The PFC is theorized to be a master regulator of working memory, yet the mechanism by which it influences other brain regions is not clear. The 2–5 Hz oscillation may allow for a flexible signal for the PFC to synchronize electrical activity with other brain regions. Fujisawa and Buzsaki (2011) reported a similar dominant 4-Hz (2–5 Hz band) oscillation in the PFC that was phase-coupled to HC theta and to neuronal firing in HC and the ventral tegmental area (VTA) during working memory task. As reviewed by Fujisawa and Buzsaki (2011), 2–5 Hz oscillations connecting PFC to other structures may be wide-spread, as its presence was visible in a number of previous reports even though the authors may not have emphasized them. Besides the VTA and HC, 2–5 Hz rhythm of PFC origin was present for example in striatal recordings (Dzirasa et al. 2010; Tort et al. 2008), and 2 and 4 Hz sharp narrow-band coherence with frontal cortical EEG was reported as far as in brainstem sympathetic circuits (Kenney et al. 1990). In the PFC-HC network, 4-Hz oscillation may
