiple modalities, in order to allow for feature sharing between modalities. To achieve this goal, an experiment was conducted in which MWL was simulated with the help of verbal logic puzzles. The puzzles came in five levels of difficulty and were presented in a random order. Participants had 1 h to solve as many puzzles as they could. Between puzzles, they gave a difficulty rating between 1 and 7, seven being the highest difficulty. Galvanic skin response, photoplethysmograms, functional near-infrared spectrograms and eye movements were collected simultaneously using LabStreamingLayer (LSL). Marker information from the puzzles was also streamed on LSL. We designed and evaluated a novel intermediate fusion multimodal DNN for the classification of PMWL using the aforementioned four modalities. Two main criteria that guided the design and implementation of our DNN are modularity and generalisability. We were able to classify PMWL within-level accurate (0.985 levels) on a seven-level workload scale using the aforementioned modalities. The model architecture allows for easy addition and removal of modalities without major structural implications because of the modular nature of the design. Furthermore, we showed that our neural network performed better when using multiple modalities, as opposed to a single modality. The dataset and code used in this paper are openly available.
... Research on olfaction has shown that odours can produce strong emotional memories (Stafford et al., 2009). When odours are present during an event they become encoded simultaneously with the other information associated with the event, before being stored in memory (Hughes, 2004). Hence, odour-associated responses can activate recall of memories (Holland et al., 2005) which in turn can lead to associative learning (Herz, 2005). ...
Purpose
The purpose of this paper is to investigate the impact of store characteristics (i.e. product availability, product quality, store layout, employee politeness, décor, music, lighting, and aroma) on the various dimensions of in-store leisure shopping experience (i.e. hedonic, flow, escapism, challenge, learning, socialising, and communitas).
Design/methodology/approach
In order to achieve the study’s objectives, a quantitative on-site survey was conducted. Respondents were interviewed upon exiting fashion retail stores.
Findings
Findings indicate that not all store characteristics impact the various dimensions of experience in the same way. Product quality and in-store music were found to be the most important in-store characteristics that affected the majority of experience dimensions. Other important store attributes that emerged were store layout and ambient scent. Conversely, product range actually had a negative impact on in-store experience.
Practical implications
By orchestrating the most influential in-store characteristics, fashion retailers could be delivering unique in-store experiences to their customers. This research shows that they would benefit from designing experiential strategies that focus on merchandise quality, price, and availability while simultaneously carefully managing ambient (music and scent) alongside design factors (store layout and décor). Careful consideration should be paid to merchandise variety in order to avoid potentially negative effects on customers’ shopping experience.
Originality/value
Until now most studies that document the relationship between store elements and shopping experiences have examined the effects of store characteristics on a limited number of experience dimensions. This study adds to the body of research into in-store leisure shopping experience in two ways: by shedding light on its multi-dimensional nature, and by analysing the effect of the different store elements on the various components of the in-store experience.
... Emotional memories allow emotional arousing 1 and are namely processed by the interaction of two temporal lobe deep structures, the amygdala nuclei and hippocampus. 2,3 From amygdaline nuclei, medial amygdala integrates olfactory information coming from the main and accessory olfactory system. 4,5 The chemical cues perceived by olfactory system seems to modulate maternal behavior, 6 aggression, 7 and reproductive behavior, 8 and, inclusively, they al-low the identification of individuals of the same species. ...
La percepción olfatoria de feromonas de alarma, como la 2-heptanona, promueve ciertas estrategias de supervivencia con la participación de la memoria emocional, integrada en estructuras del lóbulo temporal, como la amígdala y el hipocampo. En la rata Wistar, la olfacción de 2-heptanona genera conductas sugerentes de ansiedad y un incremento de la tasa de disparo neuronal del núcleo basal de la amígdala. Sin embargo, no se conoce si la 2-heptanona modifica la responsividad de la conexión amígdala medial-hipocampo. Un grupo de ratas Wistar (n=10) fue colocado dentro de una caja de acrílico impregnada con 2-heptanona; el grupo control (n=10) fue introducido en una caja limpia. Veinticuatro horas después se obtuvo el registro unitario extracelular de neuronas del hipocampo (CA1-CA3) identificadas por su conexión con la amígdala medial. Aunque la tasa de disparo basal fue similar entre los grupos experimentales, el histograma de distribución de intervalos de primer orden indicó un predominio de intervalos de breve duración en el grupo 2-heptanona. Los histogramas periestímulo indicaron que: i) las neuronas hipocampales responden con un incremento en la tasa de disparo neuronal ante la estimulación amigdalina; ii) la respuesta es de mayor magnitud y duración en el grupo previamente expuesto a 2-heptanona. Dado que una sola exposición a una feromona de alarma facilita la conexión amígdala medial-hipocampo, los resultados sugieren la formación inicial de una memoria contextual relacionada con el miedo.
... Emotional memories allow emotional arousing 1 and are namely processed by the interaction of two temporal lobe deep structures, the amygdala nuclei and hippocampus. 2,3 From amygdaline nuclei, medial amygdala integrates olfactory information coming from the main and accessory olfactory system. 4,5 The chemical cues perceived by olfactory system seems to modulate maternal behavior, 6 aggression, 7 and reproductive behavior, 8 and, inclusively, they al-low the identification of individuals of the same species. ...
