Atypical language representation as a protective factor against verbal memory decline following epilepsy surgery

An important role of neuropsychology in the preoperative evaluation of epilepsy surgery candidates is to assess risk for postoperative memory decline. One factor associated with postoperative verbal memory decline is surgery in the language-dominant temporal lobe (TL). The aim of the study was to determine whether atypical language representation has a protective effect against verbal memory decline following left temporal, frontotemporal, or hippocampal excision.

Data from 61 patients with medically refractory epilepsy, Wada testing, and pre- and postsurgical memory assessment from four comprehensive epilepsy surgery centers were gathered and examined for pre- to postsurgical memory change. Wada testing was used to determine language dominance (left vs. atypical [bilateral + right]). Postoperative memory change was examined at both the individual (using nonparametric analyses) and group (using parametric analyses) levels for the two language dominance groups.

Significant postoperative verbal memory decline was observed in the left hemisphere language-dominant group, while the atypical language group showed verbal memory improvement. Individuals with left hemisphere language dominance were more likely to show postoperative declines in verbal memory, whereas individuals with atypical language dominance were significantly less likely to decline. As expected, there were no significant differences between language groups with regard to postoperative visuospatial memory outcome.

Patients with atypical language dominance had better verbal memory outcomes following left hemisphere resections than those with left hemisphere language dominance suggesting that typical memory substrates likely reorganized along with language. Thus, atypical cerebral organization of language may be considered a protective factor against verbal memory decline following epilepsy surgery involving the left TL.