Effects of transcranial direct current stimulation combined with retrieval practice on semantic memory in patients with schizophrenia

Abstract

Background: The semantic processing deficit stands as a central feature of cognitive abnormalities in schizophrenia. Both transcranial direct current stimulation (tDCS) and retrieval practice have been demonstrated as external techniques capable of ameliorating the semantic processing deficit in individuals with schizophrenia. The inquiry examines whether the combined effect of tDCS and retrieval practice, following tDCS intervention targeting the left dorsolateral prefrontal cortex (L-DLPFC) in patients with schizophrenia, contributes to the preservation of semantic memory in these individuals. Methods: We recruited 52 patients diagnosed with schizophrenia from hospitals. After five consecutive days of tDCS intervention (2 mA × 20 mins, twice per day), we administered a word list memorization task comparing retrieval practice and restudy strategies. Subsequently, we observed their immediate and delayed memory performance through tests. Results: The semantic memory performance of the anodal group significantly surpassed that of the sham group. There was a significant interaction between stimulation type and learning strategy; regardless of the stimulation modality employed, retrieval practice outperformed restudy strategy. Notably, the semantic memory performance under retrieval practice conditions in the anodal group was significantly superior. ARC clustering scores fully mediate stimulus type and retrieval practice recall rates. Conclusions: Continuous periodic tDCS has the potential to enhance the efficacy of retrieval practice strategy, particularly in aiding patients with schizophrenia to improve the maintenance of semantic memory and refine memory organization.