Zolpidem is a GABA (A) agonist, which is indicated for the short-term management of insomnia. Recent research provide evidence suggesting that zolpidem produces spatial working memory (WM) deficits and dependence; however, the underlying mechanisms of these effects are unknown. Since the auditory N400 component of event-related potentials (ERPS) is considered as an index of memory use of context processing, the present study focused on N400 waveform of ERPs elicited during a WM task in a case suffering from zolpidem dependence. The patterns of N400 waveform of this case were compared to the patterns obtained from healthy controls. This comparison revealed that zolpidem dependence is accompanied by reduced amplitudes located at posterior brain areas and diffuse prolongation of N400. These findings may indicate that zolpidem dependence manifests alterations with regard to the memory use of context processing, involving or affecting a wide-ranging network of the brain's structures.

In two experiments, event-related brain potentials were recorded to word pairs simultaneously presented to both ears, with instructions to attend to one ear and detect occasional nonwords in that ear. This attentional manipulation yielded four patterns of word repetition on successive trials: first and second presentations attended (AA), both unattended (UU), and across ears (AU and UA). A prominent attenuation of N400 due to immediate repetition of words was observed on AA trials. However, when first presentations were ignored on UU and UA trials, no repetition effect was obtained. These findings indicate that the repetition effect on N400 depends on attentional processing of first presentations.