that can be used to control external devices. BCI’s can be exter- nal or internal to the brain and both options present their own strengths and limitations. INVASIVE V. NON-INVASIVE BCI The benefit of an invasive approach collects brain signals which have the benefit of providing high-quality (stronger) sig- nals but have the disadvantage of requiring surgical implanta- tion of a probe under the scalp with a permanent connection point outside the brain. While the resulting signals provide more accurate readings of brain signals, there is the high cost of the procedure and the risk of infection, as well as the possibility that scar tissues may form which can reduce the effectiveness of the probe. In a paper from the New England Journal of Medicine, “Neu- roprosthesis for Decoding Speech in a Paralyzed Person with Anarthria” ((https://www.nejm.org/doi/full), scientists were able to demonstrate positive results for language formulation with an invasive BCI procedure. The results they reported from their study included the ability of the patients to decode sentences via cortical activity in real-time at a median rate of 15.2 words per minute, with a median word error rate of 25.6%. In post hoc analyses, they detected 98% of the attempts by the participant to produce individual words, and they were able to classify words with 47.1% accuracy using cortical signals that were sta- ble throughout the 81-week study period. Although these types of invasive clinical studies are starting to show positive results, the real-world applications of this technology are still limited to lab-based environments.
Currently, more companies and researchers are relying on non-invasive types of brain signal sensing (EEG). EEG is a non-in- vasive method for measurement and recording of the electrical activity of the brain with no surgical intervention. EEG is typi- cally performed using small sensors, called electrodes, that are placed against the scalp to receive signals from the brain. Elec- trodes might be used “dry” (without gel), or signal collection can be enhanced using a special paste or gel between the scalp and electrode. As shown below, the electrodes can be placed any- where on the head to allow researchers to monitor brain activity and utilize those outputs to view anything thing from affective states to motor functioning to mental fixation (and many more). Using this EEG data BCI technology can provide an alternative means of communication and control for patients with ALS, es- pecially late-stage. By using sensors to detect neural activity in the brain from the occipital lobe, BCI systems can interpret the patient's intentions and translate them into commands that can be used to control external devices, such as a speech-generating device (SGD), environmental controls, or robotic devices. The occipital lobe (see Figure 1) is the brain region respon- sible for processing visual information. In the context of BCIs (Brain Computer Interfaces) for patients with ALS, the patient is presented with visual stimuli on a screen or other display. These visual stimuli can be placed in conjunction with words or com- mands that the patient may wish to communicate.
Figure 1: The occipital lobe
In this illustration, shows an implantable EEG shows the placement of the electrocorticography electrode on the participant’s speech motor cortex and the head stages used to connect the electrode to the computer.
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