1. In vertebrates as in invertebrates, protein kinase C appears to have a key role in learning and memory, probably given its involvement in synaptic plasticity. 2. Hippocampal PKC in mammalians is activated by learning in a large variety of memory tasks. However, the kind of information processed, the type of task, and the dynamics of learning processes all induce differential changes in the mode of PKC activation and in its anatomy. 3. The behaviourally induced changes in PKC activity are often varying in their magnitude. Inter-individual differences in PKC basal activity are generally correlated to the ability to learn. 4. Pharmacologic activation and inhibition of brain PKC shows that PKC activation plays an important role in cognitive function. 5. Basal PKC stores characterising each individual could be determined by genetic factors and modulated through life by individual experience. 6. The issue of PKC and memory relationships is reformulated through a comprehensive interactionist model which leads to formulating some new testable predictions.