Central control of developmental plasticity in the mammalian visual cortex

Visual experience influences the development of visual cortex functions. By manipulating retinal activity the efficacy of excitatory connections between the eyes and cortical neurones can be modified dramatically. A criterion for the enhancement or impairment of transmission is the temporal contiguity of pre- and postsynaptic activation. For a change to occur it is necessary that the cortical cells respond to retinal activity but this condition is not sufficient. Further permissive gating signals of nonretinal origin are required. It is proposed that these "now print" signals act by controlling the Ca2+-conductance of cortical dendrites. The possible role of these activity dependent modifications is discussed in the context of the development of cooperatively coupled cell assemblies.