Papers by Katherine Bryant
Brain Structure and Function, 2023
The recent development of methods for constructing directly comparable white matter atlases in pr... more The recent development of methods for constructing directly comparable white matter atlases in primate brains from diffusion MRI allows us to probe specializations unique to humans, great apes, and other primate taxa. Here, we constructed the first white matter atlas of a lesser ape using an ex vivo diffusion-weighted scan of a brain from a young adult (5.5 years) male lar gibbon. We find that white matter architecture of the gibbon temporal lobe suggests specializations that are reminiscent of those previously reported for great apes, specifically, the expansion of the arcuate fasciculus and the inferior longitudinal fasciculus in the temporal lobe. Our findings suggest these white matter expansions into the temporal lobe were present in the last common ancestor to hominoids approximately 16 million years ago and were further modified in the great ape and human lineages. White matter atlases provide a useful resource for identifying neuroanatomical differences and similarities between humans and other primate species and provide insight into the evolutionary variation and stasis of brain organization.
Communications Biology, 2023
Brain tissue is metabolically expensive. Consequently, the evolution of humans’ large brains must... more Brain tissue is metabolically expensive. Consequently, the evolution of humans’ large brains must have occurred via concomitant shifts in energy expenditure and intake. Proposed mechanisms include dietary shifts such as cooking. Importantly, though, any new food source must have been exploitable by hominids with brains a third the size of modern humans’. Here, we propose the initial metabolic trigger of hominid brain expansion was the consumption of externally fermented foods. We define “external fermentation” as occurring outside the body, as opposed to the internal fermentation in the gut. External fermentation could increase the bioavailability of macro- and micronutrients while reducing digestive energy expenditure and is supported by the relative reduction of the human colon. We discuss the explanatory power of our hypothesis and survey external fermentation practices across human cultures to demonstrate its viability across a range of environments and food sources. We close with suggestions for empirical tests.
PNAS, 2022
The biological foundation for the language-ready brain in the human lineage remains a debated sub... more The biological foundation for the language-ready brain in the human lineage remains a debated subject. In humans, the arcuate fasciculus (AF) white matter and the posterior portions of the middle temporal gyrus are crucial for language. Compared with other primates, the human AF has been shown to dramatically extend into the posterior temporal lobe, which forms the basis of a number of models of the structural connectivity basis of language. Recent advances in both language research and comparative neuroimaging invite a reassessment of the anatomical differences in language streams between humans and our closest relatives. Here, we show that posterior temporal connectivity via the AF in humans compared with chimpanzees is expanded in terms of its connectivity not just to the ventral frontal cortex but also to the parietal cortex. At the same time, posterior temporal regions connect more strongly to the ventral white matter in chimpanzees as opposed to humans. This pattern is present in both brain hemispheres.Additionally, we show that the anterior temporal lobe harbors a combination of connections present in both species through the inferior fronto-occipital fascicle and human-unique expansions through the uncinate and middle and inferior longitudinal fascicles.These findings elucidate structural changes that are unique to humans and may underlie the anatomical foundations for full-fledged language capacity.
Scholar and Feminist Online, 2019
This paper contributes to this field first by reviewing some outstanding issues pertaining to the... more This paper contributes to this field first by reviewing some outstanding issues pertaining to the question of sex/gender in the human brain, with a special focus on neuroimaging data; second by proposing several methodological interventions for more accurately interrogating sex/gender differences; and third by applying these interventions to an examination of similarities and differences between women and men in major white matter tracts using diffusion MRI (dMRI) data from a publicly available neuroimaging dataset. The interventions we describe and apply here include running empirical tests of randomization control and permutation analyses to protect against false positives, calculating measures of both difference (i.e., effect size) and overlap/similarity between groups, and reporting null results. Lastly, we discuss our findings and implications for study design with the aim to create a template for greater transparency in sex/gender neuroscience.
Digital Endocasts, 2017
The temporal lobe is a morphological specialization of primates resulting from an expansion of hi... more The temporal lobe is a morphological specialization of primates resulting from an expansion of higher-order visual cortex that is a hallmark of the primate brain. Among primates, humans possess a temporal lobe that has significantly expanded. Several uniquely human cognitive abilities, including language comprehension, semantic memory, and aspects of conceptual processing, are represented in the temporal lobe. Understanding how the temporal lobe has been modified and reorganized in the human lineage is crucial to understanding how it supports human cognitive specializations. Identifying these structural modifications requires a direct comparison with other primates, with special attention to our closest relatives, the chimpanzees. Comparative examination of data from architectonics, tract tracing, and newer imaging methodologies suggests modifications to external morphology (gyri and sulci), preferential expansion of association areas, and elaboration of white matter fasciculi, distinguishing the human temporal lobe from those of Old World monkeys. Chimpanzees and humans share some of these features of cortical expansion, although more research is needed in order to elucidate whether humans possess simply a large hominoid temporal lobe or whether important reorganization has happened since our divergence from chimpanzees.
