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Infection, Learning, and Memory: Focus on Immune Activation and Aversive Conditioning. Neurosci Biobehav Rev 2022; 142:104898. [PMID: 36183862 DOI: 10.1016/j.neubiorev.2022.104898] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 09/19/2022] [Accepted: 09/27/2022] [Indexed: 11/22/2022]
Abstract
Here we review the effects of immune activation primarily via lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, on hippocampal and non-hippocampal-dependent learning and memory. Rodent studies have found that LPS alters both the acquisition and consolidation of aversive learning and memory, such as those evoking evolutionarily adaptive responses like fear and disgust. The inhibitory effects of LPS on the acquisition and consolidation of contextual fear memory are discussed. LPS-induced alterations in the acquisition of taste and place-related conditioned disgust memory within bottle preference tasks and taste reactivity tests (taste-related), in addition to conditioned context avoidance tasks and the anticipatory nausea paradigm (place-related), are highlighted. Further, conditioned disgust memory consolidation may also be influenced by LPS-induced effects. Growing evidence suggests a central role of immune activation, especially pro-inflammatory cytokine activity, in eliciting the effects described here. Understanding how infection-induced immune activation alters learning and memory is increasingly important as bacterial and viral infections are found to present a risk of learning and memory impairment.
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Bryant KG, Barker JM. Arbitration of Approach-Avoidance Conflict by Ventral Hippocampus. Front Neurosci 2020; 14:615337. [PMID: 33390895 PMCID: PMC7773818 DOI: 10.3389/fnins.2020.615337] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 11/27/2020] [Indexed: 11/24/2022] Open
Abstract
When environmental cues or stimuli that represent both rewarding and aversive outcomes are presented, complex computations must be made in order to determine whether approach or avoidance is the better behavioral strategy. In many neuropsychiatric illnesses these computations can be skewed. In some instances, circumstances that may normally warrant avoidance instead promote approach, thus producing compulsive-like behavioral strategies that are inflexible in response to new or conflicting information. Alternatively, high sensitivity to aversion or low sensitivity to reward can result in the failure to achieve goals and loss of resilience that characterizes depressive disorders. Increases in compulsive-like behavior have been found to be associated with disrupted signaling in regions that regulate response to conflicting stimuli, including the hippocampus. Classic behavioral inhibition theories of hippocampus function in anxiety suggest that the hippocampus blocks aberrant behavior in response to anxiety related cues or stimuli. The hippocampus may act to block approach in the face of conflicting stimuli. Dysregulations of hippocampal function, as may be present in neuropsychiatric disorders, may therefore promote aberrant approach behavior. The ventral hippocampus (vHPC) subregion is key for coordinating this approach/avoidance conflict resolution, likely through its participation with cortico-striatal and mesolimbic circuits. We revisit Gray's behavioral inhibition theory of HPC function, first posited in the 1980s, and interpret in the context of new knowledge on vHPC function gained through modern technology. Taken together with the extant, classical literature on hippocampal function, we propose that these new findings suggest that vHPC circuits balance behavioral response to conflicting stimuli in a manner that is both state- and context-dependent and, further, that disruption of specific vHPC circuits tips the balance in favor of biased approach or avoidance behavioral strategies.
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Affiliation(s)
- Kathleen G Bryant
- Department of Pharmacology and Physiology, Drexel University, Philadelphia, PA, United States
| | - Jacqueline M Barker
- Department of Pharmacology and Physiology, Drexel University, Philadelphia, PA, United States
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Shinohara K, Yasoshima Y. Inactivation of the ventral hippocampus facilitates the attenuation of odor neophobia in rats. Behav Brain Res 2020; 401:113077. [PMID: 33345825 DOI: 10.1016/j.bbr.2020.113077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 12/07/2020] [Accepted: 12/12/2020] [Indexed: 11/20/2022]
Abstract
Food neophobia is a behavior observed in rodents involving reduced consumption of a novel food or drink. In the absence of negative post-ingestive consequences, consumption increases with exposure (attenuation of neophobia), which is seen as an associative safe memory. Olfaction and gustation are sensory modalities essential for the development of a food preference. However, little is known about the neural mechanisms underlying neophobia to a food-related odor stimulus. In the present study, we examined the effect of pharmacological inactivation of the ventral hippocampus (vHPC) on neophobia to orally consumed solutions in rats using muscimol, a gamma aminobutyric acid type A receptor agonist. Two different types of solutions, almond odor (benzaldehyde) and sweet taste (saccharin), were prepared. In the results, microinjections of muscimol into the bilateral vHPC before the first odor and taste exposures did not alter the neophobic reactions of the rats to each stimulus. However, in the second odor, but not taste, exposure, the muscimol-injected rats showed higher consumption in comparison to that observed in the control rats, suggesting that the vHPC inactivation facilitates the attenuation of odor neophobia. On the other hand, intra-vHPC muscimol microinjections after the first odor and taste exposures did not facilitate consumption at the second exposures. These results indicate that neural activations within vHPC during orally consuming a novel odor, but not taste, solution play an inhibitory role in the subsequent attenuation of neophobia.