The capability to perceive and emit alarm substances, such as 2-heptanone, makes animals aware of the presence of danger, leading to some strategies directed towards survival. Strategies of survival involve emotional memory which is processed by deep temporal lobe structures, such as amygdaloid complex and hippocampus. In the Wistar rat, 2-heptanone produces anxiety-like behavior and an increased firing rate of basal amygdaline neurons. However, it is unknown whether 2-heptanone modifies the responsivity of medial amygdaline-hippocampal connection. Therefore, we placed a group (n=10) of Wistar rats in a plexiglass cage impregnated with 2-heptanone. Rats from control group (n=10) were introduced into a similar clean cage. Twenty four hours later we obtained single-unit extracellular recordings from the hippocampus (CA1-CA3) neurons identified by their connection to medial amygdala. Although the basal neuronal firing rate was similar between groups, first order interval distribution histogram analysis showed that 2-heptanone produced shorter intervals of firing rate. Peristimulus histograms indicated that: i) the amygdaline stimulation produces an increased firing rate in hippocampal neurons; and ii) this response is increased and enlarged on the 2-heptanone group. Since a single exposure to an alarm pheromone seems to facilitate the amygdala-hippocampal connection, results suggest the initial formation of contextual memories related with fear.
It is likely that the encoding of emotional experiences involves a complex network of interacting brain regions. The present study used fMRI to identify brain structures involved in the encoding of negative and positive emotional stimuli. Ten subjects viewed alternating blocks of emotionally negative and positive pictures and were tested for long-term recognition memory several months later. Recognition memory for negative and positive pictures was highly correlated. Brain reactivity to negative pictures was positively correlated with better recognition memory for both negative and positive pictures in the amygdala, the insula, and the right middle frontal gyrus. Brain reactivity to positive pictures was positively correlated with better recognition memory for both negative and positive pictures in the left anterior cingulate gyrus. Activation among these brain regions was highly correlated and suggests a network of structures that interact to encode either negative or positive emotional stimuli for long-term recognition memory. Two mechanisms by which this encoding may take place are discussed.
The processing of episodic memories is believed to depend on the proper functioning of so-called bottleneck structures through which information apparently must pass in order to be stored long term. These regions are seen in the basal forebrain, the medial diencephalon, and the medial temporal lobe. We here report a case with circumscribed bilateral temporal lobe damage, principally involving the amygdaloid area. Neuropsychological investigation demonstrated preserved intelligence, intact general memory and several other undisturbed cognitive functions, but a specific, affect-related, memory disorder. We conclude from these findings that the role of the amygdala is to process mnemonic events in a way that a specific emotional significance can be found and reactivated. Therefore it is suggested that the amygdala is likely to be a bottleneck structure for affect-related long-term memory functions.
This study was conducted to compare responses to stimuli presented in three different modalities: olfactory, visual, and lexical (the written name of the object). Cognitive aspects of these responses as well as affective components were examined. The subjects were placed at random into one of three experimental groups and were tested individually. Each subject was asked to smell, to view, or to see the name of six common items and to write whatever immediately came to mind after each stimulus presentation. The results indicate that the olfactory mode produced the shortest answers, with the largest amount of affect. The results are discussed in terms of their implications about the structure and nature of concepts and how such concepts interrelate with different sensory modalities.
Odor-evoked memories are well described in literature and anecdote but have yet to be experimentally characterized. The primary purpose of this study was to provide an experimentally controlled account of the nature of odor-evoked memories experienced by men and women. Two groups of 20 subjects (10 males, 10 females) were instructed to approach an odor-rating task from a subjective (emotional) or objective (analytical) orienting set. Each subject rated 20 different odors on five rating scales (pleasantness, familiarity, intensity, arousal, degree of interest), attempted to name each odor, and then indicated whether or not the odor evoked a personal memory. When a memory was evoked the subject wrote out a brief description and rated the memory on five scales (emotionality, clarity, specificity, rarity, age). The results demonstrated that, consistent with folklore, odor-evoked memories tended to be highly emotional, vivid, specific, rare and relatively old. The most familiar odors were found to evoke the greatest number of personal memories and were most often correctly named. However, 32% of the memories were evoked without an odor name, implying that memories associated with odors do not necessarily require a verbal label in order to be elicited. Females described more emotionally intense and clearer memories than did males, and females, under the subjective set, described the most vivid memories.
A modified paired-associate learning paradigm was used to test whether odors or verbal odor labels evoked more emotional memories. Subjects were presented with emotionally positive and negative paintings (to-be-remembered items) in association with positive and negative odors and odor labels. Painting recall and associated emotional experience were tested after 48 h. Odor-evoked memories were found to be more emotional than verbally cued memories on a variety of measures. Moreover, if the cue for recall (odor or label) was hedonically congruent with the painting to be remembered, memory for original emotional experiences was enhanced. The findings are discussed within a general cognitive framework and implications for using odors to dissociate the emotional and representational aspects of memory are addressed.
Previous studies have used symptom provocation and positron emission tomography to delineate the brain systems that mediate various anxiety states. Using an analogous approach, the goal of this study was to measure regional cerebral blood flow changes associated with posttraumatic stress disorder (PTSD) symptoms.
Eight patients with PTSD, screened as physiologically responsive to a script-driven imagery symptom provocation paradigm, were exposed sequentially to audiotaped traumatic and neutral scripts in conjunction with positron emission tomography. Heart rate and subjective measures of emotional state were obtained for each condition. Statistical mapping techniques were used to determine locations of significant brain activation.
Increases in normalized blood flow were found for the traumatic as compared with control conditions in right-sided limbic, paralimbic, and visual areas; decreases were found in left inferior frontal and middle temporal cortex.
The results suggest that emotions associated with the PTSD symptomatic state are mediated by the limbic and paralimbic systems within the right hemisphere. Activation of visual cortex may correspond to the visual component of PTSD reexperiencing phenomena.
