Scott Grafton

Scott Grafton
University of California, Santa Barbara | UCSB · Department of Psychological and Brain Sciences

About

426
Publications
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43,090
Citations

Publications

Publications (426)
Poster
Full-text available
Individuals with Parkinson’s Disease (PD) may experience paradoxical kinesia (PK), the ability to temporarily overcome bradykinesia and display relatively normal motor functioning. This occurs despite the known detrimental impact of PD on the closed loop circuit (CLC) motor network through the dorsal putamen and basal ganglia. Anatomical evidence s...
Article
As evidence mounts that the cardiac-sympathetic nervous system reacts to challenging cognitive settings, we ask if these responses are epiphenomenal companions or if there is evidence suggesting a more intertwined role of this system with cognitive function. Healthy male and female human participants performed an approach-avoidance paradigm, tradin...
Preprint
Full-text available
Human movement is partly organized and executed by cortico-basal ganglia-thalamic closed-loop circuits (CLCs), wherein motor cortical areas both send inputs to and receive feedback from the basal ganglia, particularly the dorsal putamen (PUTd). These networks are compromised in Parkinson’s disease (PD) due to neurodegeneration of dopaminergic input...
Article
Full-text available
Objective The corticospinal tract (CST) is considered the most important motor output pathway comprising fibers from the primary motor cortex (M1) and various premotor areas. Damage to its descending fibers after stroke commonly leads to motor impairment. While premotor areas are thought to critically support motor recovery after stroke, the functi...
Article
Full-text available
Cyclic fluctuations in hypothalamic–pituitary–gonadal axis (HPG‐axis) hormones exert powerful behavioral, structural, and functional effects through actions on the mammalian central nervous system. Yet, very little is known about how these fluctuations alter the structural nodes and information highways of the human brain. In a study of 30 naturall...
Preprint
Humans ubiquitously increase the speed of their movements when motivated by incentives (i.e., capturing reward or avoiding loss). The complex interplay between incentivization and motor output is pertinent for unpacking the functional profiles of different circuits that link the basal ganglia with motor cortical areas. Here, we analyzed the functio...
Poster
Full-text available
People with Parkinson’s Disease (PD) experience bradykinesia (slowness of movement) due to the degradation of substantia nigra dopaminergic input to dorsal putamen (dPut), components of the classic closed loop motor circuit (CLC). Despite this, some can overcome their bradykinesia during moments of emotional arousal, a phenomenon known as paradoxic...
Preprint
Full-text available
The majority of motor recovery occurs within the first weeks after stroke and has been hypothesized to rely on similar mechanisms as motor learning. However, it remains unknown whether acute stroke patients are capable of error-based motor adaptation learning and, if so, whether such learning may be enhanced by reinforcement feedback. Here, we show...
Article
Full-text available
Active reinforcement learning enables dynamic prediction and control, where one should not only maximize rewards but also minimize costs such as of inference, decisions, actions, and time. For an embodied agent such as a human, decisions are also shaped by physical aspects of actions. Beyond the effects of reward outcomes on learning processes, to...
Article
Full-text available
Diffusion Spectrum Imaging (DSI) using dense Cartesian sampling of q ‐space has been shown to provide important advantages for modeling complex white matter architecture. However, its adoption has been limited by the lengthy acquisition time required. Sparser sampling of q ‐space combined with compressed sensing (CS) reconstruction techniques has b...
Article
Full-text available
There are known individual differences in both the ability to learn the layout of novel environments and the flexibility of strategies for navigating known environments. However, it is unclear how navigational abilities are impacted by high-stress scenarios. Here we used immersive virtual reality (VR) to develop a novel behavioral paradigm to exami...
Article
Head motion correction is particularly challenging in diffusion‐weighted MRI (dMRI) scans due to the dramatic changes in image contrast at different gradient strengths and directions. Head motion correction is typically performed using a Gaussian Process model implemented in FSL's Eddy. Recently, the 3dSHORE‐based SHORELine method was introduced th...
Preprint
Full-text available
As evidence mounts that the cardiac-sympathetic system reacts to challenging cognitive settings, we ask if these responses are passive companions or if they are instead fundamentally intertwined with cognitive function. Healthy human participants performed an approach-avoidance paradigm, trading off monetary reward for painful electric shock, while...
