Fig. 1. Pre-dose (blue) and post-dose (red) group averaged periodic BOLD responses acquired with slice thicknesses of 8 mm (a) and 4 mm (c). Averages are from voxels within ROI_dip (defined separately for each slice thickness). Magnified views are shown in panels b and d. The initial dip is clearly evident in the pre-dose responses and is absent in the corresponding post-dose responses. The length of each error bar represents the standard error across subjects and the thick black line denotes the stimulus duration. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. Comparison of the post-dose (y-axis) and pre-dose (x-axis) initial dip areas for each subject for voxels within ROI_dip. The solid line represents the line of equality. Panels a–h represent subject data acquired with slice thicknesses of 4 mm and 8 mm, respectively. The P values were computed with a paired t test (two-tailed).

Fig. 3. Magnified views of the pre-dose (blue) and post-dose (red) initial responses for each subject averaged across their respective ROI_dip. Panels a–c show the responses from the 4-mm slice thickness data, while panels d–h are for the 8-mm slice thickness data. The error bars represent the standard error across voxels. The reduction of the initial dip by caffeine is clearly present in each subject's responses. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4. Comparison of the pre-dose (top row) and post-dose (bottom row) spatial localization maps for the initial dip (left column) and the positive BOLD response (right column) for subject 1. Panels a and c show the spatial extent of the initial dip in the pre-dose and post-dose conditions, respectively, with the colorbar below panel c indicating the scale of the correlation coefficients obtained with the initial dip reference function. Panels b and d are positive BOLD spatial maps for the pre-dose and post-dose conditions, respectively. The colorbar below panel d indicates the scale of the correlation coefficients obtained with the positive BOLD reference function. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Pre-dose and post-dose baseline CBF values shown as mean (standard deviation)

Mean and standard deviation were computed across voxels in each subject's respective ROI_dip. For each subject, significance was computed with a paired t test (two-sided).