Neuroscience and Neurobiology Commons^™

Responding When Time Is Of The Essence: An Analysis Of Signal Timing In The Macaque Superior Colliculus During Reflexive Visually Guided Reaching, Amirhossein Asadian

Electronic Thesis and Dissertation Repository

The superior colliculus (SC) is a subcortical structure well known for contributing to saccades and reflexive orienting. SC neurons in primates are also active during arm movements, including those involving voluntary reaching. What is not known is whether SC neurons could contribute to reflexive visually guided reaches. A marker for such reaches is the express visuomotor response (EVR), which is generated on upper limb muscles in monkeys within 65 milliseconds. Here, we recorded the activity of SC neurons while two monkeys performed a task known to produce EVRs. When accounting for efferent delays, our results show that the SC neurons …

Harnessing Implicit Learning To Support The Discovery Of Second Language Phoneme Patterns In Adult Learners, Émilie R. Hoeppner

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Statistical learning studies have focused primarily on artificial languages, despite having an overall goal of providing insight into how we learn natural languages. Here, we investigate the impact of statistical learning on processing phonemic regularities within a second language in adult learners. Participants passively listened to Italian (L2 exposure group) or English (control group) podcasts for three weeks and completed a word rating task with ERP recorded before and after this listening period. Behaviourally, the L2 exposure group showed a nonsignificant trend towards increased sensitivity to phonotactic probability over the three weeks. At the ERP level, only the L2 group …

A Postexercise Executive Function Benefit From Passive And Active Exercise Does Not Extend To Mental Fatigue Mitigation, Gianna Jeyarajan

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A single bout of aerobic exercise improves executive function (EF) and is a benefit, in part, attributed to an increase in cerebral blood flow (CBF). It is, however, unknown whether a postexercise EF benefit mitigates mental fatigue (MF). My thesis assessed EF prior to and following separate 20-min conditions of active and passive cycle ergometry and a non- exercise control. Subsequently, a 20-min psychomotor vigilance task (PVT) was employed to determine whether the exercise intervention(s) decreased susceptibility to MF. Transcranial Doppler ultrasound was used throughout the protocol to estimate exercise- and PVT-based changes in CBF. Both exercise conditions increased CBF …

Modulation Of The Alpha Oscillation Associated With Semantic And Somatic Self-Referential Processing With Non-Invasive Brain Stimulation, Zhongjie Bao

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Who am I? What am I? While philosophers have pondered existential questions such as these for centuries, neuroscientists are beginning to reveal neural correlates that may partly underlie our semantic (verbal, psychological) and somatic (non-verbal, physical) senses of ourselves. Non-invasive brain stimulation (NIBS) can then introduce exogenous electric fields over brain regions to modulate a person’s self-referential processing (SRP). Effective NIBS protocols can help establish causal connections between brain and self-experience, helping develop clinical interventions for mental health problems.

In this dissertation, I present a series of studies investigating the neuro-electrophysiology partially mediating SRP by combining electroencephalography (EEG) with NIBS. …

Data Preprocessing And Machine Learning For Intracranial Electroencephalography, Mauricio Cespedes Tenorio

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This thesis serves to address the problem of non-standardized preprocessing of intracranial electroencephalography (iEEG) recordings by implementing a software workflow that compiles some of the most common steps followed for the preparation of this type of data. This workflow improves the consistency, replicability, and ease of use of iEEG preprocessing, facilitating the replication and extension of previous studies and the combination of separately preprocessed inter-institutional datasets. Automatic detection of artifacts for iEEG data was also explored as a potential step to include in the preprocessing workflow. Despite training the models with cross-institutional data, poor performance was observed when tested on …

The Effect Of A Single Bout Of Sub-Symptom Threshold Aerobic Exercise On Executive Function During Early Sport-Related Concussion Recovery, Alma Rahimidarabad

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Background: Impaired executive function (EF) is a primary sequela of sport-related concussion (SRC). Aerobic exercise below symptom exacerbation may improve post-SRC EF via increased cerebral blood flow (CBF). Objectives: To examine the impact of a single bout of sub-symptom threshold aerobic exercise on CBF and EF during SRC recovery. Methods: SRC participants (n = 16) and age- and sex-matched healthy controls (HC) completed 20-min of aerobic exercise at 80% of their heart rate threshold (HRt). Pre- and postexercise EF was assessed via antisaccades. Transcranial Doppler ultrasound (TCD) estimated exercise-mediated CBF changes. Results: SRC and HC participants showed an exercise-mediated increase …

