Figure 3.

The BOLD response shows linear temporal summation for closely spaced short trains of stimulation. For each animal, time series were extracted from a ROI identified in independent localizer runs. The linear response can be qualitatively observed by subtracting the n from the n + 1 conditions (dashed line). A, Optical stimulation evoked equivalent responses across multiple independent 1 s trains. Individual time series (n = 6 animals) of the BOLD fMRI response to one 1 s interval (single) and two trains of 1 s intervals (double) with an interstimulus interval of 2 s. Data are expressed as mean ± SEM (across individual runs in each animal). B, Five 1 s (quintuple) and six 1 s trains (sextuple) show an equivalent temporal linearity response (two animals) to that observed in A. C, D, Sensory stimulation yielded equivalent responses in the single − double (two animals) and quintuple − sextuple (two animals) experiments.