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The Journal of Comparative Neurology Jun 2015The insular cortex is involved in the perception of interoceptive signals, coding of emotional and affective states, and processing information from gustatory,...
The insular cortex is involved in the perception of interoceptive signals, coding of emotional and affective states, and processing information from gustatory, olfactory, auditory, somatosensory, and nociceptive modalities. This information represents an important component of episodic memory, mediated by the parahippocampal-hippocampal region. A comprehensive description of insular projections to the latter region is lacking. Previous studies reported that insular projections do not target any of the subdivisions in the hippocampal formation (the dentate gyus, the cornu ammonis [CA] fields 1, 2, and 3 and the subiculum), but, in contrast, target the parahippocampal region (perirhinal, postrhinal, lateral and medial entorhinal cortices, and pre- and parasubiculum). The present study examined the topographical and laminar organization of insular projections to the parahippocampal region in the rat with the use of anterograde tracing. Notably, our results corroborated the absence of hippocampal projections. We further showed that the perirhinal and the lateral entorhinal cortices received extensive projections from the insular cortex, primarily from its agranular areas. With the exception of a weak projection to the postrhinal cortex, projections to the remaining parahippocampal areas were either absent or very sparse. The projections to the lateral entorhinal cortex displayed a preference for the deep layers of its most lateral subdivisions, known also to receive hippocampal inputs. Projections to the perirhinal cortex primarily targeted the superficial layers with a preference for its ventral subdivision, referred to as area 35. Our findings indicate that only processed information, reflecting emotional and affective states, but not primary gustatory and viscerosensory information, has direct access to the parahippocampal-hippocampal system.
Topics: Animals; Biotin; Cerebral Cortex; Dextrans; Entorhinal Cortex; Female; Neural Pathways; Neuroanatomical Tract-Tracing Techniques; Neuronal Tract-Tracers; Parahippocampal Gyrus; Photomicrography; Phytohemagglutinins; Rats, Sprague-Dawley
PubMed: 25641117
DOI: 10.1002/cne.23742 -
Hippocampus 2007The parahippocampal region in the rodent brain includes the perirhinal, postrhinal, and entorhinal cortices, the presubiculum, and the parasubiculum. In recent years,... (Review)
Review
The parahippocampal region in the rodent brain includes the perirhinal, postrhinal, and entorhinal cortices, the presubiculum, and the parasubiculum. In recent years, the perirhinal and postrhinal cortices have been a focus in memory research because they supply highly processed, polymodal sensory information to the hippocampus, both directly and via the entorhinal cortex. Available evidence indicates that these cortices receive different complements of cortical information, which are then forwarded to the hippocampus via parallel pathways. Here we have summarized the cortical, subcortical, and hippocampal connections of the perirhinal and postrhinal cortices in order to provide further insight into the nature of the information that is processed by these regions prior to arriving in the hippocampus. As has been previously described, the cortical afferents of the rodent postrhinal cortex are dominated by structures known to be involved in the processing of visual and spatial information, whereas the cortical afferents of the perirhinal cortex result in remarkable convergence of polymodal sensory information. The two regions are also differentiated by their cortical efferents. The perirhinal cortex projects more strongly to piriform, frontal, and insular regions, whereas the postrhinal cortex projects preferentially to visual and visuospatial regions. The subcortical connections of the two regions provide further evidence that they have different functions. For example, the perirhinal cortex has strong reciprocal connections with the amygdala, which suggest involvement in processing affective stimuli. Subcortical input to the postrhinal cortex is dominated by projections from dorsal thalamic structures, particularly the lateral posterior nucleus. Although the perirhinal and postrhinal cortices are considered to contribute to the episodic memory system, many questions remain about their particular roles. A detailed description of the anatomical connections of the perirhinal and postrhinal cortices will permit the generation of new, anatomically guided, hypotheses about their role in episodic memory and other cognitive processes.
