“…The plasticity of synaptic sites (see below) exerts an additional, undetermined effect on the synaptic frequencies observed at any one time. If individual synaptic sites turn over in the adult, as has been argued in Musca for the feedback synapse of L2 (Kral and Meinertzhagen, 1989) and as is widely mooted (e.g., Wernig, Carmody, Anzil, Hansert, Marciniak, and Zucker, 1984), although not invariably found (e.g., Lichtman, Margrassi, and Purves, 19871, in the remodeling of neuromuscular junctions, the survival of different synaptic types may be variably susceptible to visual experience.…”