Noninvasive Brain-Machine Interface (BMI)

BMIs can be divided into two main groups: invasive and noninvasive. Noninvasive BMIs rely on reading the brain's activity without actually piercing the brain surface. The EEG is one of the earliest noninvasive BMIs, measuring the combined activity of massive groups of brain neurons through voltage differences between different parts of the brain. The EEG is performed by placing approximately 20 electrodes on the scalp; these electrodes are connected by wires to an amplifier, through which the signal is converted to a digital reading, which can then be filtered by a computer to remove any artificial interference. Once connected to the EEG, the subject can be shown different stimuli, and the brain’s electrical patterns in response to the stimuli can be studied.

Some EEG BMIs rely on the subject’s ability to develop control of their own brain activity using a feedback system, whereas others use algorithms that recognize EEG patterns that appear with particular voluntary intentions. Virtual-reality systems have been used to supply patients with efficient feedback systems, and subjects have been able to navigate through a virtual-reality setting by imagining themselves walking or driving. These systems can also be used for gaming TFOT.

EEG-based BMIs have been implemented to help patients suffering from body paralysis, such as the motor-neuron disease ALS. By generating certain brain patterns that are then read by the EEG, patients are able to control a computer cursor and indicate their intentions, and thereby communicate with the external world. EEGs are also reported to have enabled severely disabled tetraplegic patients grasp an object using a paralyzed hand. In these cases, the patient generated certain brain waves that were detected by an EEG and converted into external electrical muscle stimulation, which allowed the contraction of the muscles and movement of the paralyzed limb.

EEGs have many shortcomings, due to much overlapping of electrical activity in the brain as well as electrical artifacts. To achieve better resolution, electrodes can be inserted between the skull and the brain, without piercing the brain tissue, and can allegedly achieve a higher resolution of brain activity. Although noninvasive BMI techniques can improve the quality of life for some disabled patients by allowing them a limited and slow capacity of communication, they are unlikely to hold the solution for allowing patients to perform complex tasks that involve multiple degrees of freedom, such as controlling a robotic arm. These activities will be more likely achieved through invasive techniques.