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European Neuropsychopharmacology : the... Dec 2020The current study aimed to identify alterations in brain activation and connectivity related to memory suppression in posttraumatic stress disorder (PTSD) using the...
The current study aimed to identify alterations in brain activation and connectivity related to memory suppression in posttraumatic stress disorder (PTSD) using the Think/No-Think paradigm during functional magnetic resonance imaging (fMRI). Reduced activation in the parahippocampal cortex during No-Think vs. Baseline trials was found in participants with PTSD compared to controls with no history of trauma (pFWE<0.05). Trauma-related intrusive memories (r = 0.562, p = 0.046) and avoidance behaviors (r = 0.636, p = 0.020) were positively correlated with parahippocampal cortex activation during memory suppression in the PTSD group. Psychophysiological interactions (PPI) analysis identified increased functional connectivity between the inferior frontal gyrus and the parahippocampus during memory suppression in the PTSD group compared to trauma-free controls (pFWE<0.05). Our findings support a network-based phenotype for altered memory suppression in individuals with PTSD rooted in dysfunctional parahippocampal-prefrontal coupling. These data validate neural models of PTSD and offer a novel neural circuit for brain-based interventions targeting trauma-related memory.
Topics: Adult; Cerebral Cortex; Female; Humans; Magnetic Resonance Imaging; Male; Memory; Mental Recall; Middle Aged; Parahippocampal Gyrus; Photic Stimulation; Stress Disorders, Post-Traumatic; Young Adult
PubMed: 32967787
DOI: 10.1016/j.euroneuro.2020.09.634 -
Nature Communications Apr 2022An essential role of the hippocampal region is to integrate information to compute and update representations. How this transpires is highly debated. Many theories hinge...
An essential role of the hippocampal region is to integrate information to compute and update representations. How this transpires is highly debated. Many theories hinge on the integration of self-motion signals and the existence of continuous attractor networks (CAN). CAN models hypothesise that neurons coding for navigational correlates - such as position and direction - receive inputs from cells conjunctively coding for position, direction, and self-motion. As yet, very little data exist on such conjunctive coding in the hippocampal region. Here, we report neurons coding for angular and linear velocity, uniformly distributed across the medial entorhinal cortex (MEC), the presubiculum and the parasubiculum, except for MEC layer II. Self-motion neurons often conjunctively encoded position and/or direction, yet lacked a structured organisation. These results offer insights as to how linear/angular speed - derivative in time of position/direction - may allow the updating of spatial representations, possibly uncovering a generalised algorithm to update any representation.
Topics: Entorhinal Cortex; Hippocampus; Neurons; Parahippocampal Gyrus
PubMed: 35393433
DOI: 10.1038/s41467-022-29583-z -
Hippocampus Jun 2023The hippocampus is a center for spatial and episodic memory formation in rodents. Understanding the composition of subregions and circuitry maps of the hippocampus is... (Review)
Review
The hippocampus is a center for spatial and episodic memory formation in rodents. Understanding the composition of subregions and circuitry maps of the hippocampus is essential for elucidating the mechanism of memory formation and recall. For decades, the trisynaptic circuit (entorhinal cortex layer II-dentate gyrus - CA3-CA1) has been considered the neural network substrate responsible for learning and memory. Recently, CA2 has emerged as an important area in the hippocampal circuitry, with distinct functions from those of CA3. In this article, we review the historical definition of the hippocampal area CA2 and the differential projection patterns between CA2 and CA3 pyramidal neurons. We provide a concise and comprehensive map of CA2 outputs by comparing (1) ipsi versus contra projections, (2) septal versus temporal projections, and (3) lamellar structures of CA2 and CA3 pyramidal neurons.
Topics: Animals; Rodentia; Hippocampus; Pyramidal Cells; Entorhinal Cortex
PubMed: 36855258
DOI: 10.1002/hipo.23519 -
Brain Structure & Function Jan 2023Proper names are an important part of language and communication. They are thought to have a special status due to their neuropsychological and psycholinguistic profile....
Proper names are an important part of language and communication. They are thought to have a special status due to their neuropsychological and psycholinguistic profile. To what extent proper names rely on the same semantic system as common names is not clear. In an fMRI study, we presented the same group of participants with both proper and common names to compare the associated activations. Both person and place names, as well as personally familiar and famous names were used, and compared with words representing concrete and abstract concepts. A whole-brain analysis was followed by a detailed analysis of subdivisions of four regions of interest known to play a central role in the semantic system: angular gyrus, anterior temporal lobe, posterior cingulate complex, and medial temporal lobe. We found that most subdivisions within these regions bilaterally were activated by both proper names and common names. The bilateral perirhinal and right entorhinal cortex showed a response specific to proper names, suggesting an item-specific role in retrieving person and place related information. While activation to person and place names overlapped greatly, place names were differentiated by activating areas associated with spatial memory and navigation. Person names showed greater right hemisphere involvement compared to places, suggesting a wider range of associations. Personally familiar names showed stronger activation bilaterally compared to famous names, indicating representations that are enhanced by autobiographic and episodic details. Both proper and common names are processed in the wider semantic system that contains associative, episodic, and spatial components. Processing of proper names is characterized by a somewhat stronger involvement these components, rather than by a fundamentally different system.
