The relationship between stimulating light intensity and probability of light-dependent action potential generation was measured by whole-cell patch-clamp or cell-attached recording (Fig. S2C). When the stimulation this website point was moved along the axial axis of the optical fiber bundle, the threshold light intensity was

unchanged, nevertheless increasing the distance between the recorded cell and stimulation point (Fig. S3A). On the other hand, the threshold light intensity was monotonically increased when the stimulation point was moved along a line perpendicular to the bundle’s axial axis (Fig. S3B). As shown in Fig. S3B, 10–20 μm of horizontal displacement of the stimulation point from the recorded cell significantly increased the threshold intensity for action potential generation. These results indicate that the spatial specificity click here of this photostimulation method is comparable to the soma size of cortical neurons in the plane perpendicular to the axial axis of the fiber bundle, but the specificity for the

axial axis is low. This is compatible with the light intensity distribution examined in the fluorescent solution (Fig. 2D). It should be noted that when the stimulation point was moved along the axial axis of the optical fiber bundle, stimulating light propagates in the extracellular solution (Fig. S3A), not in the brain tissue. This might have caused underestimation of the spatial specificity of photostimulation in the axial axis, because blue light is heavily absorbed by brain

tissue (Yizhar et al., 2011). Using the endoscope-based method, we next manipulated motor behavior. Previous VAV2 studies have shown that electrical stimulation or optogenetic stimulation of the rodent vibrissa motor cortex results in whisker deflections (Hall & Lindholm, 1974; Aravanis et al., 2007). Each whisker on a rodent’s face is connected to single intrinsic muscle (Dorfl, 1982), and studies have shown that low-intensity electrical stimulation can evoke single-whisker movement (Hall & Lindholm, 1974; Brecht et al., 2004). Therefore, the vibrissa system provides an appropriate model to test spatial specificity of neural stimulation. We used a strain of mice expressing ChR2 in projection neurons of cerebral cortex layer 5, output cells of the motor cortex (Arenkiel et al., 2007). An optical fiber bundle was inserted into the vibrissa motor cortex, and a brief light pulse train (40 ms duration, 500 ms interval, 5 repetition) was applied through a single core in the center of the fiber bundle (Fig. 7A and B). To quantify whisker deflection, images of contralateral whiskers were captured with a video camera and their movements were tracked (Fig. 7C). Trajectories of whisker movements are shown in Fig. 7D.