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Robust and Multimodal Signals for Language in the Brain
No full textAn impressive aspect of human language is its ability to maintain consistent meaning and grammatical correctness across different sensory modalities. Elucidating the modality-invariant internal representation of language in the brain has major implications for cognitive science, brain disorders, and artificial intelligence. A pillar of linguistic studies is the notion that words have defined functions, often referred to as parts of speech, such as nouns and adjectives. This dissertation tries to answer two questions: how can we find a multimodal and generalizable representation for language processing? Is there a representation for parts of speech in the brain?
To address these questions, I recorded neural responses from 1,801 electrodes in 20 participants with epilepsy while they were presented with two-word minimal phrases consisting of an adjective and a noun, in both auditory and visual presentations. I observed neural signals that distinguished between these two parts of speech (POS), localized within a small region in the left lateral orbitofrontal cortex. The representation of POS showed invariance across several criteria: visual and auditory presentation modalities, and robustness to word properties like length, order, frequency, and semantics. The results also generalized across two different languages in a bilingual participant. I found that these selective signals provide key elements for the compositional processes of language, highlighting a localized and invariant representation of POS. Furthermore, I extended these ideas by evaluating how parts of speech are processed within full sentences. Recording activity from 1,563 electrodes in 17 participants, I found neural signals that separated nouns from verbs in sentences. This selective, invariant, and localized representation of parts of speech provides key elements for the representation of language. Going beyond POS, I also found multimodal representations for grammar and syntax processing in sentences, a first with neurophysiological signals.
In conclusion, I collected and analyzed a dataset of over 60 hours of stimuli, 40,000 two-word phrases, and 15,000 sentences by recording neural responses to audiovisual stimuli from 3,394 stereo-electroencephalography electrode contacts across 37 participants. My findings report neural representations of language that are both robust and adaptable, contributing to a deeper understanding of core linguistic processes within the human brain. This work lays a foundation for more nuanced studies of language processing. To the best of my knowledge, this is the first study to rigorously and systematically evaluate the invariant representation of parts of speech and multimodal representations for semantic and grammatical processing of sentences at the invasive neurophysiological level from the human brain.Biophysic
Dignity and Indignation, Ancient and Modern: Plato’s Thumos and Rousseau’s Amour-propre
No full textThis dissertation is a study of a forgotten part of the human psyche, a part at the core of our political nature. Thumos was originally conceived by Plato as a third principle of the mind distinct from reason and desire, a principle responsible for the attachment to justice and courage. This principle was later reconceived and subjected to probing criticism by Jean-Jacques Rousseau under the name of amour-propre. Most simply, thumos and amour-propre are responsible for three related concerns: the desire to be honored or esteemed by others, the pride that reflects our own esteem for our comparative worth or dignity, and the indignation or anger that defends such dignity. These passions and their education pose fundamental problems for any political regime: for Rousseau, amour-propre was responsible for “what is best and worst among men,” for the “virtues” that make us political beings and for the most pathological of our “vices.”
The project has two aims. The first is to recover an understanding of this psychic principle through two thinkers who examined it in greatest depth and to offer an account of why it is widely neglected in contemporary political science. The second is to explain why Rousseau turned to Plato in his critique of the 18th-century Enlightenment: why is Plato the philosopher Rousseau cites the most throughout his writings? I argue that Rousseau recovered and repurposed the thought of Plato in his effort to understand what was pathological about the amour-propre of the “bourgeois,” the human type promoted by the modern Enlightenment. Rousseau drew from Plato a conception of the natural human being as an ideal or standard from which to judge political life and its pathologies. This standard for both thinkers was characterized by the undivided unity or wholeness of the human psyche. Rousseau criticized Enlightenment efforts to ground morality on a form of public esteem that placed individuals in contradiction with themselves, preventing the unity of the mind.
The project is focused on Rousseau’s Emile, or On Education (1762) and its response to Plato’s Republic. I situate these in a broader study of each thinker’s other political writings and their contexts, from the treatment of thumos in the poetry of Homer to the critique of amour-propre in the 17th-century French Augustinians who first adopted the term. On the whole, Plato proves to be a greater critic of thumos, and Rousseau a greater optimist about amour-propre, than they are widely taken to be. Plato’s apparent promotion of thumos as a motive for civic virtue is in fact accompanied by a critique of its tendency to divide the mind: thumos gives rise to contradictory opinions on morality that are only fully resolved in the Socratic vision of the philosophic life, the rare perfection or end of human nature. Conversely, Rousseau’s influential critique of bourgeois amour-propre is in fact accompanied by a characteristically Enlightenment optimism about the possibility of reshaping the passion, on the basis not of any highest end but of its simplest and most elemental roots, toward a form of morality that would avoid setting ordinary minds in contradiction with themselves. For Rousseau this unity of mind was the precondition for genuine self-rule in any individual. Rousseau’s optimism about the educable character of amour-propre is thus a neglected theoretical foundation for the democratic political theory that he took to a new height in the Enlightenment in spite of his return to the ancient Greeks.Governmen
The Wind Beneath My Wings: A story about love, guidance, and perseverance.
