[The ultrastructural changes in the synapses of the hyperstriatum of chicks after visual imprinting].

Studies on ultrastructural changes in the accessory and ventral hyperstriatum in chicks at the 2nd and 3rd days after visual imprinting revealed significant increase in the surface of synaptic contact zones and mean width of postsynaptic thickenings in the investigated structures. The data obtained are discussed in relation to the specific role of the medial part of the ventral hyperstriatum in birds during learning and imprinting memory.