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A Cimponeriu, Y Chen, E Dinnerstein, E Kaplan; Multi-wavelength Optical Imaging Of The Cat Visual Cortex . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4750.
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Purpose:Cortical imaging of the intrinsic optical signal (IOS) has become a widespread, powerful tool in brain functional investigation. The dominant components of the IOS are due to oxy- and deoxyhemoglobin (Hb and HbO2), each with its own distinct absorption spectrum. Typically IOS is imaged at a single wavelength. In order to obtain more information about the two components, we performed time-division optical imaging by switching wavelengths in time, obtaining quasi-simultaneous two-dimensional images at several wavelengths. This extends the one-dimensional spectral measurements of Malonek & Grinvald (1996) into two dimensions. Methods:We imaged with a CCD camera the exposed visual cortex (V1 and V2) of anesthetized and paralyzed cats. The cortex was illuminated by four groups of light emitting diodes (LEDs) that alternated at the camera frame rate, 15 s-1. Light from the LEDs passed through 10 nm interference filters whose center wavelengths were chosen according to the Hb and HbO2 absorption spectra. The cats viewed horizontal and vertical drifting gratings that activated different patches of the cortex. Results:Our results suggest that the widely reported 0.1 Hz spontaneous wave and the transient evoked vasomotion wave we have reported recently (Cimponeriu & Kaplan 2001) are both primarily due to HbO2. The imaged response that is specific to the visual stimulus is caused mainly by Hb, while the HbO2 component spreads to both stimulated and unstimulated cortical regions. Conclusion:Time-division multi-wavelength optical imaging reveals quasi-simultaneous two-dimensional spatial information about the processes that contribute to the intrinsic optical signal and offers a tool to understand these processes better.
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