2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4227In this paper, I emphasize the need for integral field spectroscopy in the study of density waves (bars, spirals, m=1 modes) in the centre of galaxies. I illustrate this by focusing on the complex and time dependent structures revealed by such techniques.8 pages, 5 figures. Version with higher resolutions figures available at: http://www-obs.univ-lyon1.fr/eric.emsellem/papers/cozumel_emsellem2.ps.gzAstrophysicstext