Differential diagnosis of bipolar II disorder and major depressive disorder: Integrating multimodal approaches to overcome clinical challenges

Table 2 Comparative electroencephalography features in bipolar II disorder vs major depressive disorder

Feature category	BD-II characteristics	MDD characteristics	Clinical implication	Ref.
Power Spectrum (Alpha Band)	Resting-state alpha power close to healthy controls; no significant reduction	Significant alpha power reduction in centro-parietal regions; negatively correlated with symptom severity	Alpha power reduction may indicate MDD	[43,45]
Power Spectrum (Theta Band)	Reduced spontaneous phase variability in frontal theta	Reduced spontaneous phase variability in frontal theta	Theta reduction is a shared feature	[43]
Phase Dynamics (Alpha Band)	No significant alpha phase delay; stable phase variability	Pronounced alpha phase-cycle delay; reduced phase variability	Alpha phase delay may be MDD-specific	[43,49]
Mood-State Dependency	EEG patterns close to healthy controls during euthymic state; altered patterns during mood episodes	Abnormal EEG patterns even at rest	Reflects state-related differences between disorders	[43,45]
Machine Learning Classification	EEG features can be classified by SVM/KNN with approximately 93% accuracy	Same as BD-II	Enhances diagnostic accuracy	[50]

KNN: K-Nearest Neighbors; MDD: Major depressive disorder; EEG: Electroencephalography; SVM: Support vector machines; BD-II: Bipolar II disorder.