Thesis Statement: The consumption of externally fermented foods acted as the initial metabolic tr... more Thesis Statement: The consumption of externally fermented foods acted as the initial metabolic trigger enabling hominid brain expansion. Because brain tissue is metabolically expensive, it is thought that the evolution of humans’ large brains was only possible through a concomitant reduction in the size of another expensive organ system, the gut. However, this gut reduction must have itself been made possible by dietary changes, the nature of which are still unclear. Here, we propose that the initial metabolic trigger of hominid brain expansion may have been the consumption of externally fermented foods. We define “external fermentation” as occurring outside the body, as opposed to the internal fermentation that occurs through the gut microbiome. This practice could have begun accidentally and with limited understanding, but over time, fermentation technologies may have become increasingly intentional, socially-transmitted, and culturally-reinforced. We detail the mechanisms by whic...
Chimpanzees (Pan troglodytes) are, along with bonobos, humans’ closest living relatives. The adve... more Chimpanzees (Pan troglodytes) are, along with bonobos, humans’ closest living relatives. The advent of diffusion MRI tractography in recent years has allowed a resurgence of comparative neuroanatomical studies in humans and other primate species. Here we offer, in comparative perspective, the first chimpanzee white matter atlas, constructed from in vivo chimpanzee diffusion-weighted scans. Comparative white matter atlases provide a useful tool for identifying neuroanatomical differences and similarities between humans and other primate species. Until now, comprehensive fascicular atlases have been created for humans (Homo sapiens), rhesus macaques (Macaca mulatta), and several other nonhuman primate species, but never in a nonhuman ape. Information on chimpanzee neuroanatomy is essential for understanding the anatomical specializations of white matter organization that are unique to the human lineage.
Brain Structure and Function, 2018
Understanding the phylogeny of the human brain requires an appreciation of brain organization of ... more Understanding the phylogeny of the human brain requires an appreciation of brain organization of our closest animal relatives. Neuroimaging tools such as magnetic resonance imaging (MRI) allow us to study whole-brain organization in species which can otherwise not be studied. Here, we used diffusion MRI to reconstruct the connections of the cortical hemispheres of the chimpanzee. This allowed us to perform an exploratory analysis of the grey matter structures of the chimpanzee cerebral cortex and their underlying white matter connectivity profiles. We identified a number of networks that strongly resemble those found in other primates, including the corticospinal system, limbic connections through the cingulum bundle and fornix, and occipital-temporal and temporal-frontal systems. Notably, chimpanzee temporal cortex showed a strong resemblance to that of the human brain, providing some insight into the specialization of the two species' shared lineage.
Sciurus niger (Rodentia: Sciuridae) is a large tree squirrel which inhabits the southeastern port... more Sciurus niger (Rodentia: Sciuridae) is a large tree squirrel which inhabits the southeastern portion of North America. Currently there are ten recognized subspecies which are distinguished based on differences in morphology and ecology. While molecular work has been undertaken for a few subspecies of S. niger, the patterns of genetic differentiation of the entire species have yet to be examined. This study attempts to characterize the genetic structure of S. niger in order to help determine the validity of current subspecies ...
Chimpanzees (Pan troglodytes) are, along with bonobos, humans' closest living relatives. The adve... more Chimpanzees (Pan troglodytes) are, along with bonobos, humans' closest living relatives. The advent of diffusion tractography in recent years has allowed a resurgence of comparative neuroanatomical studies in humans and other primate species. Here, we offer, in comparative perspective, the first chimpanzee white matter atlas, coupled with surface projection maps of these major white matter tracts, constructed from in vivo chimpanzee diffusion-weighted scans. Comparative white matter atlases provide a useful tool for identifying neuroanatomical differences and similarities between humans and other primate species. Until now, comprehensive fascicular atlases have been created for humans (Homo sapiens), rhesus macaques (Macaca mulatta) , and several other nonhuman primate species, but never in a nonhuman ape. Information on chimpanzee neuroanatomy is essential for understanding the anatomical specializations of white matter organization that are unique to the human lineage.
