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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

The interface map

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

WriteNon-invasiveElectrical

Transcranial electrical stimulation

Weak currents passed between scalp electrodes shift the excitability or timing of the cortex beneath. The family covers direct current (tDCS), alternating current (tACS) and random noise (tRNS) stimulation.

Showing Transcranial electrical stimulation: Write, Non-invasive.

Where it acts
Electrodes on the scalp
Information flow
Scalp electrodes → cortex
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
Human feasibilityVery widely studied in people, with modest and mixed results. Regulatory status varies by country and use.
As a BCI application
Research frontierStudied as an adjunct to interface training and rehabilitation. No established role.
Access
Non-invasive
Mechanism
Electrical
Target
Cortex
Signal
A weak current, most of it shunted by scalp and skull

Characteristics · write interfaces

Spatial precisionDiffuse, over centimetres
Temporal precisionTonic for tDCS; rhythmic for tACS
Penetration depthMostly superficial; weak fields at depth
TargetabilityShaped by electrode placement; unselective
CoverageBroad
InvasivenessNone
ReversibilityEffects fade

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

Strengths

  • Cheap, portable and simple to apply
  • Low risk at standard doses

Trade-offs

  • Biases neurons; does not make them fire
  • Effects are small and vary between people

Common applications

  • Depression, in some markets
  • Rehabilitation research
  • Research on cognition and motor learning

Human evidence

A very large human literature, with modest and inconsistent effects for most uses.

What needs to happen next

Dosing that accounts for individual anatomy, and trials large enough to settle which effects are real.

Use cases
RestoreAugment
On the calendar
7th International Brain Stimulation Conference
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 things people want an interface to do. Each links the technology, the companies, the research, the studies and the tools behind it, and says 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 paralysisLong-term independent use of an intracortical brain–computer interface for speech and cursor controlImplanted brain-computer interface functionality during nighttime in late-stage amyotrophic lateral sclerosisAn Accurate and Rapidly Calibrating Speech NeuroprosthesisAn instantaneous voice-synthesis neuroprosthesis+12 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