No full textThis story defines the meaning of love, guidance, and perseverance through the eyes of a young, ambitious caterpillar yearning for a sense of truth, belonging, and hope in a world designed to keep him from becoming a butterfly. The Wind Beneath My Wings is a metaphor for African Americans residing in troubled environments, with high aspirations of making something of themselves, while finding ways to simply survive in the process.
Hov, the protagonist, goes through a myriad of trials and tribulations as he approaches cocoon season. All he wants to do is learn how to spread his wings and fly. The narrative takes the reader on a journey through a day of Hov’s life, the meaningful encounters that come along the way, and an intriguing insight into his unique perspective, as he aims for transformation. Hov ultimately discovers that the journey is indeed the best part when searching for truth, purpose, and belonging.Extension Studie
Mechanical Controllers for Robotic Grippers
No full textThis thesis explores the definition, design, prototyping, testing, and analysis of a mechanical controller, which is a mechanical system designed to control a robotic gripper without the use of digital or electrical systems. The intention of developing such a system is to either 1) act in parallel with conventional digital systems that coordinate the movements of a robotic gripper to provide complementary control and safety features, or 2) serve as an alternative method for manipulation in scenarios where conventional systems may be limited. This task was accomplished through the development of a ”Force-Activated Clutch” that is able to simultaneously measure the forces acting on a gripper, monitor the gripper’s position, and manipulate the gripper’s degrees of freedom to achieve a desired movement. Two complete prototypes were developed over the course of this thesis, with the second prototype serving as the basis for all testing and verification. To accompany the second prototype, a computational optimization structure was built in MATLAB to constrain and define the mechanical system’s dimensions by processing 413,343 possible designs. In the end, the prototype did not meet the technical specifications; however, the theoretical design and the exercise of the mechanism in testing affirm the viability of a mechanical controller in robotic grippers.Mechanical Engineering S
Exploring the role of Spirituality in enhancing Brain Health among People Living with Epilepsy: A case study of Accra, Ghana.
No full textThis doctoral project investigated integrating spiritual care with clinical practices in Accra, Ghana, to improve epilepsy care and promote brain health (1), encompassing neurological and mental health aspects. Brain health service users, particularly those with epilepsy, often seek assistance from traditional or faith-based centers before turning to allopathic treatment. The research question guiding this project was: "What are the barriers and opportunities for fostering collaboration between spiritual leaders and clinicians to enhance epilepsy care and promote better brain health in Ghana?" Given the cultural significance of spirituality in Ghana, understanding the potential role of spiritual leaders in epilepsy care is crucial. Through qualitative interviews and surveys conducted with both spiritual leaders and clinicians in Accra, the project examined their perspectives on collaboration to identify key challenges and opportunities. The findings revealed that spiritual leaders were generally receptive to collaboration and express a willingness to undergo training on epilepsy first aid. Additionally, they advocated for the establishment of designated spaces, like chaplaincy services, within government hospitals. However, clinicians exhibited hesitancy towards collaboration and expressed concerns about patient referrals to spiritual leaders. Despite this, both groups recognized the potential benefits of collaboration in enhancing epilepsy care and promoting better brain health.
