FMRI of visual encoding: reproducibility of activation.

fMRI, a noninvasive technique to measure brain activation, is gaining clinical interest, because its sensitivity enables individual assessments. However, more insight in the reproducibility of these measurements during higher cognitive tasks is necessary. We performed an fMRI study involving within- and between-subject reproducibility during encoding of complex visual pictures. Ten healthy subjects were studied on three occasions: twice in the same scanning session (study 1 and 2), and a third time, 3-24 days later (study 3). On all 30 occasions but one, activation was found in areas expected on the basis of previous studies, including the fusiform and lingual gyri, occipital and parietal areas, the (para)hippocampal area, and the frontal inferior sulcus. The reproducibility of the number of activated voxels in the whole brain was 72% and 63% (respectively, studies 1 and 2, and 1 and 3). The reproducibility of anatomical identical pixels that supplement these results was 49% and 36%. These reproducibility measures increase about 5-15% when only areas of expected activation are included. The quantitative measurements indicate that there is substantial variation in the volume of activation. The recognition of pictures as tested afterward explains part of this variation between subjects. Our findings indicate that whereas consistent patterns of activation exist, more insight is needed into what determines the volume of activation, especially to assess cognitive alterations in patients over time.