Table 3. Concurrent tES-fMRI (ContES 2021) checklist: main items and recommendations of the METHODOLOGICAL FACTORS category to report in concurrent tES-fMRI research.

Ratings for items (scores 1-5) are reported as mean (standard deviation) and ratings for recommendations (Yes/No) are reported as frequency of Yes (percent of Yes reports).

Categories/Sub-Categories	Main Items to Report	Item Importance (1 to 5)	Specific Recommendation to Report	Recommendation Inclusion (Yes/No)
		Mean (SD)		Yes (%)
METHODOLOGICAL FACTORS
3.1. Concurrent tES-fMRI Timing	The timing of concurrent tES within the fMRI paradigm.	4.52 (0.81)	3.1.1. Providing schematic diagrams is strongly encouraged to achieve maximum clarity for the reader.	46 (90%)
			3.1.2. Report carry-over effects between different stimulation conditions and different brain states. How such effects have been considered or mitigated should be discussed.	42 (86%)
3.2. Imaging Session Timing	The imaging events before and after concurrent tES-fMRI and respective sequences.	4.09 (0.99)	3.2.1. Report the exact timing of all imaging events (structural or functional) before and after concurrent tES-fMRI.	47 (92%)
			3.2.2. Report when the tES setup is placed on the participant e.g., if the tES setup was placed on the participant at the start of the tES-fMRI session (and was therefore on the participant during other nonfMRI sequences).	50 (96%)
			3.2.3. In tACS studies, report how stimulation frequency is matched with TR. To reduce potential sources of biases in tACS-fMRI studies, the stimulation frequency should be set such that a full number of cycles fits into the TR of the functional measurement 36 (post-mortem study). Otherwise, the tissue polarization might be averaged over the time of one volume measured.	43 (88%)
3.3. tES Experience Report	The assessment of the subjective experience of receiving tES inside the scanner.	4.06 (0.97)	3.3.1. Report the general experience (comfort/fatigue) and participant's other experiences with the stimulation - as some tES montages/protocols might be more uncomfortable/perceptible than others when lying inside the scanner and this could be a confounder when comparing across stimulation montages. Options include: assessing participant ratings of symptoms for each condition, asking participants whether they perceived stimulation or not for each condition, reporting on the presence and intensity of phosphenes/tactile sensation (in the case of tACS), etc. This is important as it could show whether participants can differentiate between stimulation conditions (e.g., between active and sham stimulation, or between different frequencies (in the case of tACS). Having different side effects between sessions does not necessarily mean that subjects can discern and are unblinded.	47 (90%)
			3.3.2. Report electric current tolerance for subject comfort (i.e., before entering scanner room (if technically possible) and/or in the scanner room and inside the scanner and/or during scanning (as appropriate)).	26 (51%)
			3.3.3. Report any instructions, training, or exposure provided before the tES-fMRI session to make the experiment more convenient for the participants.	46 (88%)
			3.3.4. Report the exact wording or provide citations of the questions or questionnaires used to report on the subjective experience of receiving tES inside the scanner in the article or its supplements.	38 (73%)
General Recommendations			0.0.1. Report handedness of subject as a potential source of variability of tES-fMRI studies. This interaction could be addressed in relevant contexts either by limiting the sample to right-handed individuals, reporting handedness with quantitative standard instruments, or through methodological/analytical approaches which should be reported.	41 (82%)
			0.0.2. If possible, present the online tES electrodes as additional bumps in the surface/mesh reconstruction. This is a good possibility to determine the exact location of the online electrodes. However, this nonbiological reconstruction may also influence simulations, so performance of additional structural T1w and T2w scans without the electrodes whenever possible is advantageous.	28 (55%)