Browsing by Author "Whaley, Meagan"

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    Applying the Short-Time Direct Directed Transfer Function to Human Electrocorticographic Recordings from a Language Task
    (2013-06-28) Whaley, Meagan; Cox, Steven J.; Embree, Mark; Tandon, Nitin; Dabaghian, Yuri
    This thesis applied the short-time direct directed transfer function (SdDTF) to time series data recordings from intracranial electrodes that measure the brain's electrical activity to determine the causal influences that occurred between brain regions during a speech production task. The combination of high temporal and spatial resolution of the electrocorticography (ECoG) recordings directly from the cortex render these measurements of brain activity desirable, particularly when analyzing the fine cognitive dynamics involved in word generation. This research applied a new method to characterize the SdDTF results by compressing across time and high gamma frequencies, generating adjacency matrices, and graphing them to visualize the influences between anatomical regions over the duration of the entire task. This consolidated SdDTF analysis technique allowed for data from a total of seven patients to be combined, generating results which were consistent with current speech production models. The results from this thesis contribute to the expansion of language research by identifying areas relevant to word generation, providing information that will help surgeons avoid irreparable damage to crucial cortex during brain surgery.
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    Dynamics of brain networks during reading
    (2015-10-05) Whaley, Meagan; Cox, Steven J; Dabaghian, Yuri; Kemere, Caleb; Tandon, Nitin
    We recorded electrocorticographic (ECoG) data from 15 patients with intractable epilepsy during a word completion task to precisely describe the spatiotemporal brain dynamics underlying word reading. Using a novel technique of analyzing grouped ECoG, cortical regions distributed throughout the left hemisphere were identified as significantly active versus baseline during our word stem completion task. Regions of activity spread from fusiform to frontal regions, including pars opercularis, pars triangularis, and pre, post, and subcentral gyri during the time period approaching articulation onset. The ECoG data recorded from electrodes within these regions were fit into linear multivariate autoregressive models, which precisely reveal the time, frequency, and magnitude of information flow between localized brain regions. Grouped network dynamics were quantified with two metrics of evaluating statistical significance of post-stimulus interactions compared to baseline. Results from both methods reveal bidirectional exchanges between frontal regions with fusiform, supporting theories which incorporate top-down and bottom-up processing during single word reading.