Preprint
Full-text available
Cyclic fluctuations in hypothalamic-pituitary-gonadal axis (HPG-axis) hormones exert powerful behavioral, structural, and functional effects through actions on the mammalian central nervous system. Yet, very little is known about how these fluctuations alter the structural nodes and information highways of the human brain. In a study of 30 naturall...
Article
We describe methods and software resources for a bioimpedance measurement technique, 'trans-radial electrical bioimpedance velocimetry' (TREV) that allows for the non-invasive monitoring of relative cardiac contractility and stroke volume. After reviewing the relationship between the measurement and cardiac contractility, we describe the general re...
Article
Full-text available
Tractography can generate millions of complex curvilinear fibers (streamlines) in 3D that exhibit the geometry of white matter pathways in the brain. Common approaches to analyzing white matter connectivity are based on adjacency matrices that quantify connection strength but do not account for any topological information. A critical element in neu...
Article
Objective: While ample evidence highlights that the ipsilesional corticospinal tract (CST) plays a crucial role in motor recovery after stroke, studies on cortico-cortical motor connections remain scarce and provide inconclusive results. Given their unique potential to serve as structural reserve enabling motor network reorganization, the question...
Preprint
Full-text available
We present ReTrace, a novel graph matching-based topological evaluation and validation method for tractography algorithms. ReTrace uses a Reeb graph whose nodes and edges capture the topology of white matter fiber bundles. We evaluate the performance of 96 algorithms from the ISMRM Tractography Challenge and the the standard algorithms implemented...
Article
Full-text available
Network neuroscience provides important insights into brain function by analyzing complex networks constructed from diffusion Magnetic Resonance Imaging (dMRI), functional MRI (fMRI) and Electro/Magnetoencephalography (E/MEG) data. However, in order to ensure that results are reproducible, we need a better understanding of within- and between-subje...
Article
Full-text available
Heuristics can inform human decision making in complex environments through a reduction of computational requirements (accuracy-resource trade-off) and a robustness to overparameterisation (less-is-more). However, tasks capturing the efficiency of heuristics typically ignore action proficiency in determining rewards. The requisite movement paramete...
Preprint
Full-text available
Diffusion Spectrum Imaging (DSI) using dense Cartesian sampling of q-space has been shown to provide important advantages for modeling complex white matter architecture. However, its adoption has been limited by the lengthy acquisition time required. Sparser sampling of q-space combined with compressed sensing (CS) reconstruction techniques has bee...
Article
Full-text available
Humans show remarkable habituation to aversive events as reflected by changes of both subjective report and objective measures of stress. Although much experimental human research focuses on the effects of stress, relatively little is known about the cascade of physiological and neural responses that contribute to stress habituation. The cold press...
Conference Paper
We present ReTrace, a novel graph matching-based topological evaluation and validation method for tractography algorithms. ReTrace uses a Reeb graph whose nodes and edges capture the topology of white matter fiber bundles. We evaluate the performance of 96 algorithms from the ISMRM Tractography Challenge and the standard algorithms implemented in D...
Article
Full-text available
Anisotropy of descending motor pathways has repeatedly been linked to the severity of motor impairment following stroke-related damage to the corticospinal tract. Despite promising findings consistently tying anisotropy of the ipsilesional corticospinal tract to motor outcome, anisotropy is not yet utilized as a biomarker for motor recovery in clin...
Preprint
Full-text available
Objective While ample evidence highlights that the ipsilesional corticospinal tract (CST) plays a crucial role in motor recovery after stroke, very few studies have assessed cortico-cortical motor connections with inconclusive results. Given their unique potential to serve as structural reserve enabling motor network reorganization, the question ar...
Poster
Full-text available
The human brain must constantly integrate its decision-making, motor planning, and action execution systems in order to seamlessly navigate, achieve goals, and earn reward. How these system interactions are encoded in the brain in preparation for the execution of complex action sequences has not been well explored. Furthermore, differences in motor...
