Spatial memory, recognition memory, and the hippocampus

TLDR

Spatial memory depends on hippocampal integrity, but its role in nonspatial tasks such as object recognition is uncertain. We investigated how the size of hippocampal lesions affects spatial and object recognition memory in rats. By creating graded dorsal and ventral hippocampal lesions and testing memory performance, we examined the relationship between lesion extent and cognitive function. Spatial memory was impaired with 30–50 % dorsal lesions and worsened with larger lesions, whereas object recognition remained intact until lesions exceeded 75 % of the hippocampus; ventral lesions impaired spatial but not recognition memory, indicating spatial memory requires more hippocampal tissue than recognition memory.

Abstract

There is wide agreement that spatial memory is dependent on the integrity of the hippocampus, but the importance of the hippocampus for nonspatial tasks, including tasks of object recognition memory is not as clear. We examined the relationship between hippocampal lesion size and both spatial memory and object recognition memory in rats. Spatial memory was impaired after bilateral dorsal hippocampal lesions that encompassed 30-50% total volume, and as lesion size increased from 50% to ≈100% of total hippocampal volume, performance was similarly impaired. In contrast, object recognition was intact after dorsal hippocampal lesions that damaged 50-75% of total hippocampal volume and was impaired only after larger lesions that encompassed 75-100% of hippocampal volume. Last, ventral hippocampal lesions that encompassed ≈50% of total hippocampal volume impaired spatial memory but did not affect object recognition memory. These findings show that the hippocampus is important for both spatial memory and recognition memory. However, spatial memory performance requires more hippocampal tissue than does recognition memory.