Unconscious elevated bottom-up processing in depression: Insights from dynamic causal modeling with EEG and fMRI

Area of Science:

• Neuroscience
• Psychiatry
• Medical Imaging

Background:

• Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) offer high temporal and spatial resolution for neural signaling.
• Major depressive disorder (MDD) is associated with altered fronto-limbic emotion regulation.
• Understanding these alterations is crucial for developing effective treatments.

Purpose of the Study:

• To investigate differences in neural processing and functional connectivity between MDD patients and healthy controls (HC).
• To differentiate the roles of EEG and fMRI in capturing bottom-up and top-down neurophysiological networks.
• To explore stimulus-related changes in unconscious and conscious emotional processing.

Main Methods:

• Sixty MDD patients and 66 HC underwent simultaneous EEG-fMRI during a priming task with emotional facial expressions.
• Dynamic causal modeling (DCM) analyzed effective connectivity between cortical (dorsolateral prefrontal cortex, fusiform gyrus) and subcortical (amygdala) regions.
• Models assessed stimulus-related changes in bottom-up and top-down neurophysiological networks for both conscious and unconscious processing.

Main Results:

• Bayesian model selection favored bottom-up processing models in EEG-DCM for both groups and conditions.
• fMRI-DCM showed mixed top-down/bottom-up models for HC, but predominantly bottom-up models for MDD.
• Amygdala activity influenced dorsolateral prefrontal cortex (DLPFC) activity differently across conscious and unconscious conditions in both groups.

Conclusions:

• EEG data primarily capture early, fast, bottom-up processing, while fMRI reflects both bottom-up and top-down regulation.
• Reduced DLPFC activity via bottom-up connectivity in early processing may impair top-down emotion regulation in MDD.
• These findings highlight distinct neural processing characteristics in MDD and the complementary roles of EEG and fMRI.