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Affiliation(s)
- Keisuke Shinohara
- Division of Behavioral Physiology, Department of Behavioral Sciences, Graduate School of Human Sciences, Osaka University, 1-2 Yamadaoka, Suita, Osaka, Japan
| | - Yasunobu Yasoshima
- Division of Behavioral Physiology, Department of Behavioral Sciences, Graduate School of Human Sciences, Osaka University, 1-2 Yamadaoka, Suita, Osaka, Japan.
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de-la-Cruz M, Millán-Aldaco D, Soriano-Nava DM, Drucker-Colín R, Murillo-Rodríguez E. The artificial sweetener Splenda intake promotes changes in expression of c-Fos and NeuN in hypothalamus and hippocampus of rats. Brain Res 2018; 1700:181-189. [PMID: 30201258 DOI: 10.1016/j.brainres.2018.09.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 08/16/2018] [Accepted: 09/04/2018] [Indexed: 12/24/2022]
Abstract
BACKGROUND Obesity is the result of the interaction of multiple variables, including the excessive increase of sugar-sweetened beverages consumption. Diets aimed to treat obesity have suggested the use of artificial sweeteners. However, recent evidence has shown several health deficits after intake of artificial sweeteners, including effects in neuronal activity. Therefore, the influence of artificial sweeteners consumption such as Splenda, on the expression of c-Fos and neuronal nuclear protein (NeuN) in hypothalamus and hippocampus remains to be determined. OBJECTIVES We investigated the effects on c-Fos or NeuN expression in hypothalamus and hippocampus of Splenda-treated rats. METHODS Splenda was diluted in water (25, 75 or 250 mg/100 mL) and orally given to rats during 2 weeks ad libitum. Next, animals were sacrificed by decapitation and brains were collected for analysis of c-Fos or NeuN immunoreactivity. RESULTS Consumption of Splenda provoked an inverted U-shaped dose-effect in c-Fos expression in ventromedial hypothalamic nucleus while similar findings were observed in dentate gyrus of hippocampus. In addition, NeuN immunoreactivity was enhanced in ventromedial hypothalamic nucleus at 25 or 75 mg/100 mL of Splenda intake whereas an opposite effect was observed at 250 mg/100 mL of artificial sweetener consumption. Lastly, NeuN positive neurons were increased in CA2/CA3 fields of hippocampus from Splenda-treated rats (25, 75 or 250 mg/100 mL). CONCLUSION Consuming Splenda induced effects in neuronal biomarkers expression. To our knowledge, this study is the first description of the impact of intake Splenda on c-Fos and NeuN immunoreactivity in hypothalamus and hippocampus in rats.
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Affiliation(s)
- Miriel de-la-Cruz
- Laboratorio de Neurociencias Moleculares e Integrativas, Escuela de Medicina, División Ciencias de la Salud, Universidad Anáhuac Mayab, Mérida, Yucatán, Mexico; Intercontinental Neuroscience Research Group
| | - Diana Millán-Aldaco
- Depto. de Neuropatología Molecular, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México, Mexico
| | - Daniela Marcia Soriano-Nava
- Laboratorio de Neurociencias Moleculares e Integrativas, Escuela de Medicina, División Ciencias de la Salud, Universidad Anáhuac Mayab, Mérida, Yucatán, Mexico; Intercontinental Neuroscience Research Group
| | - René Drucker-Colín
- Depto. de Neuropatología Molecular, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México, Mexico
| | - Eric Murillo-Rodríguez
- Laboratorio de Neurociencias Moleculares e Integrativas, Escuela de Medicina, División Ciencias de la Salud, Universidad Anáhuac Mayab, Mérida, Yucatán, Mexico; Intercontinental Neuroscience Research Group.
