Simultaneous electroencephalography-functional magnetic resonance imaging for assessment of human brain function

Abstract

Electroencephalography (EEG) and functional Magnetic Resonance Imaging (MRI) have long been used as tools to examine brain activity. Since both methods are very sensitive to changes of synaptic activity, simultaneous recording of EEG and fMRI can provide both high temporal and spatial resolution. Therefore, the two modalities are now integrated into a hybrid tool, EEG-fMRI, which encapsulates the useful properties of the two. Among other benefits, EEG-fMRI can contribute to a better understanding of brain connectivity and networks. This review lays its focus on the methodologies applied in performing EEG-fMRI studies, namely techniques used for the recording of EEG inside the scanner, artifact removal, and statistical analysis of the fMRI signal. We will investigate simultaneous resting-state and task-based EEG-fMRI studies and discuss their clinical and technological perspectives. Moreover, it is established that the brain regions affected by a task-based neural activity might not be limited to the regions in which they have been initiated. Advanced methods can help reveal the regions responsible for or affected by a developed neural network. Therefore, we have also looked into studies related to characterization of structure and dynamics of brain networks. The reviewed literature suggests that EEG-fMRI can provide valuable complementary information about brain neural networks and functions.

Preservation of EEG spectral power features during simultaneous EEG-fMRI

“…Once the participant was inside the scanner, EEG leads were carefully examined in search for loops and oriented in a straight line parallel to the B0 magnetic field, to reduce EEG artifacts and the risk of radiofrequency-induced heating of the sensors (Yan et al, 2009;Chowdhury et al, 2015;Assecondi et al, 2016). Sandbags and tape were used to minimize electrode leads movement and soft pads were placed between the receiving coil and the subject's head to reduce participant's movement (Bénar et al, 2003;Bullock et al, 2021;Ebrahimzadeh et al, 2022). The EEG amplifier was placed next to the bed of the scanner behind the 400 Gauss magnetic field iso-intensity line, in accordance with the safety guidelines provided by the vendor.…”

“…Simultaneous Electroencephalography and functional Magnetic Resonance Imaging (EEG-fMRI) records the electrophysiological and hemodynamic correlates of human brain activity non-invasively, aiming to combine the strengths of both modalities (Huster et al, 2012;Laufs, 2012;Scrivener, 2021;Ebrahimzadeh et al, 2022). EEG measures the sum of extracellular currents generated by the synchronous activity of large populations of neurons, using electrodes attached to the subject's scalp (Schomer and da Silva, 2011), while fMRI quantifies changes in cerebral blood oxygenation, blood flow and blood volume that result from neurovascular coupling responses mediated by astrocytes, blood vessels, and neurons and therefore, represents an indirect correlate of neuronal activity (Huettel et al, 2004;Figley and Stroman, 2011).…”

“…EEG measures the sum of extracellular currents generated by the synchronous activity of large populations of neurons, using electrodes attached to the subject's scalp (Schomer and da Silva, 2011), while fMRI quantifies changes in cerebral blood oxygenation, blood flow and blood volume that result from neurovascular coupling responses mediated by astrocytes, blood vessels, and neurons and therefore, represents an indirect correlate of neuronal activity (Huettel et al, 2004;Figley and Stroman, 2011). Simultaneous EEG-fMRI recording aims to better understand the complex dynamics underlying brain function by combining EEG's temporal resolution and fMRI's spatial resolution (Mulert and Lemieux, 2010;Scrivener, 2021;Ebrahimzadeh et al, 2022). Simultaneous EEG-fMRI also opens the possibility of directly studying interactions between electrophysiological and hemodynamic responses (Jorge et al, 2014) which cannot be achieved when signals are recorded independently (Mulert and Lemieux, 2010;Jorge et al, 2014;Ebrahimzadeh et al, 2022).…”

“…Simultaneous EEG-fMRI recording aims to better understand the complex dynamics underlying brain function by combining EEG's temporal resolution and fMRI's spatial resolution (Mulert and Lemieux, 2010;Scrivener, 2021;Ebrahimzadeh et al, 2022). Simultaneous EEG-fMRI also opens the possibility of directly studying interactions between electrophysiological and hemodynamic responses (Jorge et al, 2014) which cannot be achieved when signals are recorded independently (Mulert and Lemieux, 2010;Jorge et al, 2014;Ebrahimzadeh et al, 2022).…”

“…Given its large variability between and within individuals, the BCG artifact represents a major challenge for EEG-fMRI. Several signal processing tools have been developed to deal with the BCG artifact and reduce its contribution from the recordings while preserving EEG signal properties (Bullock et al, 2021;Ebrahimzadeh et al, 2022). As summarized in Bullock et al (2021) the most popular BCG correction approaches include Average Artifact Subtraction (AAS); (Allen et al, 1998), Optimal Basis Set (OBS); (Niazy et al, 2005), Independent Component Analysis (ICA); (Srivastava et al, 2005) and the combination of these: OBS-ICA (Debener et al, 2006) and AAS-ICA (Mayeli et al, 2021).…”