Intracortical arrays

Electrophysiology · reads

Intracortical microelectrode arrays are tiny penetrating electrodes implanted into the cortex, the brain's outer layer, on a small silicon array or on flexible threads. They record the electrical spikes of single neurons and of small groups of neurons, plus nearby local field potentials. The same contacts can also deliver microamp-level electrical stimulation.

Spatial resolution

50 µm (localisation error)

Temporal resolution

200 µs

Field of view

246 mm³ (sensing envelope)

Neurons covered

1026 neurons (sensing envelope)

Reads

extracellular action potentials (single- and multi-unit spikes); local field potentials

Destructive?

minimally destructive

Prerequisites

surgery: Humans: cortical arrays were implanted with a pneumatic impulse inserter and wired to a skull-fixed percutaneous pedestal; cables were connected aseptically each session, and one case had 2 days of ICU monitoring.; surgery: Rhesus macaques: craniotomy and closure methods varied; arrays were inserted orthogonally with a micromanipulator-held pneumatic inserter at ~172 kPa, with excursion matched to the 0.5–1.5 mm array length.

Theoretical spatial resolution

5 µm (localisation error)

Theoretical field of view

128 cm³ (reachable envelope)

Description

Intracortical microelectrode arrays are penetrating electrodes implanted into the cortex to record the extracellular electrical activity of nearby neurons. They capture the action potentials, or spikes, of single neurons and of small groups of neurons, and nearby local field potentials, at single-neuron and single-spike resolution; the same contacts can deliver microamp-level stimulation current. Noninvasive signals average millions of neurons through the skull, and surface electrodes average thousands and cannot reach deep brain; penetrating arrays resolve individual cells. A 96-channel silicon array is 4 by 4 mm with 1.0 to 1.5 mm shafts at 400 µm pitch; 32-contact probes on flexible threads space their contacts 50 or 75 µm apart. Silicon arrays implanted in the hand and arm areas of motor cortex have let people with severe motor impairment control cursors, orthoses and robotic arms for reaching, grasping and drinking. Flexible-thread systems put up to 3,072 electrodes on 96 leads, inserted robotically with micron precision; a 1,024-electrode device on 64 flexible leads sits flush with the skull. Human use has involved surgical cortical implantation with a pneumatic impulse inserter, wiring to a skull-fixed percutaneous pedestal, aseptic cable connection each session and, in one case, 2 days of ICU monitoring. In a 2015 review of mesoscopic neurotechnologies, penetrating arrays in humans covered a relatively small cortical area, about 1 cm², and larger coverage was limited by the risk of tissue damage.

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