Preprint
Correcting head motion artifacts in diffusion-weighted MRI (dMRI) scans is particularly challenging due to the dramatic changes in image contrast at different gradient strengths and directions. Head motion correction is typically performed using a Gaussian Process model implemented in FSL’s Eddy. Recently, the 3dSHORE-based SHORELine method was int...
Article
Full-text available
The model-free algorithms of "reinforcement learning" (RL) have gained clout across disciplines, but so too have model-based alternatives. The present study emphasizes other dimensions of this model space in consideration of associative or discriminative generalization across states and actions. This "generalized reinforcement learning" (GRL) model...
Preprint
Increasing insight into the complex human response to external states can be captured by measuring event-related cardiac sympathetic activity. However existing assays are either confounded by influence from other branches of the autonomic system, or require preprocessing steps that eliminate moment-to-moment capture of fluctuation. We accordingly t...
Preprint
The electrocardiogram (ECG) and impedance cardiography (ICG) are typically combined to estimate electromechanical features such as the pre-ejection period (PEP) and left ventricular ejection time (LVET); indicators of changes in the cardiac specific drive of the autonomic nervous system (ANS). Current methods of ICG are time intensive in subject pr...
Preprint
Full-text available
Anisotropy of descending motor pathways has repeatedly been linked to the severity of motor impairment following stroke-related damage to the corticospinal tract (CST). Despite promising findings consistently tying anisotropy of the ipsilesional CST to motor outcome, anisotropy is not yet utilized as a biomarker for motor recovery in clinical pract...
Preprint
Full-text available
Network analysis provides new and important insights into the function of complex systems such as the brain by examining structural and functional networks constructed from diffusion Magnetic Resonance Imaging (dMRI), functional MRI (fMRI) and Electro/Magnetoencephalography (E/MEG) data. Although network models can shed light on cognition and patho...
Article
Full-text available
Introduction: An accurate prediction of motor impairment from lesion information after stroke remains challenging, highlighting the complexity of structure-function relationships. While corticospinal tract (CST) integrity has been shown to correlate with motor impairment after stroke1, far less is known about the functional relevance of cortico-cor...
Article
Introduction: Motor recovery after stroke relies on reorganization processes that mainly occur within the critical period, a time-limited window of heightened neuronal plasticity in the first few weeks after stroke¹. These processes are assumed to partly depend on training-dependent motor learning, which may assist in establishing new motor control...
Article
Introduction: Structural changes post-stroke have frequently been assessed using diffusion tensor imaging (DTI). While the microstructural integrity of various parts of the corticospinal tract (CST) has been linked to motor impairment¹, it remains unclear whether the reduction in anisotropy can be attributed to descending or crossing fibers within...
Poster
Full-text available
Each day, we make countless decision-driven actions in order to achieve our goals and receive rewards. While the brain regions involved in motor planning and action selection are well-recognized, it is unclear how these activations vary across individual decision-making strategies. We designed a 360-trial fMRI task where each trial asks participant...
Preprint
Full-text available
Heuristics can inform human decision making in complex environments through a reduction of computational requirements (accuracy-resource trade-off) and a robustness to overparameterisation (less-is-more). However, tasks capturing the efficiency of heuristics typically ignore action proficiency in determining rewards. The requisite movement paramete...
Preprint
Full-text available
Tractography generates billions of complex curvilinear fibers (streamlines) in 3D that exhibit the geometry of white matter pathways. Analysis of raw streamlines on such a large scale is time-consuming and intractable. Further, it is well known that tractography computations produce noisy streamlines, and this in turn severely affect their use in s...
Article
Influential theories of skilled action posit that distinct cognitive mechanisms and neuroanatomic substrates support meaningless gesture imitation and tool use pantomiming, and poor performance on these tasks are hallmarks of limb apraxia. Yet prior research has primarily investigated brain-behavior relations at the group level; thus, it is unclear...
Preprint
Full-text available
Influential theories of skilled action posit that distinct cognitive mechanisms and neuroanatomic substrates support meaningless gesture imitation and tool use pantomiming, and poor performance on these tasks are hallmarks of limb apraxia. Yet prior research has primarily investigated brain-behavior relations at the group level; thus, it is unclear...
