Characterization of optical intrinsic signals and blood volume during cortical spreading depression.

Cortical spreading depression (CSD) was imaged in vivo in a rodent model with optical intrinsic signals (OIS). This is the first study to identify a triphasic OIS response and to characterize the rate and timing of the response. The initial OIS phase had a highly uniform wavefront, which spread at a rate characteristic of CSD, 3.5 mm/min. Later phases were more diffuse and inhomogeneous. Blood volume changes, measured with intravascular fluorescent dye, correlated in time and location with the later phases of OIS response. This suggests that the inhomogeneity of the late OIS response may be due to complex residual hemodynamic contributions, as opposed to underlying cortical circuitry.