Fig 4. Mean ‘blood volume’ signal is closely matched, temporally, by V1 arterial contraction-dilation cycle.

a: Mean trial-triggered signals and b: individual frames showing fractional signal change relative to trial-mean image. Inset square: green: ‘fixate’, black: ‘relax’. Magnified sections show arterial contraction (white walls), dilation (black walls). Grey trace in panel a: arterial signal relative to ‘parenchyma baseline,’ (Fig S11 – method for calculating arterial signal. Arterial trace shifted vertically from overall mean for visibility). c: Timing of peak arterial contraction (dilation), as phase within trial, matches peak brightening (darkening) of mean signal: red square (black diamond) respectively. d - g: Arterial signal (grey) closely matches mean signal (green) for different trial periods (d, e) and at transitions between periods (f, g); same experiment, conventions as in Fig 3b, c, f, g (traces shifted vertically for visibility). Note close matches between corresponding peaks and troughs (arrows), indicated as in Fig 3.