Box 2.

.

Wide-field optical imaging with voltage-sensitive dyes
To capture the time course of reorganization processes along with alterations in the functional characteristics of lateral connectivity at the neuronal population level, wide-field optical imaging in combination with voltage-sensitive dye (VSD) can be a useful tool (Grinvald and Hildesheim 2004; Jancke et al. 2004)
Using a tandem-lens system (Ratzlaff and Grinvald 1991) and a fast CCD camera, wide-field VSD imaging allows recording of changes in cortical activity across several millimeters of cortex (Berger et al. 2007; Chen et al. 2006; Grinvald et al. 1994; Jancke et al. 2004; Meirovithz et al. 2012; Muller et al. 2014; Onat et al. 2011a, b; Petersen et al. 2003; Roland et al. 2006; Sit et al. 2009) with high temporal (milliseconds) and spatial resolution [50 microns; for a review see Grinvald and Hildesheim (2004)]. In addition, as the method records activity from large pools of neurons with high spatiotemporal resolution, patterns of activity dynamics can be revealed that are currently still not detectable with densely spaced multi-electrode arrays. Moreover, the method avoids biases in sampling of neurons
Note that due to light scattering, the depth of the tissue staining with dye, and the applicable focal depth, the main source of the fluorescent imaging signals is derived from cortical superficial layers (> 80%) (Grinvald and Hildesheim 2004; Petersen et al. 2003). Thus, any remodeling occurring in deeper cortical layers including thalamo-cortical afferents is unlikely to be accessible. As neurons in layers 5/6 have dendritic arbors up into layers 2/3, deeper cortical layers may nonetheless contribute to the optical signal