“…Optic fibers can regrow to their appropriate retinotopic position in tectum following surgical diversion to abnormal starting positions or can relocate their appropriate piece of tectum when it has been transplanted to an inappropriate region of tectum (Sperry, 1963;Meyer, 1980Meyer, , 1984Gaze and Hope, 1983). More recent work, however, sug-gests that the formation of connections may be more flexible than implied by a rigid cell marker system (Schmidt et al, 1978;Cook, 1979;Horder and Martin, 1982; reviewed by Cowan and Hunt, 1985;Fraser, 1985). In particular, the establishment of specific synapses may be regulated by impulse activity.…”