Topics: Humans; Semantics; Temporal Lobe; Brain; Language; Entorhinal Cortex; Magnetic Resonance Imaging
PubMed: 36372812
DOI: 10.1007/s00429-022-02593-9 -
Hippocampus Apr 2020Grid cells provide a compelling example of a link between cellular activity and an abstract and difficult to define concept like space. Accordingly, a representational... (Review)
Review
Grid cells provide a compelling example of a link between cellular activity and an abstract and difficult to define concept like space. Accordingly, a representational perspective on grid coding argues that neural grid coding underlies a fundamentally spatial metric. Recently, some theoretical proposals have suggested extending such a framework to nonspatial cognition as well, such as category learning. Here, we provide a critique of the frequently employed assumption of an isomorphism between patterns of neural activity (e.g., grid cells), mental representation, and behavior (e.g., navigation). Specifically, we question the strict isomorphism between these three levels and suggest that human spatial navigation is perhaps best characterized by a wide variety of both metric and nonmetric strategies. We offer an alternative perspective on how grid coding might relate to human spatial navigation, arguing that grid coding is part of a much larger conglomeration of neural activity patterns that dynamically tune to accomplish specific behavioral outputs.
Topics: Animals; Entorhinal Cortex; Grid Cells; Humans; Models, Neurological; Spatial Navigation
PubMed: 31742364
DOI: 10.1002/hipo.23175 -
Neuron Dec 2023The subregions of the entorhinal cortex (EC) are conventionally thought to compute dichotomous representations for spatial processing, with the medial EC (MEC) providing...
The subregions of the entorhinal cortex (EC) are conventionally thought to compute dichotomous representations for spatial processing, with the medial EC (MEC) providing a global spatial map and the lateral EC (LEC) encoding specific sensory details of experience. Yet, little is known about the specific types of information EC transmits downstream to the hippocampus. Here, we exploit in vivo sub-cellular imaging to record from EC axons in CA1 while mice perform navigational tasks in virtual reality (VR). We uncover distinct yet overlapping representations of task, location, and context in both MEC and LEC axons. MEC transmitted highly location- and context-specific codes; LEC inputs were biased by ongoing navigational goals. However, during tasks with reliable reward locations, the animals' position could be accurately decoded from either subregion. Our results revise the prevailing dogma about EC information processing, revealing novel ways spatial and non-spatial information is routed and combined upstream of the hippocampus.
Topics: Mice; Animals; Goals; Hippocampus; Entorhinal Cortex; Cognition; Spatial Processing; Spatial Navigation
PubMed: 37816349
DOI: 10.1016/j.neuron.2023.09.013 -
The European Journal of Neuroscience Nov 2019The identification of neuronal markers, that is, molecules selectively present in subsets of neurons, contributes to our understanding of brain areas and the networks... (Review)
Review
The identification of neuronal markers, that is, molecules selectively present in subsets of neurons, contributes to our understanding of brain areas and the networks within them. Specifically, recognizing the distribution of different neuronal markers facilitates the identification of borders between functionally distinct brain areas. Detailed knowledge about the localization and physiological significance of neuronal markers may also provide clues to generate new hypotheses concerning aspects of normal and abnormal brain functioning. Here, we provide a comprehensive review on the distribution within the entorhinal cortex of neuronal markers and the morphology of the neurons they reveal. Emphasis is on the comparative distribution of several markers, with a focus on, but not restricted to rodent, monkey and human data, allowing to infer connectional features, across species, associated with these markers, based on what is revealed by mainly rodent data. The overall conclusion from this review is that there is an emerging pattern in the distribution of neuronal markers in the entorhinal cortex when aligning data along a comparable coordinate system in various species.
Topics: Animals; Entorhinal Cortex; Humans; Neural Pathways; Neuroanatomical Tract-Tracing Techniques; Neurons; Neuropeptides; Receptors, Neurotransmitter; Rodentia; Species Specificity
PubMed: 31293027
DOI: 10.1111/ejn.14511 -
Human Brain Mapping Apr 2023Specific subfields within the hippocampus have shown vulnerability to chronic stress, highlighting the importance of looking regionally within the hippocampus to...
Specific subfields within the hippocampus have shown vulnerability to chronic stress, highlighting the importance of looking regionally within the hippocampus to understand the role of psychosocial factors in the development of neurodegenerative diseases. A systematic review on psychosocial factors and hippocampal subfield volumes was performed and showed inconsistent results, highlighting the need for future studies to explore this relationship. The current study aimed to explore the association of psychosocial factors with hippocampal (subfield) volumes, using high-field 7T MRI. Data were from the Memory Depression and Aging (Medea)-7T study, which included 333 participants without dementia. Hippocampal subfields were automatically segmented from T2-weighted images using ASHS software. Generalized linear models accounting for correlated outcomes were used to assess the association between subfields (i.e., entorhinal cortex, subiculum, Cornu Ammonis [CA]1, CA2, CA3, dentate gyrus, and tail) and each psychosocial factor (i.e., depressive symptoms, anxiety symptoms, childhood maltreatment, recent stressful life events, and social support), adjusted for age, sex, and intracranial volume. Neither depression nor anxiety was associated with specific hippocampal (subfield) volumes. A trend for lower total hippocampal volume was found in those reporting childhood maltreatment, and a trend for higher total hippocampal volume was found in those who experienced a recent stressful life event. Among subfields, low social support was associated with lower volume in the CA3 (B = -0.43, 95% CI: -0.72; -0.15). This study suggests possible differential effects among hippocampal (subfield) volumes and psychosocial factors.
