However, a more recent study challenges the hypothesis that theta-modulated fast gamma facilitates encoding of current information. Yamamoto and colleagues found that fast gamma phase synchrony between CA1 and MEC increased at the choice point of a delayed non-match-to-place task [25], a location where memory retrieval is expected, not memory encoding. Moreover, such increases were not seen when the animal made an incorrect choice, and correct task performance was disrupted when fast gamma was suppressed at the choice point. The authors suppressed fast gamma by silencing MEC inputs to CA1. Thus, although these results support the conclusion that MEC inputs drive fast gamma in CA1, they are inconsistent with the hypothesis that fast gamma promotes memory encoding. Clearly, more studies are needed to better understand the functional significance of fast gamma in the entorhinal-hippocampal network.