The doctoral project emphasized the critical necessity of advancing research to develop and perfect strategies for including spirituality within epilepsy care frameworks. It introduced the concept of the 360-degree referral pathway for holistic brain health as a model emphasizing feasibility, sustainability, and replicability. This innovative approach advocates for a seamless integration of spiritual and medical care, offering a comprehensive solution that meets the broad spectrum of needs for individuals with epilepsy in Ghana and beyond.Public Healt
Behavioral Responses to Capital Taxation: Evidence From the Norwegian Wealth Tax
No full textTax implementations give rise to behavioral changes among taxpayers, of which tax avoidance is a critical adaptation for policymakers to understand. Using Norwegian administrative data with individual-level tax records for 2015-2022, I identify three main legal wealth tax avoidance strategies used by Norwegian taxpayers to minimize their wealth tax liability. In contrast to previous studies, focused on singular aspects of avoidance or behavioral reactions to the tax, I identify multiple avoidance methods and quantify the annual revenue losses to the government associated with each one. I estimate a total of NOK 1,754 - 2,842 million in annual wealth tax revenue, or about 18 percent of collected wealth tax revenue, is lost to legal tax avoidance techniques.Applied Mathematic
Assessment of the Influence of Implant Design on the Accuracy of Implant Placement Using Static Computer-Aided Implant Surgery: an in vitro study
No full textEvolving advances in the field of implant dentistry aim to continue improving the predictability of implant therapy in replacing missing teeth. The aim of this research project is to investigate the influence of implant body thread design on the accuracy of implant placement using computer-aided implant surgery, specifically comparing the impact of two implant designs. It was hypothesized that the more aggressive thread design of the BLX implant will lead to greater 3D deviation in both healed (type 4) and extraction socket (type 1) sites, compared to the less aggressive BLC design. The study used acrylic bone models simulating a human maxillary arch with missing teeth, and implants were placed using a complete digital workflow and the deviation between planned and actual implant positions were measured using a digital software. The results revealed BLX implants were more accurate in both type 1 and type 4 sites, and also showed that type 4 had less deviation than type 1 scenarios. Limitations of the study include the use of bone models and alloy implant replicas, which do not fully replicate human bone or titanium implant surfaces, though these limitations were standardized to isolate the variables of interest, such as thread design. Although the results showing statistical significance, more clinical research is needed to corelate clinical relevance and formulate clinical recommendations.Implant Dentistr
The Biopsychosocial Impact of Stress and Mental Health on Cancer Risk
No full textCancer remains one of the most pressing global health concerns, with incidence rates rising despite advancements in early detection and prevention. While genetic, lifestyle, and environmental factors are well-established contributors to cancer risk, the role of stress and mental health in cancer development is an emerging area of research. Chronic stress, major life stressors, mental health disorders (e.g., anxiety, depression, post-traumatic stress disorders), and hazardous substance use are increasingly recognized for their potential to influence cancer incidence. These psychosocial factors may impact biological pathways related to immune system function, inflammation, and hormonal dysregulation, yet their precise contribution to cancer risk remains underexplored. This scoping review aims to synthesize existing literature to evaluate the biopsychosocial impact of stress, mental health, and substance use on cancer risk.
A scoping review was conducted following PRISMA guidelines, analyzing studies published between 1985 and 2024. Selected studies examined associations between stress, mental health, substance use, and cancer risk, focusing on biological and behavioral pathways. The review highlights multiple pathways through which stress, mental health, and substance use may influence cancer risk. Chronic stress and mental health conditions have been associated with dysregulation of the hypothalamic–pituitary– adrenal axis, immune suppression, and increased inflammation, all of which are implicated in cancer progression. Studies also indicate that major life stressors can contribute to cancer risk by triggering prolonged physiological stress responses.
Additionally, hazardous substance uses behaviors, including alcohol and tobacco consumption, frequently co-occur with stress and mental health disorders, serving as indirect mediators that further elevate cancer risk. Findings suggest that individuals with PTSD, depression, or anxiety may be at a higher risk for specific cancers, including breast, colorectal, lung, and prostate cancers. Finally, there is a dose-response between substance use and risk of cancer. Notably, even the lowest amount of alcohol and tobaccos use increase the risk of cancer. While epidemiological studies support an association between stress, mental health, and cancer, causality remains challenging to establish due to confounding variables and reliance on self-reported data.
This scoping review underscores the complex interplay between psychological stress, mental health, and cancer risk, highlighting the need for an integrated approach to cancer prevention that includes mental health management. Addressing modifiable risk factors could enhance cancer prevention strategies by mitigating both direct biological effects and indirect behavioral influences. Future research should focus on longitudinal studies to establish causal relationships and explore potential interventions targeting stress reduction and mental health support as part of comprehensive cancer prevention programs.Extension Studie
A Choroid Plexus Apocrine Secretion Mechanism Modulates Cerebrospinal Fluid Contents and Instructs Cortical Development
No full textThe choroid plexus (ChP) plays a crucial role in brain development by regulating the composition of cerebrospinal fluid (CSF) and releasing bioactive molecules that shape neural progenitor behavior. However, the full impact of ChP secretory activity on neurodevelopment, particularly during embryonic stages, remains poorly understood. This dissertation investigates a novel apocrine secretion mechanism in the ChP and explores how maternal drug exposure—specifically with serotonergic agents—can perturb ChP function and disrupt cortical development.
