Increased attention to spatial context increases both place field stability and spatial memory.

The hippocampal formation is critical for the acquisition and consolidation of memories. When recorded in freely moving animals, hippocampal pyramidal neurons fire in a location-specific manner: they are "place" cells, comprising a hippocampal representation of the animal's environment. To explore the relationship between place cells and spatial memory, we recorded from mice in several behavioral contexts. We found that long-term stability of place cell firing fields correlates with the degree of attentional demands and that successful spatial task performance was associated with stable place fields. Furthermore, conditions that maximize place field stability greatly increase orientation to novel cues. This suggests that storage and retrieval of place cells is modulated by a top-down cognitive process resembling attention and that place cells are neural correlates of spatial memory. We propose a model whereby attention provides the requisite neuromodulatation to switch short-term homosynaptic plasticity to long-term heterosynaptic plasticity, and we implicate dopamine in this process.

The long-term stability of new hippocampal place fields requires new protein synthesis.

The hippocampus is critical for formation of spatial memories. Hippocampal pyramidal neurons in freely behaving animals exhibit spatially selective firing patterns, which taken together form an internal representation of the environment. This representation is thought to contribute to the hippocampal spatial memory system. Behavioral long-term memories differ from short-term memories in requiring the synthesis of new proteins. Does the development of the internal hippocampal representation also require the synthesis of new proteins? We found that blocking protein synthesis in the brain of mice by 95% does not affect short-term stability of newly formed hippocampal place fields but abolishes stability in the long term. By contrast, inhibiting protein synthesis does not affect the retention and recall of previously established fields in a familiar environment, indicating that protein synthesis-dependent reconsolidation is not required for recall. Our results indicate that place fields parallel both behavioral memories and the late phase of long-term potentiation in requiring the synthesis of new proteins for consolidation.