Rats that are trained in a particularly difficult olfactory-discrimination task demonstrate a dramatic increase in their capability to acquire memories of new odors, once they have learned the first discrimination task (‘rule learning’). Such rule learning is accompanied by a series of cellular modifications which share three major traits: First, they are widespread throughout the relevant cortical networks. Both physiological and morphological modifications are found in most of the studied neurons. Second, the time course in which these modifications appear and disappear is strongly correlated with the time course in which the skill is acquired and decays. However, memories for specific odors outlast these modifications by far. Thus, the identified modifications are related to rule learning (learning how to learn), rather than to long-term memory for the specific odors for which the rats are trained. Third, at the cellular level, learning-induced long-term modifications occur in the three components controlling neurons activation: The excitatory synaptic drive, mainly mediated by glutamate receptors, the intrinsic neuronal excitability, and synaptic inhibition, mediated by GABA_A receptors. Such profound, whole network modifications are not the mechanism by which memories for specific sensory inputs or sequences of events are stored. Rather, they may be the mechanism that enables neuronal ensembles to enter into a state which may be best termed “learning mode”. This state lasts for up to several days, and its behavioral manifestation is a general enhancement in learning capabilities in tasks that depend on these particular neuronal ensembles. The transition in and out of learning mode may be well described as a beyond-hebbian phenomenon, based on the facts that it results with a dramatic change in the animal’s behavior, and requires modifications in biophysical properties in most elements of the neuronal ensemble.