Since its discovery in the early 1990s, functional magnetic resonance imaging (fMRI) with blood oxygenation level dependent (BOLD) contrast has become the mainstay of human brain imaging. Today, the BOLD fMRI) signal is a widely-accepted marker of brain activity.
The acquisition parameters (APs) of fMRI aim at maximizing the signals related to neuronal activity while minimizing unrelated signal fluctuations. Currently, a diverse set of APs is used to acquire BOLD fMRI data. Here we demonstrate that some fMRI responses are alarmingly inconsistent across APs, ranging from positive to negative, or disappearing entirely, under identical stimulus conditions. These discrepancies, resulting from non-BOLD effects masquerading as BOLD signals, have remained largely unnoticed because studies rarely employ more than one set of APs.
The commonplaceness of fMRI has given the impression that this imaging method can be used in an “automatic” mode, without worrying about the biophysical basis of fMRI signal changes. Some recent studies do not report even the basic acquisition parameters (APs), such as echo time (TE), repetition time (TR), or flip angle (FA), as if these were well-established defaults with no appreciable influence on the data.
The visual stimulus consisted of a circular checkerboard (left) with the checks switching between black and white at a rate of 8 Hz. During the control condition, the subjects viewed a grey circle. The total eccentricity of the stimulus was 15°, but the scanner setup limited the view to a smaller portion, as illustrated by the red-shaded boundaries. Due to differences in head size and shape, each subject viewed a slightly different portion of the scene.
doi:10.1038/srep03920
Citation: Ville Renvall, Cathy Nangini&Riitta Hari, 'All that glitters is not BOLD: inconsistencies in functional MRI', Scientific Reports 4, Article number: 3920 doi:10.1038/srep03920
