Investigations of "Spatial" Firing in Dorsal Hippocampus of the Rat

"Spatial" units have been identified in micro-electrode recordings from dorsal hippocampus of rats. Such units fire at their maximum rates only when rats are in specific regions of the recording space, called the units' "fields", and seem to be independent of details of the animals' behavior. Spatial firing is consistent with a recent suggestion that the hippocampus functions as a "map" of the environment. Recordings were made from dorsal hippocampus of rats as the animals performed a spatial alternation task in an enclosed T-maze. Spatial firing was identified in rats which had been selectively deprived of either visual, vibrissal, auditory or olfactory sensory inputs. Results are consistent with other evidence that hippocampal spatial firing is based upon multi-modal sensory cues. Recordings were made from dorsal hippocampus of rats as the animals learned to shuttle and alternate in the T-maze when they had not been there before. In 11 out of 15 cases, spatial firing occurred during the first passage of the rat through the unit's field. In the other 4 cases, firing occurred for the first time within 15 minutes of the rat's first exposure to the field. Results are discussed in relation to theories of hippocampal function.