Measurement of the neural activation potential of rat cerebral cortex using functional optical reflection tomography

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Our research target is proposal and demonstration of a novel functional optical reflection tomography (f-ORT). This unique technique is used for measurement of spatial and temporal distribution of neural activation potential of the cerebral cortex of rats, showing that the f-ORT is effective for brain neurology.(1) A SLD is used as the light source of the existing optical coherence tomography (OCT); however, the coherence length of SLD is 10 to 20 μm which is insufficient for detection of neural activation potential. In order for the detection, the SLD was replaced by a mode-locked Ti:sapphire laser which supplied the pulsewidth as short as lOfs. This laser can provide us OCT with the spatial resolution of 3 μm after proper compensation of chromatic dispersion of the interferometer.(2) In order to the high-resolution OCX described above, we developed the 1,3-μm OCT in which the imaging depth is improved to be 1.5mm or more. Subsequently, the desired optical reflection tomography was de … More veloped by combination of the coherence-gate optics and confocal optics.(3) The imaging data must be acquired as fast as possible in order to detect the neural activation potential in synchronization with the cardiac rate. Such a high-speed data acquisition can be realized by non-mechanical optical-delay scanning. In the f-ORT, the optical-delay scanning is performed by PZT fiber phase modulators, as a result, more than 50 optical-delay scans per second were obtained. All the raster scan signals are summed up to improve drastically the signal-to-noise ratio.(4) In the preliminary experiment, a refractive index change was detected by the f-ORT when a sound stimulus was applied to a rat. The index change may correspond to the neural activation potential due to a sound stimulus. A remarkable change of the optical reflection signal was detected in a 100-μm deep area 20s after application of the sound stimulus. On the basis of research results, as mentioned above, we have been developing the f-ORT for brain neurology. Less