Papers by Kevin Sitek
Human Brain Mapping, 2021
Standard magnetic resonance imaging approaches offer high‐resolution but indirect measures of neu... more Standard magnetic resonance imaging approaches offer high‐resolution but indirect measures of neural activity, limiting understanding of the physiological processes associated with imaging findings. Here, we used calibrated functional magnetic resonance imaging during the resting state to recover low‐frequency fluctuations of the cerebral metabolic rate of oxygen (CMRO2). We tested whether functional connections derived from these fluctuations exhibited organization properties similar to those established by previous standard functional and anatomical connectivity studies. Seventeen participants underwent 20 min of resting imaging during dual‐echo, pseudocontinuous arterial spin labeling, and blood‐oxygen‐level dependent (BOLD) signal acquisition. Participants also underwent a 10 min normocapnic and hypercapnic procedure. Brain‐wide, CMRO2 low‐frequency fluctuations were subjected to graph‐based and voxel‐wise functional connectivity analyses. Results demonstrated that connections d...
Research in the field of speech perception has shown that the perception of certain speech sounds... more Research in the field of speech perception has shown that the perception of certain speech sounds is dependent on their neighboring sounds. In this paper, we will show that this phonetic context effect is significant regardless of whether the context is presented to the same ear as the base target or the isolated third formant transition. Additionally, the results hint that the effect is greater when the formant transitions are presented to the ipsilateral ear as the context segment than when they are presented to the contralateral ear. The results therefore describe a process in which the left and right auditory streams combine before most, but likely not all, phonetic information is retrieved.
Studying the human subcortical auditory system non-invasively is challenging due to its 13 small,... more Studying the human subcortical auditory system non-invasively is challenging due to its 13 small, densely packed structures deep within the brain. Additionally, the elaborate 14 three-dimensional (3-D) structure of the system can be difficult to understand based on currently 15 available 2-D schematics and animal models. We addressed these issues using a combination of 16 histological data, post mortem magnetic resonance imaging (MRI), and in vivo MRI at 7 Tesla. We 17 created anatomical atlases based on state-of-the-art human histology (BigBrain) and post mortem 18 MRI (50 μm). We measured functional MRI (fMRI) responses to natural sounds and demonstrate 19 that the functional localization of subcortical structures is reliable within individual participants 20 who were scanned in two different experiments. Further, a group functional atlas derived from the 21 functional data locates these structures with a median distance below 2mm. Using diffusion MRI 22 tractography, we revealed ...
ABSTRACTDorsal human midbrain contains two nuclei with clear laminar organization, the superior a... more ABSTRACTDorsal human midbrain contains two nuclei with clear laminar organization, the superior and inferior colliculi. These nuclei extend in depth between the superficial dorsal surface of midbrain and a deep midbrain nucleus, the periaqueductal gray matter (PAG). The PAG, in turn, surrounds the cerebral aqueduct (CA). This study examined the use of two depth metrics to characterize depth and thickness relationships within dorsal midbrain using the superficial surface of midbrain and CA as references. The first utilized nearest-neighbor Euclidean distance from one reference surface, while the second used a level-set approach that combines signed distance from both reference surfaces. Both depth methods provided similar functional depth profiles generated by saccadic eye movements in a functional MRI task, confirming their efficacy for superficial functional activity. Next, the boundaries of the PAG were estimated using Euclidean distance together with elliptical fitting, indicatin...
Studying the human subcortical auditory system non-invasively is challenging due to its small str... more Studying the human subcortical auditory system non-invasively is challenging due to its small structures deep within the brain. Additionally, the elaborate three-dimensional (3-D) structure of the system can be diZcult to understand based on currently available 2-D schematics and animal models. To address these issues, we measured functional magnetic resonance imaging (fMRI) responses from the human subcortical auditory system at 7 Tesla and validated the results by creating an atlas based on state of the art human histology (BigBrain) and post mortem MRI. Furthermore, using diffusion MRI tractography, we revealed structural connectivity maps of the human subcortical auditory pathway both in vivo (1050 μm isotropic resolution) and post mortem (200 μm isotropic resolution). This work contributes novel tools for researching the human auditory system to understand its structural organization as well as facilitates dissemination of this knowledge by making the created atlases openly ava...
