Hippocampal kindling leads to motor map expansion

Purpose: To determine whether seizure activity, repeatedly elicited in the hippocampus, could alter the functional organization of neocortical movement representations (motor maps) and whether a relation exists between the number of afterdischarges recorded in the sensorimotor neocortex and the size of the motor maps. Methods: We electrically kindled the right ventral hippocampus of Long-Evans hooded rats, twice daily, for 40 sessions and recorded the afterdischarges in the stimulated hippocampus and right sensorimotor neocortex. Between 3 and 7 days after the last seizure, we used high-resolution intracortical microstimulation to derive the forelimb-movement representations in the left (un-implanted) sensorimotor neocortex. Results: In the hippocampal kindled rats, we observed a dramatic expansion of the area of neocortex that would elicit forelimb movements compared with sham-kindled controls. The number of afterdischarges recorded in the neocortex was significantly and positively correlated with the size of the motor maps. Conclusions: Seizures propagating from the hippocampus have long-distance effects on the functional organization of motor maps.