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Browsing by Author "Burzynska, Agnieszka, committee member"

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    An investigation into the formation of representational associations in visual category learning
    (Colorado State University. Libraries, 2017) Jentink, Kade Garrett, author; Seger, Carol, advisor; Rojas, Don, committee member; Burzynska, Agnieszka, committee member
    Category learning allows us to use previous information we have accumulated, and extend it to new situations. Multiple systems are proposed to underlie learning, including: an explicit, rule-based system, and an implicit, procedural system. Information integration tasks are thought to load heavily onto the latter. In these tasks, a high degree of accuracy is reached only if participants can integrate incommensurable dimensions, often without being able to verbally describe how they are categorizing each stimulus. Learning in this type of task is thought to occur as participants associate a given stimulus with a category label, and then that label to a motor response. The present study sought to examine whether there may be an additional associative stage in which a stimulus is first associated with a "category representation" – a representation of the critical characteristics of a given category – which is then associated with a category label. Two experiments were conducted which attempted to determine whether this form of category representation is learned in information integration tasks. Both experiments reversed the category representation – category label association for a subset of stimuli and tested if subjects would transfer this reversal to the remaining stimuli, as should happen if they learned to associate each label with a single abstract category representation. Experiment 1 trained subjects with two sets of labels, each of which was associated with the same abstract category representation, to see if reversing one set of labels would alter the other. Experiment 2 trained subjects with 1 set of labels and tested if learning to reverse half of the stimulus space would transfer to the remaining half. In addition, the consistency of category label and motor response associations were manipulated in Experiment 2, with the hypothesis that subjects learning under inconsistent mappings would be forced to learn category labels and be more likely form an abstract category representation, whereas subjects learning under consistent conditions might only learn basic stimulus – response associations. Subjects in Experiment 1 did not transfer the reversal to the second set of category labels, inconsistent with the hypothesis that subjects would form an abstract category representation. However, over half the subjects in Experiment 2 did transfer reversed category label associations to untrained stimuli. Furthermore, a greater number of subjects transferred the reversals in the Inconsistent mapping condition. This is the first study to present evidence suggesting the existence of an abstract category representation and to provide a unique dissociation between consistent and inconsistent mappings for an information-integration task.
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    Associations between gait coordination, variability and motor cortex inhibition in young and older adults
    (Colorado State University. Libraries, 2018) Swanson, Clayton W., author; Fling, Brett W., advisor; Lodha, Neha, committee member; Burzynska, Agnieszka, committee member
    Interlimb coordination and mobility (postural sway and turning) diminish with age, posing a risk for gait-related injuries. Further, levels of inhibition within the motor cortex are significantly associated with coordination of the upper extremities in healthy aging, however, it is unknown if this same association exists for lower extremity control. To investigate the relationship between gait coordination and cortical inhibition we measured gait coordination via the phase coordination index and motor cortex inhibition via the cortical silent period in 14 young and 15 older adults. Gait coordination was reduced in older adults across a variety of walking conditions, as was cortical inhibition, solely in the non-dominant motor cortex. Furthermore, young adults were better able to maintain lower extremity coordination and variability with reduced cortical inhibition, whereas older adults with increased cortical inhibition demonstrated better walking performance. These findings suggest a fundamental shift in the relationship between motor cortex inhibition and lower extremity control with age, similar to previous work demonstrating an age-related difference in the association between motor cortex inhibition with bimanual control.
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    Cue competition and feature representation in a category learning task: an fMRI study
    (Colorado State University. Libraries, 2023) Jentink, Kade, author; Seger, Carol, advisor; Burzynska, Agnieszka, committee member; Rojas, Don, committee member; Thomas, Michael, committee member
    During learning, attention is limited, and therefore selecting what feature(s) to attend to in the environment is important. Sometimes, attention is captured by a cue or feature in such a way that other cues or features are not attended to, known as overshadowing. This process is not entirely understood in category learning, with some studies suggesting that it enhances learning of other features (Murphy et al., 2017), while others suggest that it inhibits (Lau et al., 2020). Furthermore, the location and organization of the neural representations that develop for category features during overshadowing has not been previously examined in this context. The present experiment used representational similarity analyses (RSA), a method for interrogating representational structure (Kriegeskorte et al., 2008), in order to examine where and how features were represented during overshadowing in a category learning task. Participants completed a category learning task in which categories were defined based on two informative features, one binary and one continuous. The binary feature was easier to learn (i.e., more salient), and it was hypothesized that it would overshadow learning of the more difficult continuous feature. This was demonstrated behaviorally: participants learned to categorize when the binary feature was present, then performed at chance when it was removed in a transfer task. Three different hypothetical models were fit to the neural data to determine underlying representational structure: a binary category model, an effector-specific motor model, and a model representing the degree of perceptual similarity for the continuous feature. During initial learning when the primary binary feature was present, the category model fit data from both early visual and object-specific areas of visual cortex, while the motor model fit data from motor-related regions including primary somatomotor cortex and the cerebellum. The perceptual similarity model for the continuous feature did not fit any task data during either Training or Transfer. However, there was a trend for the category model to fit activity in the basal ganglia and lateral occipital complex (LOC) during the Transfer task when the only information available for categorization was the continuous feature. Taken together, these results suggest that, although overshadowing inhibits use of the overshadowed continuous feature as the basis of categorization behavior, it might still contribute to activation of neural representations of category membership.
