Updating the hippocampal representation of space: place cell firing fields are controlled by a novel spatial stimulus.

To ask if the properties of spatial learning supported by the hippocampus are distinct from the properties of conditioning, we conducted a blocking-like experiment in which the measured variable was not a conditioned response but rather the ability of a novel visual stimulus to control the location of place cell firing fields after being briefly combined with a familiar, salient stimulus to form a compound stimulus. For most rats, we found that rotations of the novel stimulus on the wall of a cylindrical recording chamber produced equal rotations of firing fields, whether exposure to the compound stimulus lasted 10 min or 60 min. Thus, there was little indication that the blocking phenomenon (Kamin, 1969) acted to prevent the rapid inclusion of a new stimulus into a previously experienced cue constellation. This result is in agreement with the finding of Doeller and Burgess (2008) that blocking is seen for landmark stimuli inside an arena but not for boundary stimuli that circumscribe the arena. We conclude that the rules governing incidental spatial learning are different for the hippocampal representation of a rat's environment than for conditioning.