Biology subjects

Kaas, J. H.

Publications and source records attributed to Kaas, J. H..

7 recordsLinked to original sources

bioRxiv2026

Somatotopic Organization of the Ventroposterior Nucleus of the Thalamus in Macaque Monkeys with Dorsal Spinal Cord Injuries Sustained During Early Postnatal Development

Injuries to peripheral nerves or the spinal cord lead to changes in the topographic organization in the brain at multiple levels along the sensory pathways. In adult monkeys large-scale deafferentations due to transection of the dorsal columns of the spinal cord at cervical levels result in large-scale reorganizations such that the deafferented neurons in the hand representation of somatosensory cortical area 3b start responding to anatomically distant body parts such as the chin. However, reorganization following dorsal column injuries depends upon the age at the time of the injury. The somatotopy of areas 3b, 1 and 2 in macaque monkeys with injuries sustained on or before postnatal day (PND) 5 is very normal-like. Whereas in monkeys with injuries sustained between PND9 and PND12, a large extent of the deafferented somatosensory cortex remains unresponsive to peripheral touch, with neurons at only a few sites responding to touch on the face or arm. Here we determined the organization of the ventroposterior nucleus (VPN) of the thalamus in four of these monkeys (Macaca radiata, 3 females, 1 male) that received lesions of the dorsal columns on PND 3, 5 and 9. We show that the nature of reorganization of VPN largely resembles that of the somatosensory cortex. Somatotopy is normal-like after lesions on PND3 and 5, whereas after lesion on PND9, the deprived neurons are largely unresponsive to peripheral touch, with a limited expansion of the chin representation.

neuroscience↗

bioRxiv2026

Separable neuronal and glial correlates of visual acuity and lifespan in mammalian primary visual cortex

Visual acuity spans more than a 100-fold range in mammals and yet the neural correlates of this perceptual gradient has not been fully evaluated. Furthermore, even though the known derived features of the human brain include specific changes to the cerebral cortex and the visual system in particular, no evolution of developing life histories approach has been quantitatively applied to metrics of cell composition. In this study, we present stereological estimates of neuron and glia density in V1 and granular layer 4 in a comparative sample of primates. We then integrate these data with the literature to construct a larger comparative dataset to test for phylogenetic relationships in mammalian visual system organization. Our examination revealed a primary relationship between acuity and neuron number along with secondary relationships among cell types tied to metabolic maintenance and support across the lifespan. Retinal metabolics along with phylogenetic position accounts for a large amount of V1 neuron density, which are further related to acuity while glia are related to longevity. These results identify a dissociation in the evolutionary developmental organization and senescence of V1 that map onto first principal parameters to explore the phylogenetic position and ecological pressures acting on the mammalian visual system. In accord with the literature, humans are revealed as outliers in glial support of neuronal metabolism across the lifespan. These findings provide evidence that mammalian visual cortex varies along at least two partially separable cellular dimensions in which visual resolution differs from lifelong maintenance. Summary and SignificanceIf the cellular organization of visual cortex is shaped by a single constraint or multiple independent pressures is debated. We used stereology to test whether V1 neurons and glia make separable contributions to visual performance across the mammal lifespan. V1 neuron density, together with brain size, predicts visual acuity. The glia-to-neuron ratio is alternatively associated with maximum lifespan after controlling for neuron density. Humans and chimpanzees have nearly identical V1 neuron densities, yet humans appear show substantially elevated glial investment across the literature. These findings suggest that mammalian visual cortex evolves under at least two partially separable pressures with neuron density and spatial resolution on one hand and glia investment to sustain function across life on the other.

neuroscience↗

bioRxiv2026

Anatolution, an online platform for consensus morphology

IntroductionSupervised statistical learning for cell-level segmentation and morphometry in optical microscopy is limited less by algorithmic capacity than by the scarcity of reliable, expert-validated ground truth. In comparative neuroscience and quantitative histology, where classical stains such as Nissls method remain the primary means to study cellular morphology, this bottleneck is acute: manual annotation is expensive, subject to individual bias, and rarely performed at the scale or consistency that computational approaches demand. No existing platform integrates a stain-specific bioimage segmentation protocol, a structured multi-annotator workflow, and consensus-based quality control into a single pipeline from image ingestion to machine-readable training data. MethodsWe present Anatolution, an open-source, web-based platform designed to address the gap of quality annotations at https://anatolution.herokuapp.com/public-tool/. Anatolution organizes microscopy images, including 2D arrays or 3D volumes, into project workspaces where multiple annotators independently label cellular structures against a shared computer vision catalogue. This design enables systematic inter-rater and intra-rater reliability assessment, with consensus derived from agreement across annotators rather than from any single experts judgment. The platform enables the export of aggregated labels or annotation datasets for downstream statistical learning methods. We describe the systems architecture, its Nissl-specific segmentation pipeline, the consensus annotation workflow, and validation of inter-rater reliability. ConclusionAcross 20+ histological annotation containers annotated by up to 15 independent raters, consensus boundary agreement increased monotonically with annotator count, reaching a median Dice of 0.79 against the full-rater reference at seven annotators, with top-tier containers achieving leave-one-out ceiling values of 0.621-0.769 for cell-body segmentation. The segmentation pipeline provided effective spatial anchoring, with 88% of consensus-annotated polygons containing at least one algorithmically detected seed. Anatolution provides open-source infrastructure for producing consensus-validated training data from classical histological preparations, addressing the primary bottleneck limiting supervised learning for cell-level morphometry.

