Sustained focal cortical compression reduces electrically-induced seizure threshold.

Brain injury can often result in the subsequent appearance of seizures, suggesting an alteration in neural excitability associated with the balance between neuronal excitation and inhibition. The process by which this occurs has yet to be fully elucidated. The specific nature of the changes in excitation and inhibition is still unclear, as is the process by which the seizures appear following injury. In this study, we investigated the effects of focal cortical compression on electrically-induced localized seizure threshold in rats. Male Long Evans rats were implanted with stimulating screw electrodes in their motor cortices above the regions controlling forelimb movement. Initial seizure threshold was determined in the animals using a ramped electrical stimulation procedure prior to any compression. Following initial threshold determination, animals underwent sustained cortical compression and then following a 24 h recovery period had their seizure thresholds tested again with electrical stimulation. Reliability of threshold measurements was confirmed through repeated measurements of seizure threshold. Localized seizure threshold was significantly lowered following sustained cortical compression as compared with control cases. Taken together, the results here suggest a change in global brain excitability following localized, focal compression.