Preprint
Full-text available
This is an MRI acquisition sequence used to examine resting-state functional connectivity of open and closed loop motor circuits in healthy controls and those with Parkinson’s Disease. Scans include a Localizer, anatomical T1 MPRAGE, CMRR spin-echo AP and PA echo-planar imaging (EPI) images for field map generation, and a modified CMRR multi-echo E...
Poster
Full-text available
Fractional anisotropy (FA), a measure commonly used to quantify white matter (WM) structural integrity, is known to be sensitive to fiber orientation dispersion. Diffusion-based q-space trajectory encoding (QTE) imaging allows led to the estimation of parameters that describe diffusion tensor size, shape, and orientation (Topgaard, 2017). Independe...
Article
Full-text available
How does the brain change during learning? In functional magnetic resonance imaging studies, both multivariate pattern analysis and repetition suppression (RS) have been used to detect changes in neuronal representations. In the context of motor sequence learning, the two techniques have provided discrepant findings: pattern analysis showed that on...
Article
Full-text available
Diffusion-weighted magnetic resonance imaging (dMRI) is the primary method for noninvasively studying the organization of white matter in the human brain. Here we introduce QSIPrep, an integrative software platform for the processing of diffusion images that is compatible with nearly all dMRI sampling schemes. Drawing on a diverse set of software s...
Preprint
Video editing tools are widely used nowadays for digital design. Although the demand for these tools is high, the prior knowledge required makes it difficult for novices to get started. Systems that could follow natural language instructions to perform automatic editing would significantly improve accessibility. This paper introduces the language-b...
Poster
Full-text available
Decision making is the process of assessing the subjective value (SV) of available choices and subsequently selecting actions that maximize reward while minimizing personal cost. This process is often assessed through approach-avoidance tasks, where participants are asked to choose whether to approach or avoid an offer based on their evaluation of...
Article
Full-text available
Anxiety is characterized by low confidence in daily decisions, coupled with high levels of phenomenological stress. Ventromedial prefrontal cortex (vmPFC) plays an integral role in maladaptive anxious behaviors via decreased sensitivity to threatening vs. non-threatening stimuli (fear generalization). vmPFC is also a key node in approach-avoidance...
Conference Paper
Full-text available
Precise measurement of physiological signals is critical for the effective monitoring of human vital signs. Recent developments in computer vision have demonstrated that signals such as pulse rate and respiration rate can be extracted from digital video of humans, increasing the possibility of contact-less monitoring. This paper presents a novel ap...
Article
Full-text available
The cerebellum contains the vast majority of neurons in the brain and houses distinct functional networks that constitute at least two homotopic maps of cerebral networks. It is also a major site of sex steroid hormone action. While the functional organization of the human cerebellum has been characterized, the influence of sex steroid hormones on...
Preprint
Full-text available
Precise measurement of physiological signals is critical for the effective monitoring of human vital signs. Recent developments in computer vision have demonstrated that signals such as pulse rate and respiration rate can be extracted from digital video of humans, increasing the possibility of contact-less monitoring. This paper presents a novel ap...
Chapter
Vision-and-Language Navigation (VLN) is a task where agents must decide how to move through a 3D environment to reach a goal by grounding natural language instructions to the visual surroundings. One of the problems of the VLN task is data scarcity since it is difficult to collect enough navigation paths with human-annotated instructions for intera...
Chapter
Assessing the effects of white matter (WM) lesions on structural connectivity as measured by diffusion MRI (dMRI) is invaluable for understanding structure-function relationships. These WM lesions have many etiologies that ultimately lead to attenuation of the anisotropic signature in dMRI signals. Attenuation can produce inaccurate reconstructions...
Article
Full-text available
Humans are seamless in their ability to efficiently and reliably generate fingertip forces to gracefully interact with objects. Such interactions rarely end in awkward outcomes like spilling, crushing, or tilting given advanced motor planning. Here we combine multiband imaging with deconvolution- and Bayesian pattern component modeling of functiona...
Preprint
White matter microstructure underpins cognition and function in the human brain through the facilitation of neuronal communication, and the non-invasive characterization of this structure remains a research frontier in the neuroscience community. Efforts to assess white matter microstructure, however, are hampered by the sheer amount of information...