We studied the functional anatomy of affect-laden autobiographical memory in normal volunteers. Using H 2 ¹⁵ O positron emission tomography (PET), we measured changes in relative regional cerebral blood flow (rCBF). Four rCBF measurements were obtained during three conditions: REST, i.e., subjects lay at rest (for control); IMPERSONAL, i.e., subjects listened to sentences containing episodic information taken from an autobiography of a person they did not know, but which had been presented to them before PET scanning (nonautobiographical episodic memory ecphory); and PERSONAL, i.e., subjects listened to sentences containing information taken from their own past (autobiographical episodic memory ecphory).
Comparing IMPERSONAL with REST (nonautobiographical episodic memory ecphory) resulted in relative rCBF increases symmetrically in both temporal lobes including the temporal poles and medial and superior temporal gyri. The same loci, however, with a stronger lateralization to the right hemisphere were activated in the comparison PERSONAL to REST (autobiographical episodic memory ecphory). In addition, the right temporomesial, right dorsal prefrontal, right posterior cingulate areas, and the left cerebellum were activated. A comparison of PERSONAL and IMPERSONAL (autobiographical vs nonautobiographical episodic memory ecphory) demonstrated a preponderantly right hemispheric activation including primarily right temporomesial and temporolateral cortex, right posterior cingulate areas, right insula, and right prefrontal areas. The right temporomesial activation included hippocampus, parahippocampus, and amygdala.
These results suggest that a right hemispheric network of temporal, together with posterior, cingulate, and prefrontal, areas is engaged in the ecphory of affect-laden autobiographical information.
Electrophysiologic and lesion studies of animals increasingly implicate the amygdala in aspects of emotional processing. Yet, the functions of the human amygdala remain poorly understood. To examine the contributions of the amygdala and other limbic and paralimbic regions to emotional processing, we exposed healthy subjects to aversive olfactory stimuli while measuring regional cerebral blood flow (rCBF) with positron emission tomography. Exposure to a highly aversive odorant produced strong rCBF increases in both amygdalae and in the left orbitofrontal cortex. Exposure to less aversive odorants produced rCBF increases in the orbitofrontal cortex but not in the amygdala. Change of rCBF within the left amygdala and the left OFC was highly intercorrelated, indicating a strong functional interaction between these brain regions. Furthermore, the activity within the left amygdala was associated significantly with subjective ratings of perceived aversiveness. These findings provide evidence that the human amygdala participates in the hedonic or emotional processing of olfactory stimuli.
Positron emission tomography was used to investigate the neural substrates of normal human emotional and their dependence on the types of emotional stimulus.
Twelve healthy female subjects underwent 12 measurements of regional brain activity following the intravenous bolus administration of [15O]H2O as they alternated between emotion-generating and control film and recall tasks. Automated image analysis techniques were used to characterize and compare the increases in regional brain activity associated with the emotional response to complex visual (film) and cognitive (recall) stimuli.
Film- and recall-generated emotion were each associated with significantly increased activity in the vicinity of the medial prefrontal cortex and thalamus, suggesting that these regions participate in aspects of emotion that do not depend on the nature of the emotional stimulus. Film-generated emotion was associated with significantly greater increases in activity bilaterally in the occipitotemporparietal cortex, lateral cerebellum, hypothalamus, and a region that includes the anterior temporal cortex, amygdala, and hippocampal formation, suggesting that these regions participate in the emotional response to certain exteroceptive sensory stimuli. Recall-generated sadness was associated with significantly greater increases in activity in the vicinity of the anterior insular cortex, suggesting that this region participates in the emotional response to potentially distressing cognitive or interoceptive sensory stimuli.
While this study should be considered preliminary, it identified brain regions that participate in externally and internally generated human emotion.
To investigate possible distinct contributions of different temporal-lobe structures to odour identification, the University of Pennsylvania Smell Identification Test was administered monorhinally to seizure-free patients who had undergone one of three types of temporal-lobe resection practised in three different institutions for surgical treatment of epilepsy. The resections were neocorticectomy (Dublin), selective amygdalohippocampectomy (Zurich), or anterior temporal-lobe resection with encroachment on amygdala and hippocampus (Montreal). Resections, analysed from MRI scans, showed unexpected encroachment on medial structures in most patients of the neocorticectomy groups, and largest amygdala and hippocampal resections in the amygdalohippocampectomy groups. Impaired odour identification was observed in all patient groups, irrespective of surgical approach, with greatest impairment in the nostril ipsilateral to the resection. The finding of deficits in all three surgical groups suggests that damage in the anterior temporal area, perhaps in piriform cortex, is sufficient to disrupt performance on this task; it may be that function is disrupted in the medial temporal-lobe region by disconnection when the periamygdaloid area is damaged, even when amygdala and hippocampus are left intact. An alternative explanation for our results is that damage in any one of these areas disrupts a complex network involving several distinct temporal-lobe structures.
Emotional potentiation may be a key variable in the formation of odor-associated memory. Two experiments were conducted in which a distinctive ambient odor was present or absent during encoding and retrieval sessions and subjects were in an anxious or neutral mood during encoding. Subjects' mood at retrieval was not manipulated. The laboratory mood induction used in Experiment 1 suggested that anxiety might increase the effectiveness of an odor retrieval cue. This trend was confirmed in Experiment 2 by capturing a naturally stressful situation. Subjects who had an ambient odor cue available and were in a preexam state during encoding recalled more words than subjects in any other group. These data are evidence that heightened emotion experienced during encoding with an ambient odor can enhance the effectiveness of an odor as a cue to memory.
