Passive Spatial Perception Facilitates the Expression of Persistent Hippocampal Long-Term Depression

Learning-facilitated plasticity describes the ability of hippocampal synapses to respond with synaptic plasticity when weak afferent stimulation is coupled with a spatial learning event. Qualitative differences appear to influence whether long-term potentiation or long-term depression (LTD) are facilitated by spatial learning. At many hippocampal synapses, LTD is facilitated when rats actively explore a novel spatial context. We investigated whether learning-facilitated plasticity is expressed when an unconstrained but stationary rat observes a computer-generated spatial environment. Visual fields were separated. Novel object configurations were presented to one field; familiar constellations were presented to the other field. LTD was facilitated in the CA1 region of the hemisphere to which novel object constellations were presented. Familiar constellations had no effect. LTD facilitation was prevented by treatment with the protein translation inhibitor, anisomycin. LTD in the dentate gyrus was not facilitated by novel object constellations, suggesting that effects are not common to all hippocampal subfields. These data support a unique association of LTD in the CA1 region with learning about spatial context and indicate that rats can passively perceive space.