Biology subjects

Schmahmann, J. D.

Publications and source records attributed to Schmahmann, J. D..

4 recordsLinked to original sources

bioRxiv2018

Functional specialization is independent of microstructural variation in cerebellum but not in cerebral cortex

The human brain is understood to follow fundamental principles linking form (such as microstructure and anatomical connectivity) to function (perceptual, motor, cognitive, emotional, and other processes). Most of this understanding is based on knowledge of the cerebral cortex, where functional specialization is thought to be closely linked to microstructural variation as well as anatomical connectivity. The Universal Cerebellar Transform (UCT) theory has posited that the cerebellum has a different form-function organization in which microstructure is uniform, and in which functional specialization is determined solely by anatomical connectivity with extracerebellar structures. All cerebellar functions may thus be subserved by a common microstructural - and hence computational - substrate. Here we tested this hypothesis by measuring microstructural variation and functional specialization as indexed by magnetic resonance imaging in 1003 healthy humans. Cerebral cortex exhibited the expected pattern of microstructure-function correlation, but functional specialization was independent of microstructural variation in the cerebellum. These findings support the idea that cerebellar functional specialization is not determined by microstructure, and hence that cerebellar functions may be computationally constant across domains.\n\nSIGNIFICANCE STATEMENTThe cerebellum is estimated to contain more than half the neurons in the human brain, is known to be involved in motoric, cognitive, and emotional functions, and is implicated in many neurological and neuropsychological disorders, but remains far less studied than the cerebral cortex. The Universal Cerebellar Transform (UCT) theory posits that one uniform computation underlies all cerebellar functions across multiple domains, but testing that idea has been difficult. Here we find that unlike the cerebral cortex, in which microstructural variation is associated with functional variation, the cerebellum exhibits relatively uniform microstructure across functionally distinct regions. These findings support UCT theory, and draw a sharp distinction between form-function relations in the cerebellum versus the cerebral cortex.

neuroscience↗

bioRxiv2018

LittleBrain: a gradient-based tool for the topographical interpretation of cerebellar neuroimaging findings

Gradient-based approaches to brain function have recently unmasked fundamental properties of brain organization. Diffusion map embedding analysis of resting-state fMRI data revealed a primary-to-transmodal axis of cerebral cortical macroscale functional organization. The same method was recently used to analyze resting-state data within the cerebellum, revealing for the first time a sensorimotor-fugal macroscale organization principle of cerebellar function. Cerebellar gradient 1 extended from motor to non-motor task-unfocused (default-mode network) areas, and cerebellar gradient 2 isolated task-focused processing regions. Here we present a freely available and easily accessible tool that applies this new knowledge to the topographical interpretation of cerebellar neuroimaging findings. LittleBrain generates scatterplots that illustrate the relationship between cerebellar data (e.g., volumetric patient study clusters, task activation maps, etc.) and cerebellar gradients 1 and 2. This novel method of data mapping provides alternative, gradual visualizations that complement discrete parcellation maps of cerebellar functional neuroanatomy. We present application examples to show that LittleBrain can also capture subtle, progressive aspects of cerebellar functional neuroanatomy that would be difficult to visualize using conventional mapping techniques. Download and use instructions can be found at https://xaviergp.github.io/littlebrain.

neuroscience↗

bioRxiv2018

Triple representation of language, working memory, social and emotion processing in the cerebellum: convergent evidence from task and seed-based resting-state fMRI analyses in a single large cohort

Delineation of functional topography is critical to the evolving understanding of the cerebellums role in a wide range of nervous system functions. We used data from the Human Connectome Project (n=787) to analyze cerebellar fMRI task activation (motor, working memory, language, social and emotion processing) and resting-state functional connectivity calculated from cerebral cortical seeds corresponding to the peak Cohens d of each task contrast. The combination of exceptional statistical power, activation from both motor and multiple non-motor tasks in the same participants, and convergent resting-state networks in the same participants revealed novel aspects of the functional topography of the human cerebellum. Consistent with prior studies there were two distinct representations of motor activation. Newly revealed were three distinct representations each for working memory, language, social, and emotional task processing that were largely separate for these four cognitive and affective domains. In most cases, the task-based activations and the corresponding resting-network correlations were congruent in identifying the two motor representations and the three non-motor representations that were unique to working memory, language, social cognition, and emotion. The definitive localization and characterization of distinct triple representations for cognition and emotion task processing in the cerebellum opens up new basic science questions as to why there are triple representations (what different functions are enabled by the different representations?) and new clinical questions (what are the differing consequences of lesions to the different representations?).\n\nHIGHLIGHTS- We analyzed motor and multiple nonmotor task fMRI activations in the cerebellum.\n- Resting-state seeds were placed at each task activation peak in the cerebral cortex.\n- We describe cerebellar task topography in the largest single cohort studied to date.\n- Nonmotor cerebellar task activation revealed a pattern of triple representation.\n- Resting-state analysis revealed an overlapping pattern of triple representation.

neuroscience↗

bioRxiv2018

Functional gradients of the cerebellum: a fundamental movement-to-thought principle

A central principle for understanding the cerebral cortex is that macroscale anatomy reflects a functional hierarchy from primary to transmodal processing. In contrast, the central axis of motor and nonmotor macroscale organization in the cerebellum remains unknown. Here we applied diffusion map embedding to resting-state data from the Human Connectome Project dataset (n=1003), and show for the first time that cerebellar functional regions follow a gradual organization which progresses from primary (motor) to transmodal (DMN, task-unfocused) regions. A secondary axis extends from task-unfocused to task-focused processing. Further, these two principal gradients reveal functional properties of the well-established cerebellar double motor representation, and its relationship with the recently described triple nonmotor representation. These interpretations are further supported by data-driven clustering and cerebello-cerebral functional connectivity analyses. Importantly, these descriptions remain observable at the individual subject level. These findings, from an exceptionally large and high-quality dataset, provide new and fundamental insights into the functional organization of the human cerebellum, unmask new testable hypotheses for future studies, and yield an unprecedented tool for the topographical, macroscale interpretation of cerebellar findings.

neuroscience↗