Echoplanar functional magnetic resonance imaging (fMRI) was used in normal human subjects to investigate the role of the amygdala in conditioned fear acquisition and extinction. A simple discrimination procedure was employed in which activation to a visual cue predicting shock (CS+) was compared with activation to another cue presented alone (CS-). CS+ and CS- trial types were intermixed in a pseudorandom order. Functional images were acquired with an asymmetric spin echo pulse sequence from three coronal slices centered on the amygdala. Activation of the amygdala/periamygdaloid cortex was observed during conditioned fear acquisition and extinction. The extent of activation during acquisition was significantly correlated with autonomic indices of conditioning in individual subjects. Consistent with a recent electrophysiological recording study in the rat (Quirk et al., 1997), the profile of the amygdala response was temporally graded, although this dynamic was only statistically reliable during extinction. These results provide further evidence for the conservation of amygdala function across species and implicate an amygdalar contribution to both acquisition and extinction processes during associative emotional learning tasks.
Participation of two medial temporal lobe structures, the hippocampal region and the amygdala, in long-term declarative memory encoding was examined by using positron emission tomography of regional cerebral glucose. Positron emission tomography scanning was performed in eight healthy subjects listening passively to a repeated sequence of unrelated words. Memory for the words was assessed 24 hr later with an incidental free recall test. The percentage of words freely recalled then was correlated with glucose activity during encoding. The results revealed a striking correlation (r = 0.91, P < 0.001) between activity of the left hippocampal region (centered on the dorsal parahippocampal gyrus) and word recall. No correlation was found between activity of either the left or right amygdala and recall. The findings provide evidence for hippocampal involvement in long-term declarative memory encoding and for the view that the amygdala is not involved with declarative memory formation for nonemotional material.
Orbitofrontal cortex (OFC) is part of a network of structures involved in adaptive behavior and decision making. Interconnections between OFC and basolateral amygdala (ABL) may be critical for encoding the motivational significance of stimuli used to guide behavior. Indeed, much research indicates that neurons in OFC and ABL fire selectively to cues based on their associative significance. In the current study recordings were made in each region within a behavioral paradigm that allowed comparison of the development of associative encoding over the course of learning. In each recording session, rats were presented with novel odors that were informative about the outcome of making a response and had to learn to withhold a response after sampling an odor that signaled a negative outcome. In some cases, reversal training was performed in the same session as the initial learning. Ninety-six of the 328 neurons recorded in OFC and 60 of the 229 neurons recorded in ABL exhibited selective activity during evaluation of the odor cues after learning had occurred. A substantial proportion of those neurons in ABL developed selective activity very early in training, and many reversed selectivity rapidly after reversal. In contrast, those neurons in OFC rarely exhibited selective activity during odor evaluation before the rats reached the criterion for learning, and far fewer reversed selectivity after reversal. The findings support a model in which ABL encodes the motivational significance of cues and OFC uses this information in the selection and execution of an appropriate behavioral strategy.
It is well known that hormones influence many physiological systems involved in regulating adaptation to environmental changes. For most animals the ability to acquire and retain experience-based information is essential for adapting to changes in environmental conditions. There is now considerable evidence indicating that hormones, including opioid peptide hormones, play an important role in regulating such adaptation by modulating neurobiological processes mediating the acquisition and storage of newly acquired information (McGaugh1983, 1989a).
Substantial evidence from animal studies suggests that enhanced memory associated with emotional arousal results from an activation of beta-adrenergic stress hormone systems during and after an emotional experience. To examine this implication in human subjects, we investigated the effect of the beta-adrenergic receptor antagonist propranolol hydrochloride on long-term memory for an emotionally arousing short story, or a closely matched but more emotionally neutral story. We report here that propranolol significantly impaired memory of the emotionally arousing story but did not affect memory of the emotionally neutral story. The impairing effect of propranolol on memory of the emotional story was not due either to reduced emotional responsiveness or to nonspecific sedative or attentional effects. The results support the hypothesis that enhanced memory associated with emotional experiences involves activation of the beta-adrenergic system.
A variety of olfactory capacities were evaluated in H.M., a patient with bilateral medial temporal lobe resection. He demonstrated normal performance on a battery of tests of odour detection, discrimination of intensity, and adaptation. In striking contrast, H.M. was unable to discriminate or identify odours in same-different discriminations and in matching-to-sample tasks. Although he could name common objects using visual or tactile cues, he could not identify them by smell. These results indicate that the perceptual phenomena of odour detection and discrimination are dissociable by cerebral damage, and that structures in the medial temporal lobe play a critical role in odour discrimination.
Those who have been concerned with designs for the human brain have come to realize that it is not enough to incorporate mechanisms for the reception and processing of sensory information, its storage and retrieval, and the programming and regulation of motor output. Adaptive behavior, by its very nature, requires a system for the evaluation and sorting of environmental inputs, and the development of the most appropriate and effective responses in terms of the survival of the individual or the species.
