Neuronal activity is altered in the somatosensory cortex after removal of sensory input. (A-G) c-Fos expression was examined in P9 brain slices. Compared with control brain (A, B), c-Fos-positive neurons are decreased more in number in P9 brain slices from the contralateral side compared with ipsilateral side (C, D) after P5 unilateral ION transection. While in the brain with P5 bilateral ION transection, c-Fos-positive neurons are similarly reduced in number on both sides (E, F). Nuclear Hoechst counterstain is shown with pseudocolor (cyan), and c-Fos-positive neurons are indicated by triangles. Comparison of numbers of c-Fos-positive neurons is shown in (G); animal numbers examined are indicated. **P < 0.01; #P < 0.01 (control vs the others). (H) Patch-clamp recording was performed in layer II/III neurons of the S1 region of brain slices prepared from P7 mice. Frequency of sEPSC is reduced on both sides in mice with bilateral unilateral removal of sensory input compared with control mice, but it shows more reduction in the contralateral side compared with that in the ipsilateral side. In mice with bilateral removal of sensory input, frequency of sEPSC of the cortical neurons in the S1 is equally reduced on both sides. Representative recordings in brain slice prepared from mice with ION transection are shown in left panel, and quantification of the sEPSC frequency is shown in right two panels. At least three mice were examined in each group, and neuron numbers for each recoding are indicated. *P < 0.05, #P < 0.01 (control vs the others). Bil. ION, bilateral transection of IONs; Bil. Lesi, bilateral lesion of whisker hair follicles; Cont, contralateral side; Ipsi, ipsilateral side; Uni. ION, unilateral transection of ION; Uni. Lesi, unilateral lesion of whisker hair follicles. Scale bar, 60 μm.