Abstract
Positive blood oxygenation level-dependent (BOLD) responses (PBR), as measured by functional Magnetic Resonance Imaging (fMRI), are the most utilized measurements to non-invasively map activity in the brain. Recent studies have consistently shown that BOLD responses are not exclusively positive. Negative BOLD responses (NBR) have been reported in response to specific sensory stimulations and tasks. However, the exact relationship between NBR and the underlying metabolic and neuronal demand is still under debate. In this study, we investigated the neurophysiological basis of negative BOLD using fMRI and intra-cranial electrophysiology (electrocorticography, ECoG) measurements from the same human participants. We show that, for those electrodes that responded to visual stimulation, PBR are correlated with high-frequency band (HFB) responses. Crucially, NBR were associated with an absence of HFB power responses and an unpredicted decrease in the alpha power responses.
Highlights
Functional Magnetic Resonance Imaging is a noninvasive technique to measure brain activity via blood oxygenation level-dependent (BOLD) responses
ECoG and Functional Magnetic Resonance Imaging (fMRI) data were acquired in separate sessions from two participants, while they were presented with a unilateral visual stimulation (Fig. 1)
Contralateral visual stimulation during ECoG measurements did elicit a significant increase in the high-frequency band (HFB) power range (65–95 Hz) in N = 33 and N = 27 electrodes in participant 1 (P1) and participant 2 (P2), respectively
Summary
Functional Magnetic Resonance Imaging (fMRI) is a noninvasive technique to measure brain activity via blood oxygenation level-dependent (BOLD) responses. Positive BOLD responses (PBR) are the most widely utilized signals. Research has consistently shown that BOLD responses are not exclusively positive. Negative BOLD responses (NBR) can be elicited in specific brain locations during visual and tactile stimulations and tasks (Tootell et al 1998; Shmuel et al 2002; Smith et al 2004; Kastrup et al 2008; Klingner et al 2010; Gouws et al 2014; Fracasso et al 2018; Jorge et al 2018). In human primary visual cortex, NBR have been reported adjacent to positive BOLD responses and have been used to measure surround suppression due to stimulation outside
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