neuroscience↗

bioRxiv2025

Connections of early visual areas with posterior parietal and temporal cortex in galagos, a strepsirrhine primate

To better understand the cortical connections and organization of visual areas in galagos, we examined the interconnections among cortical visual fields and their relationships with posterior parietal cortex (PPC) and temporal regions associated with dorsal and ventral streams of visual processing. In five galagos, two to four distinguishable tracers were injected into different visual areas, allowing direct comparison of connection patterns within the same cases. To reveal distributions of labeled neurons for each injection, labeled cells were plotted from serial brain sections cut parallel to the flattened cortical surface and summed across sections to generate surface reconstructions. Alternate sections processed for cytoarchitectonic features were used to identify cortical borders, especially those of V1 and middle temporal visual area (MT). Overall, our results support the conclusion that regions of V2 and V3 represent the contralateral visual hemifield in parallel with V1 and with each other. However, dorsal V3, representing the lower visual hemifield, includes at least one discontinuity where representations of the upper visual field extend to the dorsal border of V2. This portion of V3 appears to belong to the dorsomedial visual area (DM), which extends rostrally from V2 into PPC. The dorsal part of the DL-V4 region receives projections from other parts of dorsolateral visual area (DL), central V1, V2 and V3, inferotemporal (IT) cortex, the MT complex, and PPC regions surrounding the intraparietal sulcus (IPS). More central portions of DL-V4 receive inputs from central representations of V1, V2, and V3, as well as from PPC regions lateral to the IPS, the MT complex, and upper IT cortex. The ventral part of DL receives projections from central V2, caudal PPC adjoining DM and ventral PPC, and from IT cortex. These patterns indicate that the DL-V4 region serves as a major node linking dorsal and ventral streams and likely includes more than one functionally distinct visual area. In addition, areas MT and DM show strong reciprocal connections with PPC, while the connections of IT cortex indicate that much of this region is visual in nature having strong connections with higher order visual areas and it is composed of multiple functionally specialized visual domains. Key pointsO_LIOrganization of the visual cortex in galagos is much like that in New World and Old Word monkeys. C_LIO_LIPatterns of cortical connections of early visual areas V1 and V2 support the view that dorsal V3 has a gap in the representation of the lower visual field that is occupied by the proposed dorsomedial visual area (DM). C_LIO_LIVisual areas DM and middle temporal visual area (MT) provide the major visual inputs to posterior parietal cortex (PPC) of the dorsal stream of visual processing for actions. C_LI

neuroscience↗

bioRxiv2024

The laminar organization of cell types in macaque cortex and its relationship to neuronal oscillations

The canonical microcircuit (CMC) has been hypothesized to be the fundamental unit of information processing in cortex. Each CMC unit is thought to be an interconnected column of neurons with specific connections between excitatory and inhibitory neurons across layers. Recently, we identified a conserved spectrolaminar motif of oscillatory activity across the primate cortex that may be the physiological consequence of the CMC. The spectrolaminar motif consists of local field potential (LFP) gamma-band power (40-150 Hz) peaking in superficial layers 2 and 3 and alpha/beta-band power (8-30 Hz) peaking in deep layers 5 and 6. Here, we investigate whether specific conserved cell types may produce the spectrolaminar motif. We collected laminar histological and electrophysiological data in 11 distinct cortical areas spanning the visual hierarchy: V1, V2, V3, V4, TEO, MT, MST, LIP, 8A/FEF, PMD, and LPFC (area 46), and anatomical data in DP and 7A. We stained representative slices for the three main inhibitory subtypes, Parvalbumin (PV), Calbindin (CB), and Calretinin (CR) positive neurons, as well as pyramidal cells marked with Neurogranin (NRGN). We found a conserved laminar structure of PV, CB, CR, and pyramidal cells. We also found a consistent relationship between the laminar distribution of inhibitory subtypes with power in the local field potential. PV interneuron density positively correlated with gamma (40-150 Hz) power. CR and CB density negatively correlated with alpha (8-12 Hz) and beta (13-30 Hz) oscillations. The conserved, layer-specific pattern of inhibition and excitation across layers is therefore likely the anatomical substrate of the spectrolaminar motif. Significance StatementNeuronal oscillations emerge as an interplay between excitatory and inhibitory neurons and underlie cognitive functions and conscious states. These oscillations have distinct expression patterns across cortical layers. Does cellular anatomy enable these oscillations to emerge in specific cortical layers? We present a comprehensive analysis of the laminar distribution of the three main inhibitory cell types in primate cortex (Parvalbumin, Calbindin, and Calretinin positive) and excitatory pyramidal cells. We found a canonical relationship between the laminar anatomy and electrophysiology in 11 distinct primate areas spanning from primary visual to prefrontal cortex. The laminar anatomy explained the expression patterns of neuronal oscillations in different frequencies. Our work provides insight into the cortex-wide cellular mechanisms that generate neuronal oscillations in primates.

