BCI and its type

Brain Computer Interface:
A system which takes a bio-signal measured from the person  and predicts ( it in real time / on a single trial basis ) some abstract aspects of person  cognitive state.

Types:
There are several types of brain-computer interfaces that are reported. The basic purpose of these
devices or types is to intercept the electrical signals that pass between neurons in the brain and
translate them to a signal that is sensed by external devices.

Active BCI:  An active BCI is a BCi which derives its output from the brain activity which is directly consciously controlled by the user , independent of the environment around the user.

Reactive BCI: A reactive BCI is the BCI which derive its output from the brain activity rising in reaction of some  action  or some external simulation, which is further control for some application.e.g If you follow the flicker your brain will show some kind off activity or reaction which is interpreted by the computer and give the results.

• Passive BCI: A passive BCI is a BCI which derive its output from arbitrary brain activity without the purpose of voluntary control, for enriching a human computer interaction with implicit information.In other words the thing on which you don't have to focus or concentrate the things like relaxation,resting, driving etc. 

 Brain signals are interpreted by the different methods the key motility is (EEG ) Electroencephalogram because it has dry electrode and you don't have to wash gel.
Other methods are MRI, fMRI , Ecog etc which will we discuss later.Some other methods which are considered are :

Invasive BCI: Invasive Brain Computer Interface devices are those implanted directly into the brain and have the highest quality signals. These devices are used to provide functionality to paralyzed people. Invasive BCIs are also used to restore vision by connecting the brain with external cameras and to restore the

use of limbs by using brain controlled robotic arms and legs. As they rest in the grey matter, invasive 

devices produce the highest quality signals of BCI devices but are prone to scar-tissue build-up, 

causing the signal to become weaker or even lost as the body reacts to a foreign object in the brain. 

In vision science, direct brain implants have been used to treat non-congenital i.e. acquired blindness. 

One of the first scientists to come up with working brain interface to restore sight as private 

researcher, William Dobell. He implanted first prototype into Jerry, A man blinded in adulthood, in 

1978. He inserted single array BCI containing 68 electrodes into Jerry’s visual cortex and succeeded 

in producing the sensation of seeing light. In 2002, experiment was conducted on Jens Neumann 

where Dobell used more sophisticated implant enabling better mapping of phosphenes into coherent vision and after the experiment Neumann was interviewed on CBS’s show as shown in fig 2.BCIs focusing on motor Neuroprosthetics 

 aim to either restore movement in paralyzed individuals or 

provide devices to assist them, such as interfaces with computers or robot arms. Researchers at Emory 

University in Atlanta led by Philip Kennedy and Roy Bakay were first to install a brain implant in a 

human that produced signals of high enough quality to stimulate movement. 

Partially Invasive Brain Computer Interfaces:  Partially invasive BCI devices are implanted inside the skull but rest outside the brain rather than within the grey matter. Signal strength using this type of BCI is bit weaker when it compares to Invasive BCI. They produce better resolution signals than non-invasive BCIs. Partially invasive BCIs have less risk of scar tissue formation when compared to Invasive BCI. 

Electrocorticography (ECoG) uses the same technology as non-invasive electroencephalography, but 

the electrodes are embedded in a thin plastic pad that is placed above the cortex, beneath the dura 

mater. ECoG technologies were first trade-in humans in 2004 by Eric Leuthardt and Daniel Moran 

from Washington University in St Louis. In a later trial, the researchers enabled a teenage boy to play 

Space Invaders using his ECoG implant. This research indicates that it is difficult to produce 

kinematics BCI devices with more than one dimension of control using ECoG. 

Light Reactive Imaging BCI devices are still in the realm of theory. These would involve implanting 

laser inside the skull. The laser would be trained on a single neuron and the neuron’s reflectance 

measured by a separate sensor. When neuron fires, the laser light pattern and wavelengths it reflects 

would change slightly. This would allow researchers to monitor single neurons but require less 

contact with tissue and reduce the risk of scar-tissue build up.

 Non Invasive Brain Computer Interfaces: Non invasive brain computer interface has the least signal clarity when it comes to communicating with the brain (skull distorts signal) but it is considered to be very safest when compared to other types. This type of device has been found to be successful in giving a patient the ability to move muscle implants and restore partial movement. Non-Invasive technique is one in which medical scanning devices or sensors are mounted on caps or headbands read brain signals. This approach is 

less intrusive but also read signals less effectively because electrodes cannot be placed directly on the 

desired part of the brain. One of the most popular devices under this category is the EEG or electroencephalography capable of providing a fine temporal resolution. It is easy to use, cheap and 

portable.