Medial temporal lobe resection is reported on and compared to the more standard psychosurgical techniques for the treatment of psychotic states. Three types of operations were performed, uncotomy, medial temporal lobotomy, and an orbito-temporal lobotomy. Results of the latter technique are described as encouraging. Results from uncotomy and temporal lobotomy are described as unimpressive. 30 references. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Investigated the idea that effects of environmental context change on memory for events could be enhanced by encouraging Ss to encode target items in relation to specific contextual cues. 64 undergraduates were read a list of names for common objects in 1 of 2 distinctively decorated rooms and were subsequently tested for free recall either in the same room in which the list had been recited or in the alternate environment. As each list item was read, half of the Ss in either context condition were asked to generate and report an isolated image in which the specified object was visualized as existing by itself, and half were instructed to produce an integrated image in which the object was pictured as being directly associated with a particular physical feature of the room. Results show a significant advantage in recall of constant over changed context conditions, but only for integrated-imagery items. Several reasons for the absence of context dependence in the recall of isolated-imagery items are considered, and possible consequences of overloading contextual cues are examined. (16 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Discusses the role of the amygdaloid complex in conditioning of autonomic processes during emotional learning situations. Results from studies on animals and normal humans have implicated at the simplest, the activation of β-adrenergic receptors, and the amygdaloid complex in such learning. Recent experimental results with patients with brain-damage and Urbach-Weithe disease show selective impairment of memory for emotional material (e.g., L. Cahil, et al, 1995), have confirmed this hypothesis for conscious, long-term memory. However, these autonomic processes are not required for normal retention in non-emotionally arousing situations. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Replies from eminent people show that odors have strong memory-stimulating power in a very great number of persons. Have educators and advertisers neglected them unduly? (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Three experiments, using ambient odors and incidental learning procedures, examined the effectiveness of odors as memory retrieval cues. Experiment 1 showed that a single ambient odor present on both learning and testing improved recall of a list of words over a no-odor control and a group that received the odor at encoding or retrieval only. Experiment 2 replicated this result and showed that whereas reinstating the odor context improved overall recall, recall of odor-related information was not significantly enhanced by the odor cue. Finally, Experiment 3, employing implicit and explicit retrieval tasks, demonstrated that the same odor must be present on both learning and remembering for the memory benefit to occur. The memory enhancement observed with odors was not due to the effects of semantic mediation. The results are discussed within the framework of encoding specificity of memory (e.g., E. Tulving and D. M. Thomson, 1973), and implications for odor imagery and cuing effects on odor-related material are addressed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Substantial evidence from animal and human subject studies converges on the view that memory for emotionally arousing events is modulated by an endogenous memory-modulating system consisting, at minimum, of stress hormones and the amygdaloid complex. Within the normal range of emotions experienced, this system is viewed as an evolutionarily adaptive method of creating memory strength that is, in general, proportional to memory importance. In conditions of extreme emotional stress, the operation of this normally adaptive system may underly the formation of strong, "intrusive" memories characteristic of PTSD. An improved understanding of the neurobiology of memory modulation should lead to an improved ability to treat or prevent traumatic memories. Language: en
This study determined the extent to which re-exposure to the unique combination of odours present in a museum (the Jorvik Viking Centre in York) aids the recall of a previous visit to the museum, which had typically taken place several years earlier. To test this, three groups of participants completed questionnaires about the contents of the museum, but in different conditions. One group completed the questionnaire in the presence of exactly the same distinctive odours as those present in the museum at the time of their original visit. Those in two other groups were given either a different (control) set of odours or no odours at all. After a brief delay, the same questionnaire was presented again to participants in all three groups. Those who had initially been given a novel (control) set of odours were now tested in the presence of the genuine Jorvik museum odours, while the group that had received the Jorvik odours were now tested with the control odours. The third group received no odours on either test. Only the novel odour-Jorvik odours condition led to a highly significant improvement in performance. This interaction showed that the museum odours could act as effective retrieval cues for this incidentally acquired, real-world episode.
The effect of sub-convulsive doses of GABAergic antagonists on the retention of two aversively motivated tasks, inhibitory avoidance (IA) and Y-maze discrimination (YMD), was investigated in CFW mice. In the IA task, post-training intraperitoneal injections of picrotoxin and bicuculline induced a dose-dependent enhancement of retention measured 24 h after the training, while retention was not affected by bicuculline methiodide (a GABA receptor antagonist that does not readily cross the blood-brain barrier). In the absence of footshock on the training day, post-training administration of picrotoxin and bicuculline did not affect retention test latencies. In the YMD task, the discrimination was reversed on the retention test and errors made on the reversal trials served as the index of retention of the original training. The reversal error scores of mice given post-training injections of picrotoxin or bicuculline, but not bicuculline methiodide, were significantly higher than those of saline-treated controls. These findings extend previous observations that GABAergic antagonists enhance retention of aversively motivated tasks and suggest the involvement of central GABAergic processes on memory consolidation.
These experiments examined the involvement of the intrinsic GABAergic system of the amygdaloid complex in the modulation of memory storage. Rats were chronically implanted with bilateral cannulae in the amygdala, trained in an inhibitory avoidance task, and given post-training bilateral intra-amygdala injections of either the GABA receptor antagonist bicuculline methiodide (BMI) (0.1-1.0 nmol) or the GABAA receptor agonist muscimol (0.001-0.1 nmol). As indicated by performance on a 48 h retention test, BMI enhanced retention of the inhibitory avoidance conditioning, while muscimol impaired retention. The memory-enhancement obtained with BMI (0.1 nmol) was produced by a dose lower than that necessary to induce convulsions. Post-training injections of BMI did not affect retention when injected into the caudate-putamen dorsal to the amygdala. These results suggest that the amygdaloid GABAergic system is involved in the modulation of memory storage.
These experiments examined the effects, on retention, of posttraining intra-amygdala administration of norepinephrine (NE), and propranolol. Rats were trained on a one-trial step-through inhibitory avoidance task and tested for retention 24 h later. Injections were administered bilaterally (10 μl/injection) through chronically-implanted cannulae. Low doses of NE (0.1 or 0.3 μg) administered shortly after training enhanced retention while higher doses (1.0 or 5.0 μg) were ineffective. Retention was not affected by NE administered 3 h after training. The effect of intra-amygdala NE on retention is blocked by simultaneous administration of propranolol (0.2 μg). This finding suggests that the memory-enhancing effect of NE may be mediated by β-receptors. Posttraining intra-amygdala NE also attenuated the retention deficit produced by adrenal demedullation. Further, intra-amygdala injections of propranolol (0.2 μg) blocked the enhancing effect, on retention, of posttraining s.c. injections of epinephrine. These findings suggest that activation of noradrenergic receptors in the amygdala may be involved in memory processing and may play a role in the memory-modulating effect of peripheral epinephrine.
