Mapping of the activity of brain by optical intrinsic signal imaging (OISI) provides a two-dimensional activation pattern of visual cortical areas at a resolution of a few hundred microns. However, integration of the intrinsic signal over depth results in loss of finer information about functional organization across the depth. Here, we report the first successful implementation of optical coherence tomography (OCT) at around 30 μm depth resolution to investigate cortical functions of a cat brain in vivo. This technique, named functional OCT (fOCT) provided visually evoked changes in the OCT signal. The fOCT signal shows stimulus specificity that correlates well with that of the intrinsic signals and provides depth resolved layer specific functional information.
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