The evaluation of the effects of adding transcranial direct current stimulation to memory specificity training on the extent and durability of its impact on memory specificity
Overgeneralized autobiographical memory is one of the most frequent phenomena among the patients affected by a variety of psychiatric disorders, including depression. Memory Specificity Training (MeST), as a method trying to modulate the specificity of autobiographical memory, has achieved promising outcomes in improving the specificity, as well as some of the psychiatric symptoms in the targeted patients. The main remaining concern about this intervention, which keeps it from clinical application, is its effects’ short durability and transient nature. Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation method that has been proven to be efficient in the induction of neuroplasticity. Based on this hypothesis that the increased neuroplasticity may result in lasting changes in brain circuits, this study aims to investigate the effects of the addition of tCDS to MeST on the argumentation of the strength and durability of its effects on the specificity of autobiographical memory.
Forty-six patients affected by depressive disorders were included in the study through an introduction by the collaborator psychiatrist and considering the inclusion and exclusion criteria. The inclusion criteria consisted of a minimum educational level of eighth grade, aged between 20 and 60 years old, and consent to participate. The exclusion criteria were life-threatening conditions, comorbid psychiatric disorders, developmental disorders, any kind of neurological disorders, bipolar depression, consumption of antipsychotic or/and anticonvulsant medications, and medical conditions that may interfere with mood and addiction. The diagnoses were confirmed by The Structured Clinical Interview for DSM-5 (SCID-5).Patients were divided into two equal groups of twenty-three cases receiving six sessions of MeST in addition to tDCS versus sham stimulation. The stimulations lasted for 20 minutes through the online delivery of anodal current with the intensity of 2 milliamps versus sham stimulation, both on the dorsolateral prefrontal cortex.The participants were assessed using Beck’s Inventories for Depression and Anxiety and Autobiographical Memory Test, which presented one total index and three specific, general, and alternative sub-indices.
Two groups were homogenous, considering age, gender, marital status, and level of education, as well as baseline levels of depression and anxiety according to the scores of Beck’s Inventories. Overall, changes in the score of the indices related to cues demanding specific memories showed significant changes over time that lasted at the follow-up assessment, including specific, alternative, and total indices. The trend of changes between the two groups showed differences toward the hypothesis, but the statistical significance threshold reached only in the total index of the Autobiographical Memory Test. The similar trend in the two other indices related to specific memories, including the specific and alternative indices could not meet the statistical meaningfulness.The trend of changes in the general index of the Autobiographical Memory Test did not show a meaningful trend over time among the whole samples and was also completely independent of the grouping.Altogether, the results showed that, firstly, the intervention has been accurately targeted the specific feature of the autobiographical memory, and secondly, the changes are in absolute compatibility with the hypothesis of the study that claimed the addition of tDCS augments the strength and durability of effects induced by MeST on the specificity of autobiographical memory.
The results of this study have shown that the addition of tDCS to MeST may increase the effects on the autobiographical memory specificity of MeST and their durability. These outcomes, if confirmed with larger and further studies, can promise to bridge the gap between Memory Specificity Training and clinical application.Hence, designing and conducting studies investigating the combination of tDCS and/or other non-invasive brain stimulation modalities and MeST. Such studies should investigate the improvement of the strength and durability of the outcomes at cognitive and clinical levels in the induction of lasting ameliorative effects in patients affected by depressive and other psychiatric disorders that accompany overgeneralized autobiographical memory.