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Cortical spreading depression (CSD) is an important neurophysiological phenomenon, which was first discovered more than 60 years ago. Optical intrinsic signal imaging (OISI) is a neuroimaging technique that can monitor a large region of the cortex with both higher temporal and spatial resolution. This technique is particularly suitable for the investigation of CSD wave propagation. However, all the previous work performed with OISI focused only on one hemisphere of animal brain, so the potential useful information from the contralateral side was lost. Although the feasibility of OISI of CSD has been demonstrated, reliable detection of small intrinsic optical signals associated with CSD is still challenging but very important for the better understanding of CSD. Previous investigations on OISI around 550 nm suggested three or four phases of optical responses associated with stimulation-evoked CSD, but this is still under debate. This is an important issue for considering the physiological sources of optical signals. The failure to unambiguously determine the phases of optical signals may be partly due to the loss of quantitative assessment of signal-to-noise ratio (SNR) in optical imaging. In biparietal imaging, the hemisphere without CSD would help to determine the noise level of optical recording. To our knowledge, no research visualizing the simultaneous CSD waves in the bilateral hemisphere has been conducted yet. In this study, OISI at 550 nm was selected to monitor the biparietal cortex simultaneously during CSD in rats. The study aimed to clarify the multiphases of reflectance and to compare the bilateral properties of CSD induced by pinprick or K+, and the results would improve the understanding of CSD.