This experiment examined the effect of posttraining epinephrine injections on memory-storage processes. Rats were trained with a weak footshock (0.7 mA, 0.35 sec) on a one-trial inhibitory avoidance task. The animals received epinephrine injections immediately, 10 min, 30 min, or 2 hr after training. On a retention test 24 hr after training, animals which received subcutaneous injections of epinephrine (0.01, 0.05, or 0.1 mg/kg) immediately after training had retention performance which was significantly better than that of saline control animals. A lower (0.001 mg/kg) or a higher (0.5 mg/kg) dose did not affect retention performance. Epinephrine injections (0.1 mg/kg) given 10 min after training also significantly facilitated retention, but injections given 30 min or 2 hr after training did not affect retention performance significantly. These findings suggest that the hormonal consequences of a training experience (e.g., epinephrine release) may normally modulate memory-storage processes in untreated animals.
SUBSTANTIAL anatomical and electrophysiological evidence suggests that human temporal lobe structures are involved in the processing of odour perception. The temporal lobe has both afferent and efferent connections with the olfactory bulb1,2, the major synaptic junction for primary fibres from the olfactory receptors. Olfactory auras accompany epileptic seizures of temporal lobe origin3, and electrical stimulation of the uncus and amygdala in conscious patients elicits odour sensations4. There are, however, no known quantitative studies of olfactory function in patients with surgically verified temporal lobe lesions. The present findings demonstrate that removal of the temporal lobe increases odour detection thresholds (ODT), whereas odour recognition thresholds (ORT) remain similar to those of subjects without brain damage.
Right and left temporal lobectomy patients, matched in age and intelligence, made more errors in odor recall than a control group. Patients with right temporal lobe excisions recalled significantly fewer odors correctly than patients with left temporal lobe excisions. Olfactory memory scores were not related to other memory deficits associated with left or right temporal lobe dysfunction or to intelligence or lesion size. However, in patients with right temporal lobectomy, percent of odors recalled correctly correlated positively with a general memory index. The findings presented are consistent with previous reports that the right temporal lobe is more involved with nonverbal memory than the left temporal lobe.
Ascending projections from the caudal (general-visceroceptive) part of the nucleus of the solitary tract (NTS) were studied experimentally in the rat by the aid of the anterograde autoradiographic and the retrograde horseradish peroxidase (HRP) tracer techniques. Microelectrophoretic deposits of tritiated proline and leucine which involved the caudal part of the NTS, the dorsal motor nucleus of the vagus (dmX), and portions of the hypoglossal nucleus, nucleus intercalatus and/or nucleus gracilis were found to label ascending fibers that, besides going to numerous brain stem territories that included prominently the parabrachial area, could also be traced to several forebrain structures, namely, the bed nucleus of the stria terminalis (BST), the paraventricular (PA), dorsomedial (HDM) and arcuate (ARC) nuclei of the hypothalamus, the central nucleus of the amygdaloid complex (AC), the medial preoptic area (PM) and the periventricular nucleus of the thalamus (TPV). Smaller isotope injections almost completely confined to the NTS and dmX resulted in lighter labeling of a similar set of parabrachial and forebrain projections, whereas in another case, in which the deposit was almost exclusively limited to the nucleus gracilis, no label was seen in the aforementioned structures. In another series of experiments, aimed at further localizing the neurons of origin of the prosencephalic projections under consideration, small microelectrophoretic HRP injections confined almost totally to BST, PA, HDM, AC, PM or TPV, as well as both small and large injections involving ARC, resulted in labeled neurons situated in the dorsal medullary region, mainly in the medial portion of the NTS at the level of and caudal to the area postrema.
The clinical findings relative to olfactory function are presented in 3 patients treated for psychomotor seizures by amygdalotomy (2 patients) and amygdalectomy (1 patient). Olfactory aura appears to originate in association with an amygdaloid discharge and not a hippocampal discharge. Unilateral amygdaloid lesions do not result in olfactory impairment, whereas bilateral lesions may result in marked impairments. The amygala appears to function at a relatively high level of sensory integration for olfactory stimuli. Impairment of odor differentiation and identification following bilateral lesions is relatively long lasting, whereas impairment for the rudimentary detection of odors is short lasting.
Rats (220-250 g) were bilaterally implanted with cannulae in the amygdala, trained on an inhibitory avoidance response and two weeks later, on a Y-maze discrimination response. Immediately following the training on each task, they were injected intraperitoneally (i.p.) or intra-amygdally. Retention was tested one week after training for each task. Retention of the Y-maze task was assessed by discrimination reversal training. Naloxone administered i.p. (3.0 mg/kg) significantly facilitated retention of both tasks in unoperated control rats as well as in rats implanted bilaterally with amygdala cannulae. The memory-enhancing effect of naloxone i.p. was blocked by propranolol (0.3 or 1.0 microgram) injected in the amygdala, but not when this beta-noradrenergic antagonist was injected (0.3 micrograms) into either the caudate or the cortex dorsal to the amygdala. Further, intra-amygdala injections of the beta 1-adrenoceptor blocker atenolol (0.3 or 1.0 microgram) and the beta 2-adrenoceptor blocker zinterol (0.3 or 1.0 microgram), in doses which were ineffective when administered alone, blocked naloxone-induced (3.0 mg/kg, i.p.) memory facilitation. In contrast, posttraining intra-amygdala administration (1.0 micrograms) of the alpha-antagonists prazosin (alpha 1) or yohimbine (alpha 2) did not attenuate the memory-enhancing effects of systemically administered naloxone. These findings support the view that naloxone-induced enhancement of memory is mediated by the activation of beta- but not alpha-noradrenergic receptors located within the amygdaloid complex.