Investigating Synergistic Effects Of Mild Traumatic Brain Injury And Reduced Cholinergic Tone On Attentional Deficits And Alzheimer's-Like Pathology In Haβ And Htau Mice, Elizabeth M. Teasell

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Mild traumatic brain injury (mTBI) increases the risk of Alzheimer’s disease. The early cholinergic decline in Alzheimer’s disease and cholinergic damage observed after TBI suggest a distinct role of this neural system in vulnerability to Alzheimer’s disease following TBI. This thesis evaluated the role of repetitive mTBI and cholinergic dysfunction in the development of cognitive deficits, specifically attentional deficits, and Alzheimer’s-related pathology in mice expressing humanized amyloid-beta and tau and a vesicular acetylcholine transporter knockdown to induce a mild cholinergic deficit. Using the rodent continuous performance test, it was shown that repetitive mTBI in the presence of an already vulnerable …

The Association Between Prenatal Maternal Stress, Infant Brain Volumes, And Temperament During The Covid-19 Pandemic, Amber L. Di Paolo

Electronic Thesis and Dissertation Repository

Prenatal maternal stress (PNMS) is associated with altered trajectories of infant socio-emotional and brain development, including brain structures such as the amygdala and prefrontal cortex (PFC). During the COVID-19 pandemic, which was a major global stressor, PNMS was significantly elevated, yet the impact on infant neurodevelopment remains uncertain. The objective of the present study was to determine whether PNMS during the pandemic was associated with infant amygdala and PFC volumes as well as temperament. In addition, we examined whether social support and resilience during pregnancy were protective factors.

Participants were enrolled in the Canadian ‘Pregnancy during the COVID-19 Pandemic’ cohort …

Cognitive Changes In Early Untreated Parkinson's Disease, Kunj Patel

Electronic Thesis and Dissertation Repository

Cognitive impairment is the most common non-motor symptom in Parkinson’s disease (PD), affecting up to one-third of early-stage patients. However, the cognitive profile in early PD remains unclear due to the use of heterogenous samples of disease severity, small sample sizes, and the inclusion of medication effects. This study aims to characterize cognitive deficits in early PD using a large, drug-naive sample. This study examined performance on the Montreal Cognitive Assessment and the Hopkins Verbal Learning Test from the Parkinson’s Progression Markers Initiative dataset (n= 643 patients with PD; n= 240 healthy controls). Patients were restricted to …

Cortical Thickness Changes As A Potential Biomarker For Epilepsy In People With First-Time Unprovoked Seizure, Keza T. Motlana

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Accurate epilepsy diagnosis after a First-Time Unprovoked Seizure (FTUS) remains challenging as the epileptogenic abnormalities and epileptiform EEG abnormalities used for such diagnoses infrequently occur and are often missed or misinterpreted. Expanding the scope of diagnostic abnormalities to include cortical thickness changes could enhance diagnostic efficacy. This is because cortical thickness changes are a significantly prevalent pathophysiological change that occurs in cases of epilepsy progressively, independent of seizure frequency, drug load and age. These changes are theorised to be a product of epileptogenesis, the process in which brain networks undergo disruptions becoming epileptic. This study aims to investigate whether these …

Quantifying Resting-State Functional Connectivity In Critically Brain-Injured Patients: A Graph-Theoretical Approach With Fnirs, Ira Gupta

Electronic Thesis and Dissertation Repository

Assessment of consciousness in behaviourally unresponsive patients with critical brain injuries continues to be a challenge. There remains a need for robust tools that can accurately characterize preserved cortical function and predict patient outcomes. In the present study, functional near-infrared spectroscopy is employed in conjunction with graph theory and machine learning to quantify resting-state functional connectivity in 16 acutely brain-injured patients and 23 healthy controls. Results revealed significant channel-level differences between the groups for three graph metrics, including degree, clustering coefficient, and local efficiency. Further investigation using machine learning algorithms revealed that these metrics can be used to distinguish between …

