Electrical stimulation of the RPO resulted in reliable sinusoidal oscillations in the PFC, HC, and nRE. Two prominent rhythms were observed which were generally present in all three signals to different degrees, depending on the intensity of RPO stimulation. Figure 2 shows an example in which at low intensity (0.15 mA; Fig 2B), 2–5 Hz oscillation dominated the PFC signal, theta dominated the HC signal (at 2.7 and 6.3 Hz, respectively), and both rhythms were present in the nRE (Fig. 2F). Increasing the stimulus intensity (0.33 mA; Fig. 2C) changed this pattern to synchronized theta oscillations (at 7.6 Hz) in all three locations (Fig. 2D–F). The frequency and power of both oscillations systematically changed as the RPO stimulations varied (Fig. 3A–C). As in previous studies (Li et al. 2007; Ly et al. 2013), the peak frequency of theta rhythm was between 5.4 Hz ± 0.26 and 7.4 Hz ± 0.24 and increased linearly with increasing stimulus intensity (r = 0.64, p <0.001). The frequency of PFC 2–5 Hz oscillation varied between 2.7 Hz ± 0.19 and 3.7 Hz ± 0.3
