I am trying to get my head around what questions I can expect to have answered about brain activity that cannot be answered by doing two separate EEG and fMRI experiments.

I am aware that fMRI records the BOLD signal and EEG records a collective electrical response from pyramidal neurons; so even if the first one provides good spatial resolution across the whole brain and the second one provides good time resolution for the exposed parts of the cortex (gyri), the two recording methods do not seem to be very complementary/symmetrical, in other words they do not measure the same quantities/qualities of the brain activity.

I am unsure to what is the actual benefit of using them in combination in an experiment although I acknowledge that combined EEG-fMRI can perhaps address certain questions in a within-subject analysis but this is still a bit vague.

I found this paper by Huster et al. (2012) helpful but if anyone has more suggestions/directions, that would be much more than welcome.

Huster, R. J., Debener, S., Eichele, T., & Herrmann, C. S. (2012). Methods for simultaneous EEG-fMRI: an introductory review. Journal of Neuroscience, 32(18), 6053-6060.

  • $\begingroup$ The review article you link to states the exact opposite: "However, because the strengths and weaknesses of EEG and fMRI are complementary, simultaneous EEG-fMRI may achieve what seems otherwise largely impossible, namely the noninvasive recording of human brain activity with both high spatial and high temporal resolution." Regardless, this might exactly be the part you need a more concrete example of. Good question! Welcome! $\endgroup$
    – Steven Jeuris
    Commented Mar 6, 2019 at 10:43
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    $\begingroup$ The paper gives one example in the introduction—epileptic seizures: "The first applications of EEG-fMRI were born of a clinical interest in the improved localization of the neural sources of epileptogenic EEG activity for diagnosis and presurgical planning (Ives et al., 1993). Although the onset of pathological brain activity can clearly be inferred from EEG measurements, locations in the cortex from which these pathogenic neuronal events spread cannot unambiguously be derived from EEG alone." A specific seizure happens at a particular moment in time; you need to measure it simultaneously. $\endgroup$
    – Steven Jeuris
    Commented Mar 6, 2019 at 10:46
  • $\begingroup$ Thank you Steven. That is correct. In the case of certain epileptic seizures, the EEG recording would provide the onset of the seizure and the fMRI would probably better highlight the cortical areas at the origin of the seizure. In a more common visual experiment, instead where the onset of the stimulus is known, using EEG does not seem to be as fruitful unless there are other benefits. $\endgroup$
    – ivano
    Commented Mar 6, 2019 at 11:40


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