fMRI of visual encoding: Reproducibility of activation

fMRI, a noninvasive technique to measure brain activation, is gaining clini cal interest, because its sensitivity Enables individual assessments. Howev er, 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 pict ures. Ten healthy subjects were studied on three occasions: twice in the sa me scanning session (study 1 and 2), and a third time, 3-24 days later (stu dy 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 i nferior sulcus. The reproducibility of the number of activated voxels in th e whole brain was 72% and 63% (respectively, studies 1 and 2, and 1 and 3). The reproducibility of anatomical identical pixels that supplement these r esults was 49% and 36%. These reproducibility measures increase about 5-15% when only areas of expected activation are included. The quantitative meas urements indicate that there is substantial variation in the volume of acti vation. The recognition of pictures as tested afterward explains part of th is variation between subjects. Our findings indicate that whereas consisten t patterns of activation exist, more insight is needed into what determines the volume of activation, especially to assess cognitive alterations in pa tients over time. (C) 2000 Wiley-Liss, Inc.