Artificial nerves that are capable of sensing, processing and memory functions at bio-realistic frequencies are of potential use in nerve repair and brain-machine interfaces. n-type organic electrochemical transistors are a possible building block for artificial nerves, as their positive-potential-triggered potentiation behaviour can mimic that of biological cells. However, the devices are limited by weak ionic and electronic transport and storage properties, which leads to poor volatile and non-volatile performance and, in particular, a slow response. We describe a high-frequency artificial nerve based on homogeneously integrated organic electrochemical transistors. We fabricate a vertical n-type organic electrochemical transistor with a gradient-intermixed bicontinuous structure that simultaneously enhances the ionic and electronic transport and the ion storage. The transistor exhibits a volatile response of 27 mu s, a 100-kHz non-volatile memory frequency and a long state-retention time. Our integrated artificial nerve, which contains vertical n-type and p-type organic electrochemical transistors, offers sensing, processing and memory functions in the high-frequency domain. We also show that the artificial nerve can be integrated into animal models with compromised neural functions and that it can mimic basic conditioned reflex behaviour.