Based on some properties of hippocampal circuitry, an attempt has been made to interpret behavioural changes in hippocampectomized animals. The regulation of cortically initiated information flow through the hippocampus by the unspecific inhibitory blocking, selective depression or potentiation of intrinsic hippocampal chains has been analyzed at different levels of reticulo-septal input, characteristic of different behavioural patterns. By the first mode of hippocampal regulation the ignorance of irrelevant stimuli during an automatized behaviour is achieved; temporary selective depression or strengthening of influence of certain relevant stimuli takes places in the two other modes.