Article
Full-text available
Sex steroid hormones have been shown to alter regional brain activity, but the extent to which they modulate connectivity within and between large-scale functional brain networks over time has yet to be characterized. Here, we applied dynamic community detection techniques to data from a highly sampled female with 30 consecutive days of brain imagi...
Preprint
Full-text available
Diffusion-weighted magnetic resonance imaging (dMRI) has become the primary method for non-invasively studying the organization of white matter in the human brain. While many dMRI acquisition sequences have been developed, they all sample q-space in order to characterize water diffusion. Numerous software platforms have been developed for processin...
Preprint
How does the brain change during learning? In functional magnetic resonance imaging studies, both multivariate pattern analysis and repetition suppression (RS) have been used to detect changes in neuronal representations. In the context of motor sequence learning, the two techniques have provided discrepant findings: pattern analysis showed that on...
Article
Full-text available
Producing a tool use gesture is a complex process drawing upon the integration of stored knowledge of tools and their associated actions with sensory-motor mechanisms supporting the planning and control of hand and arm actions. Understanding how sensory-motor systems in parietal cortex interface with semantic representations of actions and objects...
Article
Both artificial and biological controllers experience errors during learning that are probabilistically distributed. We develop a framework for modeling distributions of errors and relating deviations in these distributions to neural activity. The biological system we consider is a task where human subjects are required to learn to minimize the rol...
Article
Full-text available
The brain is an endocrine organ, sensitive to the rhythmic changes in sex hormone production that occurs in most mammalian species. In rodents and nonhuman primates, estrogen and progesterone’s impact on the brain is evident across a range of spatiotemporal scales. Yet, the influence of sex hormones on the functional architecture of the human brain...
Article
Full-text available
The rhythmic production of sex steroid hormones is a central feature of the mammalian endocrine system. In rodents and nonhuman primates, sex hormones are powerful regulators of hippocampal subfield morphology. However, it remains unknown whether intrinsic fluctuations in sex hormones alter hippocampal morphology in the human brain. In a series of...
Preprint
Full-text available
Sex steroid hormones have been shown to alter regional brain activity, but the extent to which they modulate connectivity within and between large-scale functional brain networks over time has yet to be characterized. Here, we applied dynamic community detection techniques to data from a highly sampled female with 30 consecutive days of brain imagi...
Article
Full-text available
Anticipatory force control is a fundamental means by which humans stave off slipping, spilling, and tilting disasters while manipulating objects. This control must often be adapted due to changes in an object’s dynamics (e.g. a lighter than expected mug of coffee) or its relation with involved effectors or digits (e.g. lift a mug with three vs. fiv...
Conference Paper
Full-text available
Although diffusion-weighted magnetic resonance imaging (dMRI) can take many forms, they all sample q-space in order to characterize water diffusion. Numerous pipelines and software platforms have been built for processing dMRI data, but most work on only a subset of sampling schemes, or implement only parts of the processing workflow. Comparisons a...
Preprint
Full-text available
The cerebellum contains the vast majority of neurons in the brain and houses distinct functional networks that constitute at least two homotopic maps of the cerebrum. While the functional organization of the human cerebellum has been characterized, the influence of sex steroid hormones on intrinsic cerebellar network dynamics has yet to be establis...
Article
Full-text available
Appraising sequential offers relative to an unknown future opportunity and a time cost requires an optimization policy that draws on a learned estimate of an environment’s richness. Converging evidence points to a learning asymmetry, whereby estimates of this richness update with a bias toward integrating positive information. We replicate this bia...
Preprint
Full-text available
Producing a tool use gesture is a complex process drawing upon the integration of stored knowledge of tools and their associated actions with sensory-motor mechanisms supporting the planning and control of hand and arm actions. Understanding how sensory-motor systems in parietal cortex interface with semantic representations of actions and objects...
Article
Full-text available
Two fundamental goals of decision making are to select actions that maximize rewards while minimizing costs and to have strong confidence in the accuracy of a judgment. Neural signatures of these two forms of value: the subjective value (SV) of choice alternatives and the value of the judgment (confidence), have both been observed in ventromedial p...