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The BCI Briefing

TechnologyHow do neural interfaces work?

How we interface with the nervous system

Every neural interface trades access, resolution and invasiveness against each other. This explorer places 32 of them on one map, by what they do and how far they have come, so that an EEG cap, a deep brain stimulator and an intracortical array can be read on the same terms.

BCI is evolving from decoding the nervous system to interacting with it.

  1. Reading
  2. Writing
  3. Closed loop
  4. Biohybrid

32 interfaces

Read

Bidirectional

Write

Non-invasive

Around the head

On the skin

Minimally invasive

Vessel or skull window

Invasive

Nerve or sense organ

On the cortex

In the cortex

Deep brain

Biohybrid · Adjacent frontier

Living neural tissue outside the body. Not an interface with a person.

Fig. 01 — The interface design spacePosition shows function and access. Fill shows maturity. Select an interface.

Colour · function

  • Read
  • Write
  • Bidirectional
  • Biohybrid

Fill · maturity as a clinical modality

  • Established
  • Human feasibility
  • Early human
  • Preclinical
  • Research frontier
  • Adjacent frontier

WriteInvasiveElectrical

Auditory brainstem implants

A small paddle of electrodes laid on the cochlear nucleus of the brainstem carries sound past a missing or severed auditory nerve. It serves people a cochlear implant cannot help, and it is the most often implanted surface stimulator in the central nervous system.

Showing Auditory brainstem implants: Write, Invasive.

Where it acts
On the cochlear nucleus, at the surface of the brainstem
Information flow
Electrode paddle → cochlear nucleus
Loading cortical surface…
Fig. 02 — Where it acts, and which way information flowsSchematic placement on a group-average cortical surface. Drag to rotate. Not a specific device or a surgical plan.

How far it has come

As a clinical modality
EstablishedAuthorised in the United States since 2000 for deafness from neurofibromatosis type 2; more than 1,000 implanted worldwide.
As a BCI application
EstablishedIn clinical use for a small group of patients. It writes sound and reads nothing, and its results are modest beside the cochlear implant's.
Access
Invasive. Open surgery at the brainstem, often in the same operation that removes a tumour.
Mechanism
Electrical
Target
Brainstem
Signal
Electrical pulses across a paddle of disc electrodes

Characteristics · write interfaces

Spatial precisionFew channels that carry distinct pitch
TargetabilityA small target; placement varies between patients
CoverageSound awareness for most, open speech for some
InvasivenessOpen surgery at the brainstem

Each track runs from low to high. A wide bar means the characteristic varies across implementations.

Strengths

  • Works where there is no usable cochlea or auditory nerve
  • Authorised for one indication since 2000, with long clinical experience

Trade-offs

  • Modest speech understanding: about a fifth of open-set sentences in tumour patients, pooled across studies
  • Results vary widely, and electrode placement is hard to control

Common applications

  • Deafness from neurofibromatosis type 2
  • People from 12 months of age whose auditory nerve does not work, under one maker's CE mark in Europe; children in the United States only in studies

Human evidence

A 2024 systematic review pooled 662 recipients with tumours and 267 without: open-set sentence understanding averaged 21.5% in the first group and 53.0% in the second. Most recipients gain awareness of sound and help with lip-reading.

What needs to happen next

Arrays that conform to the brainstem, electrodes that penetrate it and light-based stimulation are in development. Children without an auditory nerve are the group now under study.

Same site, other direction
Used by
MED-ELCochlear
Use cases
Hear
Patent activity
240 patent families name this interface, most often on stimulation, electrodes and arrays, closed loop. The patent landscape

Descriptions, ranges and maturity levels are editorial analysis, kept qualitative where the literature does not support exact comparison across technologies. Specific devices differ.

