"clearly, the progenitors of the MGE- and CGE-derived interneuron subgroups have molecular ifferences at the time that they exit the cell cycle, but are they committed at this point to a particular fate of do signals encounteres later establish their potential for differntiating into a given subgroup? A comparison of two MGE progenitor fate-mapping experiments suggests that key aspects of interneuron subgroup fate are likely to be specified as the progenitors leave the cell cycle, and not by factors encountered during migration"