Watanabe, K.; Takeda, K.; Iijima, S.; Nagahiro, T.; Ikegaya, Y.; Matsumoto, N.

Theanine, a non-proteinogenic amino acid derivative from green tea leaves, enhances object recognition memory in rats through facilitated neurogenesis. In this sense, the cellular mechanism for the theanine-enhanced object recognition memory has been elucidated to some extent, but physiological evidence still remains unclear. To tackle this issue, we chronically fed mice with theanine (or tap water) for three weeks, implanted electrodes into the hippocampus and frontal cortex, both of which are responsible for object recognition memory. We then recorded the local field potentials from the two regions during the novel object recognition task, evaluated the task performance, and broke down the neural signals in the hippocampus and frontal cortex into delta, theta, beta, low gamma, and high gamma frequency bands. The discrimination ratio of theanine-treated mice was higher than that of vehicle-treated mice. We also found that theta oscillations in the frontal cortex and beta and low gamma oscillations in the hippocampus in theanine-treated mice were simultaneously enhanced for familiar objects. These results shed light on the new physiological underpinnings of object recognition memory enhanced by exogenous substances.