The Impact Of Emotional Sounds On Arousal And Task Performance, Brian Wu

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In times of emotional arousal, it is hypothesized that neural processes are triggered to “heighten” our senses to better respond to threatening stimuli. Some studies have tested this by exposing participants to emotional sounds to determine their impacts on visual acuity but have found mixed results. Previous studies have not investigated interactions between arousal induced by emotional sounds and visual acuity. Participants (N = 42) performed an orientation detection task while presented in silence or with sounds that varied in valence. Results displayed comparable accuracy across conditions but significantly faster response times during the presentation of negative sounds on the …

Posture Dependant Changes In Perceptual Threshold During Light Touch Foot Sole Stimulation, Justin Watts

Electronic Thesis and Dissertation Repository

Light touch sensitivity of the foot sole is typically measured when individuals are seated or lying down; yet, a critical function of foot sole cutaneous feedback is to support standing and walking activities. The objective of this study was to evaluate the differences in how individuals perceive light touch stimulation across the foot sole when they are in different postures. To accomplish this, we measured the light touch perceptual threshold(LTPT) in standing, seated, and supine postures in 19 volunteers (9 males), using Semmes-Weinstein Monofilaments. Perceptual thresholds were calculated at three foot sole locations (1^st metatarsal, lateral arch, and heel) …

Microstructural Mri Evolution During Adult Mouse Brain Maturation And Concussion Recovery, Naila Rahman

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Mild traumatic brain injury (mTBI), also called concussion, has become a significant public health concern. Current clinical neuroimaging techniques lack the sensitivity and specificity required to reliably detect signs of concussion, as large-scale changes are absent. Diffusion magnetic resonance imaging (dMRI) has arguably had the greatest influence to-date of neuroimaging modalities in mTBI, but previous studies have reported inconsistent findings, as standard dMRI lacks specificity and provides a limited model of neuroanatomy. This thesis explores the application of microstructural MR methods, that go beyond standard dMRI to improve sensitivity and specificity, to a preclinical model of mTBI and adult brain …

Towards Understanding And Improving Speech Processing, Sonia Yasmin

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This dissertation explores mechanisms for understanding and improving speech processing. First, I used EEG to investigate the acoustic and semantic processing of continuous naturalistic speech masked by multi-talker babble. I found that different features of the same speech signal are reflected in different aspects of the neural tracking response, which are themselves differentially affected by noise. These findings point to a complex relationship between speech intelligibility and neural speech encoding.

Next, I systematically reviewed the current advancements in speech enhancement technologies. I find that speech enhancement algorithms are limited in their generalizability to speech-noise (i.e., babble). I demonstrate that, for …

Frontoparietal Circuitry Underlying Saccade Control In The Common Marmoset, Janahan Selvanayagam

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Our visual world is full of far more stimuli than can be processed simultaneously. Yet we are able to efficiently extract behaviourally relevant information from a scene, primarily by performing rapid saccadic eye movements. These processes are under the control the frontoparietal network, two critical nodes of which are: the lateral intraparietal area (LIP) and the frontal eye fields (FEF). Extensive research in the macaque has causally implicated these areas in visual attention and oculomotor control. However, the organization of the activity of single neurons in these areas across cortical layers remains poorly understood as these regions are deep within …

Outclimbing Cognitive Decline: Age, Western Diet, Resistance Exercise, And The Brain., Leila Dzinic

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Increased age and obesity diminish motivation, perseverance, and spatial memory function. Aerobic exercise interventions have successfully rescued some of these processes. However, in older and heavier populations aerobic exercise is not as sustainable due to high risk of injury. Resistance exercise consists of physical activity where maximum oxygen consumption is not increased and has been proposed as a safe and effective intervention for this population. Here, we used touchscreen-based cognitive testing to elucidate the influence of resistance exercise on motivation and spatial memory in aged, diet-induced obese mice, using a water restriction procedure I develop in Chapter 2. Mice underwent …

Characterizing The Spatial Distribution Of Inhibitory Interneurons Across Early Sensory And Association Areas In Callithrix Jacchus, Nika Khajehdehi

