The γ−decay associated with the warm rotation of the superdeformed (SD) nuclei 151 Tb and 196 Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the SD well. A Monte Carlo simulation of the γ-decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength at low excitation energy, which may be related to the evidence for octupole vibrations in both mass regions.PACS numbers: 21.10. Re;23.20.Lv;25.70.Gh;27.70.+q;27.80.+w The thermally excited, rapidly rotating atomic nucleus is an ideal laboratory for studying structure properties beyond mean field. In particular, the γ-decay which cools the hot compound nucleus at high angular momentum is a powerful tool for investigating the transition from the chaotic regime around the particle binding energy to the cold, ordered system close to the yrast line [1,2,3]. This topic, mostly investigated in normally deformed (ND) nuclei [1,2,4,5,6,7], becomes particularly interesting and challenging, both experimentally and theoretically, in the case of very elongated systems. The study of superdeformed (SD) nuclei requires, in fact, high selectivity and high statistics experiments, in order to focus on the small fraction of the γ-decay (≈ few %) which finally gets trapped into the SD well and populates discrete rotational bands. At present, there is only partial experimental information available for few SD nuclei [8,9,10,11,12], whose interpretation is based on models which are either rather schematic [9,11,12] or depend on several parameters [8,10].The aim of this letter is to make a substantial step forward in the understanding of the population and decay of warm SD nuclei in the mass regions A=150 and A=190, where superdeformation is a well established phenomenon, by a comparative and comprehensive study of the nuclei 151 Tb and 196 Pb. For the first time, several independent observables are extracted from quasicontinuum γ-coincidence spectra. This provides strong experimental constraints on the dynamics of the γ-decay flow and of the tunneling through the potential barriers between SD and ND excited states, over a wide spin range. A key point of this work is the development of a new Monte Carlo simulation of the γ-cascades in the SD well. This makes use of discrete levels calculated microscopically with the cranked shell model. In addition, the coupling between excited SD and ND configurations is included, based on penetration probabilities obtained from a microscopical model [13]. It is anticipated that such a detailed study of the order-to-chaos region reveals the influence of nuclear structure effects. In particular, an enhancement in the E1 strength around 1-2 MeV, which could be related to octupole vibrations, is found to play an important role.The experiments were performed at the Vivitron in Strasbourg (F) with the EUROBALL IV array [14]. The reaction used were 130 Te( 27 Al,6n) 151 Tb (at 155 MeV) ...