VNS (implanted)

Implanted & surgical write · writes

Implanted vagus nerve stimulation uses a pulse generator placed below the collarbone, wired to a coil-shaped cuff wrapped around the left vagus nerve in the neck. It writes by electrically activating vagal nerve fibers, typically with brief 20–30 Hz pulses whose current is gradually raised. It acts on the brain only indirectly, through nerve signals relayed to a brainstem hub. Most stimulation runs on a schedule or is triggered with a magnet, but some versions read heart rate, an indirect body signal, and stimulate automatically when a sudden rise hints at a possible seizure.

Spatial resolution

2.47 mm

Temporal resolution

33.3–50 ms (inter-pulse interval)

Field of view

28.7–72.1 mm³

Reads

heart rate (ictal tachycardia)

Writes

electrical activation of vagal nerve fibers

Destructive?

minimally destructive

Prerequisites

surgery: Typically outpatient implantation of a programmable pulse generator: neck incision and carotid-sheath dissection expose the vagus nerve; a subclavicular subcutaneous generator pocket is created and the lead tunneled to it.; anesthesia: General anesthesia.

Theoretical spatial resolution

1.06 mm

Theoretical temporal resolution

600–700 µs (inter-pulse interval)

Description

Implanted cervical VNS (vagus nerve stimulation) is electrical stimulation of the left vagus nerve in the neck from a programmable pulse generator placed below the clavicle. A helical cuff with a 2- or 3-mm inner diameter wraps the left mid-cervical vagus; the left side is favored because right-sided stimulation carries greater cardiac risk. Typical settings are 20–30 Hz, 250-µs pulses, starting at 0.5 mA and titrated upward to at most 3.5 mA. It affects the brain indirectly: the pulses drive vagal afferent fibers that project to the nucleus of the solitary tract (NTS) and its downstream pathways, with no direct stimulation of brain tissue. Which fiber classes carry the effect is disputed, with A- and B-fiber recruitment described by one account and afferent C-fibers by another.

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