Input driven synchronization of chaotic neural networks with analyticaly determined conditional Lyapunov exponents

Recurrent neural networks (RNNs) with random, but sufficiently strong and balanced coupling display well known high-dimensional chaotic dynamics. Here, we investigate if externally applied inputs to these RNNs can stabilize globally synchronous, input-dependent solutions, in spite of the strong chaos-inducing coupling. We find that when the balance between excitation and inhibition is exact, that is when the row-sum of the weights is constant and 0, a globally applied input can readily synchronize all neurons onto a synchronous solution. The stability of the synchronous solution is analytically explored in this work with a master stability function. For any synchronous solution to the network dynamics, the conditional Lyapunov spectrum can be readily determined so long as the connection weight matrix is diagonalizable. The stability of the synchronous solution is critically dependent on the largest real eigenvalue component of the RNN weight matrix. We find that the smaller the maximum real component of the weight matrix eigenvalues, the more readily the network synchronizes. Further, the conditional Lyapunov exponents are easily computed numerically for any synchronization signal without simulating the RNN. Finally, for certain oscillatory synchronization signals, the conditional Lyapunov exponents can be determined analytically.