In situ hybridizations for per1 (upper) and per2 (middle panels) expression in four sagittal brain sections from sleep deprived (SD, right) and control (left panels) mice. All sections were taken close to mid-line (see lower panel; red vertical line in coronal section indicates the plane of the sagittal sections). per was expressed mostly in cortex and cerebellum and SD induced an increase in both these areas, confirming our own per1 expression data (Fig. 4). These data were taken, with permission, from the publicly available in situ studies of the Allen Institute for Brain Science , done in collaboration with Drs. T.S. Kilduff and J.P. Wisor of SRI International. The experimental protocol was identical to that of the 6 h SD in the present study; both SD and control animals were sacrificed at ZT6. ID numbers of sections: per1 control: 145-0202054795 at 3625; SD: 153-0202055093 at 3825; per2 control: 140-0205056163 at 3500; SD: 132-0205058042 at 3300. Lower right panel is the histological view (Nissl stain) of the upper right panel (per1-SD) with cerebral cortex (CTX), thalamus (TH), hypothalamus (HY), and cerebellum (CB). The presence of EEG electrodes in some mice caused cortical damage during brain removal.