Alpha phase locking predicts residual working memory performance in schizophrenia.

BACKGROUND Working memory (WM) deficits are a core feature of schizophrenia. Recent electrophysiological evidence indicates that the brain systems for visual encoding are especially impaired. However, patients still achieve performance levels clearly above chance, which indicates the existence of residual mechanisms supporting WM encoding. The present study presents evidence that alpha phase locking of the electroencephalogram is a marker for such residual cognitive mechanisms. METHODS Alpha phase locking during encoding into WM was compared between 17 patients with early-onset schizophrenia (EOS) and 17 healthy control subjects. Results of phase locking were correlated with accuracy. A median split based on alpha phase locking in patients was used to compare accuracy between control subjects and patients with high and low alpha phase locking. RESULTS Alpha phase locking increased with WM memory load in both EOS and control subjects, although alpha phase locking was generally reduced in EOS. Furthermore, for EOS, a positive correlation between alpha phase locking and performance was obtained. Additionally, patients exhibiting high phase locking did not differ in performance from control subjects. CONCLUSIONS These results provide the first evidence for a relationship between alpha phase locking and visual WM encoding. This neural mechanism seems to be preserved in some patients with schizophrenia and then allows them to attain normal performance levels.