The Interwoven Architecture of the Amygdala, Hippocampus, and Isocortex
Poster No:
1712
Submission Type:
Abstract Submission
Authors:
Doruk Yigit Eriguc1, Sofie Valk1
Institutions:
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony
First Author:
Co-Author:
Introduction:
The hippocampus and amygdala are complex structures with distinct subfields and subnuclei, associated with specific structural and functional roles. They both are connected to each other and also to regions in the isocortex including prefrontal cortex, entorhinal cortex, parietal cortex and various subcortical areas for hippocampus (Mišić et al., 2014; Eichenbaum, 2017; Maller et al, 2019; Huang et al., 2021) ; prefrontal cortex, and various subcortical areas for amygdala (McDonald, 1998; Pitkänen et al., 2000; Ghashghaei et al., 2007; Tamietto et al., 2012). They play a key role in higher-order cognitive, memory, and emotional/motivational processes, often working together. While the systemic embeddings of the hippocampus and amygdala are understudied, their extensive connectivity and crucial roles in cognitive-emotional functions makes it important to study their functional organization. In this work, we studied how the amygdala and hippocampus are embedded within the isocortical networks. We examined their positions in large-scale brain networks by analyzing their functional connectivity at a subfield/subnuclei level.
Methods:
We focused on the functional organization of hippocampal and amygdalar subregions and their interwoven relationships with the isocortex, using 1 hour (4 times 15 minutes) of high-quality 3T resting-state functional MRI data from the Human Connectome Project Young Adult dataset (subsample of 200 individuals, mean age 29, 118 females). First we mapped the connectivity patterns of the amygdala and hippocampus subregions with each other and the isocortex. We then examined which areas are commonly connected to both structures. Next, we applied dimensionality reduction (diffusion embedding) on resting-state functional connectivity (FC), resulting in gradients explaining major organizational axes of co-organization of amygdala nuclei and hippocampal subfields. Finally, these gradients were projected onto the isocortex by correlating them with FC matrices. This allowed us to identify the relationships between the hippocampus, amygdala, and large-scale isocortical networks at a subregion level.
Results:
Our results suggest an interdigitated organization in the hippocampus and amygdala with specific subregions in each structure being closely aligned with certain subregions from either structure, rather than a clear hippocampus-amygdala divide (Fig. 1a). Moreover, we observed overlaps of the functional projections of the hippocampal subfields and amygdalar nuclei to the isocortex, in ventral somatosensory, temporal and medial frontal regions (Fig. 1b). Exploring to what extent the interdigitation of hippocampus-amygdala was reflected in the isocortical profile, we generated their shared organizational axes. We found that the first gradient differentiated centromedial-anterior amygdala and hippocampal body to basolateral amygdala, hippocampal head and tail, whereas second gradient differentiated anterior-posterior hippocampus within the hippocampus, and basolateral-centromedial nuclei within the amygdala. The functional patterning in the projection to isocortex of the first gradient indicates that hippocampal-amygdalar gradient follows the task-negative (default mode network, paralimbic areas) / task-positive (control and attention networks) divide of cortex.
Conclusions:
Here we illustrate the interwoven organization of the amygdala subnuclei and hippocampal subfields and how this reflects their shared association with the isocortex using resting-state fMRI. Our findings advance understanding of the interplay between these structures and their contribution to cortical function, offering a starting point for future studies into their contributions to human cognition and emotion.
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Anatomy and Functional Systems 1
Cortical Anatomy and Brain Mapping
Subcortical Structures 2
Keywords:
Limbic Systems
Sub-Cortical
Other - hippocampus - amygdala
1|2Indicates the priority used for review
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Provide references using APA citation style.
Eichenbaum, H. (2017). Prefrontal–hippocampal interactions in episodic memory. Nature Reviews Neuroscience, 18(9), 547-558.
Ghashghaei, H. T., Hilgetag, C. C., & Barbas, H. (2007). Sequence of information processing for emotions based on the anatomic dialogue between prefrontal cortex and amygdala. Neuroimage, 34(3), 905-923.
Maller, J. J., Welton, T., Middione, M., Callaghan, F. M., Rosenfeld, J. V., & Grieve, S. M. (2019). Revealing the hippocampal connectome through super-resolution 1150-direction diffusion MRI. Scientific Reports, 9(1), 2418.
McDonald, A. J. (1998). Cortical pathways to the mammalian amygdala. Progress in Neurobiology, 55(3), 257-332.
Mišić, B., Goñi, J., Betzel, R. F., Sporns, O., & McIntosh, A. R. (2014). A network convergence zone in the hippocampus. PLoS Computational Biology, 10(12), e1003982.
Pitkänen, A., Pikkarainen, M., Nurminen, N., & Ylinen, A. (2000). Reciprocal connections between the amygdala and the hippocampal formation, perirhinal cortex, and postrhinal cortex in rat: a review. Annals of the New York Academy of Sciences, 911(1), 369-391.
Tamietto, M., Pullens, P., de Gelder, B., Weiskrantz, L., & Goebel, R. (2012). Subcortical connections to human amygdala and changes following destruction of the visual cortex. Current Biology, 22(15), 1449-1455.
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