Orientation dependency of intrinsic optical signal dynamics in cat area 18.

Imaging studies based on intrinsic optical signals have been primarily performed by analyses of the signal amplitude as opposed to using the temporal information of the intrinsic optical signals. The present study focused on the dynamics of these signals in cat area 18, and quantitatively compared the waveforms after presentation of different stimuli across the same cortical regions. Optical imaging based on intrinsic signals was conducted on 18 hemispheres of 9 cats. For the visual stimuli, gratings with orientations that changed from horizontal (0°) to 157.5° in 22.5° steps were used. The signal time course was examined at each pixel, with the peak delay defined as the amount of time required after the stimulus onset for the intrinsic optical signal to reach its negative maximum. In the area that showed significant orientation preference to 0° and 90° but not to their 22.5° separated nearby angles, the delays were 1.92 ± 0.22s and 1.99 ± 0.29s (mean ± SE, n = 18), respectively. Delays of 2.31 ± 0.20s and 2.28 ± 0.25s were observed in the cortical areas that selectively responded to the orientation gratings of 45°and 135° but not their nearby angles. Statistically, the delays in areas exhibiting oblique orientation preferences were significantly longer than those showing cardinal orientation preferences. These results demonstrate anisotropy for the intrinsic optical signal dynamics in the cat area 18. The possible neural mechanisms underlying were discussed.