Abstract
Experiments on the thalamus, dorsal column nuclei and spinal cord in the adult cat and rat show that partial destruction of afferents to these regions leads to the immediate unmasking of certain types of activity which are normally inhibited. Chronic studies show that some cells begin to respond to afferent nerve impulses after a period in which the cell seems to have lost all inputs. Sprouting of terminals from remaining areas is one possible explanation for these late changes but one must also consider the possibility that the new connections result from axons which were already present but which normally were ineffective.