The salience network causally influences default mode network activity during moral reasoning

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Social Neuroscience

Background:

• Large-scale brain networks coordinate human behavior, with specific networks implicated in neurodegenerative diseases.
• Alzheimer's disease affects the default mode network (DMN), while frontotemporal dementia (FTD) impacts the salience network (SN).
• Previous studies show DMN activation during moral reasoning in healthy individuals, but altered responses in FTD patients.

Purpose of the Study:

• To investigate the modulatory role of the salience network in regulating default mode network activity during moral reasoning.
• To explore the causal influence of the SN on the DMN in the context of moral decision-making.
• To understand network interactions underlying abnormal moral reasoning in behavioral variant frontotemporal dementia (bvFTD).

Main Methods:

• Functional magnetic resonance imaging (fMRI) to assess network activity in bvFTD patients and healthy controls.
• Granger causality analysis of neuroimaging data to determine directed functional connectivity between SN and DMN.
• Comparison of moral dilemma responses between bvFTD patients and controls.

Main Results:

• bvFTD patients with SN atrophy showed abnormally utilitarian responses to personal moral dilemmas.
• Reduced DMN recruitment was observed in bvFTD patients compared to controls during moral reasoning.
• Granger causality analysis revealed directed functional connectivity from SN to DMN in healthy subjects, which was diminished in bvFTD patients.

Conclusions:

• The salience network exerts a causal influence on the default mode network during moral reasoning.
• This SN-DMN interaction is crucial for appropriate moral decision-making, and its disruption contributes to bvFTD.
• Findings support a revised dual-process model of moral reasoning and offer insights into social cognition deficits in dementia.