Intrinsic optical imaging of neural activities using the laser speckle phenomenon

我们构建了一种新的光学成像系统，利用激光散斑现象来检测中枢神经系统的神经活动。该系统不仅可以检测本征光信号，还可以用压敏染料检测非本征光信号。我们已经对新的光学成像系统的可行性进行了初步的检验。在大鼠体感觉皮层中检测到光反射的变化，以响应细小的胡须移动。该系统由空间分辨率为756×574像素的低噪声CCD摄像机、464ch光电二极管阵列、模拟视频增强放大器和高分辨率视频显示器组成，并由高速PC机控制。从视频信号中减去参考图像。产生的信号随后由图像处理器放大和数字化。差值增强图像的这种数字化相当于12比特以上的数字化。对于功能成像，单个晶须偏转1或2秒，同时记录8帧每帧500毫秒。对于第一次测量，我们检查了本征信号的作用谱，并比较了本征信号在不同波长下的时间进程。此外，我们还分析了诱发的本征信号的FFT谱。因此，我们已经能够检测到在晶须移动过程中产生的相对清晰的光学响应，并且我们可以检测到响应的FFT谱的变化。

We have constructed a new optical imaging system using the laser speckle phenomenon to detect neural activities from the central nervous system. This system makes us possible to detect not only intrinsic optical signals but also extrinsic optical signals with voltage-sensitive dyes. We have made a preliminary examination of feasibility of the new optical imaging system. Optical reflectance changes were detected in the rat somatosensory cortex in response to small whisker movements. This system was composed of a low noise CCD camera that provides a spatial resolution of 756×574 pixels, a 464ch photodiode array, an analog video enhancement amplifier and high resolution video displays, which were controlled by a high speed PC computer. A reference image was subtracted from the video signal. The resulting signal was then amplified and digitized by an image processor. This digitization of the differential-enhanced image was equivalent to more than 12 bit digitization. For the functional imaging, a single whisker was deflected for 1 or 2 sec while 8 frames of 500 msec each were recorded. For the first measurements, we examined the action spectrum of the intrinsic signal and compared the time course of the intrinsic signal at different wavelength. Moreover, we analyzed FFT spectrum of the evoked intrinsic signals. Consequently, we have been able to detect the relatively clear optical responses elicited during the whisker movement, and we could detect changes in FFT spectrum of the response.