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.
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.
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 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 connectomes to assess structural convergence.
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.
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