Spreading depression (SD) consists of a transient suppression of all neuronal activity that
spreads slowly across regions of gray matter. The paper is divided into three parts. Martins-
Ferreira describes 30 years of research on SD in the isolated retina. Much of this work has
relied on the prominent intrinsic optical signals that accompany SD in the retina. By inducing
SD to propagate in circles with a velocity of 3.7 mm min− 1, it is possible to investigate the
finely balanced electrochemical equilibrium that maintains the traveling wave. SD is …