Topics: Animals; Cerebral Cortex; Neural Pathways; Parahippocampal Gyrus; Rats; Terminology as Topic
PubMed: 17604355
DOI: 10.1002/hipo.20314 -
Hippocampus Jan 2017The advent of high-resolution magnetic resonance imaging (MRI) has enabled in vivo research in a variety of populations and diseases on the structure and function of...
The advent of high-resolution magnetic resonance imaging (MRI) has enabled in vivo research in a variety of populations and diseases on the structure and function of hippocampal subfields and subdivisions of the parahippocampal gyrus. Because of the many extant and highly discrepant segmentation protocols, comparing results across studies is difficult. To overcome this barrier, the Hippocampal Subfields Group was formed as an international collaboration with the aim of developing a harmonized protocol for manual segmentation of hippocampal and parahippocampal subregions on high-resolution MRI. In this commentary we discuss the goals for this protocol and the associated key challenges involved in its development. These include differences among existing anatomical reference materials, striking the right balance between reliability of measurements and anatomical validity, and the development of a versatile protocol that can be adopted for the study of populations varying in age and health. The commentary outlines these key challenges, as well as the proposed solution of each, with concrete examples from our working plan. Finally, with two examples, we illustrate how the harmonized protocol, once completed, is expected to impact the field by producing measurements that are quantitatively comparable across labs and by facilitating the synthesis of findings across different studies. © 2016 Wiley Periodicals, Inc.
Topics: Hippocampus; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Parahippocampal Gyrus; Pattern Recognition, Automated
PubMed: 27862600
DOI: 10.1002/hipo.22671 -
Journal of Psychiatric Research Jul 2013Patients with schizophrenia show widespread cortical thickness reductions throughout the brain. Likewise, reduced expression of the γ-Aminobutyric acid (GABA)...
Patients with schizophrenia show widespread cortical thickness reductions throughout the brain. Likewise, reduced expression of the γ-Aminobutyric acid (GABA) synthesizing enzyme glutamic acid decarboxylase (GAD1) and a single nucleotide polymorphism (SNP) rs3749034 in the corresponding gene have been associated with schizophrenia. We tested whether this SNP is associated with reduced cortical thickness, an intermediate phenotype for schizophrenia. Because of the well known interactions between the GABAergic and dopaminergic systems, we examined whether associations between GAD1 rs3749034 and cortical thickness are modulated by the catechol-O-methyltransferase (COMT) Val158Met genotype. Structural MRI and genotype data was obtained from 94 healthy subjects enrolled in the Mind Clinical Imaging Consortium study to examine the relations between GAD1 genotype and cortical thickness. Our data show a robust reduction of cortical thickness in the left parahippocampal gyrus (PHG) in G allele homozygotes of GAD1 rs3749034. When we stratified our analyses according to the COMT Val158Met genotype, cortical thickness reductions of G allele homozygotes were only found in the presence of the Val allele. Genetic risk variants of schizophrenia in the GABAergic system might interact with the dopaminergic system and impact brain structure and functioning. Our findings point to the importance of the GABAergic system in the pathogenesis of schizophrenia.
Topics: Adolescent; Adult; Catechol O-Methyltransferase; Chi-Square Distribution; Female; Genotype; Glutamate Decarboxylase; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Methionine; Middle Aged; Parahippocampal Gyrus; Polymorphism, Single Nucleotide; Valine; Young Adult
PubMed: 23566421
DOI: 10.1016/j.jpsychires.2013.03.010 -
NeuroImage Aug 2021Landmark objects are points of reference that can anchor one's internal cognitive map to the external world while navigating. They are especially useful in indoor...
Landmark objects are points of reference that can anchor one's internal cognitive map to the external world while navigating. They are especially useful in indoor environments where other cues such as spatial geometries are often similar across locations. We used functional magnetic resonance imaging (fMRI) and multivariate pattern analysis (MVPA) to understand how the spatial significance of landmark objects is represented in the human brain. Participants learned the spatial layout of a virtual building with arbitrary objects as unique landmarks in each room during a navigation task. They were scanned while viewing the objects before and after learning. MVPA revealed that the neural representation of landmark objects in the right parahippocampal place area (rPPA) and the hippocampus transformed systematically according to their locations. Specifically, objects in different rooms became more distinguishable than objects in the same room. These results demonstrate that rPPA and the hippocampus encode the spatial significance of landmark objects in indoor spaces.
