Brain Computer Interface Classification

Invasiveness

• Invasive
  • Invasive BCIs are implanted inside the skull or brain.

• Non-Invasive
  • Non-invasive BCIs are placed outside of the skull.

Activity

• Active BCI:
  • “An active BCI is a BCI which derives its outputs from brain activity which is directly consciously controlled by the user, independently from external events, for controlling an application.”
  • Measures Phasic states (switching attention, type of imagined movement, ...)

• Reactive BCI:
  • “A reactive BCI is a BCI which derives its outputs from brain activity arising in reaction to external stimulation, which is indirectly modulated by the user for controlling an application.”
  • Measures Event-related states (surprised/not surprised, committed error, event noticed/not noticed, ...)

• Passive BCI:
  • “A passive BCI is a BCI which derives its outputs from arbitrary brain activity without the purpose of voluntary control, for enriching a human-computer interaction with implicit information.”
  • Measures Tonic states (degree of “relaxation”, cognitive load, ...)

Source

Input and Output

These are the 5 types of BCI systems based on the possible combinations of input and output sources for the brain (neuroimaging / neurostimulation) and body (peripheral inputs and outputs such as keyboards and screens).

• [A] Open-Loop Efferent BCI
  • Brain signals control an external device.
    • An example is the original BrainGate BCI where an implantable array let a patient control a computer cursor.

• [B] Open-Loop Afferent BCI
  • Electrical stimulation to the brain by a device.
    • An example is the original deep brain stimulation (DBS) used for Parkinson's treatment in which a neural implant gives off stimulation to the brain.

• [C] Closed-Loop Efferent BCI
  • Brain signals control an external device and then feedback is given to the user that enables them to change brain signals.
    • An example would be the BrainGate BCI, in which the computer with the cursor also gave off instructions due to the signals it was picking up that then are relayed back to the patient to change the brain signals and thereby affect cursor control.

• [D] Closed-Loop Afferent BCI
  • Electrical stimulation to the brain by a device and moderated by movement monitoring
    • An example is a Parkinson's DBS-BCI in which a tremor of the wrist causes the electrical stimulation to change.

• [E] Bidirectional Afferent Closed-Loop BCI
  • Electrical stimulation to the brain is modulated depending on the recordings.
    • An example is Neuropace's BCI in treating epilepsy in which recordings of brain signals are used to modulate the electrical stimulation output.

Source