An electrode array is a structured collection of multiple recording or stimulating electrodes, enabling simultaneous measurement of neural activity from many locations — providing spatial resolution and information content far beyond what a single electrode can achieve.

Types of Electrode Arrays

Silicon-Based Penetrating Arrays

  • Utah Array: 96-electrode 10x10 grid; pneumatically inserted into cortex; gold standard for human BCI research
  • Michigan Array (NeuroNexus): Planar silicon probes with electrodes distributed along the shank depth, enabling recording across cortical layers
  • Neuropixels: Massively parallel research probe with up to 966 recording sites on a single shank; primarily used in rodent research; too large for current human use

Flexible Penetrating Arrays

  • Neuralink polymer threads: 64 flexible threads with 16 electrodes each (1,024 total) inserted by robotic insertion; lower stiffness than silicon aims to reduce foreign body response
  • Syringe-injectable mesh electronics: Research platform from Charles Lieber's lab at Harvard; injectable through a needle

Surface/ECoG Arrays

  • Clinical ECoG strips/grids: Platinum disk electrodes on silicone substrate; 4-64 contacts; used clinically for epilepsy monitoring
  • Precision Layer 7: 1,024-electrode flexible ECoG array delivered via slit craniotomy
  • µECoG arrays: Sub-mm electrode spacing for highest spatial resolution surface recording

Endovascular

  • Synchron Stentrode: 16-electrode stent-based array in cerebral blood vessel

Deep Brain Stimulation Leads

  • Medtronic 3387/3389: Standard quadripolar DBS leads; 4 cylindrical contacts
  • Directional leads (Abbott Infinity, Boston Scientific Vercise): Segmented contacts enabling current steering

Key Performance Parameters

  • Electrode count: Higher count captures more neurons; current clinical limit ~1,024 (Neuralink, Precision)
  • Electrode impedance: Lower impedance = better signal-to-noise ratio; target <500 kΩ for recording
  • Electrode spacing (pitch): Determines spatial resolution; 400 µm (Utah Array), 1mm (clinical ECoG), 75 µm (Neuropixels)
  • Biocompatibility: ISO 10993 testing; material must not cause toxic, carcinogenic, or immunogenic response
  • Charge injection capacity: For stimulation arrays; determines safe stimulation amplitude