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Brain oscillatory correlates in working memory and attentional control processes
Brain oscillatory correlates in working memory and attentional control processes
Human working memory and selective attention processes in need of top-down cognitive control rely on interactions within local neural populations and between distant brain areas in a fronto-parietal neural network. Brain oscillatory dynamics drawing on slow oscillatory activity in the theta frequency range are associated with (1) information exchange between global and local networks needed for the integration of top-down controlled mental templates and bottom-up visual processing, through transient phase-synchronization with fast gamma activity, (2) the prefrontal top-down control of remote brain areas, where frontal-midline theta phase may provide cyclic windows of opportunity in which task-active posterior areas can access prefrontal resources, or are denied access and (3) the coordination of excitable periods within the fronto-parietal network, through long-range theta coherence. In this thesis, four research projects are presented. In a newly developed visual search task, we demonstrated that in conditions where participants kept a single targets' properties in mind for visual search, cross-frequency synchronization between theta and gamma phase transiently increased in right posterior cortex, but not in conditions where one out of multiple mental templates was successfully matched. Thereby, we extend previous work proposing transient theta-gamma phase synchronization as a neural correlate of matching incoming sensory information with top-down controlled mental templates, and we provide novel evidence for limitations in memory matching during multiple template search. Second, we probed the causal relevance of more sustained fronto-parietal interaction, during voluntary resource allocation in visuospatial working memory. We found frontal-midline theta phase dependent effects of TMS over right, but not left, parietal cortex on working memory performance, when prioritizing contralateral visuospatial information during working memory maintenance. TMS selectively disrupted task accuracy when delivered during the more excitatory frontal-midline theta phase (i.e. the trough). Based on this pilot data, we recommend effect size estimates and implications for follow-up studies. Third, we conducted a pre-registered study using multi-site theta tACS for synchronizing or desynchronizing a left fronto-parietal network, but could not reproduce a beneficial or detrimental effect on verbal working memory performance in an easy letter recognition task. Our results indicate that a beneficial effect of synchronous fronto-parietal theta tACS can only be observed in a working memory task of high difficulty. In order to make our contribution to increasing reproducibility and robustness in transcranial brain stimulation research, we next investigated the usefulness of Bayes Factor analyses over conventional tests to differentiate between cases where a particular application of TBS had no effect or whether results were merely inconclusive. In a series of simulated TBS experiments with differing sample size and effect size, we show that Bayes factors tests may be highly useful for demonstrating conclusive evidence for non-effects and outline how they can be used in practice.
cognitive control, fronto-parietal network, non-invasive brain stimulation, reproducibility, theta oscillations
Biel, Anna Lena
2021
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Biel, Anna Lena (2021): Brain oscillatory correlates in working memory and attentional control processes. Dissertation, LMU München: Graduate School of Systemic Neurosciences (GSN)
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Abstract

Human working memory and selective attention processes in need of top-down cognitive control rely on interactions within local neural populations and between distant brain areas in a fronto-parietal neural network. Brain oscillatory dynamics drawing on slow oscillatory activity in the theta frequency range are associated with (1) information exchange between global and local networks needed for the integration of top-down controlled mental templates and bottom-up visual processing, through transient phase-synchronization with fast gamma activity, (2) the prefrontal top-down control of remote brain areas, where frontal-midline theta phase may provide cyclic windows of opportunity in which task-active posterior areas can access prefrontal resources, or are denied access and (3) the coordination of excitable periods within the fronto-parietal network, through long-range theta coherence. In this thesis, four research projects are presented. In a newly developed visual search task, we demonstrated that in conditions where participants kept a single targets' properties in mind for visual search, cross-frequency synchronization between theta and gamma phase transiently increased in right posterior cortex, but not in conditions where one out of multiple mental templates was successfully matched. Thereby, we extend previous work proposing transient theta-gamma phase synchronization as a neural correlate of matching incoming sensory information with top-down controlled mental templates, and we provide novel evidence for limitations in memory matching during multiple template search. Second, we probed the causal relevance of more sustained fronto-parietal interaction, during voluntary resource allocation in visuospatial working memory. We found frontal-midline theta phase dependent effects of TMS over right, but not left, parietal cortex on working memory performance, when prioritizing contralateral visuospatial information during working memory maintenance. TMS selectively disrupted task accuracy when delivered during the more excitatory frontal-midline theta phase (i.e. the trough). Based on this pilot data, we recommend effect size estimates and implications for follow-up studies. Third, we conducted a pre-registered study using multi-site theta tACS for synchronizing or desynchronizing a left fronto-parietal network, but could not reproduce a beneficial or detrimental effect on verbal working memory performance in an easy letter recognition task. Our results indicate that a beneficial effect of synchronous fronto-parietal theta tACS can only be observed in a working memory task of high difficulty. In order to make our contribution to increasing reproducibility and robustness in transcranial brain stimulation research, we next investigated the usefulness of Bayes Factor analyses over conventional tests to differentiate between cases where a particular application of TBS had no effect or whether results were merely inconclusive. In a series of simulated TBS experiments with differing sample size and effect size, we show that Bayes factors tests may be highly useful for demonstrating conclusive evidence for non-effects and outline how they can be used in practice.