gamma oscillations were dominant in stratum lacunosum-moleculare, not stratum radiatum [35]. Spikes from projection neurons in layer III of MEC were phase-locked to the gamma activity in stratum lacunosum-moleculare, suggesting that this activity was driven by MEC [35]. The reason for the frequency differences between these results and the earlier results [30] may be due to the use of anesthesia in the majority of experiments in the Lastoczi and Klausberger study [35]. In line with this idea, example recordings obtained by Lastoczi and Klausberger from an anesthesia-free mouse showed ~70 Hz gamma in stratum lacunosum-moleculare (see Figure 1C in [35]). Additionally, the authors recorded multiple interneurons in the apical dendritic region of CA1. Some of these interneurons fired phase-locked to ~20–45 Hz oscillations, while others phase-locked to ~60–100 Hz oscillations. These results support the hypothesis that different classes of interneurons in CA1 drive slow and fast gamma activity. These different gamma-generating interneuron classes are likely activated by different inputs arriving at different theta phases. Recent evidence raises the possibility that interneurons activated during slow gamma from CA3 inhibit fast gamma from MEC. Specifically, OLM interneurons in CA1, which are activated by CA3, inhibit inputs from entorhinal cortex while at the