Molecular autism, 2018
One of the most reported neural features of autism spectrum disorder (ASD) is the alteration of m... more One of the most reported neural features of autism spectrum disorder (ASD) is the alteration of multiple long-range white matter fiber tracts, as assessed by diffusion-weighted imaging and indexed by reduced fractional anisotropy (FA). Recent methodological advances, however, have shown that this same pattern of reduced FA may be an artifact resulting from excessive head motion and poorer data quality and that aberrant structural connectivity in children with ASD is confined to the right inferior longitudinal fasciculus (ILF). This study aimed at replicating the observation of reduced FA along the right ILF in ASD, while controlling for group differences in head motion and data quality. In addition, we explored associations between reduced FA in the right ILF and quantitative ASD characteristics, and the involvement of the right ILF in visual processing, which is known to be altered in ASD. Global probabilistic tractography was performed on diffusion-weighted imaging data of 17 adol...
Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery, 2017
Objective The radiologic evaluation of patients with hearing loss includes computed tomography an... more Objective The radiologic evaluation of patients with hearing loss includes computed tomography and magnetic resonance imaging (MRI) to highlight temporal bone and cochlear nerve anatomy. The central auditory pathways are often not studied for routine clinical evaluation. Diffusion tensor imaging (DTI) is an emerging MRI-based modality that can reveal microstructural changes in white matter. In this systematic review, we summarize the value of DTI in the detection of structural changes of the central auditory pathways in patients with sensorineural hearing loss. Data Sources PubMed, Embase, and Cochrane. Review Methods We used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement checklist for study design. All studies that included at least 1 sensorineural hearing loss patient with DTI outcome data were included. Results After inclusion and exclusion criteria were met, 20 articles were analyzed. Patients with bilateral hearing loss comprised 60.8% of all s...
Frontiers in Human Neuroscience, 2016
Studying the human subcortical auditory system non-invasively is challenging due to its small str... more Studying the human subcortical auditory system non-invasively is challenging due to its small structures deep within the brain. Additionally, the elaborate three-dimensional (3-D) structure of the system can be diZcult to understand based on currently available 2-D schematics and animal models. To address these issues, we measured functional magnetic resonance imaging (fMRI) responses from the human subcortical auditory system at 7 Tesla and validated the results by creating an atlas based on state of the art human histology (BigBrain) and post mortem MRI. Furthermore, using diffusion MRI tractography, we revealed structural connectivity maps of the human subcortical auditory pathway both in vivo (1050 μm isotropic resolution) and post mortem (200 μm isotropic resolution). This work contributes novel tools for researching the human auditory system to understand its structural organization as well as facilitates dissemination of this knowledge by making the created atlases openly ava...
eLife, 2019
Studying the human subcortical auditory system non-invasively is challenging due to its small, de... more Studying the human subcortical auditory system non-invasively is challenging due to its small, densely packed structures deep within the brain. Additionally, the elaborate three-dimensional (3-D) structure of the system can be difficult to understand based on currently available 2-D schematics and animal models. Wfe addressed these issues using a combination of histological data, post mortem magnetic resonance imaging (MRI), and in vivo MRI at 7 Tesla. We created anatomical atlases based on state-of-the-art human histology (BigBrain) and postmortem MRI (50 mm). We measured functional MRI (fMRI) responses to natural sounds and demonstrate that the functional localization of subcortical structures is reliable within individual participants who were scanned in two different experiments. Further, a group functional atlas derived from the functional data locates these structures with a median distance below 2 mm. Using diffusion MRI tractography, we revealed structural connectivity maps of the human subcortical auditory pathway both in vivo (1050 mm isotropic resolution) and post mortem (200 mm isotropic resolution). This work captures current MRI capabilities for investigating the human subcortical auditory system, describes challenges that remain, and contributes novel, openly available data, atlases, and tools for researching the human auditory system. Introduction Understanding the structure of the human subcortical auditory pathway is a necessary step to research its role in hearing, speech communication, and music. However, due to methodological issues in human research, most of our understanding of the subcortical (thalamic, midbrain, and brainstem) auditory pathway arises from research conducted in animal models. This might be problematic because, while the organization of the auditory pathway is largely conserved across mamma-lian species (Malmierca and Hackett, 2010; Schofield, 2010), the form and function of each structure may not be analogous (Moore, 1987). In this paper, we show that three human imaging modalities-histology, postmortem magnetic resonance imaging (MRI), and in vivo MRI at ultra high-field (7 Tesla)-can identify the structures of the subcortical auditory pathway at high spatial resolution (between 50 and 1100 mm).
