It has been shown that the amplitude of gamma oscillations modulates the phase of theta rhythm in the hippocampus [1]. In this work, we reproduce the single node Neural Mass Model (NMM) proposed in [2] to study the phase-amplitude coupling and the directionality of the oscillations in the hippocampus. The aim is to determine a particular condition of the model which can reproduce the experimental results obtained in [1]. In addition, a NMM comprised of a given number of nodes has been developed on the basis of the neural mass model proposed in [3].