Scholar and Feminism Online, 2019
Brain Structure & Function, 2018
Understanding the phylogeny of the human brain requires an appreciation of brain organization of ... more Understanding the phylogeny of the human brain requires an appreciation of brain organization of our closest animal relatives.
Neuroimaging tools such as magnetic resonance imaging (MRI) allow us to study whole-brain organization in species which
can otherwise not be studied. Here, we used diffusion MRI to reconstruct the connections of the cortical hemispheres of the
chimpanzee. This allowed us to perform an exploratory analysis of the grey matter structures of the chimpanzee cerebral
cortex and their underlying white matter connectivity profiles. We identified a number of networks that strongly resemble
those found in other primates, including the corticospinal system, limbic connections through the cingulum bundle and fornix,
and occipital–temporal and temporal–frontal systems. Notably, chimpanzee temporal cortex showed a strong resemblance
to that of the human brain, providing some insight into the specialization of the two species’ shared lineage.
The temporal lobe is a morphological specialization of primates resulting from an expansion of hi... more The temporal lobe is a morphological specialization of primates resulting from an expansion of higher-order visual cortex that is a hallmark of the primate brain. Among primates, humans possess a temporal lobe that has significantly expanded. Several uniquely human cognitive abilities, including language comprehension, semantic memory, and aspects of conceptual processing, are represented in the temporal lobe. Understanding how the temporal lobe has been modified and reorganized in the human lineage is crucial to understanding how it supports human cognitive specializations. Identifying these structural modifications requires a direct comparison with other primates, with special attention to our closest relatives, the chimpanzees. Comparative examination of data from architectonics, tract tracing, and newer imaging methodologies suggests modifications to external morphology (gyri and sulci), preferential expansion of association areas, and elaboration of white matter fasciculi, distinguishing the human temporal lobe from those of Old World monkeys. Chimpanzees and humans share some of these features of cortical expansion, although more research is needed in order to elucidate whether humans possess simply a large hominoid temporal lobe or whether important reorganization has happened since our divergence from chimpanzees.
The Neuroethics Blog, Apr 23, 2013
[Describing the experiences of subject MMo] Eights are yellow, for example, a square feels like m... more [Describing the experiences of subject MMo] Eights are yellow, for example, a square feels like mashed potatoes, and the name Steve is somehow like poached eggs. (Cytowic p. 26) "…I [asked the vendor] what kind of ice cream she had. 'Fruit ice cream,' she said. But she answered in such a tone that a whole pile of coals, of black cinders, came bursting out of her mouth, and I couldn't bring myself to buy any ice cream after she'd answered that way…" (Record of patient "S", Luria p. 82)
The Emory Wheel, Apr 15, 2013
Brain, Behavior and Evolution, Aug 10, 2012
Vesicular glutamate transporters (VGLUTs) reuptake glutamate into synaptic vesicles at excitatory... more Vesicular glutamate transporters (VGLUTs) reuptake glutamate into synaptic vesicles at excitatory synapses. VGLUT2 is localized in the cortical terminals of neuronal somas located in the main sensory nuclei of the thalamus. Thus, immunolabeling of cortex with antibodies to VGLUT2 can reveal geniculostriate terminal distributions in species in which connectivity cannot be studied with tract-tracing techniques, permitting broader comparative studies of cortical specializations. Here, we used VGLUT2 immunohistochemistry to compare the organization of geniculostriate afferents in primary visual cortex in hominid primates (humans, chimpanzees, and an orangutan), Old World monkeys (rhesus macaques and vervets), and New World monkeys (squirrel monkeys). The New and Old World monkeys had a broad, dense band of terminal-like labeling in cortical layer 4C, a narrow band of labeling in layer 4A, and additional labeling in layers 2/3 and 6, consistent with results from conventional tract-tracing studies in these species. By contrast, although the hominid primates had a prominent layer 4C band, labeling of layer 4A was sparse or absent. Labeling was also present in layers 2/3 and 6, although labeling of layer 6 was weaker in hominids and possibly more individually variable than in Old and New World monkeys. These findings are consistent with previous observations from cytochrome oxidase histochemistry and a very small number of connectivity studies, suggesting that the projections from the parvocellular layers of the lateral geniculate nucleus to layer 4A were strongly reduced or eliminated in humans and apes following their evolutionary divergence from the other anthropoid primates.
