Phylogeny of neocortical-hippocampal projections provides insight in the nature of human memory
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eLife assessment
This valuable work discusses the phylogenetic conservation of the hippocampal region and primary sensory cortical regions in mammalian species. The authors propose that species-specific differences in behavior and mnemonic functions may be due to differences in cortico-hippocampal connectivity patterns. However, the manuscript, in its present form, is speculative, and the strength of evidence for this proposition is incomplete.
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Abstract
Throughout mammalian evolution, the hippocampal region, unlike the neocortex, largely preserved its cytoarchitectural organization and its role in mnemonic functions. This contrast raises the possibility that the hippocampal region receives different types of cortical input across species, which may be reflected in species-specific memory-related differences. To test this hypothesis, we examined differences in unimodal and transmodal cortical input to the hippocampal region in the rat, marmoset, macaque and human. Our results demonstrate that unlike unimodal cortical input, transmodal cortical input to the hippocampal region was selectively preserved during mammalian evolution. These findings suggest that memory-related processes in different species likely operate on different types of sensory information. Our observations provide a comparative anatomical framework elucidating the process of dimensionality reduction underlying the formation of human memory.
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eLife assessment
This valuable work discusses the phylogenetic conservation of the hippocampal region and primary sensory cortical regions in mammalian species. The authors propose that species-specific differences in behavior and mnemonic functions may be due to differences in cortico-hippocampal connectivity patterns. However, the manuscript, in its present form, is speculative, and the strength of evidence for this proposition is incomplete.
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Reviewer #1 (Public Review):
The paper itself has a reasonable aim, to compare the inputs to the hippocampus from cortical regions across mammals. But for some reason, the conclusions that are reached are very limited. We know for example that the main laboratory rodents investigated, rats and mice, are nocturnal, live in underground tunnels, and have a very wide field of view with no fovea. In contrast, primates have a highly developed cortical system for vision and a fovea, and so have very different capabilities to rodents, as they have an ability to identify people or objects at a distance, and to remember where they have been seen. Despite this major difference in the visual cortical processing in these different mammals, somehow important points are missed in this paper about how the cortical processing is organised in these …
Reviewer #1 (Public Review):
The paper itself has a reasonable aim, to compare the inputs to the hippocampus from cortical regions across mammals. But for some reason, the conclusions that are reached are very limited. We know for example that the main laboratory rodents investigated, rats and mice, are nocturnal, live in underground tunnels, and have a very wide field of view with no fovea. In contrast, primates have a highly developed cortical system for vision and a fovea, and so have very different capabilities to rodents, as they have an ability to identify people or objects at a distance, and to remember where they have been seen. Despite this major difference in the visual cortical processing in these different mammals, somehow important points are missed in this paper about how the cortical processing is organised in these different mammals, and how this is reflected in the anatomy.
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Reviewer #2 (Public Review):
Summary:
The manuscript emphasizes a phylogenetic conservation of the hippocampal region and primary sensory cortical regions in mammalian species. The authors then propose that the evident species-specific differences in behavior and memory-related functions may be due to differences in type and amount of cortico-hippocampal connectivity.
Strengths:
The authors are well-established researchers with a long history of excellent results and publications. The question (co-influence of cortical and hippocampal connections) is potentially interesting.
Weaknesses:
The treatment is very broad and macro scale, ignoring the likelihood that hippocampal-cortical connectivity and behavioral outcomes result from multiple differences at a more micro-scale. The designated "mammalian" sample is also broad. Thus, it can …
Reviewer #2 (Public Review):
Summary:
The manuscript emphasizes a phylogenetic conservation of the hippocampal region and primary sensory cortical regions in mammalian species. The authors then propose that the evident species-specific differences in behavior and memory-related functions may be due to differences in type and amount of cortico-hippocampal connectivity.
Strengths:
The authors are well-established researchers with a long history of excellent results and publications. The question (co-influence of cortical and hippocampal connections) is potentially interesting.
Weaknesses:
The treatment is very broad and macro scale, ignoring the likelihood that hippocampal-cortical connectivity and behavioral outcomes result from multiple differences at a more micro-scale. The designated "mammalian" sample is also broad. Thus, it can appear incomplete as a sample, and incompletely discussed.
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