Figure 4.

Cortical-cortical, hippocampal-hippocampal, and cortical-hippocampal coherence of the slow oscillation during urethane anesthesia. Representative field recordings from the HPC and two distant cortical sites [fCTX and posterior occipital cortex (pCTX)] are shown in A, and recordings from the fCTX and two isotypic points in the right HPC (RHPC) and left HPC (LHPC) are shown in B. Although cortical EEG traces in A and hippocampal EEG traces in B look almost identical, there is more variation between cortical and hippocampal field activity. The bottom panel shows coherence measurements between the above sites for seven different experiments in A and six other experiments in B (filled squares represent measures for data shown in top panel). Averages and SEM are offset to the right of each pairwise plot. These demonstrate that although cortical-cortical and hippocampal-hippocampal coherence of the SO is relatively invariable and extremely high, cortical-hippocampal coherence tends to be more variable and significantly lower. NS, Not significant; LfCTX, left fCTX; fiss, fissure.