Volume of Activated Tissue (VAT) [Neurosurgery Wiki]

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====== Volume of Activated Tissue (VAT) ======

The Volume of Activated Tissue (VAT) refers to the estimated region of brain tissue that is modulated or influenced by the electrical field generated during [[deep_brain_stimulation]] (DBS). It is a critical concept in DBS research and programming, helping correlate anatomical stimulation sites with clinical outcomes.

===== Definition and Modeling =====
VAT is calculated using biophysical models that incorporate:

Electrode type and contact configuration

Stimulation parameters (amplitude, pulse width, frequency)

Tissue conductivity and impedance

Patient-specific or normative neuroanatomy

Modern tools such as Lead-DBS or SimBio simulate VAT using finite element models (FEM) and overlay it onto brain imaging data.

===== Clinical Relevance =====

Mapping clinical effects: The extent and location of the VAT can explain the patient’s therapeutic response or side effects.

Target optimization: Adjusting parameters to maximize the VAT's overlap with desired networks or tracts (e.g., the [[ocd_response_tract]]) improves efficacy.

Comparative studies: VATs from different patients or targets (e.g., [[anteromedial_subthalamic_nucleus]] vs. [[superolateral_medial_forebrain_bundle]]) can be compared to identify common therapeutic regions.

===== In Research =====
In the Coenen et al. (Mol Psychiatry, 2025) study:

VATs were reconstructed for 26 patients with DBS targeting amSTN or slMFB.

These were used to correlate anatomical activation with improvements on the [[yale_brown_obsessive_compulsive_scale]].

VATs were mapped onto normative [[connectomic_analysis|connectomes]] to assess structural convergence.

===== Limitations =====

VAT is a model-based estimate, not a directly measurable biological entity.

Precision depends on the accuracy of electrode localization and tissue modeling.

Does not account for dynamic physiological changes or long-term plasticity.

===== Visualization =====
Most VATs are visualized as 3D volumetric fields centered around the active contacts on the DBS lead. These can be overlaid onto:

T1/T2-weighted MRI

Diffusion tractography (to analyze fiber engagement)

Functional connectivity maps