Use of short intertrial intervals in single-trial experiments: a 3T fMRI-study.
We investigated the detectability of task-related changes in the fMRI-signal in an averaged single trial design under systematic variation of intertrial intervals (ITI) in the range between 4 and 12 s. Investigation of the signal timecourses showed a shortening of the baseline period and subsequently a reduction in signal amplitude with decreasing ITI. The main finding is that effect size, i.e., the ratio of task-related signal changes and error variance remained approximately constant from ITI of 12 s down to 6 s. At ITI = 4 s, the effect size was reduced by about 50%. The effects of ITI reduction were comparable in all six cortical ROI which were analyzed. In two subcortical ROI, effect size was already reduced at longer ITI. At ITI = 4 s, the rising flank of the BOLD response was delayed compared to longer ITI. When the data were corrected for the temporal overlap of successive BOLD-responses, the signal amplitudes at ITI = 4 s were comparable to the amplitudes measured at an interval of 12 s. This indicated that the amplitude reduction was mainly due to a linear superposition of the contiguous BOLD-responses.
Pollmann
S
S
Max-Planck-Institute of Cognitive Neuroscience, Leipzig, Germany.
Wiggins
C J
CJ
Norris
D G
DG
von Cramon
D Y
DY
Schubert
T
T
D000328:Adult; D001519:Behavior / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards*; D008297:Male; D010100:Oxygen / Q000097:blood; D012016:Reference Values
D010100:Oxygen