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The prefrontal cortex (PFC) is one of the cortical areas responsible for complex cognitive abilities, a function that is believed to arise from increased persistent activity within its microcircuits. Activity within microcircuits is regulated by parvalbumin-containing (PV), calbindin-containing (CB), and calretinin-containing (CR) inhibitory interneurons (INs). It remains unclear how the distribution of activity-regulating INs differs across cortical areas such that persistent activity increases specifically within association areas, allowing for their complex functions. This thesis aims to address this gap by characterizing the spatial distributions and differences in relative proportions of INs across early sensory areas and association areas of the …

Investigating Task-Free Functional Connectivity Patterns In Newborns Using Functional Near-Infrared Spectroscopy, Homa Vahidi

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Robust functional connectivity in sensorimotor resting-state network (RSN) has been linked to positive neurodevelopmental outcomes in neonates. In the current study, we aimed to map the developmental trajectory of sensorimotor RSN in awake neonates using functional near-infrared spectroscopy (fNIRS). We acquired fNIRS resting-state data from 41 healthy newborns (17 females, gestational age range=36+0 to 42+1 weeks) within the first 48 hours after birth. At the group level, we observed robust positive connectivity in numerous channel-pairs across the sensorimotor network, especially in the left hemisphere. Next, we examined the relationship between functional connectivity, gestational age and postnatal age, while controlling for …

The Adaptor Protein P66shc Governs Central Nervous System Cell Metabolism And Resistance To Aβ Toxicity, Asad Lone

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Alzheimer’s disease (AD), a progressive and irreversible neurodegenerative disorder, and is the leading cause of dementia worldwide. It has been posited that AD is caused by the gradual deposition of toxic amyloid-b (Ab) plaques in the brain- that cause oxidative stress and eventually leads to neuronal death and synaptic loss. However, multiple therapies that either interfere with the production, or enhance the removal of Ab from the brain, have ultimately failed to slow or prevent AD. With the ever-increasing burden of AD worldwide, there exists an urgent need for novel therapeutic targets. The adult human brain is an energy demanding …

Neural Responses To Magnetic Orientation Information In Songbirds, Madeleine Ir Brodbeck

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Effective navigation and orientation is essential for animals to survive. The study of migratory birds provides insights into these processes, particularly through mechanisms like the geomagnetic compass, which uses Earth's magnetic field for directional information. A brain region in songbirds relevant to this is cluster N, known for its potential role in processing geomagnetic information. Notably, cluster N appears exclusive to nocturnally migratory birds, being active solely at night, and lesion studies reveal that an intact cluster N is necessary for geomagnetic compass orientation. However, given the scarcity of empirical data concerning cluster N, substantial questions persist regarding its function. …

Aging Effects On The Motivational Consequences Of Unsuccessful Memory Recall, Rachel Sargeson

Electronic Thesis and Dissertation Repository

The present thesis addressed whether experiences of failed recall for names of familiar faces could induce states of curiosity and drive memory benefits. Experiment 1 investigated whether older adults exhibit the same familiarity preference in information seeking, following an unsuccessful recall attempt for names of previously studied faces, as seen in younger adults. Experiment 2 considered whether acting on the curiosity induced by unsuccessful recall of names associated with familiar faces could provide benefits for the relearning of those names in both age groups. The older adults displayed a similar, if not more pronounced, positive relationship between familiarity and subsequent …

Invariant Object Recognition In Deep Neural Networks And Humans, Haider Al-Tahan

Electronic Thesis and Dissertation Repository

Invariant object recognition, a cornerstone of human vision, enables recognizing objects despite variations in rotations, positions, and scales. To emulate human-like generalization across object transformations, computational models must perform well in this aspect. Deep neural networks (DNNs) are popular models for human ventral visual stream processing, though their alignment with human performance remains inconsistent. We examine object recognition across transformations in human adults and pretrained feedforward DNNs. DNNs are grouped in model families by architecture, visual diet, and learning goal. We focus on object rotation in depth, and observe that object recognition performance is better preserved in humans than in …

Cortical Activation During Mobility In An Indoor Real-World Environment: A Mobile Eeg Study, Sam Marshall

Electronic Thesis and Dissertation Repository

Human mobility requires neurocognitive inputs to safely navigate the environment. Previous research has examined neural processes that underly walking using mobile neuroimaging technologies, yet few studies have incorporated true real-world methods without a specific task imposed on participants (e.g., dual-task, motor demands). The present study utilized mobile electroencephalography to examine and compare theta, alpha, and beta frequency band power (μV2) in young adults during sitting and walking in laboratory and real-world environments. Our findings support that mobility and environment may modulate neural activity, as we observed increased brain activation for walking compared to sitting, and for real-world walking compared to …

Selective Recruitment Of Cerebellum In Cognition, Ladan Shahshahani

Electronic Thesis and Dissertation Repository

Previous studies of cerebellar function in humans have shown that it is activated by a myriad of tasks ranging from motor learning and language to working memory and more. These studies have prompted a deviation from the traditional view of the cerebellum as a purely motor structure. However, the precise contribution of the cerebellum to these tasks remains ambiguous.

