IMPLICIT MEMORY AND EXPLICIT MEMORY PROFILES COMPARISONS BETWEEN PATIENTS WITH DIFFERENT MOOD DISORDERS
Authors: Liang *Yi-Jie , Huang Chih-Chun , Chang Yun-Hsuan , Wang Tzu-Yun , Lane Hsien-Yuan 
Published: February 2025

Background

With the rising prevalence of mood disorders, there is a growing focus on distinguishing between Major Depressive Disorder (MDD) and Bipolar Disorder (BD), given their initial similarity in depressive episodes. Misdiagnosis can delay appropriate treatment1-3. Scholars collaborate to differentiate these disorders through neurocognitive, structural brain, and clinical factors4,5.

Aims

This study posits that cognitive distinctions may be linked to documented brain structural changes (e.g., prefrontal cortex-hippocampus-cerebellum) and proposes the hypothesis of semantic and procedural memory impairments in BD patients.

Methods

The study was conducted in two stages for analysis. In Stage 1, the Serial Reaction Time Task (SRTT) performance of three groups— Healthy Controls (HC, n=79), Major Depressive Disorder (MDD, n=45), and Bipolar Disorder (BD, n=50)— was compared. In Stage 2, a further comparison was made between HC (n=74), MDD (n=31), and BD (n=15), who underwent both the List Test and SRTT. Semantic memory and procedural memory were assessed using the List Test (a subtest of the Wechsler Memory Scale) and SRTT, respectively. Symptom severity was quantified using the Hamilton Depression Rating Scale (HDRS) and the Young Mania Rating Scale (YMRS). Demographic and clinical variables were analyzed using Multivariate Analysis of Variance (MANOVA). Standardized test scores and clinical variables were examined for correlations using Pearson's correlation.

Results

The study's findings revealed that the Bipolar Disorder (BD) group exhibited poorer performance in both semantic and procedural memory compared to the other two groups. When the severity of emotional states varied, BD's procedural memory was impacted by its onset, while Major Depressive Disorder (MDD) was influenced by somatic anxiety, psychological anxiety, duration, and onset. However, when emotional state severity remained consistent, only MDD's procedural memory was affected by psychological anxiety and duration. Clinical characteristics of BD were only linked to semantic memory in terms of onset, whereas MDD was affected by somatic anxiety, psychological anxiety, anorexia, and onset. In the BD group, procedural memory learning was influenced by overall depression, psychological anxiety, and anorexia. Similarly, MDD was affected by psychological anxiety and anorexia, as well as by duration and onset. Semantic memory learning was found to be associated solely with clinical features (specifically, psychological anxiety) in the BD group. Overall, this study indicates that the SRTT's ability to differentiate between BD and MDD is higher.

Conclusions & Discussions

This study posits that the BD group's inferior memory retention and learning performance, compared to the MDD and HC groups, may be linked to alterations in neural circuits governing memory6. The greater the changes in the relevant brain regions, the more profound the impact on these neural circuits7,8. Furthermore, somatic anxiety in MDD patients is shown to have a significant association with memory performance. Both duration and onset appear to be correlated with memory performance in both Bipolar Disorder (BP) and Major Depressive Disorder (MDD). In future research, it may be valuable to consider the influence of clinical variables in memory-related comparative studies.

References

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