Hippocampal place cells have the interesting property of increasing their firing rate when a freely moving animal increases its running speed through the cell's place field. A previous study from this laboratory showed that this movement-related firing property is disrupted by lesions of the perirhinal cortex (PrhC). It is possible, therefore, that PrhC lesions disrupt speed-modulated sensory information such as optic flow or motor efferent or proprioceptive input that might be available to the hippocampus from the PrhC. To test this hypothesis, rats with single unit recording electrodes implanted in the CA1 region of the hippocampus received different levels of optic flow stimulation in both a freely moving and a passive movement condition. The effects of PrhC lesions were also tested. Although increasing the amount of optic flow information available decreased place field size, it had no discernable effect on the movement-firing rate relationship in the place cells of control animals run in the free-movement condition. In lesioned animals the relationship was disrupted, replicating our previous results. In the passive movement condition many place cells stopped firing. In those cells that did fire, however, the movement-firing rate relationship was no longer evident. These data indicate that the movement-firing rate relationship is not driven by vestibular or optic flow cues, but rather depends on either motor efferent or proprioceptive input, or that it results from some other form of input that may be modulated by self-motion, such as from the vibrissae.
2009 Wiley-Liss, Inc.