SUSTAINED iontophoresis of NMDA potentiated visual responses for minut
es after the application in 16 of 38 cells (42%), peaking 3 min after
the end of the application and declining to control levels within 12 m
in. Potentiation was also seen after application of ACPD (36%, n = 14)
and AMPA (29%, n = 14), but not after application of ACh (n = 20). AC
h also excites dLGN cells, but does not interact with amino acid recep
tors, and ACh receptors are not directly involved in the transmission
of visual information. We suggest that this modulation is a form of vi
sually induced potentiation which permits dynamic modification of the
strength of visual information to be relayed to the cortex depending u
pon the history of previous activity levels.