Research Article: FMRI Effective Connectivity and TMS Chronometry: Complementary Accounts of Causality in the Visuospatial Judgment Network

Date Published: December 14, 2009

Publisher: Public Library of Science

Author(s): Tom A. de Graaf, Christianne Jacobs, Alard Roebroeck, Alexander T. Sack, Bernhard T. Baune.

Abstract: While traditionally quite distinct, functional neuroimaging (e.g. functional magnetic resonance imaging: fMRI) and functional interference techniques (e.g. transcranial magnetic stimulation: TMS) increasingly address similar questions of functional brain organization, including connectivity, interactions, and causality in the brain. Time-resolved TMS over multiple brain network nodes can elucidate the relative timings of functional relevance for behavior (“TMS chronometry”), while fMRI functional or effective connectivity (fMRI EC) can map task-specific interactions between brain regions based on the interrelation of measured signals. The current study empirically assessed the relation between these different methods.

Partial Text: Cognitive neuroscience today knows several fundamentally different methods to study brain function. These methods may conceptually be divided into functional neuroimaging versus functional interference techniques. Functional neuroimaging aims to identify which brain regions are activated during the execution of certain mental functions. Methods such as electro- or magnetoencephalography (MEG or EEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI) are all suitable methods to measure brain activity in humans that engage in sensory, motor, or cognitive processing. Functional interference techniques actively intervene in neural processing, for instance by permanently or transiently changing (often disrupting) the neural mechanisms at work. Invasive interference techniques, including cooling, microstimulation, and lesioning, are mainly used in animal studies. The only non-invasive interference techniques that can be safely used in human neuroscience are transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS).

The current study addressed several questions of causality and interaction in brain network function. We aimed to reveal functionally relevant TMS target regions with fMRI EC analysis. Using TMS Neuronavigation to stimulate fMRI EC-identified clusters in single participants, we thus tested the behavioral relevance of an fMRI EC functional network underlying visuospatial judgment. Moreover, the time-resolved aspect of our TMS design allowed us to evaluate the commensurability of TMS chronometry and fMRI EC, in terms of suggested information flows. And therefore, to evaluate the extent to which both methods are overlapping, or complementary, in terms of insights yielded.



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