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    Machine learning and deep learning applications in neuroimaging for brain age prediction
    (Colorado State University. Libraries, 2023) Vafaei, Fereydoon, author; Anderson, Charles, advisor; Kirby, Michael, committee member; Blanchard, Nathaniel, committee member; Burzynska, Agnieszka, committee member
    Machine Learning (ML) and Deep Learning (DL) are now considered as state-of-the-art assistive AI technologies that help neuroscientists, neurologists and medical professionals with early diagnosis of neurodegenerative diseases and cognitive decline as a consequence of unhealthy brain aging. Brain Age Prediction (BAP) is the process of estimating a person's biological age using Neuroimaging data, and the difference between the predicted age and the subject's chronological age, known as Delta, is regarded as a biomarker for healthy versus unhealthy brain aging. Accurate and efficient BAP is an important research topic, and hence ML/DL methods have been developed for this task. There are different modalities of Neuroimaging such as Magnetic Resonance Imaging (MRI) that have been used for BAP in the past. Diffusion Tensor Imaging (DTI) is an advanced quantitative Neuroimaging technology that gives insight into microstructure of White Matter tracts that connect different parts of the brain to function properly. DTI data is high-dimensional, and age-related microstructural changes in White Matter include non-linear patterns. In this study, we perform a series of analytical experiments using ML and DL methods to investigate the applicability of DTI data for BAP. We also investigate which Diffusivity Parameters, which are DTI metrics that reflect direction and magnitude of diffusion of water molecules in the brain, are relevant for BAP as a Supervised Learning task. Moreover, we propose, implement, and analyze a novel methodology that can detect age-related anomalies (high Deltas), and can overcome some of the major and fundamental limitations of the current supervised approach for BAP, such as "Chronological Age Label Inconsistency". Our proposed methodology, which combines Unsupervised Anomaly Detection (UAD) and supervised BAP, focuses on addressing a fundamental challenge in BAP which is how to interpret a model's error. Should a researcher interpret a model's error as an indication of unhealthy brain aging or the model's poor performance that should be eliminated? We argue that the underlying cause of this problem is the inconsistency of chronological age labels as the ground truth of the Supervised Learning task, which is the common basis of training ML/DL models. Our Unsupervised Learning methods and findings open a new possibility to detect irregularities and abnormalities in the aging brain using DTI scans, independent of inconsistent chronological age labels. The results of our proposed methodology show that combining label-independent UAD and supervised BAP provides a more reliable and methodical way for error analysis than the current supervised BAP approach when it is used in isolation. We also provide visualization and explanations on how our ML/DL methods make their decisions for BAP. Explainability and generalization of our ML/DL models are two important aspects of our study.
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    No association of leg strength asymmetry with walking performance, fatigability or fatigue in multiple sclerosis
    (Colorado State University. Libraries, 2018) Proessl, Felix, author; Rudroff, Thorsten, advisor; Fling, Brett, committee member; Burzynska, Agnieszka, committee member
    Background: One of the first signs of Multiple Sclerosis (MS) is weakness on one side of the body, which is associated with an increased reliance on the stronger leg during walking as indicated by asymmetric muscle activity. The role of leg strength asymmetry on walking performance, fatigue and fatigability is unknown in people with MS (PwMS). Objective: The purpose of this cross-sectional study was to determine whether leg strength asymmetry is associated with walking performance, objective measures of fatigability, or subjective perceptions of fatigue during a 6-minute walk test (6MWT). Methods: Maximal knee extensor strength was assessed in 19 PwMS, and a symmetry index was calculated based on the objectively defined more- and less-affected leg. Walking ability was determined by measuring the total distance covered during a 6MWT and fatigability by calculating the change in distance covered between minutes six and one. Perceptions of fatigue were assessed by obtaining ratings of perceived exertion (RPE) using the modified Borg 10-point scale during the first and the final minute of the 6MWT. Results: PwMS covered less distance (P=0.01) and perceived greater exertion (P<0.01) during minute six compared to minute one. Maximal knee extensor strength was different between the more- and less-affected side (P<0.01). The magnitude of asymmetry did not correlate with walking performance, fatigability, or perceptions of fatigue. Conclusions: Maximal knee extensor strength asymmetry may not play an important role in walking performance, fatigability or fatigue in PwMS. Future asymmetry studies should include the flexor muscles and measures of sensory function.
