Browsing by Author "Harezlak, J."

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    Ictal propagation of high frequency activity is recapitulated in interictal recordings: effective connectivity of epileptogenic networks recorded with intracranial EEG
    (Elsevier, 2014-11-01) Korzeniewska, A.; Cervenka, M. C.; Jouny, C. C.; Perilla, J. R.; Harezlak, J.; Bergey, G. K.; Franaszczuk, P. J.; Crone, N. E.; Department of Biostatistics, Richard M. Fairbanks School of Public Health
    Seizures are increasingly understood to arise from epileptogenic networks across which ictal activity is propagated and sustained. In patients undergoing invasive monitoring for epilepsy surgery, high frequency oscillations have been observed within the seizure onset zone during both ictal and interictal intervals. We hypothesized that the patterns by which high frequency activity is propagated would help elucidate epileptogenic networks and thereby identify network nodes relevant for surgical planning. Intracranial EEG recordings were analyzed with a multivariate autoregressive modeling technique (short-time direct directed transfer function--SdDTF), based on the concept of Granger causality, to estimate the directionality and intensity of propagation of high frequency activity (70-175 Hz) during ictal and interictal recordings. These analyses revealed prominent divergence and convergence of high frequency activity propagation at sites identified by epileptologists as part of the ictal onset zone. In contrast, relatively little propagation of this activity was observed among the other analyzed sites. This pattern was observed in both subdural and depth electrode recordings of patients with focal ictal onset, but not in patients with a widely distributed ictal onset. In patients with focal ictal onsets, the patterns of propagation recorded during pre-ictal (up to 5 min immediately preceding ictal onset) and interictal (more than 24h before and after seizures) intervals were very similar to those recorded during seizures. The ability to characterize epileptogenic networks from interictal recordings could have important clinical implications for epilepsy surgery planning by reducing the need for prolonged invasive monitoring to record spontaneous seizures.
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    Predictors of CNS Injury as Measured by Proton Magnetic Resonance Spectroscopy in the Setting of Chronic HIV infection and CART
    (Springer US, 2014-06) Harezlak, J.; Cohen, R.; Gongvatana, A.; Taylor, M.; Buchthal, S.; Schifitto, G.; Zhong, J.; Daar, E. S.; Alger, J.; Brown, M.; Singer, E.; Campbell, T. B.; McMahon, D.; So, Y. T.; Yiannoutsos, C. T.; Navia, B. A.; HIV Neuroimaging Consortium; Department of Biostatistics, Richard M. Fairbanks School of Public Health
    The reasons for persistent brain dysfunction in chronically HIV-infected persons on stable combined antiretroviral therapies (CART) remain unclear. Host and viral factors along with their interactions were examined in 260 HIV-infected subjects who underwent magnetic resonance spectroscopy (MRS) Metabolite concentrations (NAA/Cr, Cho/Cr, MI/Cr and Glx/Cr) were measured in the basal ganglia, the frontal white matter and grey matter and the best predictive models were selected using a bootstrap-enhanced Akaike Information Criterion (AIC). Depending on the metabolite and brain region, age, race, HIV RNA concentration, ADC stage, duration of HIV infection, nadir CD4, and/or their interactions were predictive of metabolite concentrations, particularly the basal ganglia NAA/Cr and the mid-frontal NAA/Cr and Glx/Cr whereas current CD4 and the CPE index rarely or did not predict these changes. These results show for the first time that host and viral factors related to both current and past HIV status contribute to persisting cerebral metabolite abnormalities and provide a framework for further understanding neurological injury in the setting of chronic and stable disease.