The intermediate medial part of the hyperstriatum ventrale (IMHV), part of the avian forebrain, is essential for early learning in the domestic chick. Persistent potentiation (PP) can sometimes be induced in the IMHV in vitro. One can predict success from events which occur during the stimulation (1 min at 5 Hz) which is used for induction: the original response must be transiently replaced by a later, slower response (the LPSR). has a comparatively high threshold of activation, its rate of development is inversely related to magnesium concentration and it can be eliminated by NMDA antagonists, as can the induction of PP. PP in the IMHV is therefore dependent upon NMDA receptors and the LPSR represents the activation of these receptors.