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Yiannakas A, Rosenblum K. The Insula and Taste Learning. Front Mol Neurosci 2017; 10:335. [PMID: 29163022 PMCID: PMC5676397 DOI: 10.3389/fnmol.2017.00335] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 10/03/2017] [Indexed: 12/29/2022] Open
Abstract
The sense of taste is a key component of the sensory machinery, enabling the evaluation of both the safety as well as forming associations regarding the nutritional value of ingestible substances. Indicative of the salience of the modality, taste conditioning can be achieved in rodents upon a single pairing of a tastant with a chemical stimulus inducing malaise. This robust associative learning paradigm has been heavily linked with activity within the insular cortex (IC), among other regions, such as the amygdala and medial prefrontal cortex. A number of studies have demonstrated taste memory formation to be dependent on protein synthesis at the IC and to correlate with the induction of signaling cascades involved in synaptic plasticity. Taste learning has been shown to require the differential involvement of dopaminergic GABAergic, glutamatergic, muscarinic neurotransmission across an extended taste learning circuit. The subsequent activation of downstream protein kinases (ERK, CaMKII), transcription factors (CREB, Elk-1) and immediate early genes (c-fos, Arc), has been implicated in the regulation of the different phases of taste learning. This review discusses the relevant neurotransmission, molecular signaling pathways and genetic markers involved in novel and aversive taste learning, with a particular focus on the IC. Imaging and other studies in humans have implicated the IC in the pathophysiology of a number of cognitive disorders. We conclude that the IC participates in circuit-wide computations that modulate the interception and encoding of sensory information, as well as the formation of subjective internal representations that control the expression of motivated behaviors.
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Affiliation(s)
- Adonis Yiannakas
- Sagol Department of Neuroscience, University of Haifa, Haifa, Israel
| | - Kobi Rosenblum
- Sagol Department of Neuroscience, University of Haifa, Haifa, Israel
- Center for Gene Manipulation in the Brain, University of Haifa, Haifa, Israel
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Kanoski SE, Grill HJ. Hippocampus Contributions to Food Intake Control: Mnemonic, Neuroanatomical, and Endocrine Mechanisms. Biol Psychiatry 2017; 81:748-756. [PMID: 26555354 PMCID: PMC4809793 DOI: 10.1016/j.biopsych.2015.09.011] [Citation(s) in RCA: 166] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 08/22/2015] [Accepted: 09/21/2015] [Indexed: 10/23/2022]
Abstract
Food intake is a complex behavior that can occur or cease to occur for a multitude of reasons. Decisions about where, when, what, and how much to eat are not merely reflexive responses to food-relevant stimuli or to changes in energy status. Rather, feeding behavior is modulated by various contextual factors and by previous experiences. The data reviewed here support the perspective that neurons in multiple hippocampal subregions constitute an important neural substrate linking the external context, the internal context, and mnemonic and cognitive information to control both appetitive and ingestive behavior. Feeding behavior is heavily influenced by hippocampal-dependent mnemonic functions, including episodic meal-related memories and conditional learned associations between food-related stimuli and postingestive consequences. These mnemonic processes are undoubtedly influenced by both external and internal factors relating to food availability, location, and physiological energy status. The afferent and efferent neuroanatomical connectivity of the subregions of the hippocampus is reviewed with regard to the integration of visuospatial and olfactory sensory information (the external context) with endocrine and gastrointestinal interoceptive stimuli (the internal context). Also discussed are recent findings demonstrating that peripherally derived endocrine signals act on receptors in hippocampal neurons to reduce (leptin, glucagon-like peptide-1) or increase (ghrelin) food intake and learned food reward-driven responding, thereby highlighting endocrine and neuropeptidergic signaling in hippocampal neurons as a novel substrate of importance in the higher-order regulation of feeding behavior.
