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Ashesh D. Mehta, M.D., Ph.D., Minah Suh, Ph.D., Sonya Bahar, Ph.D., Theodore Schwartz, M.D.

INTRODUCTION: Optical imaging of intrinsic signal is a novel method for measuring the population of neurons participating in epileptiform events. Depending on the wavelength of light whose reflectance is measured, the intrinsic optical signal carries information about blood flow, the oxygenation state of hemoglobin, and cell volume changes. The optimal wavelength for imaging epileptiform events has not yet been determined.

METHODS: The brains of 24 rats were exposed by thinning the skull. A charge-coupled device camera was focused on the brain, which was illuminated with 540, 630, or 700 nm light. Images were acquired at 10 Hz. Interictal spikes (IIS) were produced by bicuculline iontophoresis. Images obtained after individual IIS were divided by images obtained immediately before the IIS. These divided images were averaged over multiple IIS at each of the three wavelengths, and the average...