Brain Connectivity

Brain connectivity refers to the ways in which brain regions communicate — either through anatomical white-matter pathways, known as structural connectivity, or through synchronized activity in the absence of external stimulation, known as functional connectivity. rTMS does not affect only the stimulation site: it remodels entire networks through network-level plasticity.

Why it matters

Depression, anxiety, and many psychiatric disorders are now understood as connectivity disorders — not as damage to a single isolated structure. This means that treatment must target the network, not only the node. Circuit neuromodulation through rTMS, when applied to the DLPFC, can transmit stimulation across the broader cortico-limbic network.

Mechanism

• Structural connectivity: bundles of myelinated axons, or white-matter tracts, measured with DTI (Diffusion Tensor Imaging).
• Functional connectivity (FC): correlations in the BOLD signal on fMRI between distant brain regions during rest, measured with resting-state fMRI.
• Default Mode Network (DMN): active during rest; hyperconnectivity in depression is associated with rumination.
• Central Executive Network (CEN): DLPFC and posterior parietal cortex; often underconnected in MDD.
• Salience Network: ACC and insula; dysregulated in many psychiatric disorders.
• rTMS over the left DLPFC increases functional connectivity between the DLPFC and sgACC, particularly in anticorrelated regions. This change is associated with clinical improvement.

Clinical significance

Predictive biomarker: baseline negative correlation between DLPFC and sgACC predicts antidepressant response to rTMS.

Subgroup identification: connectivity-based fMRI biotypes can help identify which patients with treatment-resistant depression (TRD) may benefit more from specific rTMS protocols.

Explicit relations (Entity Graph)

• Brain connectivity → modulated by → rTMS
• DLPFC → functionally connected to → sgACC
• DLPFC–sgACC anticorrelation → predicts → rTMS antidepressant response
• Default Mode Network → hyperactive in → MDD
• Central Executive Network → hypoactive in → MDD
• rTMS at DLPFC → normalizes → CEN-DMN balance
• Structural connectivity → measured by → DTI
• Functional connectivity → measured by → resting-state fMRI

References

• Fox MD, Buckner RL, White MP, Greicius MD, Pascual-Leone A (2012). Efficacy of transcranial magnetic stimulation targets for depression is related to intrinsic functional connectivity with the subgenual cingulate. Biological Psychiatry.
• Siddiqi SH, Taylor SF, Cooke D, Pascual-Leone A, George MS, Fox MD (2020). Distinct symptom-specific treatment targets for circuit-based neuromodulation. American Journal of Psychiatry.
• Weigand A, Horn A, Caballero R, et al. (2018). Prospective validation that subgenual connectivity predicts antidepressant efficacy of transcranial magnetic stimulation sites. Biological Psychiatry.
• Hoogendam JM, Ramakers GMJ, Di Lazzaro V (2010). Physiology of repetitive transcranial magnetic stimulation of the human brain. Brain Stimulation.