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Affiliation(s)
- Scott E. Kanoski
- Department of Biological Sciences, University of Southern California
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Adaikkan C, Rosenblum K. A molecular mechanism underlying gustatory memory trace for an association in the insular cortex. eLife 2015; 4:e07582. [PMID: 26452094 PMCID: PMC4703067 DOI: 10.7554/elife.07582] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Accepted: 10/08/2015] [Indexed: 12/17/2022] Open
Abstract
Events separated in time are associatively learned in trace conditioning, recruiting more neuronal circuits and molecular mechanisms than in delay conditioning. However, it remains unknown whether a given sensory memory trace is being maintained as a unitary item to associate. Here, we used conditioned taste aversion learning in the rat model, wherein animals associate a novel taste with visceral nausea, and demonstrate that there are two parallel memory traces of a novel taste: a short-duration robust trace, lasting approximately 3 hr, and a parallel long-duration weak one, lasting up to 8 hr, and dependent on the strong trace for its formation. Moreover, only the early robust trace is maintained by a NMDAR-dependent CaMKII- AMPAR pathway in the insular cortex. These findings suggest that a memory trace undergoes rapid modifications, and that the mechanisms underlying trace associative learning differ when items in the memory are experienced at different time points.
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Affiliation(s)
| | - Kobi Rosenblum
- Sagol Department of Neurobiology, University of Haifa, Haifa, Israel
- Center for Gene Manipulation in the Brain, University of Haifa, Haifa, Israel
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Differential contribution of hippocampal subfields to components of associative taste learning. J Neurosci 2014; 34:11007-15. [PMID: 25122900 DOI: 10.1523/jneurosci.0956-14.2014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The ability to associate the consumption of a taste with its positive or negative consequences is fundamental to survival and influences the behavior of species ranging from invertebrate to human. As a result, for both research and clinical reasons, there has been a great effort to understand the neuronal circuits, as well as the cellular and molecular mechanisms, underlying taste learning. From a neuroanatomical perspective, the contributions of the cortex and amygdala are well documented; however, the literature is riddled with conflicting results regarding the role of the hippocampus in different facets of taste learning. Here, we use conditional genetics in mice to block NMDA receptor-dependent plasticity individually in each of the three major hippocampal subfields, CA1, CA3, and the dentate gyrus, via deletion of the NR1 subunit. Across the CA1, CA3, and dentate gyrus NR1 knock-out lines, we uncover a pattern of differential deficits that establish the dispensability of hippocampal plasticity in incidental taste learning, the requirement of CA1 plasticity for associative taste learning, and a specific requirement for plasticity in the dentate gyrus when there is a long temporal gap between the taste and its outcome. Together, these data establish that the hippocampus is involved in associative taste learning and suggest an episodic component to this type of memory.
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Henderson YO, Victoria NC, Inoue K, Murphy AZ, Parent MB. Early life inflammatory pain induces long-lasting deficits in hippocampal-dependent spatial memory in male and female rats. Neurobiol Learn Mem 2014; 118:30-41. [PMID: 25451312 DOI: 10.1016/j.nlm.2014.10.010] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Revised: 10/20/2014] [Accepted: 10/29/2014] [Indexed: 11/17/2022]
Abstract
The present experiment tested the hypothesis that neonatal injury disrupts adult hippocampal functioning and that normal aging or chronic stress during adulthood, which are known to have a negative impact on hippocampal function, exacerbate these effects. Male and female Sprague-Dawley rats were given an intraplantar injection of the inflammatory agent carrageenan (1%) on the day of birth and their memory was tested in the hippocampal-dependent spatial water maze in adulthood and again in middle age. We found that neonatal injury impaired hippocampal-dependent memory in adulthood, that the effects of injury on memory were more pronounced in middle-aged male rats, and that chronic stress accelerated the onset of these memory deficits. Neonatal injury also decreased glucocorticoid receptor mRNA in the dorsal CA1 area of middle-aged rats, a brain region critical for spatial memory. Morphine administration at the time of injury completely reversed injury-induced memory deficits, but neonatal morphine treatments in the absence of injury produced significant memory impairments in adulthood. Collectively, these findings are consistent with our hypothesis that neonatal injury produces long-lasting disruption in adult hippocampal functioning.