These experiments examined the effect of posttraining administration of naloxone and beta-endorphin in rats with lesions of the stria terminalis (ST). Rats with sham or bilateral ST lesions were trained either in an inhibitory avoidance task or in a Y-maze discrimination task and, immediately after training, received an ip injection of saline, naloxone (0.5, 2.0 or 5.0 mg/kg in the avoidance task; 3.0 mg/kg in the Y-maze task), or beta-endorphin (10.0 micrograms/kg). Retention of each task was tested 24 hr following training. In the Y-maze task, retention was assessed by training on a reversed discrimination. The ST lesions did not affect retention of either task in otherwise untreated animals. However, in both tasks, ST lesions attenuated the memory-enhancing effects of naloxone as well as the memory-impairing effects of beta-endorphin. These findings are consistent with other recent evidence suggesting that the amygdala may be involved in posttraining memory modulation.
We report that peripheral nerves have a functional adenylate cyclase-coupled beta-adrenergic receptor. The pharmacological specificity of this receptor is shown to be of the beta 2 subtype. Two peripheral nerves, the sciatic from the frog and rat and the vagus from the rat, responded to beta 2-agonists with 10-50-fold increases in intracellular cyclic AMP level. This increase was inhibited by the beta-adrenergic antagonist propranolol. In contrast, a central nerve tract, the corpus callosum, responded to isoproterenol with only a minimal one- to twofold increase in cyclic AMP level. These studies demonstrate that peripheral nerves have beta 2-adrenergic receptors that are responsive to exogenously applied catecholamines and suggest a role for these ligands in the previously described modulation of axonal conduction.
Recent evidence of preserved skill learning in patients with "global" amnesia has led to the postulation of a qualitative distinction between functionally separate memory systems, one of which may remain preserved when the other is profoundly impaired. On one account, the separate memory systems support either the learning of declarative knowledge, i.e., facts and associations, or the learning of procedural knowledge, i.e., knowledge that permits the expression of skilled performance without reference to specific facts or associations. In an effort to develop a rodent model of amnesia that illustrates the same distinction between memory systems, rats were trained in a series of discrimination and reversal problems using olfaction, a sensory modality in which they rapidly learn new associations. Rats with bilateral fornix, amygdala, or combined fornix and amygdala damage learned successive two-odor discriminations as quickly as normal and sham-operated control subjects. Furthermore, all groups rapidly acquired the skills of discrimination as revealed in the development of a learning set. Subsequent presentation of a reversal of one discrimination elicited a marked dissociation among groups: Normal rats and rats with amygdala lesions required many more trials to acquire the reversal than to acquire a new discrimination problem, whereas rats with fornix lesions learned the reversal rather easily. A detailed analysis of response strategies suggested that normal rats and rats with amygdala lesions first extinguished the prior response tendencies and then abandoned the learning set skills and treated the reversal much as they did the initial discrimination problem.(ABSTRACT TRUNCATED AT 250 WORDS)
Single unit activity was recorded from the cortical, medial, and basal nuclei of the amygdala of anesthetized rats during controlled presentation of odor stimuli. Some of the odors were derived from volatile organic compounds, while others consisted of the odor of natural substances. The odors elicited responses in 46% of cortical nucleus units, in 42% of basal nucleus units, and in a smaller proportion (21%) of medial nucleus units. In samples of hippocampal and cortical single units also tested for response to odors, 33% of hippocampal units responded, while no cortical units responded. These results are consistent with the general idea that the amygdala has some role in the processing of odors that are important in many species-typical actions. However, no support was found for the hypothesis that certain amygdala units respond exclusively to particular natural odors.
The effect on retention of the post-training intraperitoneal administration of ACTH1-24 (0.2 or 2.0 micrograms/kg), epinephrine HCl (5.0 or 50.0 micrograms/kg), human beta-endorphin (0.1 or 1.0 microgram/kg), naloxone (0.4 mg/kg), and of the combination of naloxone or beta-endorphin with ACTH or epinephrine was studied in two different but closely related step-down inhibitory avoidance tasks in rats: task 1 (5 cm high 25 X 25 cm platform; 0.5 mA continuous footshock) and task 2 (7 X 25 cm platform, 0.3 mA discontinuous footshock). In task 1, saline control animals showed good retention in a test session carried out 24 hr later; beta-endorphin, ACTH and epinephrine caused amnesia; beta-endorphin potentiated the amnesic effect of ACTH and epinephrine; and naloxone caused memory facilitation and reversed the amnesic effect of ACTH and epinephrine. In task 2, control animals showed poor retention; beta-endorphin caused amnesia at the dose of 0.1 but not 1.0 microgram/kg; the other three drugs caused memory facilitation; naloxone potentiated the facilitatory effect of ACTH and epinephrine; and beta-endorphin reversed it and transformed it into a deep amnesia. These findings suggest that an opioid-mediated amnesic mechanism modulates the effect of ACTH and epinephrine on memory consolidation, either by dampening that effect when training parameters tend to make it facilitatory, or by enhancing it when training conditions tend to make it amnesic. On the basis of these and previous data it seems likely that the amnesic effect of ACTH and epinephrine could be mediated by endogenous beta-endorphin release.