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    Residual effects of cannabis on attention toward and awareness of emotional facial expressions: event-related potential studies
    (Colorado State University. Libraries, 2018) Torrence, Robert D., author; Rojas, Donald C., advisor; Troup, Lucy J., advisor; Nerger, Janice, committee member; Burzynska, Agnieszka, committee member
    Cannabis use has increased since legalization in various states within the United States of America. Although much of the research on the neurological and psychological effects of cannabis has been on non-human animals, the current research suggests that it can have anxiolytic effects but also decrease some cognitive functioning (e.g. memory, emotional processing, etc.). Individuals with high anxiety has been suggested to have increased attentional bias towards threat-related stimuli. The purpose of the current two studies was to examine the residual effects cannabis has on attentional bias towards and awareness of emotional facial expressions. Both experiments used event-related potential (ERP) to measure brain activity related to attentional processing. Experiment 1 used a dot-probe task with fearful and neutral facial expression to examine attentional bias. The second experiment used a backward masking paradigm to restrict awareness of facial expressions (i.e. fearful, happy, and neutral). The results indicated that cannabis use was associated with differences in attentional processing. Specifically, experiment 1 suggested cannabis users had reduced attentional bias towards fearful facial expressions as compared to non-users. The results from experiment 2 suggested an opposite effect, cannabis users had increased processing of emotional facial expressions. An explanation of the difference in results is the cannabis users in experiment 1 used less frequently than users in experiment 2. The results of both studies suggested cannabis use has an inverse relationship with anxiety related attentional processing of emotional expressions.
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    The Association Between Occupational Complexity and White Matter in the Brain
    (Colorado State University. Libraries, 2024) Diaz, Jazmin, author; Thomas, Michael, advisor; Burzynska, Agnieszka, committee member; Davalos, Deana, committee member; Fisher, Gwenith, committee member
    Occupational complexity (OCC) refers to experiences that increase one's environmental stimulation in a job and provide greater opportunities for skill development. Understanding the association between OCC and brain white matter is critical in aging research as it can elucidate the potential protective effects of stimulating environments on brain health and shed light on strategies for preserving microstructural integrity as individuals age. The current study examines whether working a complex job is associated with white matter integrity, determined by fractional anisotropy (FA). Participants included 58 healthy adults aged 18-85 (M = 49.2, SD =21.7) who completed diffusion-weighted imaging scans and a subcategory of a validated work survey to assess OCC. A principal component analysis reduced the survey items to four meaningful constructs. Higher age was consistently associated with lower FA. Information processing was significantly associated with FA in the inferior longitudinal fasciculus. Additionally, a significant interaction between information processing and age in the forceps major suggests the effect of OCC on FA is dependent on age. These findings highlight that while OCC is associated with FA, its effects may vary by regions and age, pointing to a more nuanced relationship between work characteristics and brain health.
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    What's the matter with white matter? An evaluation of postural control mechanisms in multiple sclerosis
    (Colorado State University. Libraries, 2020) Richmond, Sutton B., author; Fling, Brett W., advisor; Peterson, Daniel, committee member; Leach, Heather, committee member; Burzynska, Agnieszka, committee member
    Interacting with environments that are constantly varying is difficult and, as bipedal mammals, keeping an upright posture requires a great deal of spatial and temporal acuity. The studies encompassing this doctoral dissertation provide mechanistic insight into the gait and balance of both neuro-typical and -atypical (i.e. people living with multiple sclerosis) adults to understand the neural underpinnings contributing to reduced locomotion and postural control, thereby increasing risks of falls and injury. Enhanced comprehension of the underlying mechanisms for postural control were attained through the abridgment of multiple scientific disciplines including biomechanics, neuromechanics, and neuroimaging to apply advanced concepts to identify biomarkers for future therapeutic interventions. The outcomes from this work demonstrate that, in comparison to neurotypical adults, the people with multiple sclerosis walked with a more conservative and asymmetric gait pattern regardless of speed or cognitive load. Poorer microstructural integrity of transcallosal sensorimotor white matter fiber tracts was strongly associated with these behavioral deficits, thereby establishing a structure-function relationship that comprised both static and dynamic postural control. Implications from this research provide a base of knowledge for how the brain successfully coordinates and controls movements, laying a foundation for future neurorehabilitation approaches that increase independence and overall quality of life.