Simultaneous recordings of visual evoked potentials and BOLD MRI activations in response to visual motion processing

Abstract

Visual motion processing in humans was studied by simultaneous 32-channel electroencephalography (EEG) recordings of visual evoked potentials and BOLD MRI activations at 2.9 T. The paradigms compared three different random dot patterns (12 s duration) with stationary random dots (18 s) or with each other. The stimuli represented pattern reversal (500 ms switches between two stationary patterns), motion onset (200 ms of starfield motion followed by 1000 ms of stationary dots) and motion reversal (reversal of moving starfield directions every 1000 ms). Whereas motion-evoked visual potentials, and in particular the N2 component in occipito-temporal channels, were most prominent for motion onset, the most extended BOLD MRI activations and strongest signal changes in V5/MTþ were obtained in response to motion reversal. These apparently contradictory findings most likely reflect different physiological aspects of the neural activity associated with visual motion processing. For example, desynchronized activity of subpopulations of cortical neurons inside V5/MTþ is expected to attenuate visual evoked potentials in scalp recordings while continuously driving metabolic demands that lead to sustained BOLD MRI responses. The understanding of the physiological correlates and neural processes underlying either technique is fundamental to exploring fully the potential of combined EEG-MRI for studying human brain function at both high temporal and spatial resolution.

Complex relationship between BOLD signal and synchronization/desynchronization of human brain MEG oscillations

“…The oscillatory EEG-or MEG-activity can be further subdivided into frequency bands, which correspond to certain states and operations of the brain [Basar, 1988;Lopes da Silva and van Leeuwen, 1969]. Correlations of positive BOLD-responses could be demonstrated with scalprecorded and intracranial low frequency oscillations, including epileptic spike activity [Aghakhani et al, 2004;Benar et al, 2002;Salek-Haddadi et al, 2002], surface-negative slow cortical potentials [Hinterberger et al, 2003;Nagai et al, 2004], and event-related potentials across different task conditions [Henning et al, 2005;Huettel et al, 2004;Matsumoto et al, 2005;Mulert et al, 2004;Schulz et al, 2004]-all of which are generated by synchronized activity of cortical neuronal populations. However, recently, another MEG/fMRI-study by Singh et al [2002] conducted in humans provided indirect evidence that the opposite relationship may also be found, i.e., a positive BOLD-response correlating with cortical non-phase-locked desynchronization of electromagnetic field oscillations.…”

Spatiotemporal patterns of oscillatory brain activity during auditory word recognition in children: A synthetic aperture magnetometry study

“…In view of the current literature, it is more likely that both ERS and ERD represent aspects of neuronal activation that contribute to the hemodynamic response detected with fMRI and this differs across brain regions and across task requirements (Henning et al, 2005;Huettel et al, 2004).…”

Real-time artifact filtering in continuous VEPs/fMRI recording

“…These studies also investigated the possibility of recording a good quality EEG signal inside an MR scanner, as well as to obtain high quality MR images in the presence of EEG equipment, assuring patient safety. These findings opened the way to the acquisition of EEG and fMRI in the study of epilepsy (Bast et al, 2007;Hamandi et al, 2006), the neural mechanisms of sleep (Czisch et al, 2004;Horovitz et al, 2008;Schabus et al, 2007) and the VEPs (Becker et al, 2005;Bonmassar et al, 1999;Comi et al, 2005;Henning et al, 2005;Im et al, 2006;Lemieux et al, 1997;Sammer et al, 2005).…”

“…Conversely, functional Magnetic Resonance Imaging (fMRI) exploits changes in the BOLD signal coupled with neuronal activity in order to localize brain activation, with a high spatial resolution but low temporal resolution (Ogawa et al, 1992). VEPs and fMRI have thus complementary features and their integration may provide more detailed information than either method alone (Di Russo et al, 2005;Henning et al, 2005). Given the inherent variability of evoked cortical responses and BOLD contrast, the integration of both methods would be more reliable using simultaneous recordings, which explore the subject's brain activity in the same state and provide precise information derived from different biophysical origins on the processing of visual stimuli at the same time (Bonmassar et al, 2001).…”

“…Continuous VEPs-fMRI acquisition is very challenging since the fast varying gradient fields and the radio-frequency pulses induce a very intense electric noise that obscures the EEG signal (HuangHellinger et al, 1995;Ives et al, 1993), thus requiring a careful experimental setup and a sophisticated artifact removal technique in order to filter out the noise and retains the evoked responses in the signal. Such a challenging technique has been applied quite rarely (Becker et al, 2005;Comi et al, 2005;Henning et al, 2005;Im et al, 2006;Sammer et al, 2005), by means of the same filtering algorithm (Allen et al, 2000(Allen et al, , 1998. One study investigated steadystate VEPs (SS-VEPs) (Sammer et al, 2005), while other authors recorded transient VEPs (T-VEPs) using a stimulation based on a sequence of letters (Comi et al, 2005), pattern reversal (Becker et al, 2005;Im et al, 2006), and motion patterns (Henning et al, 2005).…”