The Central Sulcus, Apr 2012
In Scripto Magazine, Jan 2011
Journal of Mammalogy, Oct 1, 2012
We examined intraspecific relationships in the eastern fox squirrel (Sciurus niger) and the easte... more We examined intraspecific relationships in the eastern fox squirrel (Sciurus niger) and the eastern gray squirrel (S. carolinensis) using sequence variation in a portion of the mitochondrial DNA cytochrome-b gene and part of the D-loop in the control region. These closely related species are codistributed temperate forest obligates that have similar generation time and population ecologies. For both species, we documented high haplotype diversity, low nucleotide variation, and several groups of divergent haplotypes. However, there is a general lack of spatial structure in maternal lineages within each species. For S. carolinensis, we observed a pattern of population genetic structure that suggests the presence of at least 2 distinct refugial populations that evolved in isolation during the Pleistocene (approximately 98.3–266.3 thousand years ago [kya]) and subsequently expanded to the species' current range following the last glacial maximum. For S. niger, the genetic structure was much less pronounced, with fewer strongly diverged haplotypes. This finding suggests that eastern fox squirrels persisted in either a single population in a glacial refugium or as several refugial populations that maintained gene flow throughout the Pleistocene. For both species, there is evidence that scattered populations were present in multiple, small refugia close to the Laurentide Ice Sheet, allowing rapid range expansion following glacial recession. Taken together, our results indicate that S. niger and S. carolinensis underwent multiple episodes of genetic divergence during isolation in glacial refugia, followed by range expansion and contact that resulted in admixture of divergent maternal lineages within each species during interglacials. Examination of our data further indicates that the most recent range expansion in both species occurred within the past 12–20 kya.
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Papers by Katherine Bryant
Neuroimaging tools such as magnetic resonance imaging (MRI) allow us to study whole-brain organization in species which
can otherwise not be studied. Here, we used diffusion MRI to reconstruct the connections of the cortical hemispheres of the
chimpanzee. This allowed us to perform an exploratory analysis of the grey matter structures of the chimpanzee cerebral
cortex and their underlying white matter connectivity profiles. We identified a number of networks that strongly resemble
those found in other primates, including the corticospinal system, limbic connections through the cingulum bundle and fornix,
and occipital–temporal and temporal–frontal systems. Notably, chimpanzee temporal cortex showed a strong resemblance
to that of the human brain, providing some insight into the specialization of the two species’ shared lineage.
Neuroimaging tools such as magnetic resonance imaging (MRI) allow us to study whole-brain organization in species which
can otherwise not be studied. Here, we used diffusion MRI to reconstruct the connections of the cortical hemispheres of the
chimpanzee. This allowed us to perform an exploratory analysis of the grey matter structures of the chimpanzee cerebral
cortex and their underlying white matter connectivity profiles. We identified a number of networks that strongly resemble
those found in other primates, including the corticospinal system, limbic connections through the cingulum bundle and fornix,
and occipital–temporal and temporal–frontal systems. Notably, chimpanzee temporal cortex showed a strong resemblance
to that of the human brain, providing some insight into the specialization of the two species’ shared lineage.
set. These sequences included representatives of the following 8 subspecies: S. n. bachmani, S. n. cinereus, S. n. limitis, S. n. ludovicianus, S. n. niger, S. n. rufiventer, S. n. subauratus, and S. n. vulpinus. The compiled data set of 258 individuals belonging to 8 subspecies yielded 125 unique haplotypes, indicating extremely high levels of diversity in the control region. Several tree-based methods recovered two distinct shallow clades which do not correspond to geographic regions or subspecies. A parsimony-based minimum spanning network revealed two haplotype clusters which correspond to the two clades found in the tree-based methods. The haplotypes are closely linked in a star- shaped phylogenetic network; several of the most frequent haplotypes were internal, while the majority were unique to single populations and presented distal positions in the network. Overall there was a lack of genetic structure amongst populations with most of the variance explained by within population genetic diversity. Despite poor branch support, the congruent recovery of the two S. niger clades via both clustering-based and optimality criterion-based methods supports the separation of haplotypes into two major haplogroups. These results indicate that the currently recognized subspecies based on alpha taxonomic characters are not concordant with the mitochondrial history of S. niger. Instead, my findings suggest that the control region haplotype distribution in fox squirrels may be the result of repeated and rapid habitat expansions/retractions during glacial events in the Pleistocene. The shallow divergence between haplotypes across wide geographic distances suggest that the patterns of morphological and ecological differentiation the we observe within S. niger may have occurred much more recently than previously thought.
Radboud University, Nijmegen, The Netherlands
March 6 and 7 2023