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Affiliation(s)
- Yoko O Henderson
- Neuroscience Institute, Georgia State University, P.O. Box 5030, Atlanta, GA 30302-5030, United States.
| | - Nicole C Victoria
- Neuroscience Institute, Georgia State University, P.O. Box 5030, Atlanta, GA 30302-5030, United States.
| | - Kiyoshi Inoue
- Department of Psychiatry and Behavioral Sciences, Yerkes National Primate Center, Emory University School of Medicine, 954 Gatewood Rd., Atlanta, GA 30322, United States; Center for Translational Social Neuroscience, Yerkes National Primate Center, Emory University School of Medicine, 954 Gatewood Rd., Atlanta, GA 30322, United States.
| | - Anne Z Murphy
- Neuroscience Institute, Georgia State University, P.O. Box 5030, Atlanta, GA 30302-5030, United States.
| | - Marise B Parent
- Neuroscience Institute, Georgia State University, P.O. Box 5030, Atlanta, GA 30302-5030, United States; Department of Psychology, Georgia State University, P.O. Box 5010, Atlanta, GA 30302-5010, United States.
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Uematsu A, Kitamura A, Iwatsuki K, Uneyama H, Tsurugizawa T. Correlation Between Activation of the Prelimbic Cortex, Basolateral Amygdala, and Agranular Insular Cortex During Taste Memory Formation. Cereb Cortex 2014; 25:2719-28. [PMID: 24735672 DOI: 10.1093/cercor/bhu069] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Conditioned taste aversion (CTA) is a well-established learning paradigm, whereby animals associate tastes with subsequent visceral illness. The prelimbic cortex (PL) has been shown to be involved in the association of events separated by time. However, the nature of PL activity and its functional network in the whole brain during CTA learning remain unknown. Here, using awake functional magnetic resonance imaging and fiber tracking, we analyzed functional brain connectivity during the association of tastes and visceral illness. The blood oxygen level-dependent (BOLD) signal significantly increased in the PL after tastant and lithium chloride (LiCl) infusions. The BOLD signal in the PL significantly correlated with those in the amygdala and agranular insular cortex (IC), which we found were also structurally connected to the PL by fiber tracking. To precisely examine these data, we then performed double immunofluorescence with a neuronal activity marker (c-Fos) and an inhibitory neuron marker (GAD67) combined with a fluorescent retrograde tracer in the PL. During CTA learning, we found an increase in the activity of excitatory neurons in the basolateral amygdala (BLA) or agranular IC that project to the PL. Taken together, these findings clearly identify a role of synchronized PL, agranular IC, and BLA activity in CTA learning.
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Affiliation(s)
- Akira Uematsu
- Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan Current address: Laboratory for Neural Circuitry of Memory, RIKEN Brain Science Institute, Saitama 351-0198, Japan
| | - Akihiko Kitamura
- Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan
| | - Ken Iwatsuki
- Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan Current address: Department of Nutritional Science and Food Safety, Tokyo University of Agriculture, Tokyo 156-8502, Japan
| | - Hisayuki Uneyama
- Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan
| | - Tomokazu Tsurugizawa
- Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki 210-8681, Japan
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Parent MB, Darling JN, Henderson YO. Remembering to eat: hippocampal regulation of meal onset. Am J Physiol Regul Integr Comp Physiol 2014; 306:R701-13. [PMID: 24573183 DOI: 10.1152/ajpregu.00496.2013] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A wide variety of species, including vertebrate and invertebrates, consume food in bouts (i.e., meals). Decades of research suggest that different mechanisms regulate meal initiation (when to start eating) versus meal termination (how much to eat in a meal, also known as satiety). There is a very limited understanding of the mechanisms that regulate meal onset and the duration of the postprandial intermeal interval (ppIMI). In the present review, we examine issues involved in measuring meal onset and some of the limited available evidence regarding how it is regulated. Then, we describe our recent work indicating that dorsal hippocampal neurons inhibit meal onset during the ppIMI and describe the processes that may be involved in this. We also synthesize recent evidence, including evidence from our laboratory, suggesting that overeating impairs hippocampal functioning and that impaired hippocampal functioning, in turn, contributes to the development and/or maintenance of diet-induced obesity. Finally, we identify critical questions and challenges for future research investigating neural controls of meal onset.
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Affiliation(s)
- Marise B Parent
- Neuroscience Institute, Georgia State University, Atlanta, Georgia; and Department of Psychology, Georgia State University, Atlanta, Georgia
| | - Jenna N Darling
- Neuroscience Institute, Georgia State University, Atlanta, Georgia; and
| | - Yoko O Henderson
- Neuroscience Institute, Georgia State University, Atlanta, Georgia; and
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12
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Ventral hippocampal neurons are shaped by experience to represent behaviorally relevant contexts. J Neurosci 2013; 33:8079-87. [PMID: 23637197 DOI: 10.1523/jneurosci.5458-12.2013] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Memories can be recalled at different levels of resolution, from a detailed rendition of specific events within a single experience to a broad generalization across multiple related experiences. Here we provide evidence that neural representations reflecting the specificity or generality of memories are differentially represented along the dorsoventral axis of the CA3 area of the rat hippocampus. In dorsal CA3, neurons rapidly associate the identity of events with specific locations whereas, in more ventrally located CA3 regions, neurons gradually accumulate information across extended training to form representations that generalize across related events within a spatial context and distinguish events across contexts.