All 32 interfaces as a table
Every interface, with its function, access, mechanism, target and maturity
InterfaceFunctionAccessMechanismTargetClinical modalityBCI application
ReadNon-invasiveElectricalCortexEstablishedHuman feasibility
ReadNon-invasiveMagneticCortexEstablishedResearch frontier
ReadNon-invasiveOpticalCortexHuman feasibilityResearch frontier
ReadNon-invasiveElectricalMuscle / neuromotorEstablishedEstablished
ReadMinimally invasiveElectricalCortexHuman feasibilityHuman feasibility
ReadMinimally invasiveAcousticCortex, Deep brainEarly humanPreclinical
ReadInvasiveElectricalPeripheral nerve, Muscle / neuromotorEarly humanEarly human
ReadInvasiveElectricalCortexEstablishedHuman feasibility
ReadInvasiveElectricalCortexHuman feasibilityHuman feasibility
ReadInvasiveElectricalDeep brain, CortexEstablishedEarly human
WriteNon-invasiveMagneticCortexEstablishedResearch frontier
WriteNon-invasiveElectricalCortexHuman feasibilityResearch frontier
WriteNon-invasiveAcousticCortex, Deep brainEarly humanResearch frontier
WriteInvasiveElectricalPeripheral nerveEstablishedEarly human
WriteInvasiveElectricalRetinaHuman feasibilityHuman feasibility
WriteInvasiveElectricalCochleaEstablishedEstablished
WriteInvasiveElectricalBrainstemEstablishedEstablished
WriteInvasiveElectricalCortexEstablishedEarly human
WriteInvasiveElectricalCortexEarly humanEarly human
WriteInvasiveOptical, MolecularCortex, Deep brain, RetinaEarly humanPreclinical
WriteInvasiveElectricalDeep brainEstablishedEarly human
BidirectionalInvasiveElectricalPeripheral nerve, Muscle / neuromotorEarly humanEarly human
BidirectionalInvasiveElectricalCortexEstablishedEarly human
BidirectionalInvasiveElectricalCortex, Deep brainEstablishedHuman feasibility
BidirectionalInvasiveElectricalCortex, Spinal cordEarly humanEarly human
BidirectionalInvasiveElectricalCortexEarly humanEarly human
BidirectionalInvasiveElectricalDeep brain, CortexEstablishedEarly human
BidirectionalInvasiveElectricalDeep brainEstablishedHuman feasibility
BiohybridEx vivoElectrical, BiologicalCultured neural tissueAdjacent frontierAdjacent frontier
BiohybridEx vivoElectrical, Optical, BiologicalCultured neural tissueAdjacent frontierAdjacent frontier
BiohybridEx vivoBiological, ElectricalCultured neural tissueAdjacent frontierAdjacent frontier
BiohybridEx vivoBiological, ElectricalCultured neural tissueAdjacent frontierAdjacent frontier

Use-case explorer

Start from what people want to do

Nine human goals. Each one connects the technology, the companies, the research, the studies and the tools behind it, and says plainly what is available today.

Decoding attempted speech or writing into text and voice.

Can someone who cannot speak hold a conversation again?

Research participants with paralysis have used implanted BCIs to produce text and synthesised voice from attempted speech. All such systems remain in early feasibility studies.

Latest milestoneA single surface implant decoded speech and upper-body gestures at the same time in three participants.

Technology
EEGMEG / OPMEndovascularECoGIntracorticalsEEG
Companies
NeuralinkSynchronPrecision NeuroscienceParadromicsBlackrock NeurotechBrainGateStairMedNeuroXessNeuCyber NeuroTechABILITY NeurotechJiMEDg.tec medical engineeringArayaCognixion
Research
Simultaneous speech and gesture decoding for multimodal communication in paralysisAn Accurate and Rapidly Calibrating Speech NeuroprosthesisAn instantaneous voice-synthesis neuroprosthesisA high-performance speech neuroprosthesisA high-performance neuroprosthesis for speech decoding and avatar control+10 more
Clinical
VOICEConnect-OneBrainGate2BRAVOUNPCortiCom+3 more
Tools
BRANDtorch_brainimg_pipeMNE-PythonBraindecode
Datasets
Brain-to-Text '25Brain-to-Text Benchmark '24LibriBrain / LibriBrain100Podcast ECoG
Frontier
Speech & CommunicationCognitive Interfaces
On the calendar
BCI Meeting 2027

Why do such different devices exist for the same goal? Each trades signal quality against surgical access. Read the dossier