Processing lexical semantics and phonology in epilepsy

Abstract

The neuroanatomical underpinnings of processing lexical semantics and phonology have been investigated in several clinical and imaging studies. However, the effects of epileptic seizures on these processes remain unclear. Addressing this issue, we administered the ‘Ambiguous Word Test’ (Roikou et al., 2003) to 35 epileptic patients (20 diagnosed with temporal lobe epilepsy, 14 left-sided, 6 right-sided, and 15 diagnosed with idiopathic generalized epilepsy) and 39 healthy controls. The test assessed their ability to select the appropriate word to fill out sentences against alternative words that were phonologically or semantically similar to the correct option. Patients overall produced significantly more errors as compared to controls across conditions. Characteristically, though, patients with temporal lobe epilepsy demonstrated significantly more phonological mistakes than both patients with idiopathic generalized epilepsy and controls. In particular, phonological processing of verbs was heavily impaired in temporal lobe epileptics, while it was preserved in idiopathic generalized epileptics. Moreover, epileptic patients in toto showed significantly more semantic mistakes than controls. Both left- and right-sided temporal lobe epileptics showed phonological impairments, whereas only left-sided temporal lobe epileptics made more semantic mistakes than controls. These findings are discussed in the light of relevant neurolinguistic theories and experimental studies, addressing issues on epilepsy and language that require further investigation.