Seizures, but not lowered seizure thresholds, results in larger neocortical motor maps and concomitant disruptions in skilled motor behaviour

Abstract

Kindling of the sensorimotor neocortex has been found to result in reorganization of the somatotopic map of movement representations as well as disruptions of skilled forelimb behaviours. It has been suggested that the repeated seizures induced during kindling altered motor maps, thereby disrupting the motor engram necessary for the production of skilled movements. However, kindling leads to neural changes other than those associated with repeated seizures, and the role of these comorbid effects is often overlooked. Our lab has developed a stimulation paradigm, which allows for the dissociation of the two main effects of kindling; repeated seizures and the reduction of afterdischarge (seizure) threshold. In the current study, we have utilized this paradigm to examine the effects of electrical stimulation on motor maps and skilled forelimb behaviour. We found that repeated seizures with no concomitant reduction of afterdischarge threshold resulted in large motor maps, as well as task specific deficits in skilled forelimb use and deficiencies in task acquisition. Rats that had reduced seizure thresholds and few seizures did not show alterations in map size or skilled forelimb use. These results suggest that movement disturbances following kindling are the result of repeated seizures, and not other stimulation-induced effects such as reduction of afterdischarge threshold. These results also corroborate the relationship between the integrity of movement representations and the ability to perform skilled motor tasks.