Frontiers in Human Neuroscience, 2016
Persistent developmental stuttering is characterized by speech production disfluency and affects ... more Persistent developmental stuttering is characterized by speech production disfluency and affects 1% of adults. The degree of impairment varies widely across individuals and the neural mechanisms underlying the disorder and this variability remain poorly understood. Here we elucidate compensatory mechanisms related to this variability in impairment using whole-brain functional and white matter connectivity analyses in persistent developmental stuttering. We found that people who stutter had stronger functional connectivity between cerebellum and thalamus than people with fluent speech, while stutterers with the least severe symptoms had greater functional connectivity between left cerebellum and left orbitofrontal cortex (OFC). Additionally, people who stutter had decreased functional and white matter connectivity among the perisylvian auditory, motor, and speech planning regions compared to typical speakers, but greater functional connectivity between the right basal ganglia and bilateral temporal auditory regions. Structurally, disfluency ratings were negatively correlated with white matter connections to left perisylvian regions and to the brain stem. Overall, we found increased connectivity among subcortical and reward network structures in people who stutter compared to controls. These connections were negatively correlated with stuttering severity, suggesting the involvement of cerebellum and OFC may underlie successful compensatory mechanisms by more fluent stutterers.
PLOS ONE, Dec 13, 2013
As we talk, we unconsciously adjust our speech to ensure it sounds the way we intend it to sound.... more As we talk, we unconsciously adjust our speech to ensure it sounds the way we intend it to sound. However, because speech production involves complex motor planning and execution, no two utterances of the same sound will be exactly the same. Here, we show that auditory cortex is sensitive to natural variations in self-produced speech from utterance to utterance. We recorded event-related potentials (ERPs) from ninety-nine subjects while they uttered “ah” and while they listened to those speech sounds played back. Subjects' utterances were sorted based on their formant deviations from the previous utterance. Typically, the N1 ERP component is suppressed during talking compared to listening. By comparing ERPs to the least and most variable utterances, we found that N1 was less suppressed to utterances that differed greatly from their preceding neighbors. In contrast, an utterance's difference from the median formant values did not affect N1. Trial-to-trial pitch (f0) deviation and pitch difference from the median similarly did not affect N1. We discuss mechanisms that may underlie the change in N1 suppression resulting from trial-to-trial formant change. Deviant utterances require additional auditory cortical processing, suggesting that speaking-induced suppression mechanisms are optimally tuned for a specific production.
Proceedings of the Chicago Linguistic Society 48
Duplex perception experiments explore how a speech unit is processed simultaneously as a speech a... more Duplex perception experiments explore how a speech unit is processed simultaneously as a speech and non-speech sound. Two adjacent speech sounds do not need to be heard in the same ear for phonetic context effects to be active. Our experiments combine these paradigms by presenting two syllables dichotically with formants of the target syllable presented contralaterally to the rest of the target. When hearing an ambiguous stimulus between /d/ and /g/, subjects are more likely to hear /g/ after /al/ and /d/ after /ar/. This context effect is significant regardless of whether the context is presented to the same ear as the base target or the isolated third formant transition, demonstrating that the auditory system must combine streams before completing all phonetic analysis. Additionally, there is a greater context effect when the formant transitions are presented to the ipsilateral ear as the context segment than when they are presented contralaterally. The difference in compensation effects between Experiments 1 and 2 (where the formant transition is presented contralaterally to the context) shows that some phonetic processing occurs before the left and right auditory streams converge. Separating the formant chirp (responsible for cuing /d/ vs. /g/) from the context is more crucial to analysis than separating the base target from the context. Phonetic context effects, while working adequately across streams, are more influential within one stream.
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