Electrophysiological correlates of the BOLD signal for EEG-informed fMRI

Abstract

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are important tools in cognitive and clinical neuroscience. Combined EEG–fMRI has been shown to help to characterise brain networks involved in epileptic activity, as well as in different sensory, motor and cognitive functions. A good understanding of the electrophysiological correlates of the blood oxygen level-dependent (BOLD) signal is necessary to interpret fMRI maps, particularly when obtained in combination with EEG. We review the current understanding of electrophysiological–haemodynamic correlates, during different types of brain activity. We start by describing the basic mechanisms underlying EEG and BOLD signals and proceed by reviewing EEG-informed fMRI studies using fMRI to map specific EEG phenomena over the entire brain (EEG–fMRI mapping), or exploring a range of EEG-derived quantities to determine which best explain colocalised BOLD fluctuations (local EEG–fMRI coupling). While reviewing studies of different forms of brain activity (epileptic and nonepileptic spontaneous activity; cognitive, sensory and motor functions), a significant attention is given to epilepsy because the investigation of its haemodynamic correlates is the most common application of EEG-informed fMRI. Our review is focused on EEG-informed fMRI, an asymmetric approach of data integration. We give special attention to the invasiveness of electrophysiological measurements and the simultaneity of multimodal acquisitions because these methodological aspects determine the nature of the conclusions that can be drawn from EEG-informed fMRI studies. We emphasise the advantages of, and need for, simultaneous intracranial EEG–fMRI studies in humans, which recently became available and hold great potential to improve our understanding of the electrophysiological correlates of BOLD fluctuations.

Oscillatory dynamics in the dorsal and ventral attention networks during the reorienting of attention

“…That is, decreased alpha activity within a region is thought to signify the active engagement of that region during cognitive processes (Klimesch, ; Klimesch et al, ), and similar proposals have been made regarding beta band modulations (Neuper & Pfurtscheller, ). In congruence with this interpretation, simultaneous EEG‐fMRI research has demonstrated negative associations between alpha/beta activity and fMRI activation during cognitive tasks (Michels et al, ; Murta, Leite, Carmichael, Figueiredo, & Lemieux, ; Scheeringa et al, ). Taken together, the theta activity seen in bilateral visual cortices likely reflects early coding mechanisms, while alpha activity observed in bilateral LOC likely indicate processing of specific features inherent to the target stimuli.…”

Multiple sclerosis-related white matter microstructural change alters the BOLD hemodynamic response

“…[16][17][18][19][20][21] Under such conditions, BOLD signal reflects approximate linear changes in local neural activity. [22][23][24][25][26][27] This archetypal relationship between BOLD and neural activity is maintained via functional hyperemia and may be disrupted when there are aberrations in the functional hyperemic response. [12][13][14] MS features damage to specific WMMS (i.e.…”

A study of the electro-haemodynamic coupling using simultaneously acquired intracranial EEG and fMRI data in humans

“…Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is a non-invasive imaging technique commonly used to localise the neuronal activity underlying sensory, or cognitive functions, sleep, or rest (which may include epileptic activity), commonly captured by electrophysiological techniques (Murta et al, 2015). The fMRI whole-brain mapping capability complements the electroencephalogram (EEG) temporal richness, particularly relevant in epilepsy, providing localising information with potential clinical relevance.…”