Prefrontal cortex lesions modify the spatial properties of hippocampal place cells

It has previously been proposed that the prefrontal cortex has a role in 'executive processes' and memory function. These activities presumably require modulation of activity in posterior cortex. On the basis of this hypothesis, it was proposed that prefrontal cortex lesions might alter neural activity in the hippocampus, a region implicated in memory processing. A major feature of hippocampal activity is place-related firing. Single unit recordings of CA1 complex spike cells ('place cells'; n = 64) were made as rats with prefrontal lesions (n = 6) or sham surgeries (n = 7) foraged freely. The spatial information content provided by spikes in cells of lesion animals was significantly greater than in sham-group animals, although the size of their place fields was not affected. The location of the firing fields of lesion-group rats were less stable across time when either 5 h or 3 min intervals were inserted between successive recordings of the same cell. It was hypothesized that animals with prefrontal lesions may be overly influenced by local, less stable environmental cues than sham rats. This may explain both the spatial information content and stability findings. These findings indicate that prefrontal cortex normally modulates spatial responses in the hippocampus.