Figure 10.

In vivo PA850 B-scan images of hemodynamic changes in the cortex of the rat brain at the position of bregma +1 mm (S1FL region) during left-forepaw electrical stimulation. (A) PA data collected in a block-design paradigm that utilized electrical stimulation of the left forepaw. The protocol began with 300 s in the baseline state. Then, a constant 3-Hz electrical pulse train with an intensity of 5 mA was delivered for 60 s during the active “Stimulation ON” state, which was followed by another 300-s period for recovery. PA B-scan imaging was started simultaneously with the baseline period and then stopped immediately at the end of the recovery period. PA B-scan images were acquired at an excitation wavelength of 850 nm. (B) Example plot of the PA signal from the S1FL region (outlined with solid yellow lines in (C–F)). Data from the baseline, stimulation ON (yellow rectangle) and recovery periods can be seen in the plot. The baseline intensity at t = 0 was subtracted from all PA signals. Baseline-subtracted US/PA-overlaid B-scan images at the baseline period and 1, 2, or 5 min after left-forepaw stimulation are shown in (C–F), respectively. Cerebral hemodynamics within a rat brain were also monitored in real time with 850-nm excitation (Movie S1). Significant differences in PA signals at 850 nm were observed in the contralateral S1FL ROI between the stimulation ON/OFF conditions. PA, photoacoustic; PA850, PA signal at an 850-nm excitation wavelength; S1FL, primary somatosensory cortex of the forepaw; US, ultrasound; ROI, region of interest; A.U., arbitrary units.