Fig. 1

a The dorsal surface of the rat cerebral cortex viewed through the plano-concave lens. After the left somatosensory cortex was exposed by craniotomy, the lens was placed on the cortex. To keep measurements of the area near the midline of the cerebral cortex as broad as possible, we used half of the lens. Despite the marginal zone of the cerebral cortex being curved, we succeeded in obtaining a two-dimensional image where focus was maintained over an entire image. b Relative location of the photographed area in the top view of the rat brain. The area surrounded by a thick broken line is the photographed area in (a), and the semicircle indicates the plano-concave lens. Dimensions of the plano-concave lens: 10 mm diameter; 3 mm center thickness; 20 mm radius of curvature of the curved surface. c A vertical cross-section of the brain with a plano-concave lens. The position of the section plane is the symmetry plane of the lens and indicated by dotted line in (b)