Our experiments first used the 5HT2C receptor agonist WAY-161503 to directly activate ChP secretion. Ex vivo imaging at embryonic day 14.5 revealed that WAY-161503 triggers robust calcium signaling in ChP epithelial cells, which induces a high-capacity release of proteins into the CSF. Proteomic analysis identified hundreds of proteins involved in essential neurodevelopmental pathways, including SHH, WNT, BMP, and IGF signaling, highlighting the ChP’s potential to influence multiple progenitor populations and cortical development simultaneously. Notably, we found that activating ChP secretion altered progenitor fate, leading to changes in the balance of cortical excitatory neuron populations and disrupting cortical architecture. These findings suggest that precise regulation of ChP secretion is critical for healthy brain development, and disruptions could have long-lasting consequences.
Building on these insights, we tested whether maternal exposure to LSD—a serotonergic hallucinogen that acts on 5HT2C and related receptors—would similarly affect ChP function and cortical development. Pregnant mice were administered either acute or repeated doses of LSD, and offspring cortical architecture was assessed postnatally. The LSD-exposed offspring exhibited significant reductions in Tbr1+ deep-layer neurons, altered Satb2+ excitatory neuron populations, and shifts in cortical organization that varied with both sex and exposure regimen. Although we did not perform proteomics after LSD exposure, the observed cortical disruptions align with the hypothesis that serotonergic compounds can alter ChP secretion and downstream neurodevelopmental processes. The behavioral consequences of these cortical changes were also evident, as mice exhibited hyperactivity, increased rotations in the open field test, and disrupted sensorimotor gating, particularly in male offspring.
Together, these findings demonstrate the importance of ChP-CSF signaling in neurodevelopment and highlight the risks posed by maternal drug exposure. The disruptions observed with both WAY-161503 and LSD raise concerns about the use of 5HT2C agonists in pregnant populations, especially as several such compounds are currently in clinical development. This work opens new avenues for investigating the broader pharmacological impact of ChP secretion and calls for further research into how the ChP-CSF axis shapes brain development and behavior. Understanding these mechanisms will be essential for identifying potential therapeutic risks and safeguarding healthy brain development.Medical Science
COMPARATIVE MICROVASCULAR PROFILING IN SPEECH-RELATED BRAIN REGIONS USING ARTERIAL SPIN LABELING MAGNETIC RESONANCE IMAGING: A STUDY OF HEALTHY INDIVIDUALS AND MOYAMOYA PATIENTS
No full textCerebral perfusion, which represents the delivery of oxygen-rich blood to the brain, is vital for maintaining cognitive and neurovascular function. Critically, it progressively declines with age and in the presence of cerebrovascular disease. Arterial spin labeling (ASL) magnetic resonance imaging (MRI) is a noninvasive imaging technique that uses radiofrequency labeled arterial blood water as an endogenous tracer to measure cerebral blood flow (CBF; measure of perfusion) and arterial transit time (ATT; the time it takes blood to reach brain tissue). ASL is well-suited for studying microvascular changes across the lifespan and in clinical populations, due to its quantitative, safe, and repeatable nature.
This study leverages ASL to examine CBF in cortical regions involved in speech and auditory processing across two populations: (1) neurologically normal adults from the Human Connectome Project–Aging (HCP-A), and (2) patients with MMD, a rare but severe cerebrovascular condition, from the Vanderbilt Assessment of Multi-Model MRI Patients at Risk for Stroke with Intracranial Stenosis (VAMMPRIS) dataset.
In the healthy cohort, aging was associated with widespread declines in CBF and increases in ATT in left-lateralized language regions. Even in the absence of overt disease, individuals taking antihypertensive medications exhibited significantly reduced CBF and delayed ATT in multiple regions, highlighting the impact of systemic vascular burden on brain perfusion. Individuals with Moyamoya Disease (MMD) showed more pronounced reductions in CBF across all speech-related cortical regions, reflecting severe hypoperfusion. Sex-stratified analysis revealed that males with Moyamoya exhibited a steeper age-related decline in CBF than their female counterparts.
Detection of subtle and severe perfusion deficits with ASL MRI demonstrates its potential as a tool for monitoring cerebrovascular health across the spectrum of aging, hypertension, and disease. By characterizing how CBF is altered in specific brain regions, this study contributes to a better understanding of how vascular risk factors shape neurovascular aging and highlights the clinical value of ASL in identifying individuals at risk for cerebrovascular conditions.Biomedical Engineering A