Common Pathway Hypothesis [Neurosurgery Wiki]

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====== Common Pathway Hypothesis ======

The common pathway hypothesis is a conceptual model in [[neurosurgery]] and [[psychiatric_neuromodulation]] proposing that different anatomical targets for [[deep_brain_stimulation]] (DBS) in neuropsychiatric disorders may ultimately converge on a shared functional circuit responsible for symptom improvement.

===== Origin and Application =====

Initially formulated to explain why distinct DBS targets—such as the [[subthalamic_nucleus]], [[internal_capsule]], or [[superolateral_medial_forebrain_bundle]]—can lead to similar therapeutic outcomes in conditions like [[treatment-resistant_obsessive-compulsive_disorder]] (TR-OCD) and [[treatment-resistant_depression]].

The hypothesis suggests that different anatomical entry points modulate a core subcortical-cortical network, yielding therapeutic effects through a final common pathway.

===== Role in DBS for OCD =====
In the context of OCD:

The hypothesis has been used to justify multiple DBS targets including the [[anteromedial_subthalamic_nucleus]] and the [[slMFB|superolateral medial forebrain bundle]].

The [[ocd_response_tract]] (ORT) has been proposed as the anatomical correlate of this common pathway.

===== Criticism and Reappraisal =====
Recent studies, such as Coenen et al. (Mol Psychiatry, 2025), challenge the oversimplification of the common pathway hypothesis:

The slMFB appears to encompass a wider range of OCD sub-networks, suggesting a more distributed and nuanced connectomic model.

The overlap between ORT and specific targets like the amSTN may not fully account for clinical efficacy.

The idea of a singular common tract may mask the functional diversity and anatomical specificity of DBS effects in OCD.

===== Alternative Views =====

[[network_neuroscience]] and individualized [[connectomic_analysis]] are emerging as more precise tools to understand DBS mechanisms.

These approaches emphasize targeting personalized dysfunctional circuits rather than relying on a single tract or common endpoint.