Topics: Adult; Brain Mapping; Female; Hippocampus; Humans; Magnetic Resonance Imaging; Male; Parahippocampal Gyrus; Spatial Learning; Young Adult
PubMed: 33882351
DOI: 10.1016/j.neuroimage.2021.118081 -
Hippocampus 2006The present review considers research on the hippocampus and related areas from humans and experimental animals and makes three main points. First, many of the... (Review)
Review
The present review considers research on the hippocampus and related areas from humans and experimental animals and makes three main points. First, many of the anatomical details of the hippocampus and adjacent cortical areas in the parahippocampal region are conserved across mammals. Second, the functional role of these areas in declarative memory is also conserved across species. Third, an evolutionary approach will be key to understanding exactly how the local circuitry of the hippocampus and parahippocampal region supports declarative memory. To highlight the utility of this approach, a schematic model is described in which separate streams of spatial and nonspatial information converge on the hippocampus. By this view, a fundamental function of the mammalian hippocampus is to combine incoming information about spatial context from the postrhinal (parahippocampal in primates) cortex and medial entorhinal area with incoming information about nonspatial items from the perirhinal cortex and lateral entorhinal area. The underlying neurobiological computations that arise from local circuitry enable item-in-context memory and are proposed to be fundamental to many examples of declarative memory, including episodic memory in humans and spatial memory in experimental animals.
Topics: Animals; Biological Evolution; Hippocampus; Humans; Memory; Nerve Net; Neural Pathways; Orientation; Parahippocampal Gyrus; Space Perception; Species Specificity
PubMed: 16881079
DOI: 10.1002/hipo.20205 -
Philosophical Transactions of the Royal... Jul 2012In this paper, we present two novel perspectives on the function of the left inferior frontal gyrus (LIFG). First, a structured sequence processing perspective... (Review)
Review
In this paper, we present two novel perspectives on the function of the left inferior frontal gyrus (LIFG). First, a structured sequence processing perspective facilitates the search for functional segregation within the LIFG and provides a way to express common aspects across cognitive domains including language, music and action. Converging evidence from functional magnetic resonance imaging and transcranial magnetic stimulation studies suggests that the LIFG is engaged in sequential processing in artificial grammar learning, independently of particular stimulus features of the elements (whether letters, syllables or shapes are used to build up sequences). The LIFG has been repeatedly linked to processing of artificial grammars across all different grammars tested, whether they include non-adjacent dependencies or mere adjacent dependencies. Second, we apply the sequence processing perspective to understand how the functional segregation of semantics, syntax and phonology in the LIFG can be integrated in the general organization of the lateral prefrontal cortex (PFC). Recently, it was proposed that the functional organization of the lateral PFC follows a rostro-caudal gradient, such that more abstract processing in cognitive control is subserved by more rostral regions of the lateral PFC. We explore the literature from the viewpoint that functional segregation within the LIFG can be embedded in a general rostro-caudal abstraction gradient in the lateral PFC. If the lateral PFC follows a rostro-caudal abstraction gradient, then this predicts that the LIFG follows the same principles, but this prediction has not yet been tested or explored in the LIFG literature. Integration might provide further insights into the functional architecture of the LIFG and the lateral PFC.
Topics: Brain; Cognition; Humans; Language; Music; Nerve Net; Neuroimaging; Parahippocampal Gyrus; Prefrontal Cortex; Psychomotor Performance; Reaction Time; Transcranial Magnetic Stimulation
PubMed: 22688637
DOI: 10.1098/rstb.2012.0009 -
Hippocampus 2005Single-unit recording studies of monkeys have shown that neurons in perirhinal and entorhinal cortex exhibit activity reductions following stimulus repetition, and some...