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Wheeler DS, Chang SE, Holland PC. Odor-mediated taste learning requires dorsal hippocampus, but not basolateral amygdala activity. Neurobiol Learn Mem 2013; 101:1-7. [PMID: 23274135 PMCID: PMC3602369 DOI: 10.1016/j.nlm.2012.12.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 12/17/2012] [Accepted: 12/18/2012] [Indexed: 10/27/2022]
Abstract
Mediated learning is a unique cognitive phenomenon in which mental representations of physically absent stimuli enter into associations with directly-activated representations of physically present stimuli. Three experiments investigated the functional physiology of mediated learning involving the use of odor-taste associations. In Experiments 1a and 1b, basolateral amygdala lesions failed to attenuate mediated taste aversion learning. In Experiment 2, dorsal hippocampus inactivation impaired mediated learning, but left direct learning intact. Considered with past studies, the results implicate the dorsal hippocampus in mediated learning generally, and suggest a limit on the importance of the basolateral amygdala.
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Affiliation(s)
- Daniel S Wheeler
- Department of Psychological and Brain Sciences, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
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Abstract
PURPOSE To examine the effect of dopamine depletion in nucleus accumbens on trace conditioning; to distinguish the role of core and shell sub-regions, as far as possible. MATERIAL/METHODS 6-hydroxydopamine was used to lesion dopamine terminals within the core and shell accumbens. Experiment 1 assessed conditioning to a tone conditioned stimulus that had previously been paired with footshock (unconditioned stimulus) at a 30s trace interval. Experiment 2 subsequently assessed contiguous conditioning (at 0s trace) using a light conditioned stimulus directly followed by the unconditioned stimulus. RESULTS Both sham and shell-lesioned animals showed the normal trace effect of reduced conditioning to the trace conditioned stimulus but 6-hydroxydopamine injections targeted on the core subregion of the nucleus accumbens abolished this effect and enhanced conditioning to the trace conditioned stimulus. However, the depletion produced by this lesion placement extended to the shell. In Experiment 2 (at 0s trace), there was no effect of either lesion placement as all animals showed comparable levels of conditioning to the light conditioned stimulus. Neurochemical analysis across core, shell and comparison regions showed some effects on noradrenalin as well as dopamine. CONCLUSIONS The pattern of changes in noradrenalin did not systematically relate to the observed behavioural changes after core injections. The pattern of changes in dopamine suggested that depletion in core mediated the increased conditioning to the trace conditioned stimulus seen in the present study. However, the comparison depletion restricted to the shell subregion was less substantial, and a role for secondarily affected brain regions cannot be excluded.
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Are the dorsal and ventral hippocampus functionally distinct structures? Neuron 2010; 65:7-19. [PMID: 20152109 DOI: 10.1016/j.neuron.2009.11.031] [Citation(s) in RCA: 2317] [Impact Index Per Article: 165.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/19/2009] [Indexed: 12/11/2022]
Abstract
One literature treats the hippocampus as a purely cognitive structure involved in memory; another treats it as a regulator of emotion whose dysfunction leads to psychopathology. We review behavioral, anatomical, and gene expression studies that together support a functional segmentation into three hippocampal compartments: dorsal, intermediate, and ventral. The dorsal hippocampus, which corresponds to the posterior hippocampus in primates, performs primarily cognitive functions. The ventral (anterior in primates) relates to stress, emotion, and affect. Strikingly, gene expression in the dorsal hippocampus correlates with cortical regions involved in information processing, while genes expressed in the ventral hippocampus correlate with regions involved in emotion and stress (amygdala and hypothalamus).
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Ramos JM. Remote spatial memory and the hippocampus: Effect of early and extensive training in the radial maze. Learn Mem 2009; 16:554-63. [DOI: 10.1101/lm.1480309] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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