Seizure-induced changes in place cell physiology: relationship to spatial memory.

Status epilepticus (SE) is a frequent neurological emergency associated with a significant risk of morbidity in survivors. Impairment of hippocampal-specific memory is a common and serious deficit occurring in many of the survivors. However, the pathophysiological basis of cognitive deficits after SE is not clear. To directly address the cellular concomitants of spatial memory impairment, we recorded the activity of place cells from CA1 in freely moving rats subjected to SE during early development and compared this activity to that in control rats. Place cells discharge rapidly only when the rat's head is in a cell-specific part of the environment called the "firing field." This firing field remains stable over time. Normal place cell function seems to be essential for stable spatial memory for the environment. We, therefore, compared place cell firing patterns with visual-spatial memory in the water maze in SE and control rats. Compared with controls, place cells from the SE rats were less precise and less stable. Concordantly, the water maze performance was also impaired. There was a close relationship between precision and stability of place cells and water maze performance. In contrast, a single, acute, chemically induced seizure produced cessation of place cell activity and spatial memory impairment in water maze performance that reversed within 24 hr. These results strongly bolster the idea that there is a relationship between abnormal place cells and spatial memory. Our findings also suggest that the defects in place cell and spatial memory after SE and acute chemically induced seizures result from different processes.