A prevalent assumption in fMRI studies is interpreting BOLD activation as evidence of the cerebellum's involvement in specific tasks. However, this interpretation is potentially misleading, especially considering that the BOLD signal predominantly represents cerebellar input, with output activity largely absent. Consequently, …

Modelling Prenatal Hypoxia As A Risk Factor For Schizophrenia Vulnerability In Patient-Derived Cerebral Organoids, Dana M. Gummerson

Electronic Thesis and Dissertation Repository

Prenatal hypoxia during fetal development is a significant environmental risk factor linked to schizophrenia (SCZ) vulnerability. However, hypoxia’s impact on human brain development at the cellular level remains unclear. Our laboratory has developed human cerebral organoids using induced pluripotent stem cells (iPSCs) derived from healthy control or SCZ patient cell lines to address these questions. This creates a platform that allows for the investigation into the pathophysiology of SCZ and hypoxia in tandem. Organoids were exposed to hypoxic conditions at one month of development, mimicking the early stages of cortical growth in the human fetus. Results reveal innate differences in …

Visual Cortical Traveling Waves: From Spontaneous Spiking Populations To Stimulus-Evoked Models Of Short-Term Prediction, Gabriel B. Benigno

Electronic Thesis and Dissertation Repository

Thanks to recent advances in neurotechnology, waves of activity sweeping across entire cortical regions are now routinely observed. Moreover, these waves have been found to impact neural responses as well as perception, and the responses themselves are found to be structured as traveling waves. How exactly do these waves arise? Do they confer any computational advantages? These traveling waves represent an opportunity for an expanded theory of neural computation, in which their dynamic local network activity may complement the moment-to-moment variability of our sensory experience.

This thesis aims to help uncover the origin and role of traveling waves in the …

Neural Dynamics Of Visual Processes In Challenging Visibility Conditions, Saba Charmi Motlagh

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In our daily visual experience, our brain effortlessly categorizes countless objects, enabling us to perceive and interpret the world around us. This core object recognition process is vital for our survival and adaptive behavior, allowing us to recognize objects despite variations in appearance. The incredible speed at which we accomplish this task is a testament to the efficiency of our visual system and the significance of visual processing is evident in the allocation of nearly half of the neocortex in primates to this function. Unraveling the intricacies of how the human visual system tackles this complex challenge has long been …

White Matter Connectome Associations With Reading Functions In Children, Chenglin Lou

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This thesis investigated associations between the white matter connectome and reading in children with a wide range of reading abilities. It is well established that the connectome supports the interplay among brain regions and connections within an integrated system. In this dissertation, I examine the hypothesis that it could therefore represent multiple mapping processes among reading components and further explain variations in reading performance. Such associations between the organization of the connectome and reading skills have not been well explored. This thesis aimed to address this issue by considering both the relationship between connectome measures and standardized reading performance out …

Examining The Emergence Of Mood And Anxiety Molecular Phenotypes Resulting From Chronic Prenatal Nicotine Exposure In Cerebral Organoids, Emma K. Proud

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Prenatal nicotine exposure (PNE) from maternal smoking disrupts regulatory processes vital to fetal development. These changes result in long-term behavioural impairments, including mood and anxiety disorders, that manifest later in life. However the relationship underlying PNE, and the underpinnings of mood/anxiety molecular phenotypes remains elusive. To model nicotine exposure during prenatal development, our study used human cerebral organoids that were chronically exposed to nicotine and collected for molecular analyses. Short-term, nicotine altered molecular markers of neural identity, mood/anxiety disorders and those involved in maintaining the excitatory/inhibitory (E/I) balance in the cortex. RNA sequencing further revealed transcriptomic changes in genes pertaining …