An extravascular or intravascular neural interface is disclosed and can include three C-ring portions, with at least two including an electrode, an electrode pair or an electrode array. The portions are formed of a flexible material that is configured to enable the portions to self-size to fit around or against a surface of a target vessel when the neural interface is released at a position along the target vessel. A spinal portion configured to house electrical conductors for the electrodes is connected to one or more portions. The portions may be spaced sufficient apart to permit radial expansion and contraction of a target vessel around or within which the neural interface is placed, to reduce nerve compression, open trench low-pressure unrestricted blood-flow, and to enhance fluid exchange with the target vessel. The portions may be arranged in a low helix angle forming at least two full turns.
