EEG and fMRI agree: Mental arithmetic is the easiest form of imagery to detect

- fMRI or EEG during mental imagery can be used to detect awareness.
- No study has verified agreement between fMRI and EEG for this purpose.
- fMRI and EEG were recorded simultaneously during 6 imagery tasks.
- Mental arithmetic produced the best fMRI and EEG responses in most healthy subjects.
- Overall, fMRI and EEG provide converging evidence at the individual level.

fMRI and EEG during mental imagery provide alternative methods of detecting awareness in patients with disorders of consciousness (DOC) without reliance on behaviour. Because using fMRI in patients with DOC is difficult, studies increasingly employ EEG. However, there has been no verification that these modalities provide converging information at the individual subject level. The present study examined simultaneous EEG and fMRI in healthy volunteers during six mental imagery tasks to determine whether one mental imagery task generates more robust activation across subjects; whether activation can be predicted from familiarity with the imagined activity; and whether EEG and fMRI converge upon the same conclusions about individual imagery performance. Mental arithmetic generated the most robust activation in the majority of subjects for both EEG and fMRI, and level of activation could not be predicted from familiarity, with either modality. We conclude that overall, EEG and fMRI agree regarding individual mental imagery performance.