Differential response characteristics in nonepileptic and epileptic seizure patients on a test of verbal learning and memory

Investigators have found it difficult to separate patients with nonepileptic seizures (NES) from those with true epileptic seizures (ES) using quantitative measures of neuropsychological test performance. We examined qualitative response characteristics on the California Verbal Learning Test of 41 patients undergoing continuous video/audio-EEG monitoring in an effort to distinguish these patient groups (12 patients with left temporal [LT] foci, 11 with right temporal [RT] foci, and 18 with NES). NES patients explicitly recognized fewer target words compared with ES patients. In addition, NES patients rarely made false-positive errors, which resulted in failure to endorse a significant number of items on the recognition list. This response tendency is called a negative response bias. In contrast, LT patients endorsed a high number of items on the recognition test, which resulted in a positive response bias. RT patients demonstrated no consistent response tendency. In our sample, a negative response bias index (ie, a cutoff score < 0) showed a sensitivity of 61% and a specificity of 91%. We propose that failure to explicitly recognize words following repeated exposure may reflect aspects of psychological denial in NES patients. Response bias indices may thus help identify patients with NES and may begin to explain the psychological mechanisms underlying this complex disorder.