For g modes the relevant property are sharp variations in the buoyancy frequency, giving rise to departures from the uniform period spacing in Eq. (2). This has been used extensively to characterize the properties of pulsating white dwarfs (for a review, see Fontaine & Brassard 2008). The variation in the buoyancy frequency outside convective cores also has a substantial effect on g modes in main-sequence stars, particularly visible when, as in the case of slowly pulsating B stars, high-order modes are observed. Miglio et al. (2008) carried out a careful analysis of the resulting signatures in the period spacings. Remarkably, this behaviour was recently observed in CoRoT **data** on a B star (Degroote et al. 2010a,b), promising very valuable constraints on the mixing outside convective cores in such stars.