Impact of anterior callosal disconnection on picture naming in frontal lobe epilepsy surgery

Epilepsy surgery in focal, drug-resistant frontal lobe epilepsy can be curative and resection is aimed at seizure freedom. The cognitive impact of surgery, however, is less clear-cut. On one hand, resection of the epileptogenic zone can disconnect essential brain networks and therefore cause dysfunction. On the other hand, surgery may prompt recovery of normal brain function by restoring normal electrical activity as propagating epileptic discharges affect cognition outside the epileptogenic zone. To understand the impact of surgery on cognitive outcome, we investigated picture naming in 51 patients undergoing frontal lobe epilepsy surgery (28 left-hemisphere-dominant; 23 language-dominant) preoperatively and at 12 months follow-up using complementary voxel-based lesion symptom mapping, tractwise voxel-based disconnectome and tractography analyses to investigate cortical regions and white matter structures associated with language performance. Naming performance significantly improved 1 year after surgery compared with preoperatively, irrespective of the operated hemisphere or dominance. Improved naming performance was associated with freedom from seizures with impaired awareness. No damage to any region or white matter structure was associated with language decline. Voxel-based disconnectome analysis identified a region in the anterior corpus callosum associated with improved naming. This was confirmed by the tractography disconnectome analysis showing that naming improvement was linked to anterior callosal disconnection between regions linking presupplementary/supplementary motor areas, posterior middle frontal and inferior frontal gyri bilaterally. Our results suggest that seizure reduction can underlie language improvement: in line with results from hemispherotomy or callosotomy, isolating epileptic activity from the language network through callosal disconnection may support cognitive recovery.