Browsing by Author "Wibral, Michael"

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    Cortical Oscillatory Activity Is Critical for Working Memory as Revealed by Deficits in Early-Onset Schizophrenia
    (SOC NEUROSCIENCE, 2009) Haenschel, Corinna; Bittner, Robert A.; Waltz, James; Haertling, Fabian; Wibral, Michael; Singer, Wolf; Linden, David E. J.; Rodriguez, Eugenio
    Impairments in working memory (WM) are a core cognitive deficit in schizophrenia. Neurophysiological models suggest that deficits during WM maintenance in schizophrenia may be explained by abnormalities in the GABAergic system, which will lead to deficits in high-frequency oscillations. However, it is not yet clear which of the three WM phases (encoding, maintenance, retrieval) are affected by dysfunctional oscillatory activity. We investigated the relationship between impairments in oscillatory activity in a broad frequency range (3-100 Hz) and WM load in the different phases of WM in 14 patients with early-onset schizophrenia and 14 matched control participants using a delayed matching to sample paradigm.
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    The Dual Facet of Gamma Oscillations: Separate Visual and Decision Making Circuits as Revealed by Simultaneous EEG/fMRI
    (2014) Castelhano, Joao; Duarte, Isabel Catarina; Wibral, Michael; Rodriguez, Eugenio; Castelo-Branco, Miguel
    It remains an outstanding question whether gamma-band oscillations reflect unitary cognitive processes within the same task. EEG/MEG studies do lack the resolution or coverage to address the highly debated question whether single gamma activity patterns are linked with multiple cognitive modules or alternatively each pattern associates with a specific cognitive module, within the same coherent perceptual task. One way to disentangle these issues would be to provide direct identification of their sources, by combining different techniques. Here, we directly examined these questions by performing simultaneous EEG/fMRI using an ambiguous perception paradigm requiring holistic integration. We found that distinct gamma frequency sub-bands reflect different neural substrates and cognitive mechanisms when comparing object perception states vs. no categorical perception. A low gamma sub-band (near 40 Hz) activity was tightly related to the decision making network, and in particular the anterior insula. A high gamma sub-band (approximate to 60 Hz) could be linked to early visual processing regions. The demonstration of a clear functional topography for distinct gamma sub-bands within the same task shows that distinct gamma-band modulations underlie sensory processing and perceptual decision mechanisms. Hum Brain Mapp 35:5219-5235, 2014. 2014 Wiley Periodicals, Inc.