The brain exhibits a number of EEG rhythms, generated by synchronous neuronal activity, that appear in particular behavioral contexts. Local rhythmic activity is particularly prominent in the hippocampal formation. This structure, which exhibits mainly feedforward excitatory connections, is crucial for learning and memory associated with episodes in one's own life and a site of critical neuropathologies in Alzheimer's disease and temporal lobe epilepsy. This chapter explores how phase-response techniques from the mathematical discipline of non-linear dynamics can be applied in cellular electrophysiological experiments. These techniques are a powerful tool for studying synchronization under normal conditions, as well as in pathological conditions like epilepsy. Applying phase-response methods in principal cells of the entorhinal cortex, this chapter elucidates that layer 2 spiny stellate cells synchronize strongly via mutual excitation. Layer 3 pyramidal cells also synchronize via mutual excitation, but less strongly. The inwardly rectifying cation conductance gH is a crucial determinant of the ability of interconnected excitatory networks to synchronize. Manipulation of gH experimentally can lead to opposing effects on excitability and synchronization. These results are discussed in the context of animal models of epilepsy.