Modulation of calcium-dependent postsynaptic depression contributes to an adaptive sensory filter

The ability of organisms to ignore unimportant patterns of sensory input ma y be as critical as the ability to attend to those that are behaviorally re levant. Mechanisms used to reject irrelevant inputs range from peripheral f ilters, which allow only restricted portions of the spectrum of possible in puts to pass, to higher-level processes, which actively select stimuli to b e "attended to." Recent studies of several lower vertebrates demonstrate th e presence of adaptive sensory filters, which "learn," with a time course o f a few minutes, to cancel predictable patterns of sensory input without co mpromising responses to novel stimuli. Predictable stimuli include "reaffer ent" stimuli, which occur as a result of an animal's own activity, as well as stimuli that are simply repetitive. The adaptive characteristic of these filters depends on an anti-Hebbian form of synaptic plasticity that modula tes the strength of multisensory dendritic inputs resulting in the genesis of "negative image'' signals, which cancel the predicted pattern of sensory afference. This report provides evidence that the mechanism underlying the anti-Hebbian plasticity involves the modulation of a calcium-dependent for m of postsynaptic depression.