Electrodes and Cuff Designer

Electrodes & Cuff Designer

golgi models a broad range of cuff and intrafascicular electrodes, fits them to the imported nerve, and supports arbitrary multi-contact (N-polar) montages with per-contact current fractions — the basis for current steering and selective stimulation.

Source: cuff_designer.py (parametric ASCENT-style primitives), golgi/scene/cuff_fit.py (PCA fitting), golgi/scene/electrode_patches.py (renderable + meshable contacts), golgi/state_defaults/electrode.py + cuff.py (defaults).

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Electrode types

Set via the Designs drawer (GUI) or electrode_type in set_electrodes. Each type has its own geometry parameters (defaults shown):

Type (electrode_type)	Contacts	Models	Key parameters
bipolar ring-pair	2	standard two-ring cuff	axial separation (4 mm), ring width (0.6 mm)
tripolar (anode-cathode-anode)	3	guarded tripole	ring separation (2 mm), ring width (0.6 mm)
ring-array (NxM)	rows × cols	segmented multi-contact ring array	rows (2), cols (4), row separation (3 mm), contact width (0.6 mm), contact arc (60°)
helical (Livanova-style)	bands (2)	LivaNova helical spiral	bands (2), pitch (12 mm/turn), band arc (180°), band separation (8 mm)
LIFE (longitudinal intrafascicular)	rows × cols	Boretius/Rossini intrafascicular wires	contacts/wire, # wires, contact spacing, wire spacing, contact length, wire Ø (80 µm), target fascicle
TIME (transverse intrafascicular)	rows × cols	Boretius 2010 transverse ribbon	rows, cols, row/col spacing (230 µm pitch), contact width, ribbon width/thickness, chord angle, target
DUKE (ASCENT preset)	preset-dependent	ASCENT cuff library (LivaNova, MultiContact)	via the Cuff Designer dialog (see below)

Intrafascicular electrodes (LIFE/TIME) are auto-positioned to the nerve cross-section centroid — or to a chosen target fascicle — when the design is refit.

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Contact polarities & current steering

Every contact carries a polarity and an optional current fraction:

POLARITY_CHOICES = ("off", "anode", "cathode", "ground")

• Defaults are derived from the electrode type — e.g. bipolar → [anode, cathode], tripolar → [anode, cathode, anode], arrays → a checkerboard of cathodes/anodes.
• Current fractions split the total stimulus current within a polarity group. None means "equal share" (the solver uses 1/N); explicit fractions let you specify, say, a 60/40 split between two cathodes. The GUI shows a per-group sum-check chip (green at Σ = 1).
• The FEM driver injects I_patch = I_stim · sign(polarity) · fraction, conserving charge (Σ anode = −Σ cathode = I_stim).

Because the field is solved as a per-contact lead-field basis, you can re-weight contacts (steer current) and sweep amplitude without re-solving the FEM — see Finite-Element Solver and Recruitment Sweeps & Selectivity. Legacy projects that used the old "active" role are migrated to "anode" automatically.

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Fitting the cuff to the nerve

golgi places a cuff on a real, possibly curved nerve via a PCA pipeline (cuff_fit.py):

1. Global PCA aligns the nerve's long axis with +z.
2. Cuff origin is chosen along that axis from an anchor (trunk low-z end, branched high-z end, or centroid) plus an axial offset and small transverse nudges.
3. Local PCA refinement re-aligns to the nerve's local trajectory at that location (handling curvature and oblique cross-sections).
4. Auto-sizing sets the cuff inner radius to clear the nerve by a user margin; the outer radius adds the wall thickness.

refit_design_geometry() re-runs this whenever a design's geometry or position changes (the per-row Refit button, the design-sweep generator, and headless run_mesh all call it). With multiple designs on one nerve, the first design anchors the shared mesh frame and each cuff is placed in its own local frame — so switching designs moves only the cuff.

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The Cuff Designer (ASCENT presets)

The DUKE type opens the Cuff Designer dialog — a pure-Python re-implementation of ASCENT's COMSOL "part primitive" library, with a live 3-D preview. It builds complex, literature-accurate cuffs from parametric primitives:

Primitive	Role	Builds
CuffFill_Primitive	fill	solid/annular bore fill (saline / insulation)
TubeCuff_Primitive	insulator	hollow silicone shell (optional angular gap)
CircleContact_Primitive	conductor (+ recess)	curved disc contact on the inner wall
LivaNova_Primitive	insulator + conductor	helical insulator with a central conductor band

Bundled preset families include LivaNova (LN, helical bipolar) and MultiContact (MCT, segmented ring array). The dialog exposes only the user-editable parameters per preset (cuff radius, wall thickness, length, contact size/recess, helix pitch/turns, contact pitch, …); everything else is derived from a COMSOL-flavored expression DAG ("1.109 [mm]", unit brackets, cross-references, math functions). Roles are colour-coded in the preview — silicone grey, contacts gold, fill translucent blue.

The standalone cuff_designer.py module can also be used programmatically: load_cuff_presets(dir) → preset dicts, render_design(preset, param_overrides, ns_extras) → a list of (instance, primitive, mesh, role) tuples (PyVista meshes, SI units).

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From contacts to mesh and field

electrode_patches.py turns each electrode into two things: renderable PolyData (tinted by polarity in the viewport) and patch dictionaries (the electrode_config.json the solver reads as current boundary conditions). Ring contacts become axial/helical patches; LIFE/TIME contacts become cylindrical bands / ribbon rectangles. These tagged facets are what the FEM solver injects current through.

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References

• Navarro X, et al. (2005). A critical review of interfaces with the peripheral nervous system for the control of neuroprostheses and hybrid bionic systems. J Peripher Nerv Syst. — cuff vs intrafascicular (LIFE/TIME) interface overview.
• Veraart C, Grill WM, Mortimer JT (1993). Selective control of muscle activation with a multipolar nerve cuff electrode. IEEE Trans Biomed Eng 40:640. — multipolar cuffs and current steering.
• Musselman ED, Cariello JE, Grill WM, Pelot NA (2021). ASCENT: a pipeline for sample-specific computational modeling of electrical stimulation of peripheral nerves. PLOS Comput Biol. — the cuff part-primitive library the DUKE designer reimplements.
• Bucksot JE, et al. (2019). Flat electrode contacts for vagus nerve stimulation. PLOS ONE. — cuff contact geometry.

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See also

Meshing · Finite-Element Solver · Recruitment Sweeps & Selectivity · GUI Walkthrough · Configuration Reference