[The ultrastructural characteristics of the synapses during the acquisition of a passive avoidance reaction and of imprinting in chicks].

Studies on morphometric parameters of synapses in the visual projection zone of the accessory and associative zone of the ventral hyperstriatum in both hemispheres of the brain in 4-day chicks after visual imprinting and alimentary aversive learning revealed specific changes in the longevity of postsynaptic dense regions and in the number of vesicles in active zone. The role of the structures studied in sensory perception, learning and memory is discussed.