A detailed study of the slow manifold of a model exhibiting mixed-mode
oscillations is presented. A scenario for the emergence of mixed-mode states
which does not involve phase locking on a 2-torus is constructed. We show that
mixed-modes correspond to the periodic orbits embedded in the horseshoe-type
strange set and demonstrate how transformations of this set determine the
transitions of mixed-mode states into each other.Comment: RevTex, 10 eps fig., 9 page