Topics: Humans; Organ Size; Hippocampus; CA1 Region, Hippocampal; Aging; Entorhinal Cortex; Magnetic Resonance Imaging
PubMed: 36583397
DOI: 10.1002/hbm.26185 -
NeuroImage Apr 2022Risk-taking differs between humans, and is associated with the personality measures of impulsivity and sensation-seeking. To analyse the brain systems involved,...
Risk-taking differs between humans, and is associated with the personality measures of impulsivity and sensation-seeking. To analyse the brain systems involved, self-report risk-taking, resting state functional connectivity, and related behavioral measures were analyzed in 18,740 participants of both sexes from the UK Biobank. Functional connectivities of the medial orbitofrontal cortex, ventromedial prefrontal cortex (VMPFC), and the parahippocampal areas were significantly higher in the risk-taking group (p < 0.001, FDR corrected). The risk-taking measure was validated in that it was significantly associated with alcohol drinking amount (r = 0.08, p = 5.1×10), cannabis use (r = 0.12, p = 6.0×10), and anxious feelings (r = -0.12, p = 7.6×). The functional connectivity findings were cross-validated in two independent datasets. The higher functional connectivity of the medial orbitofrontal cortex and VMPFC included higher connectivity with the anterior cingulate cortex, which provides a route for these reward-related regions to have a greater influence on action in risk-taking individuals. In conclusion, the medial orbitofrontal cortex, which is involved in reward value and pleasure, was found to be related to risk-taking, which is associated with impulsivity. An implication is that risk-taking is driven by specific orbitofrontal cortex reward systems, and is different for different rewards which are represented differently in the brains of different individuals. This is an advance in understanding the bases and mechanisms of risk-taking in humans, given that the orbitofrontal cortex, VMPFC and anterior cingulate cortex are highly developed in humans, and that risk-taking can be reported in humans.
Topics: Adult; Aged; Connectome; Female; Gyrus Cinguli; Humans; Impulsive Behavior; Magnetic Resonance Imaging; Male; Middle Aged; Parahippocampal Gyrus; Prefrontal Cortex; Reward; Risk-Taking
PubMed: 35007715
DOI: 10.1016/j.neuroimage.2022.118893 -
Journal of Alzheimer's Disease : JAD 2020Posterior cortical atrophy (PCA) and logopenic progressive aphasia (LPA) are two of the most common variants of atypical Alzheimer's disease (AD). Both PCA and LPA are...
BACKGROUND
Posterior cortical atrophy (PCA) and logopenic progressive aphasia (LPA) are two of the most common variants of atypical Alzheimer's disease (AD). Both PCA and LPA are associated with relative sparing of hippocampus compared to neocortex, although hippocampal atrophy is observed. It is unclear whether regional patterns of hippocampal subfield involvement differ between PCA and LPA, and whether they differ from typical AD.
OBJECTIVE
To assess volume of specific subfields of the hippocampus in PCA, LPA, and typical AD.
METHODS
Fifty-nine patients with PCA and 77 patients with LPA were recruited and underwent T1-weighted MRI and Pittsburgh Compound B (PiB) PET at Mayo Clinic. Thirty-six probable AD patients and 100 controls were identified from the Alzheimer's Disease Neuroimaging Initiative. Hippocampal subfield volumes were calculated using Freesurfer, and volumes were compared between PCA, LPA, AD, and controls using Kruskal-Wallis and Dunn tests.
RESULTS
The LPA and PCA groups both showed the most striking abnormalities in CA4, presubiculum, molecular layer of the hippocampus, molecular and granule cell layers of the dentate gyrus, and the hippocampal-amygdala transition area, although atrophy was left-sided in LPA. PCA showed smaller volume of right presubiculum compared to LPA, with trends for smaller volumes of right parasubiculum and fimbria. LPA showed a trend for smaller volumes of left CA1 compared to PCA. The AD group showed smaller volumes of the right subiculum, CA1, and presubiculum compared to LPA.
CONCLUSION
Patterns of hippocampal subfield atrophy differ across the different syndromic variants of AD.
Topics: Aged; Alzheimer Disease; Aniline Compounds; Atrophy; CA1 Region, Hippocampal; CA2 Region, Hippocampal; CA3 Region, Hippocampal; Case-Control Studies; Dentate Gyrus; Female; Hippocampus; Humans; Image Interpretation, Computer-Assisted; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Middle Aged; Organ Size; Parahippocampal Gyrus; Positron-Emission Tomography; Thiazoles
PubMed: 33074228
DOI: 10.3233/JAD-200625