In Experiment 1, subjects were presented with either the odors or the names of 15 common objects. In Experiment 2, subjects were presented with either the odors, photographs, or names of 16 common objects. All subjects were asked to describe an autobiographical memory evoked by each cue, to date each memory, and to rate each memory on vividness, pleasantness, and the number of times that the memory had been thought of and talked about prior to the experiment. Compared with memories evoked by photographs or names, memories evoked by odors were reported to be thought of and talked about less often prior to the experiment and were more likely to be reported as never having been thought of or talked about prior to the experiment. No other effects were consistently found, though there was a suggestion that odors might evoke more pleasant and emotional memories than other types of cues. The relation of these results to the folklore concerning olfactory cuing is discussed.
This study examined the involvement of the amygdala in the effects of glucocorticoids on the formation of memory for aversive training. Male Sprague-Dawley rats with neurochemically induced lesions of either the basolateral (BLA), central (CEA), or medial amygdala (MEA) were trained in a one-trial inhibitory avoidance task. Systemic (sc) injections of either vehicle, corticosterone (0.3 mg/kg) or the more selective glucocorticoid receptor (GR) agonist dexamethasone (0.3 mg/kg) were administered immediately after training, and retention was tested 48 h later. Retention of animals with lesions of the CEA was impaired, but retention of animals with BLA or MEA lesions was unimpaired. CEA-lesioned animals had increased locomotor activity as indicated by the number of crossings between the starting and shock compartments. Dexamethasone enhanced retention in sham-operated controls as well as in animals with lesions of the CEA, but did not enhance retention of animals with BLA or MEA lesions. Post-training corticosterone did not affect retention. Neither dexamethasone nor corticosterone altered the number of crossings between compartments. These findings are consistent with previous evidence suggesting that the effects of glucocorticoids on memory storage are mediated by an activation of GRs, and indicate that the BLA and MEA nuclei are critical areas involved in integrating these hormonal influences on learning and memory.
Although neuropsychological studies of the amnesic patient H. M. provide compelling evidence that normal memory function depends on the medial temporal lobe, the full extent of his surgical resection has not been elucidated. We conducted magnetic resonance imaging studies to specify precisely the extent of his bilateral resection and to document any other brain abnormalities. The MRI studies indicated that the lesion was bilaterally symmetrical and included the medial temporal polar cortex, most of the amygdaloid complex, most or all of the entorhinal cortex, and approximately half of the rostrocaudal extent of the intraventricular portion of the hippocampal formation (dentate gyrus, hippocampus, and subicular complex). The collateral sulcus was visible throughout much of the temporal lobe, indicating that portions of the ventral perirhinal cortex, located on the banks of the sulcus, were spared; the parahippocampal cortex (areas TF and TH) was largely intact. The rostrocaudal extent of the ablation was approximately 5.4 cm (left) and 5.1 cm (right). The caudal 2 cm, approximately, of the hippocampus body (normal length, approximately 4 cm) was intact, although atrophic. The temporal stem was intact. Outside the temporal lobes, the cerebellum demonstrated marked atrophy, and the mammillary nuclei were shrunken. The lateral temporal, frontal, parietal, and occipital lobe cortices appeared normal for age 66 years. The mediodorsal thalamic nuclei showed no obvious radiological changes. These findings reinforce the view that lesions of the hippocampal formation and adjacent cortical structures can produce global and enduring amnesia and can exacerbate amnesia beyond that seen after more selective hippocampal lesions.
A series of five experiments examined the differential mnemonic roles of the hippocampus and caudate-putamen and the modulatory influence of the amygdala on hippocampal and caudate-putamen memory processes. Findings indicate that (a) posttraining intrahippocampal injections of amphetamine selectively enhance memory in a hidden platform water maze task, (b) posttraining intracaudate injections of amphetamine selectively enhance memory in a visible platform water maze task, (c) posttraining intra-amygdala injections of amphetamine enhance memory in both water maze tasks, (d) preretention intrahippocampal lidocaine injections block expression of the memory enhancing effects of posttraining intrahippocampal amphetamine injections in the hidden platform task, (e) preretention intracaudate lidocaine injections block expression of the memory enhancing effects of posttraining intracaudate amphetamine injections in the visible platform task, (f) preretention intra-amygdala lidocaine injections do not block the memory enhancing effect of posttraining intra-amygdala amphetamine injections on either task, (g) in the hidden platform task, posttraining intrahippocampal, but not intracaudate, lidocaine injections block the memory enhancing effects of posttraining intra-amygdala amphetamine, (h) in the visible platform task, posttraining intracaudate, but not intrahippocampal, lidocaine injections block the memory enhancing effects of posttraining intra-amygdala amphetamine. The findings indicate a double dissociation between the roles of the hippocampus and caudate-putamen in memory and suggest that the amygdala exerts a modulatory influence on both the hippocampal and caudate-putamen memory systems.
Conditioning processes have been proposed to play a role in the development of anxiety disorders. As yet, the neurobiologic correlates of emotional learning have not been fully understood in these patients. Accordingly, brain activity was studied in subcortical and cortical regions involved in the processing of negative affect during differential aversive classical conditioning.
Twelve patients with social phobia and 12 healthy control subjects were presented with paired conditioned (CS; neutral facial expressions) and unconditioned stimuli (US; negative odor vs unmanipulated air). Functional magnetic resonance imaging (fMRI) was utilized to examine regional cerebral activity during habituation, acquisition,a nd extinction trials. Activity was measured with echo-planar-imaging (EPI), and signal intensity in individually defined anatomic regions were analyzed.
Subjective ratings of emotional valence to the CS indicated that behavioral conditioning occurred in both groups. The presentation of CS associated with negative odor led to signal decreases in the amygdala and hippocampus of normal subjects, whereas an opposite increased activation in both regions was observed in patients. Regional differences were not found during habituation and extinction.
Results suggest that conditioned aversive stimuli are processed in subcortical regions, with phobic patients differing from control subjects.