Remote sensing of broadband (<1 Hz to 300 kHz) lightning signals related to terrestrial gamma-ray flashes (TGFs) indicates that gamma-rays in TGFs are typically produced during a slow process that creates a considerable charge moment change within a few milliseconds. This slow process is usually punctuated by one or more fast discharges one of which is involved in gamma-ray production. The observed complexity of TGF-associated lightning emissions can be interpreted in the context of the initial development of normal intra-cloud lightning flashes, where the upward negative leader drives the millisecond-scale current and may also provide the seed electrons for avalanche multiplication in the upper part of active thunderstorms.