Targeting depression circuitry with H1 coil Transcranial Magnetic Stimulation: a retrospective circuit mapping study.

Area of Science:

• Neuroscience
• Psychiatry
• Medical Engineering

Background:

• Transcranial magnetic stimulation (TMS) is a promising treatment for depression.
• The efficacy of TMS may depend on precise targeting of specific brain circuits.
• The H1 coil, used for TMS, is thought to target brain regions more broadly and deeply than figure-of-8 coils, but its circuit specificity for depression has not been established.

Purpose of the Study:

• To investigate whether targeting a specific brain circuit with H1 coil TMS influences depressive symptom improvement.
• To identify the brain circuit targeted by H1 coil TMS that correlates with depression improvement.
• To determine the relationship between the electric field's connectivity and depression symptom reduction.

Main Methods:

• Retrospective analysis of 97 patients who received H1 coil TMS and had brain MRIs.
• Modeling of individual electric (E-)fields using SimNIBS software.
• Estimation of E-field connectivity using a normative connectome and correlation with depression symptom scores (Quick Inventory of Depressive Symptomatology).

Main Results:

• H1 coil E-fields associated with depression improvement were preferentially connected to a distinct brain circuit (p=0.0005).
• This identified circuit showed significant similarity to a predefined causal depression circuit derived from prior studies (spatial r=0.59, p=0.04).
• Greater connectivity similarity between E-fields and the depression circuit correlated with greater symptom improvement (r=0.41, p<0.001).

Conclusions:

• H1 coil TMS treatment for depression converges on a specific, identifiable causal brain circuit.
• More posterior coil positioning increases overlap with this depression circuit, suggesting optimized targeting.
• Further prospective studies are required to confirm these findings and refine H1 coil targeting for depression.