Single-unit recording studies of monkeys have shown that neurons in perirhinal and entorhinal cortex exhibit activity reductions following stimulus repetition, and some have suggested that these "repetition suppression" effects may represent neural signals that support recognition memory. Critically, repetition suppression effects are most pronounced at short intervals between stimulus repetitions. Here, we used event-related functional magnetic resonance imaging (fMRI) to identify repetition suppression effects in the human medial temporal lobe and determine whether these effects are sensitive to the length of the interval between repetitions. Twenty-one participants were scanned while performing a continuous recognition memory task in which the interval between item repetitions was parametrically varied from 2 to 32 intervening items. We found evidence of repetition suppression in the anterior parahippocampal gyrus, but only when the repetition interval was relatively short. Moreover, bilateral hippocampal regions showed lag-sensitive repetition effects. Our results demonstrate that activity in the human medial temporal cortex, like that of monkeys, exhibits repetition suppression effects that are sensitive to the length of the interval between repetitions.
Topics: Adolescent; Adult; Female; Humans; Magnetic Resonance Imaging; Male; Parahippocampal Gyrus; Recognition, Psychology; Time Factors
PubMed: 15889401
DOI: 10.1002/hipo.20087 -
Nature Reviews. Neuroscience Oct 2000Recent neurobiological studies have begun to reveal the cognitive and neural coding mechanisms that underlie declarative memory--our ability to recollect everyday events... (Review)
Review
Recent neurobiological studies have begun to reveal the cognitive and neural coding mechanisms that underlie declarative memory--our ability to recollect everyday events and factual knowledge. These studies indicate that the critical circuitry involves bidirectional connections between the neocortex, the parahippocampal region and the hippocampus. Each of these areas makes a unique contribution to memory processing. Widespread high-order neocortical areas provide dedicated processors for perceptual, motor or cognitive information that is influenced by other components of the system. The parahippocampal region mediates convergence of this information and extends the persistence of neocortical memory representations. The hippocampus encodes the sequences of places and events that compose episodic memories, and links them together through their common elements. Here I describe how these mechanisms work together to create and re-create fully networked representations of previous experiences and knowledge about the world.
Topics: Animals; Hippocampus; Humans; Maze Learning; Memory; Mental Recall; Neocortex; Nerve Net; Neurons; Parahippocampal Gyrus
PubMed: 11252767
DOI: 10.1038/35036213 -
Human Brain Mapping Jan 2023Parahippocampal cortex (PHC) is a vital neural bases in spatial navigation. However, its functional role is still unclear. "Contextual hypothesis," which assumes that...
Parahippocampal cortex (PHC) is a vital neural bases in spatial navigation. However, its functional role is still unclear. "Contextual hypothesis," which assumes that the PHC participates in processing the spatial association between the landmark and destination, provides a potential answer to the question. Nevertheless, the hypothesis was previously tested using the picture categorization task, which is indirectly related to spatial navigation. By now, study is still needed for testing the hypothesis with a navigation-related paradigm. In the current study, we tested the hypothesis by an fMRI experiment in which participants performed a distance estimation task in a virtual environment under three different conditions: landmark free (LF), stable landmark (SL), and ambiguous landmark (AL). By analyzing the behavioral data, we found that the presence of an SL improved the participants' performance in distance estimation. Comparing the brain activity in SL-versus-LF contrast as well as AL-versus-LF contrast, we found that the PHC was activated by the SL rather than by AL when encoding the distance. This indicates that the PHC is elicited by strongly associated context and encodes the landmark reference for distance perception. Furthermore, accessing the representational similarity with the activity of the PHC across conditions, we observed a high similarity within the same condition but low similarity between conditions. This result indicated that the PHC sustains the contextual information for discriminating between scenes. Our findings provided insights into the neural correlates of the landmark information processing from the perspective of contextual hypothesis.
Topics: Humans; Parahippocampal Gyrus; Cerebral Cortex; Cognition; Spatial Navigation; Magnetic Resonance Imaging; Brain Mapping
PubMed: 36066186
DOI: 10.1002/hbm.26069