Noninvasive, real-time monitoring of brain tissue viability is crucial for the patients with stroke, traumatic brain injury, etc. For this purpose, measurement of intrinsic optical signal (IOS) is attractive because it can provide direct information about the viability of brain tissue noninvasively. We performed simultaneous measurements of IOSs that are related to morphological characteristics, i.e., light scattering, and energy metabolism for rat brains during saline infusion as a model with temporal loss of brain tissue viability. The results showed that the scattering signal was steady in an initial phase but showed a drastic, triphasic change in a certain range of infusion time, during which the reduction of CuA in cytochrome c oxidase started and proceeded rapidly. The start time of triphasic scattering change was delayed for about 100 s by lowering brain temperature from 29°C to 24°C, demonstrating the optical detection of cerebroprotection effect by brain cooling. Electron microscopic observation showed morphological changes of dendrite and mitochondria in the cortical surface tissue after the triphasic scattering change, which was thought to be associated with the change in light scattering we observed. These findings suggest that the simultaneous measurement of the intrinsic optical signals related to morphological characteristics and energy metabolism is useful for monitoring tissue viability in brain.