neuroscience↗

bioRxiv2023

Folding of the cerebellar cortex is clade-specific in form, but universal in degree

Like the cerebral cortex, the surface of the cerebellum is repeatedly folded. Unlike the cerebral cortex, however, cerebellar folds in a given brain are much thinner and more numerous; repeat themselves largely along a single direction, forming long strips transverse to the mid-sagittal plane, like an accordion; and occur in the smallest of cerebella, including those of lissencephalic mammals and non-mammal vertebrates. We have shown previously that while the location of folds in mammalian cerebral cortex is clade-specific, the overall degree of folding strictly follows a universal power law relating cortical thickness, and the exposed and total surface areas. This law is derived from a statistical-physics model for gyrification that postulates that folding results from the interplay between axonal elongation dynamics and the self-avoiding nature of the expanding cortical surfaces. Since both aspects are present in the cerebellum, we hypothesize that a similar relation across species also exists therein. Furthermore, given the modular organization of cerebellar architecture and circuitry, as well as the transverse orientation of the folia, it is plausible that this relation is reflected in the degree of folding of the mid-sagittal section of the cerebellum, which greatly facilitates analysis. Here we show that a strict universal scaling law does apply to the folding of the mid-sagittal sections of the cerebellum of 53 species belonging to six mammalian clades, spanning a large range of sizes and degrees of gyrification. This folding is hierarchical and can be explicitly separated into branching orders, such that position of the 1st-order folds is largely stereotypical across all mammals examined. Subsequent nth-order folds become progressively less stereotypical, and folding within such cerebellar subsections scales with power laws whose exponents decrease monotonically with branching order, converging to the exponents predicted by a two-dimensional version of the same gyrification model that describes cortical folding. We propose that the changes in scaling exponent with branching order occurs as increasing amounts of white matter are included in the folding volume of the cerebellum, reflecting the difference between the outside-in development of the cerebellar cortex around a preexisting core of already connected white matter, compared to the inside-out development of the cerebral cortex with a white matter volume that develops as the cerebral cortex itself gains neurons. Our data strongly indicate that the mammalian cerebellum folds as a multi-fractal object, emerging from the interplay between clade-specificity and universality, and between phylogenetical contingency and the physics of self-organization. Thus, repeated folding, one of the most recognizable features of biology, can arise simply from the universal applicability of physical principles, without the need for invoking selective pressures in evolution; and diversity arises within the constraints imposed by physics.

neuroscience↗

bioRxiv2022

Overall patterns of eye-specific retino-geniculo-cortical projections to layers III, IV and VI in primary visual cortex of the prosimian galago, and correlation with cytochrome oxidase blobs.

Studies in galago have not provided a comprehensive description of the organization of eye specific retino-geniculate-cortical projections to the recipient layers in V1. Here we demonstrate the overall patterns of ocular dominance domains in layers III, IV and VI revealed after injecting the transneuronal tracer wheat germ agglutinin conjugated to horseradish peroxidase (WGA- HRP) into one eye. We also correlate these patterns with the array of cytochrome oxidase (CO) blobs in tangential sections through the unfolded and flattened cortex. In layer IV, we observed for the first time that eye-specific domains form an interconnected pattern of bands 200-250 um wide arranged such that they do not show orientation bias and do not meet the V1 border at right angles, as is the case in macaques. We also observed distinct patterns of ocular dominance patches in layer III and layer VI. The patches in layer III, likely corresponding to patches of K LGN input described previously, align with layer IV ocular dominance columns (ODCs) of the same eye dominance. Moreover, the layer III patches overlap partially with virtually all CO blobs in both hemispheres, implying that CO blobs receive K LGN input from both eyes. Finally, we found that CO blobs straddle the border between neighboring layer IV ODCs. These results, together with studies showing that a high percentage of cells in CO blobs are monocular, suggest that CO blobs consist of ipsilateral and contralateral subregions that are in register with underlying layer IV ocular dominance columns of the same eye dominance. In macaques and humans, CO blobs are centered on ODCs in layer IV. Our finding that CO blobs in galago straddle the border of neighboring layer IV ODCs suggests that this may represent an alternative way by which visual information is processed by eye specific modular architecture in mammalian V1.

neuroscience↗