Neuroscience is nowadays one of the most collaborative and active scientific research fields as it has been increasingly involving the participation of experts from other disciplines. Computational and mathematical aspects of neuroscience are currently playing an important role both in modeling and replicating experimental findings and in explaining the underlying mechanisms of neurophysiological or cognitive processes. The aim of this Fourth Workshop on Neurodynamics, NDy'26 (previous editions were NDy'23 NDy'18, NDy'14) is to present an overview of successful achievements in this rapidly developing collaborative field by putting together different types of applications of nonlinear dynamics (geometrical tools in dynamical systems, numerical methods, computational schemes, dynamical measures, machine learning...) to different problems in neuroscience (mononeuronal dynamics, network activity, cognitive problems, ...).