An Event Related Potentials Study of Semantic Coherence Effect during Episodic Encoding in Schizophrenia Patients

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

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.

TRIAL REGISTRATION

The present trial has been registered in the American Registry of Clinical Trials Center (ID: NCT06538259|| http://clinicaltrials.gov/ ) (Retrospectively Registered Date: 08/03/2024).

Retrieval practice improves memory in patients with schizophrenia: new perspectives for cognitive remediation

BACKGROUND

Schizophrenia is associated with severe cognitive deficits, particularly episodic memory deficits, that interfere with patients' socio-professional functioning. Retrieval practice (also known as testing effect) is a well-established episodic memory strategy that involves taking an initial memory test on a previously learned material. Testing later produces robust long-term memory improvements in comparison to the restudy of the same material both in healthy subjects and in some clinical populations with memory deficits. While retrieval practice might represent a relevant cognitive remediation strategy in patients with schizophrenia, studies using optimal procedures to explore the benefits of retrieval practice in this population are still lacking. Therefore, the purpose of our study was to investigate the benefits of retrieval practice in patients with schizophrenia.

METHODS

Nineteen stabilised outpatients with schizophrenia (DSM-5 criteria) and 20 healthy controls first studied a list of 60 word-pairs (30 pairs with weak semantic association and 30 non associated pairs). Half the pairs were studied again (restudy condition), while only the first word of the pair was presented and the subject had to recall the second word for the other half (retrieval practice condition). The final memory test consisted in a cued-recall which took place 2 days later. Statistical analyses were performed using Bayesian methods.

RESULTS

Cognitive performances were globally altered in patients. However, in both groups, memory performances for word-pairs were significantly better after retrieval practice than after restudy (56.1% vs 35.7%, respectively, Pr(RP > RS) > 0.999), and when a weak semantic association was present (64.7% vs 27.1%, respectively; Pr(weak > no) > 0.999). Moreover, the positive effect of RP was observed in all patients but one.

CONCLUSIONS

Our study is the first to demonstrate that retrieval practice efficiently improves episodic memory in comparison to restudy in patients with schizophrenia. This learning strategy should therefore be considered as a useful tool for cognitive remediation programs. In this perspective, future studies might explore retrieval practice using more ecological material.