Working memory network dysfunction in bipolar I vs. bipolar II disorder: a systematic review of task-fMRI evidence.

Authors

Hao Yu, Tingting Wang, Yi Wang, Junfan Liang, Qing Zou, Jiaqi Xiang, Yang Lu, Kezhi Liu

Published in

Frontiers in psychiatry. Volume 17. Pages 1800042. Epub Jun 16, 2026.

Abstract

Working memory impairment is one of the core cognitive phenotypes in bipolar disorder. However, whether the task-based functional magnetic resonance imaging mechanisms underlying working memory processing are consistent between bipolar disorder type I (BD-I) and type II (BD-II) remains unclear. This systematic review summarizes task-based fMRI evidence, with a focus on characterizing the neural correlates of working memory in BD-II and comparing them with BD-I.
Following the PRISMA 2020 guidelines, PubMed, Embase, and Web of Science were systematically searched for studies published between January 2011 and June 2025. Eligible studies included task-based fMRI investigations in adults using working memory paradigms that separately reported results for BD-I and BD-II. A total of 22 studies were included for qualitative synthesis.
Across 22 task-based fMRI studies, the qualitative evidence suggests potentially different patterns of working-memory network engagement in BD-I and BD-II; however, subtype-specific inference is constrained by the very limited BD-II literature, with only three studies including BD-II samples (one BD-II-only study and two direct BD-I vs BD-II comparisons). In BD-I, studies more often reported altered or less efficient recruitment of executive-control regions/networks and reduced task-related suppression of default-mode regions under higher cognitive load and/or emotional distraction. In BD-II (based on sparse evidence), euthymic samples were generally reported to show relatively preserved recruitment and performance, whereas depressive-state or higher-demand conditions were associated with attenuated load-related upregulation. In a single emotional-interference paradigm, BD-II showed stronger inverse DLPFC-amygdala coupling, which may reflect context-specific modulation of fronto-limbic interactions.
The current task-fMRI literature provides preliminary, hypothesis-generating indications that BD-I and BD-II may not be fully captured by a simple severity-continuum account, but firm subtype-specific conclusions are not yet warranted given the scarcity of BD-II studies and the limited number of direct BD-I/BD-II comparisons. Across studies, BD-I findings have more often been interpreted within neural inefficiency/limited-scalability accounts and reduced task-related DMN suppression, whereas BD-II findings-based on sparse evidence-have been reported as more state- and context-dependent. Larger, harmonized studies with direct BD-I/BD-II comparisons and mood-state stratification are needed to test these provisional patterns.

PMID:
42389395
Bibliographic data and abstract were imported from PubMed on 02 Jul 2026.

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